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Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    The risks of drinking sugar sweetened drinks | WURcast
    Kampman, E. - \ 2019
    Wageningen : WURcast
    sugar - health - diseases - blood sugar - carbohydrates - soft drinks
    The consumption of sugar-sweetened drinks increases rapidly. What is the danger of these drinks? This lesson is part of the WageningenX MOOC called 'Nutrition and Cancer'.
    Evaluation of fungal degradation of wheat straw cell wall using different analytical methods from ruminant nutrition perspective
    Nayan, Nazri ; Erven, Gijs van; Kabel, Mirjam A. ; Sonnenberg, Anton S.M. ; Hendriks, Wouter H. ; Cone, John W. - \ 2019
    Journal of the Science of Food and Agriculture 99 (2019)8. - ISSN 0022-5142 - p. 4054 - 4062.
    carbohydrates - in vitro gas production - lignin - lignin quantification - pyrolysis-GC/MS - white-rot fungi

    BACKGROUND: White rot fungi have been used to improve the nutritive value of lignocellulose for ruminants. In feed analysis, the Van Soest method is widely used to determine the cell wall contents. To assess the reliability of this method (Method A) for determination of cell wall contents in fungal-treated wheat straw, we compared a combined monosaccharide analysis and pyrolysis coupled to gas chromatography with mass spectrometry (Py-GC/MS) (Method B). Ruminal digestibility, measured as in vitro gas production (IVGP), was subsequently used to examine which method explains best the effect of fungal pretreatment on the digestibility of wheat straw. RESULTS: Both methods differed considerably in the mass recoveries of the individual cell wall components, which changed on how we assess their degradation characteristics. For example, Method B gave a higher degradation of lignin (61.9%), as compared to Method A (33.2%). Method A, however, showed a better correlation of IVGP with the ratio of lignin to total structural carbohydrates, as compared to Method B (Pearson's r of −0.84 versus −0.69). Nevertheless, Method B provides a more accurate quantification of lignin, reflecting its actual modification and degradation. With the information on the lignin structural features, Method B presents a substantial advantage in understanding the underlying mechanisms of lignin breakdown. Both methods, however, could not accurately quantify the cellulose contents – among others, due to interference of fungal biomass. CONCLUSION: Method A only accounts for the recalcitrant residue and therefore is more suitable for evaluating ruminal digestibility. Method B allows a more accurate quantification of cell wall, required to understand and better explains the actual modification of the cell wall. The suitability of both methods, therefore, depends on their intended purposes.

    Direct and Long-Term Metabolic Consequences of Lowly vs. Highly-Digestible Starch in the Early Post-Weaning Diet of Mice
    Fernández-Calleja, José M.S. ; Bouwman, Lianne M.S. ; Swarts, Hans J.M. ; Oosting, Annemarie ; Keijer, Jaap ; Schothorst, Evert M. van - \ 2018
    Nutrients 10 (2018)11. - ISSN 2072-6643
    adipose tissue - amylopectin - amylose - C57BL mice - carbohydrates - glycemic index - indirect calorimetry - metabolic flexibility - nutrition - sexual dimorphism

    Starches of low and high digestibility have different metabolic effects. Here, we examined whether this gives differential metabolic programming when fed in the immediate post-weaning period. Chow-fed mice were time-mated, and their nests were standardized and cross-fostered at postnatal days 1⁻2. After postnatal week (PW) 3, individually housed female and male offspring were switched to a lowly-digestible (LDD) or highly-digestible starch diet (HDD) for three weeks. All of the mice received the same high-fat diet (HFD) for nine weeks thereafter. Energy and substrate metabolism and carbohydrate fermentation were studied at the end of the HDD/LDD and HFD periods by extended indirect calorimetry. Glucose tolerance (PW 11) and metabolic flexibility (PW14) were analyzed. Directly in response to the LDD versus the HDD, females showed smaller adipocytes with less crown-like structures in gonadal white adipose tissue, while males had a lower fat mass and higher whole body fat oxidation levels. Both LDD-fed females and males showed an enlarged intestinal tract. Although most of the phenotypical differences disappeared in adulthood in both sexes, females exposed to LDD versus HDD in the early post-weaning period showed improved metabolic flexibility in adulthood. Cumulatively, these results suggest that the type of starch introduced after weaning could, at least in females, program later-life health.

    Human Milk Oligosaccharides in Colostrum and Mature Milk of Chinese Mothers : Lewis Positive Secretor Subgroups
    Elwakiel, M. ; Hageman, J.A. ; Wang, W. ; Szeto, I.M. ; Goudoever, J.B. van; Hettinga, K.A. ; Schols, H.A. - \ 2018
    Journal of Agricultural and Food Chemistry 66 (2018)27. - ISSN 0021-8561 - p. 7036 - 7043.
    carbohydrates - genetic polymorphisms - lactation stage - variability

    To study the variability in human milk oligosaccharide (HMO) composition of Chinese human milk over a 20-wk lactation period, HMO profiles of 30 mothers were analyzed using CE-LIF. This study showed that total HMO concentrations in Chinese human milk decreased significantly over a 20-wk lactation period, independent of the mother's SeLe status, although with individual variations. In addition, total acidic and neutral HMO concentrations in Chinese human milk decreased over lactation, and levels are driven by their mother's SeLe status. Analysis showed that total neutral fucosylated HMO concentrations in Chinese human milk were higher in the two secretor groups as compared to the nonsecretor group. On the basis of the total neutral fucosylated HMO concentrations in Chinese human milk, HMO profiles within the Se+Le+ group can be divided into two subgroups. HMOs that differed in level between Se+Le+ subgroups were 2′FL, DF-L, LNFP I, and F-LNO. HMO profiles in Dutch human milk also showed Se+Le+ subgroup division, with 2′FL, LNT, and F-LNO as the driving force.

    No Adverse Programming by Post-Weaning Dietary Fructose of Body Weight, Adiposity, Glucose Tolerance, or Metabolic Flexibility
    Bouwman, Lianne M.S. ; Fernández-Calleja, José M.S. ; Swarts, Hans J.M. ; Stelt, Inge van der; Oosting, Annemarie ; Keijer, Jaap ; Schothorst, Evert M. van - \ 2018
    Molecular Nutrition & Food Research 62 (2018)2. - ISSN 1613-4125
    carbohydrates - indirect calorimetry - metabolic programming - metabolism - monosaccharides
    Scope: Metabolic programming can occur not only in the perinatal period, but also post-weaning. This study aims to assess whether fructose, in comparison to glucose, in the post-weaning diet programs body weight, adiposity, glucose tolerance, metabolic flexibility, and health at adult age. Methods and results: Three-week-old male and female C57BL6/JRccHsd mice are given an intervention diet with 32 energy percent (en%) glucose or fructose for only 3 weeks. Next, all animals are switched to the same 40 en% high fat diet for 9 weeks. Neither body weight nor adiposity differs significantly between the animals fed with glucose or fructose diets at any point during the study in both sexes. Glucose tolerance in adulthood is not affected by the post-weaning diet, nor are activity, energy expenditure, and metabolic flexibility, as measured by indirect calorimetry. At the end of the study, only in females fasting serum insulin levels and HOMA-IR index are lower in post-weaning fructose versus glucose diet (p = 0.02), without differences in pancreatic β-cell mass. Conclusions: Our present findings indicate no adverse programming of body weight, adiposity, glucose tolerance, and metabolic flexibility by dietary (solid) fructose in comparison to glucose in the post-weaning diet in mice.
    Probing the bacterial cell wall with chemical biology tools
    Sminia, Tjerk J. - \ 2017
    Wageningen University. Promotor(en): H. Zuilhof; W.M. de Vos, co-promotor(en): T. Wennekes. - Wageningen : Wageningen University - ISBN 9789463437080 - 196
    bioengineering - sugars - labelling - synthesis - biochemical techniques - akkermansia muciniphila - gastrointestinal microbiota - carbohydrates - bioengineering - suikers - etiketteren - synthese - biochemische technieken - akkermansia muciniphila - microbiota van het spijsverteringskanaal - koolhydraten

    After DNA and proteins, carbohydrates are the third language of life. Chapter 1 introduces the reader to this class of biomolecules, also called sugars or glycans, that can be found on the outer surface of almost all cells and plays a critical role as the social messengers of a cell. Although our knowledge about the role of glycans in eukaryotic cells has increased considerably in recent decades, our understanding of the glycan layer on bacterial cells is still very limited. Besides the carbohydrates that are present in both eukaryotes and prokaryotes an additional wide range of unique (e.g. microbial sialic acid), often very complex (e.g. pseudaminic acid), carbohydrates is present in prokaryotes. This chapter briefly introduces two research fields, carbohydrate chemistry and chemical biology, that when combined provide a powerful way to investigate the biological role of these unique bacterial carbohydrates at the molecular level. This chemistry-based approach, termed chemical microbiology, often starts with the development of a chemical synthesis for a target bacterial carbohydrate. Subsequently, the synthetic route towards this target allows for the introduction of unnatural functional groups, like chemical reporters, that result in the molecular tools needed to study their biological function. The studies described in this thesis, focus on developing such molecular tools to study the role of glycans and glycoconjugates in human gut bacteria and human-associated bacteria.

    Chapter 2 provides an overview of metabolic oligosaccharide engineering (MOE) a popular chemical biology technique to label glycans in living cells. In MOE, carbohydrates derivatives are synthesised with unnatural chemical reporters and used to study their incorporation in glycans of eukaryote to prokaryote species. The progress in this field over the last 6 years is reviewed in detail with a special emphasis on the synthesis of the unnatural carbohydrates from commercially available sources. The principle behind MOE is that these unnatural carbohydrates with e.g. azide, alkyne, cyclopropene, or isonitrile chemical reporter groups, are still recognised by the endogenous enzymes in the cell that salvage this new carbohydrate. In this way they can enter the associated biochemical pathways and end up in newly biosynthesised cellular glycans. Subsequent labelling techniques, such as strain promoted azide alkyne cycloaddition or tetrazine ligation, enable the visualisation of these incorporated unnatural carbohydrates with for instance fluorescence microscopy.

    Metabolic labelling is further explored in chapter 3. Key cell envelope glycoconjugates in the mucin-degrading gut microbiota member, Akkermansia muciniphila, were subjected to chemistry-based functional analysis, with Escherichia coli being used as a control species. Two novel non-toxic peptidoglycan (PG) probes were designed and synthesised to investigate the presence of PG in this species. Their design was based on the natural d-alanine dipeptide motif found in PG. Inspired by the fact that d-alanine dipeptide-derivatives were previously reported to be incorporated in newly synthesised PG, we synthesised a cyclopropene and isonitrile d-alanine dipeptide. Our probes proved to be non-toxic, as shown by growth and viable count analysis, and were therefore superior over existing PG probes. Another beneficial property was that the probes also did not influence the specific growth rate of A. muciniphila or E. coli. The PG probes were successfully incorporated into the peptidoglycan layer of A. muciniphila and visualised using a tetrazine click-ligation with a fluorophore. Our analysis proved for the first time that A. muciniphila has a PG layer. Besides PG labelling, we also investigated metabolic labelling of other glycoconjugates on the outer surface of A. muciniphila. This part of the study showed that azido-monosaccharide derivatives of N-acetylglucosamine, N-acetylgalactosamine, and fucose are successfully processed by A. muciniphila salvage pathways and incorporated into its surface glycoconjugates. Especially 6-azido-fucose was readily processed by the recently discovered l-fucose salvage pathway of A. muciniphila. The two compatible labelling techniques were next combined in a dual labelling experiment. Our isonitrile dipeptide peptidoglycan probe and 6-azido-fucose were successfully incorporated into A. muciniphila. Subsequent fluorescent labelling with bio-orthogonal techniques resulted in dual labelling of peptidoglycan and fucose-containing glycans in live A. muciniphila cells.

    With the positive results of MOE in A. muciniphila in hand, chapter 4 describes the further investigation of MOE. After successful validation of our Ac4FucAz probe for MOE in Bacteroides fragilis we continued their application in other human gut microbiota members, including the butyrate-producing Anaerostipes rhamnosivorans, Intestimonas butyriciproducens, and Eubacterium hallii. Labelling of these human gut microbes proved to be rather challenging with a-specific cellular labelling with the fluorophore being the major problem. Initial results, however, did show that a 6-azido-l-rhamnose probe resulted in fluorescent labelling of A. rhamnosivorans, which provides initial evidence for the existence of an as of yet undocumented salvage pathway. In this species the 6-azido-fucose probe was not salvaged. Via confocal microscopy and flow cytometry analysis we observed that the 6-azido-rhamnose probe was selective for A. rhamnosivorans in the presence of A. muciniphila. Such a co-culture experiment is a first step in mimicking the complex human gut microbiome. For E. hallii Ac4GalNAz gave clear metabolic labelling and the majority of the cell population could be labelled with the fluorescent dye after a strain-promoted azide alkyne cycloaddition. Other glycan probes (Ac4GlcNAz, Ac4FucAz, and Neu5Az) also resulted in labelling, but not as prominent as Ac4GalNAz. Surprisingly, MOE has never been reported for the common lab strain Escherichia coli MG1655. Curious to investigate this in more detail we started MOE in E. coli. However, no labelling was obtained when Ac4GlcNAz probe was added to E. coli, most likely due to the fast growth, metabolism and turnover. Only, when fresh Ac4GlcNAz probe was added every 30 minutes, metabolic labelling in E. coli was observed. To further investigate the influence of GlcNAc metabolism in E. coli on MOE, single-gene knock-outs of E. coli GlcNAc metabolism from the Keio collection were investigated. Labelling was observed for NagA (N-acetyl glucosamine 6 P deacetylase) and NagK (N-acetyl-d-glucosamine kinase) E. coli mutants. Both enzymes are involved in the last step of the biosynthesis towards UDP-N-acetylglucosamine. When the overall E. coli metabolism was inhibited, after addition of the respiration inhibitor sodium azide, no metabolic labelling was observed. These results indicate that MOE in E. coli is possible, but challenging and can only be performed under specific circumstances.

    An investigation into the total synthesis of pseudaminic acid, a sialic acid produced by specific human-associated prokaryotes, is described in chapter 5. Sialic acids are typically found at the terminal positions of surface glycoconjugates in both eukaryotes and prokaryotes. Other related microbial sialic acids are legionaminic and acinetaminic acid. The total synthesis of these microbial sialic acids is notoriously difficult, as exemplified by the fact that only a few chemical synthesis routes towards them are currently known. Our total synthesis of pseudaminic acid started from the readily available amino acid l-threonine that was transformed into a key versatile Garner aldehyde derivative intermediate. With this aldehyde in hand, the Henry nitro-aldol condensation reaction was investigated. After studying numerous conditions, such as asymmetric catalysis or elongated reaction times, and extensive optimisation efforts we were never able to obtain the Henry reaction product to continue with this route. As an alternative, a tethered aminohydroxylation was investigated for its ability to introduce the key functional group and stereochemistry onto an intermediate obtained from the Garner aldehyde derivative. This reaction indeed gave the desired amino-alcohol motif in the correct stereochemistry, but another diastereomer proved very difficult to separate from the desired product. After some additional transformations and protection steps we obtained a derivative in which the primary alcohol could be oxidised to provide a hexose intermediate that resembles the hexose intermediate present in pseudaminic acid biosynthesis. This key hexose intermediate will likely enable a subsequent Barbier reaction, a chain elongation step, in future studies. With most of the key transformations accomplished, the completion of a pseudaminic total synthesis based on l-threonine should soon be possible. Besides finishing the total synthesis, future work should also focus on adapting this synthesis route to allow installation of chemical reporter groups on pseudaminic acid for its application in MOE.

    Chapter 6 is the general discussion about all the work mentioned in the other chapters. It also contains additional information and suggestions for further research in the field of chemical microbiology.

    The evaluation of energy in fish feed
    Haidar, Mahmoud - \ 2017
    Wageningen University. Promotor(en): J.A.J. Verreth, co-promotor(en): J.W. Schrama. - Wageningen : Wageningen University - ISBN 9789463438049 - 155
    oreochromis niloticus - fish feeding - feed formulation - digestible energy - dietary protein - dietary fat - carbohydrates - growth - feed evaluation - fish culture - aquaculture - oreochromis niloticus - visvoeding - voersamenstelling - verteerbare energie - voedingseiwit - voedingsvet - koolhydraten - groei - voederwaardering - visteelt - aquacultuur

    New and alternative plant ingredients are increasingly incorporated in fish feed due to the scarcity of captured fish and increased fishmeal and fish oil prices. As a result, current fish feeds are characterized by a highly variable ingredients composition, leading to a similar variability in the dietary macronutrients composition, especially the carbohydrates fraction. Appropriate formulation of the energy component in fish feeds requires information on nutrient digestibility, energy requirements for maintenance, and the efficiency of utilization of digestible energy for growth (kgDE). In fish feed formulation, the energy evaluation is based on digestible energy (DE) basis. The main assumptions of this DE system are that maintenance requirements and kgDE are independent of dietary factors. The main objective of this thesis was to evaluate and improve the DE system for Nile tilapia. Data showed that, opposite to what is assumed in literature and irrespective of the feeding level applied, an optimal digestible protein to digestible energy ratio (DP/DE) for young Nile tilapia could not be detected. In addition, it was expected that Nile tilapia would show a maximal protein deposition in relation to a wide range of DP/DE ratios, however, this was either observed. Further investigations showed that different body compartments/organs responded differently in terms of protein and fat composition as a result of changes in the dietary DP/DE ratio. In tilapia, viscera and the “rest” fraction (head, skin, fins and bones) were the main site for fat retention. In addition, protein content of fillets seems to be constant (about 17%) and not affected by dietary factors in Nile tilapia. In addition, the effect of using new plant ingredients in Nile tilapia diets was also investigated. The results showed that the ingredients composition had an effect on the maintenance requirements of Nile tilapia. Further, changes in the ratio of starch vs non starch carbohydrates revealed that energy retention was lower when more dietary fibers were included. In addition, the net energy retention differed also when the levels of digestible protein, fat and carbohydrates changed in the diets. The latter results proved that kgDE was not constant and was dependent on diet composition. All aforementioned results led us to calculate the energetic efficiencies of digestible protein, fat and carbohydrates for net energy retention. These estimated efficiencies were used to propose a net energy evaluation system being feasible for Nile tilapia.

    Samenstelling van blad, stengel en rhizomen in relatie tot optimaal oogst-tijdstip van Miscanthus x giganteus
    Kasper, G.J. ; Kolk, J.C. van der; Putten, J.C. van der - \ 2017
    Wageningen : Wageningen Livestock Research (Wageningen Livestock Research rapport 1022) - 27
    brandstofgewassen - biobased economy - miscanthus - grassen - oogsttijdstip - gewasopbrengst - akkerbouw - plantensamenstelling - suikergehalte - lignine - pectinen - droge stof - koolhydraten - stengels - wortelstokken - fuel crops - biobased economy - miscanthus - grasses - harvesting date - crop yield - arable farming - plant composition - sugar content - lignin - pectins - dry matter - carbohydrates - stems - rhizomes
    A plurality of components (such as sugars, lignin, pectin) of Miscanthus x giganteus has been studied in stem, leaf, and rhizomes for the harvest times July and January in view of the optimal harvest time. Additional literature search shows that the end of October is the optimum time for harvesting on the basis of the maximum above-ground dry matter yield and sugar yield, and dry matter yield in the next year. It will have to be investigated whether the optimal harvest time also applies to long-term research.
    Mild disintegration of green microalgae and macroalgae
    Postma, Richard - \ 2016
    Wageningen University. Promotor(en): Michel Eppink; Rene Wijffels, co-promotor(en): Giuseppe Olivieri. - Wageningen : Wageningen University - ISBN 9789462579477 - 181
    algae - chlorella vulgaris - bioprocess engineering - biorefinery - proteins - milling - carbohydrates - biobased economy - disintegrators - technology - extraction - algen - chlorella vulgaris - bioproceskunde - bioraffinage - eiwitten - maling - koolhydraten - biobased economy - desintegrators - technologie - extractie

    An increased worldwide protein demand for food and feed and the necessity to release the water soluble proteins in the first stage of the cascade biorefinery require the development of mild protein extraction technologies. Cell disintegration is the first hurdle and is considered as one of the most energy consuming steps. Therefore, this thesis focused on the development of a mild, scalable and energy efficient disintegration technology for green microalgae and macroalgae (seaweed) aimed on extraction of water soluble components (like proteins and carbohydrates).

    For microalgae disintegration, two main technologies were investigated. First of all the conventional technology bead milling and second a novel approach using Pulsed Electric Field (PEF). In Chapter 2 a benchmark was set by means of bead milling for the release of water soluble protein from the green microalgae Chlorella vulgaris. Overall, protein yields between 32 and 42% were achieved, while the energy consumption was reduced with 85% by selective protein extraction to values as low as 0.81 kWh kgDW-1. Remarkably, the benchmark was much better than expected.

    In Chapter 3 the bead mill was further optimized by decreasing the applied bead size, furthermore the applicability of bead milling on two additional microalgae species (Neochloris oleoabundans, Tetraselmis suecica) was shown. In addition, to be able to better understand the disintegration mechanism, the so-called stress model was applied. This model describes the comminution process in a bead mill as function of the amount of bead contacts and the force of each impact. The release kinetics could be improved and thereby the specific energy consumption could be reduced to 0.45‒0.47 kWh kgDW-1 by using 0.3 mm beads for all algae.

    Chapter 4 describes a screening on the applicability of PEF, over a broad range of operating conditions, for the extraction of water soluble proteins from the microalgae C. vulgaris and N. oleoabundans. No substantial protein yields were observed under the investigated conditions. This led to the conclusion that PEF is not suitable to release water soluble proteins, not even at specific energy consumptions much higher than those for the benchmark, bead milling.

    In Chapter 5 it was attempted to improve the performance of PEF by investigating the synergistic effect with the processing temperature. The PEF experiments were performed using a pilot scale continuous flow electroporation unit in which the processing temperature was controlled between 25 – 65 °C. The results showed that under the tested conditions, the combined PEF-Temperature treatment did not cause substantial disintegration of the algal cells to effectively release water soluble proteins.

    In addition to the microalgae, macroalgae were subject of investigation in the search for new protein sources in Chapter 6. Four batch technologies were used to disintegrate the green macroalgae Ulva lactuca, being; osmotic shock, enzyme incubation, PEF and High Shear Homogenization (HSH). In descending order the highest protein yields per treatment; HSH (~40%) > enzyme degradation (~25%) > osmotic shock (~20%) > PEF (~15%).

    In the final chapter the main results and remaining bottlenecks are discussed and a future outlook on microalgae disintegration is presented. To date, bead milling is the only technology able to disintegrate fresh microalgae at specific energy consumptions below 10% of the total energy available from the algae and release substantial amounts of water soluble protein. The future outlook was based on a techno-economic evaluation, which showed that the cultivation costs are limiting the economic feasibility of microalgae biorefinery. Future focus should be on the cultivation.

    Influence of pectin supplementation on feed fermentation characteristics in rats and pigs
    Tian, L. - \ 2016
    Wageningen University. Promotor(en): Harry Gruppen; Henk Schols. - Wageningen : Wageningen University - ISBN 9789462577282 - 142
    pigs - rats - pectins - feed supplements - dietary fibres - digestion - digestive tract - carbohydrates - microbial flora - nutrition physiology - animal nutrition - food chemistry - varkens - ratten - pectinen - voedersupplementen - voedingsvezels - spijsvertering - spijsverteringskanaal - koolhydraten - microbiële flora - voedingsfysiologie - diervoeding - voedselchemie

    The physiological effects of dietary fiber (DFs) depend on several factors including structural features of the DFs, composition and activity of colonic microbiota, and products formed during fermentation. In this thesis, the influence of pectin supplementation to feed fermentation characteristics in rats and pigs was studied. The non-starch polysaccharides (NSP) present in the selected feed ingredient oats were characterized. Distinct populations of arabinoxylans (AXs) were observed in oats, compared to those reported for other cereals like wheat and barley. The fate of cereal AXs and soybean pectin during fermentation and the consequent effects on appetite regulation and fat accumulation were studied in rats as a model. Oat AXs were fermented less rapidly than wheat AXs in the caecum of rats. Soy pectin was fermented more early and efficiently than cereal AXs. A significant inverse correlation between rat retroperitoneal fat-pad weight and concentration and relative SCFA proportion of butyrate was observed. In a following in vivo rat experiment, commercial soy pectin together with three other soluble pectins originating from citrus and sugar beet and differing in their methyl esterification were individually supplemented to the diets. Their effects on the utilization of the different DFs present in the feed and the consequent effect on the microbial community in the colon of rats was studied. All pectins were fermented rapidly and consequently shifted fermentation of other consumed DFs (e.g. cereal AXs) to more distal part of colon, although low-methyl esterified pectin was more efficiently fermented by the microbiota than high-methyl esterified pectin. Results suggested that pectins can confer beneficial health effects through modulation of the gut microbiota. In a last in vivo experiment, citrus pectins together with a hydrothermal treated soybean meal were supplemented to pig diets to study their effect on the digestion and fermentation of carbohydrates in both the small and large intestine. Pectins, and more particularly low-methyl esterified pectin, decreased the ileal digestibility of digestible starch resulting in more starch to be fermentated in the proximal colon of pigs. Consequently, also the fermentation patterns of DFs and the microbiota composition was affected. All pectins tested shaped the colonic microbiota from a Lactobacillus-dominated microbiota to a Prevotella-dominated community, with potential health-promoting effects.

    How mushrooms feed on compost: conversion of carbohydrates and linin in industrial wheat straw based compost enabling the growth of Agaricus bisporus
    Jurak, E. - \ 2015
    Wageningen University. Promotor(en): Harry Gruppen, co-promotor(en): Mirjam Kabel. - Wageningen : Wageningen University - ISBN 9789462573116 - 156
    paddestoelen - champignonmest - koolhydraten - degradatie - substraten - compostering - agaricus bisporus - mushrooms - mushroom compost - carbohydrates - degradation - substrates - composting - agaricus bisporus


    In this thesis, the fate of carbohydrates and lignin was studied in industrial wheat straw based compost during composting and growth of Agaricus bisporus. The aim was to understand the availability and degradability of carbohydrates in order to help improve their utilization in the compost. The wheat straw based compost was characterized as being composed mainly of cellulose and lowly substituted xylan. During the first phase of composting, ester-bound substituents were removed from the xylan backbone and during the second phase of composting 50% of carbohydrates present in the original material where metabolized in a uniform manner. Lignin structure, however, remained unaltered during these composting stages. Over the period of A. bisporus mycelium growth, 20% of the original xylan became water soluble while xylan structures remained rather similar and the remaining water insoluble xylan was partially degraded. In addition, 40% of lignin was metabolized during mycelium growth with an increase in the ratio of syringyl to guaiacyl lignin units from 0.5 to 0.7 in mycelium grown compost compared to the basic compost mixture. During the fruiting body formation minor changes in lignin structure occurred, while accumulation of xylan substituents was observed for arabinosyl residues and glucuronic acid substituents. Finally, putative genes encoding carbohydrate degrading enzymes were identified in A. bisporus’ genome. Genes involved in the pentose and hexose catabolic pathway were found to be upregulated in A. bisporus mycelium. A. bisporus was found to produce both xylan and cellulose degrading enzymes and maximum activity was observed during the formation of the 1st flush of mushrooms. But, as observed from the remaining xylan structures analyzed, A. bisporus lacks the enzymatic activity to degrade xylan substituted with two arabinosyl- residues and glucuronic acid substituted xylan.

    Edita Jurak

    How Mushrooms feed on compost: Conversion of carbohydrates and linin in industrial wheat straw based compost enabling the growth of Agaricus bisporus

    Gestational diabetes mellitus in Tanzania : public health perspectives
    Mwanri, A.W. - \ 2015
    Wageningen University. Promotor(en): Edith Feskens, co-promotor(en): J.L. Kinabo; K. Ramaiya. - Wageningen : Wageningen University - ISBN 9789462572645 - 202
    diabetes mellitus - voedselintolerantie - zwangerschap - zwangerschapscomplicaties - obesitas - koolhydraten - diabetes mellitus - food intolerance - pregnancy - pregnancy complications - obesity - carbohydrates

    Gestational diabetes mellitus in Tanzania – public health perspectives


    Background: Gestational diabetes mellitus (GDM) is defined as carbohydrate intolerance resulting in hyperglycaemia of variable severity with onset or first recognition during pregnancy. Women with GDM are at increased risk for preeclampsia during pregnancy and for delivery complications. In most cases GDM ends after pregnancy, but it increases the risk for future type 2 diabetes, and cardiovascular diseases, to both the mother and the child. With the current increase in prevalence of overweight/obesity and type 2 diabetes in Tanzania and other Sub Saharan African countries, it is possible that GDM may exist and may be on the rise.

    Methods: A cross-sectional survey was done in 2011 through 2013 where 910 women in Tanzania (609 from urban, 301 from rural areas) were studied during their usual antenatal clinic visits. Weight, height, mid upper arm circumference (MUAC), blood pressure and haemoglobin levels were measured by a trained technician. Blood glucose was measured at fasting and at two hours after 75 g oral glucose tolerance test. Women were classified as having GDM using WHO 1999 criteria. Sociodemographic information was collected through face-to-face interviews using structured questionnaire or retrieved from the antenatal clinic card. Dietary intake data was collected using 24-hour recall interview and foods were categorised into groups based on dietary diversity. The international physical activity questionnaire (IPAQ) was used to assess activities in the past one week. Information on birth outcome was obtained from 466 urban mothers (response rate 77%) through telephone interviews. To estimate the burden of GDM in the region, we additionally conducted a systematic search of published literature on the prevalence and risk factors of GDM in Sub Saharan Africa. Out of the 22 reviewed studies, 15 studies graded as having low or moderate risk of bias were included in a meta-regression analysis. Finally, a review of literature regarding the health system and antenatal care was done and supported by a survey to assess antenatal care services in 24 health facilities that provide maternal and childcare services in Dar es Salaam region.

    Results: The prevalence of GDM was much higher among women residing in the urban (8.4%) compared to those in the rural areas (1.0%), which was much higher compared to 0% reported in the 1990s. Prevalence of GDM was higher for women who had a previous stillbirth, family history of type 2 diabetes and MUAC ≥28 cm, and lower for women with normal haemoglobin concentrations compared to those with anaemia. Likewise, the prevalence of hypertension disorders of pregnancy (HDP) was higher in urban (8.9%) compared to rural areas (5.3%). Risk factors for HDP in urban women were advanced maternal age, high MUAC, gestional age and being HIV positive, and in rural women age and gestational age.

    We reviewed 22 studies conducted in six out of the 47 Sub saharan African countries. Heterogeneity between the studies was high and it could not be significantly explained by study setting, population, diagnostic criteria, or the year the study was done. Nevertheless, a relatively higher prevalence was observed in studies done after the year 2000, when women at risk were selected and when more current diagnostic criteria were used. The prevalence was up to about 14.0% when women with at least one risk factor were studied. In Dar es Salaam women, despite a high prevalence of anemia and HIV, the prevalence of macrosomia was higher (5.9%) compared to the prevalence of low birth weight (3.6%). Presence of GDM (OR 3.46, 95% CI 1.01-11.85) and birth weight of the previous child (OR 2.42, 95% CI 1.17-4.99) were the main predictors of macrosomia and HDP (OR 3.75, 95% CI 1.11-12.68) was the main predictor of low birth weight. Although glucose testing in urine appeared to be universally done in the urban setting, the sensitivity of this test for detection of GDM is low. Therefore selective blood glucose testing should be implemented and HIV testing and counselling may be used as an entry point.

    Conclusions: The prevalence of GDM and HDP was higher in the urban compared to the rural areas in Tanzania, indicating an increasing in women who are at risk for delivery complications, poor pregnancy outcomes, type 2 diabetes and cardiovascular diseases in later life. The risk factors observed can be used to identify risk groups for screening and as target for prevention interventions. To inform policy makers and for better health care planning, further studies on the costs for blood glucose testing during the usual antenatal clinic visits and on the management of women with GDM are warranted.

    Koolhydraten bieden scala aan mogelijkheden voor gezonde levensmiddelen
    Schols, H.A. - \ 2014
    Wageningen : Wageningen UR
    voedingsvezels - koolhydraten - voeding en gezondheid - voedingsstoffen - analytische methoden - voedselonderzoek - dietary fibres - carbohydrates - nutrition and health - nutrients - analytical methods - food research
    Koolhydraten in onze voeding leveren energie en zorgen voor een gemakkelijke stoelgang. Van de vele verschillende koolhydraatmoleculen, waaronder tal van soorten kleine suikers, zetmeel en voedingsvezels, weten we echter betrekkelijk weinig. Dat geldt ook voor hun rol tijdens het bewaren en verwerken van levensmiddelen of voor de invloed van koolhydraten op de gezondheid.
    GM1-derived carbohydrates for pathogen and antibody detection : synthesis and biological evaluation
    Garcia Hartjes, J. - \ 2014
    Wageningen University. Promotor(en): Han Zuilhof, co-promotor(en): Tom Wennekes. - Wageningen : Wageningen University - ISBN 9789462571273 - 240
    koolhydraten - moleculaire detectie - antilichamen - pathogenen - remmers - biotesten - carbohydrates - molecular detection - antibodies - pathogens - inhibitors - bioassays
    Dietary carbohydrates and denitrification in recirculating aquaculture systems
    Meriac, A. - \ 2014
    Wageningen University. Promotor(en): Johan Verreth. - Wageningen : Wageningen University - ISBN 9789462570351 - 129
    dieren - vissen - aquacultuur - koolhydraten - denitrificatie - aquacultuur en milieu - feces - vezels - recirculatie aquacultuur systemen - animals - fishes - aquaculture - carbohydrates - denitrification - aquaculture and environment - faeces - fibres - recirculating aquaculture systems

    Due to overfishing of global fish stocks and increasing fish meal prices, plant ingredients are being increasingly used as an alternative source of protein in fish feeds. However, the inclusion of unpurified plant ingredients will also increase the content of fibers in feeds. Fibers are nearly indigestible and will therefore increase solid waste production in aquaculture. This solid waste can be used to as a carbon source for denitrification to control nitrate levels in recirculating aquaculture systems (RAS), thereby reducing both solid and dissolved waste production. Additionally, fibers can change the recovery characteristics and lower the degradability of fecal waste. Therefore, this study investigates how changes in the dietary carbohydrate composition can affect waste production, system performance and denitrification in RAS. Furthermore, ultrasound treatment (to decrease particle size in fecal waste) and enzymatic conditioning (to increase fiber degradability) were tested as possible means to increase the bioavailability of carbon in fecal waste for denitrification.

    Comparing a high fiber (HNSP) and low fiber (LNSP) diet in RAS stocked with rainbow trout confirmed that the fibers in the HNSP diet increase fecal waste production. Although the HNSP diet produced more fecal waste than the LNSP diet, both diets produced the same amount of biodegradable fecal carbon. Since feces removal was higher in RAS using the HNSP diet, the load of degradable organic matter on the biofilters was lower with the HNSP diet than with the LNSP diet. Furthermore, fecal waste produced with the HNSP diet contained larger particles than feces of the LNSP diet, which could also improve the recovery of fecal waste with microscreens. Feces produced with the HNSP diet were also less degradable than feces produced with the LNSP diet. By using fecal waste as an internal carbon source for denitrification, solid and dissolved waste emissions from RAS could be reduced by ~50% for the HNSP diet. However, only approximately half of the supplied cellulose and hemicellulose were degraded in the denitrification reactors, whereas lignin was not degraded at all. Thus, the overall degradability of organic carbon in fecal waste was limited by fibers as hemicellulose, cellulose and lignin. Ultrasound and enzymatic conditioning did not sufficiently increase the degradability of fecal waste. Nonetheless, fibers originating from unpurified plant ingredients may also have beneficial effects on RAS performance by increasing fecal recovery. A more selective choice of feed ingredients could be used to increase the recovery and degradability of fecal waste in RAS.

    Fructan biosynthesis in crop plants : the molecular regulation of fructan biosynthesis in chicory (Cichorium intybus L.)
    Arkel, J. van - \ 2013
    Wageningen University. Promotor(en): Harro Bouwmeester, co-promotor(en): Ingrid van der Meer. - S.l. : s.n. - ISBN 9789461736635 - 158
    cichorium intybus - gewassen - zea mays - solanum tuberosum - transgene planten - koolhydraten - fructanen - biosynthese - inuline - polymerisatie - cichorium intybus - crops - zea mays - solanum tuberosum - transgenic plants - carbohydrates - fructans - biosynthesis - inulin - polymerization

    Fructan is a polymer of fructose produced by plants and microorganisms. Within the plant kingdom about 45.000 species accumulate fructan as storage carbohydrate in addition to, or instead of, starch. Fructan accumulating species are mainly found in temperate and sub-tropical regions with seasonal or sporadic rainfall. During the last decades, the use of fructan in the (food) industry has rapidly evolved, because of its health promoting characteristics and interesting functional properties.Chicory (Cichorium intybus L.) is a biennial taproot-bearing crop plant that is grown for the production of inulin on an industrial scale. Inulin, a ß(2,1) linked linear fructan with a terminal glucose residue, is stored in the chicory taproots. The degree of polymerisation (DP) determines the application of the inulin and hence the value of the crop. This leads us to the central question of this thesis:

    What regulates the fructan yield and the degree of polymerisation, and how can we modify this?

    The DP is highly dependent on the field conditions and harvest time, and therefore the first step in answering this question was tostudy the regulation of fructan (inulin) metabolism throughout the growing season. This is described in Chapter 2. Metabolic aspects of inulin production and degradation in chicory were monitored in the field and under controlled conditions. We determined the concentrations of soluble carbohydrates, the inulin mean degree of polymerisation (mDP), inulin yield, gene expression and activity of enzymes involved in inulin metabolism in the taproots. Inulin biosynthesis - catalysed by sucrose: sucrose 1-fructosyltransferase (EC (1-SST) and fructan: fructan 1-fructosyltransferase (EC (1-FFT) - started at the onset of taproot development. Inulin yield increased with time following a sigmoid curve reaching a maximum in November. The maximum inulin mDP of 15 was reached in September and then gradually decreased. Based on the changes observed in the pattern of inulin accumulation, we defined three phases in the growing season and analysed product formation, enzyme activity and gene expression in these defined periods. The results were validated by performing experiments under controlled conditions in climate rooms. Our results show that the decrease in 1-SST is not regulated by day length and temperature. From mid-September onwards the mDP decreased gradually although inulin yield still increased. This is most probably the result from back-transfer activity of 1-FFT and fructan exohydrolase activity (EC (1-FEH). In plants 1-FEH catalyses the breakdown of fructan in order to release the stored carbohydrates necessary in periods of stress, like cold or drought periodsor flowering. This information was used to design two strategies to obtain the desired, increased inulin DP and yield. Overexpression of 1-SSTwas performed to increase the mDP and to keep the sucrose concentration low, to prevent 1-FFT from depolymerizing inulin. The result was a higher mDP during the growing season. Unfortunately, no effect on the mDP was seen at the end of the growing season, most probably due to activity of FEH. Secondly, anFEH I antisense fragment was introduced into chicory in order to block depolymerisation at the end of the growing season. This resulted in a reduction in FEH Iexpression upon cold induction, but had only minor effects on the mDP. The degradation of inulin was most probably caused by the remaining 1-FEH activity. Overall this study showed that inulin metabolism in chicory is tightly regulated, but also revealed options to further steer inulin metabolism in chicory.

    The next step in answering the central question was to study the regulation of the genes involved in fructan biosynthesis. In Chapter 3this was studied at three different levels. Firstly, fructan gene expression and carbohydrate concentrations were studied in axial sections of mature chicory root, revealing the highest expression levels and carbohydrate levels in the phloem. Correlations were found between the gene expression patterns of 1-SST, 1-FFT and the carbohydrate levels, suggesting a possible involvement of sugars in the regulation of 1-SSTand 1-FFTgene expression. Secondly, the induction of 1-SSTand 1-FFTexpression was studied in excised chicory leaves. Expression of both 1-SSTand 1-FFTwas induced upon sucrose and glucose feeding, suggesting that both genes are at least partly regulated in the same way. Upon fructose feeding, the induction of fructan biosynthesis was less pronounced than with sucrose. The expression of 1-SSTwas induced by fructose but this resulted in only low amounts of 1-kestose. The expression of 1-FFTwas not induced upon fructose feeding.Thirdly, to further unravel the mechanism of induction, the promoters of 1-SSTand 1-FFTfrom chicory were isolated and characterized through in silicoand in planta(only 1-FFT) analysis. Computational analysis of fructosyltransferase (FT) promoters revealed elements that are common in fructan biosynthesis-promoters among different species and also occur in Arabidopsis promoter sequences. One of these elements is predominantly present in genes involved in sugar metabolism and transport. This element did also contain a core sequence involved in MYB transcription factor binding important for fructan biosynthesis activation in wheat, as was published recently. An 1100bp 1-FFTpromoter fragment was shown to be functional in transgenic chicory and in the non-fructan accumulating plants species, Arabidopsis and potato. Application of carbohydrates resulted in the expression of the reporter gene GUS comparable to 1-FFTexpression upon carbohydrate feeding in chicory. This study provides information on the regulation of inulin biosynthesis, suggestions for studies on transcription factors, and provides a promoter for steering the expression of fructan biosynthetic genes in transgenic plants. An alternative way for the production of inulin with the desired DP and yield, circumventing the problems in chicory rather than trying to solve them, is the introduction of the fructan biosynthetic pathway in non-fructan metabolizing and catabolizing plant species.

    Towards this end we have expressed the inulin synthesizing enzymes, 1-SST and 1-FFT from Jerusalem artichoke, in maize and potato, as described inChapter 4. Transgenic maize plants produced inulin type fructan (at 3.2 milligram per gram kernel) and kernel development was not affected. Potato tubers expressing 1-SSTaccumulated 1.8 milligram inulin per gram tuber while tubers with a combined expression of 1-SSTand 1-FFTaccumulated 2.6 milligram inulin per gram tuber. Inulin accumulation in maize kernels was modulated by kernel development, first peaking in young seeds and then decreasing again through degradation during late kernel development. In potato, inulin mDP was relatively stable throughout tuber development and little evidence of degradation was observed. The accumulation of 1-kestose in transgenic maize correlated positively with kernel sucrose concentration and introduction of the fructan biosynthetic pathway in a high-sucrose maize background increased inulin accumulation to 41 milligram per gram kernel kernel. This study shows the importance of sugar availability and the absence of degradation mechanisms in platform crops for tailor-made fructan production.

    Further evaluation of the production of tailor-made inulin and putative platform crops is discussed in Chapter5.Here we come to the conclusion that the mDP, the distribution and yield depend on the origin of the fructan biosynthesis genes and the availability of sucrose in the host. The combination of genes from different origins could result in new types and different lengths of fructan molecules resulting in (new) specific properties of fructan. Limitations for the production of tailor-made fructan in chicory are not seen in putative new platform crops, such as sugar beet, sugarcane and rice.

    The work described in this thesis on fructan biosynthesis in chicory and in new platform crops has resulted in new insights that will lead new applied and fundamental research in this field.

    Physiological ecology of the frankincense tree
    Mengistu Woldie, T. - \ 2011
    Wageningen University. Promotor(en): Frans Bongers; G. Fetene, co-promotor(en): Frank Sterck. - S.l. : s.n. - ISBN 9789085859277 - 127
    boswellia - koolstof - ecologie - plantenfysiologie - tappen (rubber) - bosgebieden - koolhydraten - bladoppervlakte - bomen - harsen - harswinning - ethiopië - boswellia - carbon - ecology - plant physiology - tapping - woodlands - carbohydrates - leaf area - trees - resins - resin extraction - ethiopia

    Keywords: Boswellia papyrifera, carbon balance, drylands, Ethiopia, frankincense, tapping

    The degradation of frankincense tree dominated woodlands has been attributed to climatic
    conditions and human activities. We lack however information on how such factors influence the
    resource balance and productivity of trees. The aim of this study was to evaluate the impact of
    resin tapping on the whole tree carbon gain, storage and allocation pattern of frankincense trees
    (Boswellia papyrifera (Del.) Hochst) in the dry woodlands of northern Ethiopia. I hypothesized
    that the intensive resin tapping of frankincense trees reduces tree vitality, particularly under
    relatively dry conditions. I established experimental plots in the highland woodlands of
    Abergelle and the lowland woodlands of Metema, and applied tapping treatments to similar sized
    adult trees (DBH 20 +/- 3cm). For these trees I also collected data on leaf gas exchange, crown
    traits, carbon storage, carbon allocation, growth and frankincense production during a period of
    two years (2008-2009).
    Trees follow similar leaf gas exchange patterns in contrasting environments, but differ in
    annual crown carbon gain between highland and lowland sites. Highland trees of Boswellia had a
    higher photosynthetic capacity, were exposed to higher light conditions, but had a shorter leaf
    lifespan than lowland trees. Integrating these effects, I showed that the annual crown carbon gain
    is higher in the highland trees than in lowland trees. Lowland trees are mainly constrained by
    clouded conditions and resultant low light levels during the wet season, limiting their carbon
    gain. Moreover, carbon gain was also restricted by atmospheric drought, and much less by soil
    water deficit during the growing season. The production of frankincense was not affected by the
    annual tree carbon gain implying that trees with smaller total leaf area may suffer sooner from
    carbon starvation by tapping.
    Tapping reduced storage carbohydrate concentrations in wood, bark and root tissues
    indicating that continuous tapping depletes the carbon reserves. A large part of the carbohydrate
    concentration in the plant tissues was starch. Boswellia trees have more total nonstructural
    carbohydrates (TNC) concentrations and pool sizes in wood than in root and bark tissues.
    Because tapped trees face depleting carbon storage pools during the dry tapping season and
    cannot fully replenish these pools during the wet season, tapped trees may face higher risks of
    carbon starvation compared to untapped trees in the long term.
    Estimated total annual carbon sinks to the different plant components were 38-68% of the
    annual carbon gain in both study sites. However, Boswellia trees also establish mycorrhizal
    associations which may consume an additional 20% of gross primary production. On a wholetree
    basis, the percentage of autotrophic respiration may exceed all other costs. The foliage
    construction costs and incense production are the second and third largest carbon sinks,
    respectively. Contrary to our expectation, the sum of all dry season carbon costs was higher than
    the total amount of consumed TNC during the dry season. The high carbon costs during the dry
    season imply that trees do not fully depend on TNC to pay for the carbon costs during the dry
    season. With the exception of carbon allocation to foliage production and maintenance, a higher
    gross primary production does not enhance an overall increase in carbohydrate investments in
    the other sinks. Therefore, the carbon allocation pattern is constrained not exclusively by the
    absolute amount of carbon gained but also by other factors.
    The results clearly indicate that continuous tapping depletes the amount of stored carbon,
    the leaf area production and the reproductive effort. These negative effects were however site
    specific and could possibly be apparent sooner for smaller trees than for larger ones. Thus,
    guidelines for resin tapping of Boswellia trees should consider tapping intensity, tapping
    frequency, environmental conditions and tree size and should focus on maintaining vital trees
    and populations for the future.

    Background information and biorefinery status, potential and Sustainability: Task 2.1.2 Market and Consumers; Carbohydrates
    Bos, H.L. ; Harmsen, P.F.H. ; Annevelink, E. - \ 2010
    Wageningen : Wageningen UR - Food & Biobased Research (Star-Colibri Deliverable 2.1.2) - 28
    koolhydraten - markten - biobased economy - chemie op basis van biologische grondstoffen - biopolymeren - bioraffinage - reststromen - coproductie - carbohydrates - markets - biobased economy - biobased chemistry - biopolymers - biorefinery - residual streams - coproduction
    This report was produced to give an overview of present and future market for biorefinery products based on carbohydrates. Various studies show that there is a wealth of possible molecules and products that can be produced from carbohydrates. Carbohydrates already find significant application in starch products and cellulose plastics and fibres. However, for a biorefinery to operate in an economically sustainable way, applications for (preferably all) biomass ingredients need to be found. Presumably the optimal mix of applications will be a combination of larger volume/smaller value and smaller volume/higher value applications. For this study we therefore have taken a molecular approach. Looking at the size of possible end markets for the molecules that can be based on carbohydrates a number of main products come into view: dialcohols, dioic acids, 2,5 furan dicarboxylic acid and ethanol. These molecules with a wide application range can serve as basis targets for the carbohydrate stream of a biorefinery, provided the production processes are optimised to make them competitive to the petrochemical counterparts. Speciality applications for the resulting side streams will then need to be found on a case by case basis.
    Plant - Microbiele Brandstofcel (MFC): exudate productie : het optimaliseren van wortelexudatie met een split-root systeem
    Khodabaks, M. ; Blok, C. ; Berg, C.C. van den; Snel, J.F.H. - \ 2009
    Bleiswijk : Wageningen UR Greenhouse Horticulture - 13
    akkerbouw- en tuinbouwbedrijven - kassen - exudaten - wortelexudaten - secreties - aminozuren - organische zuren - micro-organismen - organische stof - suikers - koolhydraten - teelt onder bescherming - microbiële brandstofcellen - glastuinbouw - biobased economy - crop enterprises - greenhouses - exudates - root exudates - secretions - amino acids - organic acids - microorganisms - organic matter - sugars - carbohydrates - protected cultivation - microbial fuel cells - greenhouse horticulture
    De plant microbiële brandstofcel of Plant Microbial Fuel Cell (Plant$MFC) is een technologie die het op basis van een nieuw principe mogelijk maakt direct elektriciteit of biofuels aan een plant te onttrekken, zonder dat deze geoogst hoeft te worden (Strik en Helderman, 2004). Levende planten zetten door fotosynthese zonne-energie om in energiehoudende biomassa zoals eiwitten, suikers, zetmeel, cellulose en ligine. Van de netto vastgelegde koolstof wordt doorgaans een fractie van 40 tot 60 % naar de wortels getransporteerd. Van de hoeveelheid koolstof getransporteerd naar het wortelstelsel wordt door planten een fractie van 50 tot 70 % uitgescheiden naar de bodem in oplosbare vorm (exudaten en secreties). Deze exudaten en secreties bestaan onder andere uit suikers, aminozuren, organische zuren en koolhydraten welke gemakkelijk door micro-organismen kunnen worden omgezet. De uitgescheiden organische stof kan deels door natuurlijk voorkomende micro-organismen worden omzet in electriciteit. Als deze electriciteit in de een of ander vorm wordt opgevangen en benut is sprake van een MFC. In een MFC is het zaak het aandeel en de activiteit van de electriciteit producerende micro-organismen hoog te maken en te houden
    Schimmels veroorzaken merendeel van de plantenziekten : voortdurende wapenwedloop tussen plant en schimmel
    Kierkels, T. ; Heuvelink, E. - \ 2008
    Onder Glas 5 (2008)3. - p. 4 - 5.
    schimmel - plantenziekteverwekkende schimmels - koolhydraten - assimilatie - ziekteresistentie - antagonisten - ondersteunende maatregelen - gewasbescherming - glastuinbouw - moulds - plant pathogenic fungi - carbohydrates - assimilation - disease resistance - antagonists - support measures - plant protection - greenhouse horticulture
    Schimmels kunnen niet zelf assimileren en maken daarom gebruik van dat vermogen van planten. Cruciaal is dat ze planten moeten binnendringen om bij de koolhydraten te kunnen komen. Daartoe hebben ze tal van manieren ontwikkeld, mechanisch en chemisch. De plant op zijn beurt zet blokkades en chemie in om de schimmels te weren. Een goed groeiende, gezonde plant is in het algemeen weerbaar genoeg. Inzicht in de 'wapenwedloop' tussen schimmel en plant wijst een teler de weg naar ondersteunende maatregelen
    Onderzoek moet uniformer stek bij siergewassen opleveren (o.a. interview met Hendrik-Jan van Telgen)
    Staalduinen, J. van; Telgen, H.J. van - \ 2007
    Onder Glas 4 (2007)8. - p. 54 - 55.
    siergewassen - rozen - potplanten - vermeerderingsmateriaal - stekken - fotosynthese - meting - technieken - koolhydraten - beworteling - onderzoek - glastuinbouw - snijbloemen - ornamental crops - roses - pot plants - propagation materials - cuttings - photosynthesis - measurement - techniques - carbohydrates - rooting - research - greenhouse horticulture - cut flowers
    Het slagingspercentage en de uniformiteit van stekken worden mede bepaald door inwendige factoren, zoals fotosynthesecapaciteit en de koolhydraatstatus in het blad. Met behulp van diverse meettechnieken onderzoekt een projectteam of op basis van de gemeten waarden voorspellingen mogelijk zijn over de mate van beworteling en uitgroei. Als dat zo is, kunnen deze technieken bijdragen aan optimalisatie van de bedrijfsprocessen op vermeerderingsbedrijven
    Het effect van voersamenstelling op bacteriële darmaandoeningen bij varkens = The effect of feed composition on bacterial intestinal diseases in pigs
    Meulen, J. van der; Peet-Schwering, C.M.C. van der - \ 2007
    Lelystad : Animal Sciences Group (Rapport / Animal Sciences Group, Divisie Veehouderij 83) - 14
    varkens - dierhouderij - diervoeding - voersamenstelling - koolhydraten - darmziekten - diergezondheid - bacterieziekten - dysenterie - varkensdysenterie - colitis - enteritis - salmonellose - pigs - animal husbandry - animal nutrition - feed formulation - carbohydrates - intestinal diseases - animal health - bacterial diseases - dysentery - swine dysentery - colitis - enteritis - salmonellosis
    Feed composition, and especially carbohydrate composition, may affect the development of enteric bacterial diseases. Also the kind of feed ingredients (soybean or not) and feed treatment (milling size, pelletizing, fermentation) may be important. A more coarse grinding, no pelletizing and fermentation may be preferable in the reduction of the development of enteric bacterial diseases.
    Chemical composition of lamina and sheath of Lolium perenne as affected by herbage management
    Hoekstra, N.J. ; Struik, P.C. ; Lantinga, E.A. ; Schulte, R.P.O. - \ 2007
    NJAS Wageningen Journal of Life Sciences 55 (2007)1. - ISSN 1573-5214 - p. 55 - 73.
    afsnijhoogte - grasbestand - voedergewassen - lolium perenne - hergroei - rotaties - chemische samenstelling - graslandbeheer - voedingswaarde - lignine - totale hoeveelheid droge stof - koolhydraten - stikstof - vezelgehalte - bloeiwijzen - cutting height - herbage - fodder crops - lolium perenne - regrowth - rotations - chemical composition - grassland management - nutritive value - lignin - total solids - carbohydrates - nitrogen - fibre content - inflorescences - water-soluble carbohydrate - neutral detergent fiber - dairy-cows - nitrogen application - nutritive-value - ryegrass varieties - animal nutrition - milk-production - rumen function - l. cultivars
    The quality of grass in terms of form and relative amounts of energy and protein affects both animal production per unit of intake and nitrogen (N) utilization. Quality can be manipulated by herbage management and choice of cultivar. The effects of N application rate (0, 90 or 390 kg N ha¿1 year¿1), duration of regrowth period (2¿3, 4¿5, or 6¿7 weeks), and cutting height (8 or 12 cm) on the mass fractions of nitrogen (N), water-soluble carbohydrates (WSC), neutral detergent fibre (NDF), acid detergent fibre (ADF), lignin and ash in lamina and sheath material of a high-sugar (Aberdart) and a low-sugar (Respect) perennial ryegrass (Lolium perenne) cultivar, were studied in a factorial field experiment during four seasons in 2002 and 2003. Expressing NDF and ADF mass fractions in g per kg WSC-free dry matter (DM) increased the consistency of treatment effects. The high-sugar cultivar had generally higher WSC mass fractions than the low-sugar cultivar, especially during the late season. Moreover, the relative difference in WSC mass fraction between the two cultivars tended to be higher for the lamina material than for the sheath material, which suggests that the high-sugar trait may be more important under grazing conditions, when lamina forms the bulk of the intake, than under mowing regimes. Longer regrowth periods and lower N application rates increased WSC mass fractions and decreased N mass fractions; interactions between regrowth period and N application rate were highly significant. The mass fractions of NDF and ADF were much less influenced. The NDF mass fraction in terms of g per kg WSC-free DM tended to be higher at lower N application rates and at longer regrowth periods. The effect of cutting height on herbage chemical composition was unclear. In conclusion, high-sugar cultivars, N application rate and length of the regrowth period are important tools for manipulating herbage quality.
    Rumen development in veal (preruminant) calves
    Suárez, B.J. - \ 2006
    Wageningen University. Promotor(en): Seerp Tamminga, co-promotor(en): Walter Gerrits; Jan Dijkstra. - [S.l.] : S.n. - ISBN 9789085045366 - 174
    vleeskalveren - pensontwikkeling - pensfermentatie - concentraten - ruwvoer (roughage) - voer - samenstelling - koolhydraten - enzymactiviteit - mestresultaten - kalvervoeding - veal calves - rumen development - rumen fermentation - concentrates - roughage - feeds - composition - carbohydrates - enzyme activity - fattening performance - calf feeding
    Historically, veal calves were fed until slaughter weight with only milk replacer and, in absence of solid feed the physiological development of the forestomachs was limited. In 1997, a new EU legislation stipulated that a minimum amount of solid feed (fiber) has to be provided for the welfare of the calves (solid feed supply reduce abnormal oral behaviors in veal calves; Van Putten, 1982; Veissier et al., 1998); however, no specifications were made about the type and source of feed.

    Rumen development is triggered by the production of VFA resulting from fermentation ofOMin the rumen (Flatt et al., 1958). Butyrate, and to a lesser extent propionate stimulate the development of the rumen mucosa; mostly because of their use as energy sources by the rumen epithelium (Sander et al., 1959; Tamate et al., 1962). In rearing calves, information on rumen fermentation of different sources of dietary carbohydrates is relatively well documented (Davis and Drackley, 1998; Lesmeister and Heinrichs, 2004) but only a few experiments have been conducted in veal calves.

    Based on earlier research (Blokhuis et al., 2000) it was hypothesized that stimulating early rumen development in veal calves would be beneficial to their subsequent performance and health. Therefore in vivo experiments were designed to establish the effects of stimulating an early rumen development in veal calves, aiming to optimize nutrient utilization from rumen fermentation and to prevent health problems in the lower gastrointestinal tract (e.g. ulcers in abomasum). In addition the potential interactions of feeding solid feed with a milk replacer based diet were investigated. Finally but not least, the development and evaluation (comparison) of techniques for estimating fermentation characteristics of different substrates, to facilitate the choice of feed ingredient for veal calves diets was also carried out. 

    Chapter 2:This study was conducted to evaluate the effects of concentrate intake, differing in carbohydrates composition in addition to a milk replacer, on growth performance and rumen fermentation characteristics in veal calves. Accordingly, 160 Holstein Friesian x Dutch Friesian male calves, were fed with one of the following treatments: 1) milk replacer control (CONTROL), 2) pectin-based concentrate (PECTIN), 3) neutral detergent fiber (NDF) based concentrate, 4) starch-based concentrate (STARCH) and 5) mixed concentrate (MIXED) (equal amounts of concentrates of treatments 2, 3, and 4). Concentrate diets were provided in addition to a commercial milk replacer Results: Calves showed an ADG varying between 0.70 and 0.78 kg/d, with a rumen fermentation in concentrates fed calves characterized by a low pH (4.9 - 5.2), relatively low VFA concentrations between 100 and 121 mmol/L and high concentrations of reducing sugars (33-66 g/kg DM). Calves fed the CONTROL diet had higher lactate concentration (21mmol/L) than concentrate fed calves (between 5 and 11 mmol/L). Results indicated that the carbohydrate source can influence intake, growth rate and rumen fermentation in young veal calves.

    Chapter 3:This experiment aimed to gain an insight into the effects of age (calves were euthanized either at the end of 8 or 12 weeks of age) and concentrate supplementation, differing in carbohydrates composition, on rumen development in young veal calves. Moreover, some selected plasma metabolites as predictors of rumen development were evaluated. Diets treatments correspond to those described in Chapter 2. Results: Feeding concentrates differing in carbohydrate composition to veal calves promoted rumen development compared with calves fed milk replacer only. In most calves, a poorly developed rumen mucosa was observed. Coalescing rumen papillae with embedded hair, feed particles and cell debris were found in all calves fed concentrate diets. Calves fed concentrates had significantly heavier rumens than calves fed CONTROL. Although the variation in carbohydrate composition caused variation in rumen development, the latter was generally small. In the dorsal location of the rumen, calves fed concentrate diets showed an increased ratio of mucosa to serosa length (RMSL) than calves fed CONTROL. Mucosa thickness (MCT) and muscle thickness (MST) were bigger in the ventral and in the dorsal locations of the rumen, respectively.

    At 8 weeks, calves fed concentrate diets had higher plasma acetate concentrations than calves on the CONTROL treatment. However, at 12 weeks, only NDF fed calves showed significantly higher plasma acetate concentrations. For plasma BHBA concentration no differences were observed among treatments at 12 weeks. Results from a principal component analysis indicated that veal calves, in addition to rumen volatile fatty acids (VFA) concentrations, other factors are likely to affect rumen development.  

    Chapter 4:This experiment was designed based on the results obtained in experiment 1 (Chapter 2 and 3) where in concentrate-fed veal calves a rumen environment, characterized by a sub clinical acidosis (pH< 5.2), relatively low VFA concentrations (100-120 mmol/L) and a rumen mucosa characterized by poorly shaped papillae with feed and cell debris embedded between them (referred as plaque formation) were observed. Feeding only roughage to young calves generally does not promote rapid papillae development (Nocek and Kesler, 1980); however, roughage consumption and its inherent coarseness stimulate the development of the rumen wall (Tamate et al., 1962) and rumination (Hodgson, 1971) and the healthiness of the rumen mucosa (Haskins et al., 1969). Information concerning the effects of roughage intake on veal calves performance and rumen development is scarce (Blokhuis et al., 2000; Cozzi et al., 2002). Therefore, it was hypothesized that adding small amount of roughage to a concentrate diet will improve and stimulates the development of the rumen wall, without having negative effects on calf's performance. Sixty four male Holstein Friesian x Dutch Friesian veal calves (46 kg ± 3.0 kg), were fed on of the following diets: 1) C100= concentrate only, 2) C70-S30= concentrate (70%) with straw (30%), 3) C70-G30= concentrate (70%) with dried grass (30%), 4) C70-G15-S15= concentrate (70%) with dried grass (15%) and straw (15%), 5) C70-CS30= concentrate (70%) with corn silage (30%), 6) C40-CS60= concentrate (40%) with corn silage (60%), 7) C70-CS30-AL= concentrate (70%) with corn silage (30%) ad libitum, 8) C70-G15-S15-AL= concentrate (70%) with dried grass (15%) and straw (15%) ad libitum. All dietary treatments were provided in addition to a commercial milk replacer. Concentrate was provided as pellets and roughage was chopped. Results: Roughage and intake level affects rumen fermentation and rumen development of veal calves. Substitution of part of the concentrate by roughage did not affect DMI and ADG, but among roughage sources feeding straw reduced DMI and ADG. The addition of roughage did not affect rumen pH (pH >5.3). Rumen fermentation was characterized by high total volatile fatty acids (VFA) and reducing sugars (RS) concentrations. Cobalt recovery, as an indication of milk leakage was found in the rumen, varying between 20.5 and 34.9 %, but it was not affected by dietary treatments. Roughage addition decreased the incidence of plaque formation and the incidence of calves with poorly developed rumen mucosa. However, morphometric parameters of the rumen wall were hardly influenced by the type and level of roughage. Results indicated that in veal calves, the addition of roughage to concentrate diets did not affect growth performance and positively influenced the macroscopic appearance of the rumen wall.

    Chapter 5:Several methodologies have been developed to characterize feedstuffs in terms of digestibility and degradability, comprising in vivo , in situ and in vitro methods.

    The gas production technique (GPT) provides gas production profiles that give an indication of the fermentative characteristics of the feed. The objective of this experiment was to estimate fermentation kinetic parameters of various solid feeds supplied to veal calves using the GPT, and to study the effect of adaptation of the rumen microflora to these solid feeds on their subsequent fermentation patterns. Thus, from the in vivo experiment described in Chapter 2 and 3; three out of five dietary treatments were selected as inoculum sources: pectin ( PECTIN ), neutral detergent fiber ( NDF ), and starch ( STARCH ). Sugar beet pulp ( SBP ), sugar beet pectin ( SBPec) , native corn starch ( NCS ), soy bean hulls ( SBH ) and crystalline cellulose ( AVICEL) were selected as substrates. For the second in vitro experiment, three out of eight dietary treatments (from the in vivo experiment described in Chapter 4) were selected as inocula. The selected diet treatments were: C100= concentrate only, C70-S30 = concentrate (70%) with straw (30%) and C70-CS30 = concentrate (70%) with corn silage (30%). For this gas production experiment, straw ( STRAW ), soy bean hulls ( SBH ), native corn starch ( NCS ) and sugar beet pectin ( SBPec ) were chosen as in vitro substrates.

    For both in vivo experiments, cumulative gas production was measured over time (72 h) as an indicator of the kinetics of fermentation. Fermentation end-products, including volatile fatty acids and ammonia, and organic matter loss, were also measured. Results : In both experiments significant differences between the inoculum sources, in terms of both fermentation kinetics characteristics and end-products of fermentation were observed. Similarly, significant effects were also observed for substrate compositions. Differences between the fermentation characteristics of NCS, SBPec and SBH, were consistent for both experiments. The total VFA production was not different among these substrates in both experiments. Finally, for both experiments, there was a significant inocula and substrate interaction which may indicate differences in the microbial activity occurring between the calves. Therefore, it was concluded that rumen inoculum from adapted animals should be used to obtain a more accurate assessment of feed ingredients in veal calf diets.

    Chapter 6 (General discussion) focused in four points: a) Factors influencing rumen development in rearing and veal calves; b) The importance of ruminal drinking in veal calves fed solids feeds; c) Effects of feeding strategies on ruminal pH and buffering capacity of rumen contents in veal calves; d) comparative analysis of the results obtained from the GPT (results presented in Chapter 5) and the PDE activities (results presented in Chapter 2 and 4).
    Limiting factors for the enzymatic accessibility of soybean protein
    Fischer, M. - \ 2006
    Wageningen University. Promotor(en): Harry Gruppen; Fons Voragen. - [S.l.] : S.n. - ISBN 9789085044963 - 139
    sojaeiwit - hydrolyse - aggregatie - koolhydraten - eiwitextractie - eiwitvertering - eiwitverteerbaarheid - peptiden - soya protein - hydrolysis - aggregation - carbohydrates - protein extraction - protein digestion - protein digestibility - peptides
    Soy is a commonly used ingredient is food and animal feed. With particular focus on the in-soluble fractions, this thesis deals with the effects of proteases and carbohydrate degrading enzymes on different soybean meals subjected to different extent of heating. The primary aim is to improve the understanding of enzymatic hydrolysis of SBM with emphasis on proteins and to identify barriers limiting the efficiency of the process. The results show that aggregation behavior of peptides during enzymatic processing of soy proteins is potentially a limiting factor for efficacy of protein extraction. Surprisingly, it is also demonstrated that aggregation is not limited to in vitro incubations, but is also occurring in vivo in the digestive system of pigs.
    Prebiotics in piglet nutrition? Fermentation kinetics along the GI tract
    Awati, A.A. - \ 2005
    Wageningen University. Promotor(en): Martin Verstegen, co-promotor(en): B.A. Williams; M.W. Bosch. - Wageningen : S.n. - ISBN 9789085041641 - 143
    biggen - anti-infectieuze middelen - koolhydraten - fermentatie - kinetica - voedertoevoegingen - microbiële ecologie - varkensvoeding - voedingsfysiologie - piglets - antiinfective agents - carbohydrates - fermentation - kinetics - feed additives - microbial ecology - pig feeding - nutrition physiology

    Keywords: fermentation, gas production, piglets

    The generalized theory behind the carbohydrate to protein fermentation in the GIT is that in presence of fermentable carbohydrate substrate, microbes prefer to ferment carbohydrate source to derive energy and use the nitrogen available for their own growth. With this background information, it was hypothesized that inclusion of fermentable carbohydrates in the piglet diet will reduce the protein fermentation, which will be confirmed by reduced levels of ammonia and branched chain fatty acids in end product profile of the fermentation. The aim of this thesis was to study the effects of inclusion of fermentable carbohydrates in weaning piglets' diet, on GIT fermentation and any changes in microbial community composition and activity. Weaning process in an intensified pig production system brings many sudden changes in the environmental and physical factors in piglets' life. These sudden changes, especially in diet cause serious imbalance in the microbial community. Quicker stabilization and diversification of microbial community post weaning, is crucial in attending the gut health and reducing the risk of pathogenic infections by 'Colonization resistance: As part of this overall aim, the in vitro cumulative gas production technique was used to study the fermentation of selected fermentable substrates. While these substrates namely lactulose, inulin, wheat starch and sugar beet pulp (SBP) were included in test diet and their effect on GIT fermentation was studied in vivo. The combination of microbial community analysis based on fingerprinting techniques such as denaturing gradient gel electrophoresis (DGGE) with nutritional analysis of fermentation end product profiles, was used in vivo and in vitro studies. In in vivo trials, emphasis was given on using combination of slow fermenting carbohydrate sources such as, SBP and wheat starch with fast fermenting lactulose and inulin. The hypothesis behind this approach was to induce carbohydrate fermentation along the GIT, by providing carbohydrate substrate for the microbiota in different parts of GIT. Especially by taking in to account the difference in the transit time of feed in the different parts of GIT, it was expected that fast fermenting lactulose and inulin would be fermented in small intestine while wheat starch somewhere in the beginning of the large intestine while, SBP will reach the distal part of colon. It was found that fermentation along the GIT was improved or in other words skewed more towards the carbohydrate fermentation in vivo. It was observed in vivo that inclusion of fermentable carbohydrates in the diet reduces the protein fermentation in the GIT and ammonia concentration in end product profile. This decrease was observed along the GIT and in time in faecal fermentation end product profiles post weaning. Microbial community analysis using fingerprinting techniques revealed that inclusion of fermentable carbohydrates stabilized and diversified microbial community in the ileum as well as in the colon by day 10 post weaning. This way, the prebiotic effects of fermentable carbohydrates was evidenced. -
    Effects of prebiotics, probiotics and synbiotics in the diet of young pigs
    Shim, S.B. - \ 2005
    Wageningen University. Promotor(en): Martin Verstegen, co-promotor(en): J.M.A.J. Verdonk. - s.l. : S.n. - ISBN 9789085041931 - 178
    biggen - probiotica - koolhydraten - anti-infectieuze middelen - voedertoevoegingen - microbiële ecologie - fermentatie - spijsverteringsstelsel - varkensvoeding - voer - diergezondheid - groei - voedingsfysiologie - piglets - probiotics - carbohydrates - antiinfective agents - feed additives - microbial ecology - fermentation - digestive system - pig feeding - feeds - animal health - growth - nutrition physiology

    Keywords: prebiotics, piglets, gut health
    Prebiotics are non-digestible carbohydrates that are not metabolized in the small intestine and fermented in the large intestine. Oligofructose are non-digestible oligosaccharides which may stimulate beneficial bacteria in the gut and may affect the gut ecosystem. Prebiotic effects will depend largely on their chemical structure (degree of polymerization). Dietary inclusion of probiotics in young pig diets may beneficially affect gut microbiota. Synbiotics, a combination of prebiotics and probiotics may also stimulate the gut ecosystem. The objective of this thesis was to evaluate the effects of pre-, pro- and synbiotics on the gut ecosystem, and some performance parameters. A series of in vivo and in vitro experiments were carried out using suckling and weaned piglets. The experimental results are discussed in this thesis. Overall, it was concluded that synbiotics, a combination of multi-strain probiotics and oligofructose, can positively affect performance especially feed intake, and can improve the gut health. However, we did not observe a clear synergistic effect compared to supplementing oligofructose or probiotics alone. A combination of high and low polymer inulin will probably be more beneficial for the intestinal ecosystem and health than using either high- or low polymer inulin alone. The present studies show that the pre-, pro- and synbiotic treatments affect gut microbiota and performance of young pigs.
    Vitaliteit van Freesiaknollen: opsporen van kritische factoren voor de vitaliteit van freesiaknollen in verband met heterogeniteit in de oogstfase
    Heij, G. ; Kersten, M. ; Slootweg, G. - \ 2004
    Naaldwijk : Praktijkonderzoek Plant & Omgeving B.V. (Rapport PPO ) - 21
    freesia - bloembollen - teelt onder bescherming - plantenontwikkeling - groeifasen, rijp - bollen - selectie - kwaliteit - planttijd - koolhydraten - nederland - freesia - ornamental bulbs - protected cultivation - plant development - maturity stage - bulbs - selection - quality - planting date - carbohydrates - netherlands
    Gastrointestinal Health Benefits of Soy Water-soluble Carbohydrates in Young Broiler Chickens
    Lan, Y. - \ 2004
    Wageningen University. Promotor(en): Martin Verstegen; Seerp Tamminga; G. Erdi, co-promotor(en): B.A. Williams. - [S.I.] : S.n. - ISBN 9789064649240 - 265
    vleeskuikens - pluimvee - koolhydraten - sojabonen - spijsverteringsstelsel - spijsverteringskanaal - diergezondheid - fermentatie - kinetica - darmen - morfologie - blindedarm - melkzuurbacteriën - immunoglobulinen - voedselbeperking - pluimveevoeding - diervoeding - broilers - poultry - carbohydrates - soyabeans - digestive system - digestive tract - animal health - fermentation - kinetics - intestines - morphology - caecum - lactic acid bacteria - immunoglobulins - food restriction - poultry feeding - animal nutrition
    Odour from pig production facilities: its relation to diet
    Dinh Phung, P.D. Le; Becker, P.M. ; Aarnink, A.J.A. ; Jongbloed, A.W. ; Peet-Schwering, C.M.C. van der - \ 2004
    Wageningen : Agrotechnology and Food Innovations (Rapport / Agrotechnology & Food Innovations 115) - ISBN 9789067547666 - 66
    varkensstallen - stankemissie - varkensvoeding - voersamenstelling - eiwitgehalte - koolhydraten - pig housing - odour emission - pig feeding - feed formulation - protein content - carbohydrates
    Onderzoek naar de mogelijkheden om de geur van varkens aangenamer te maken
    Housing conditions and carbohydrate source affect within-day variation of energy metabolism in growing pigs
    Rijnen, M.M.J.A. ; Borne, J.J.G.C. van den; Schrama, J.W. ; Gerrits, W.J.J. - \ 2003
    In: Progress in research on energy and protein metabolism / Souffrant, W.B., Metges, C.C., Wageningen : Wageningen Academic Publishers (EAAP Scientific Series 109) - ISBN 9789076998244 - p. 367 - 370.
    varkens - varkensstallen - energiemetabolisme - circadiaan ritme - koolhydraten - pigs - pig housing - energy metabolism - circadian rhythm - carbohydrates
    In the present study, effects of housing conditions (i.e. individual vs. group housing) and carbohydrate source (i.e. sugar beet pulp vs. maize starch) on energy metabolism and circadian rhythms in energy expenditure and physical activity were studied in growing pigs in a 2 x2 factorial design. No interactions between housing conditions and diet composition were present. Digestibility and metabolisability of dietary energy was higher for individually housed pigs than for group-housed pigs. Circadian rhythms in energy expenditure and energy expenditure for physical activity were clearly affected by housing conditions and diet composition. Total energy expenditure, as well as activity related energy expenditure, was increased during the dark phase of the day in individually housed pigs when compared with group-housed pigs. Pigs fed the sugar beet pulp based diet had a reduced energy expenditure on physical activity, which mainly occurred during the night.
    Effects of flavour absorption on foods and their packaging materials
    Willige, R.W.G. van - \ 2002
    Wageningen University. Promotor(en): A.G.J. Voragen; J.P.H. Linssen. - S.l. : S.n. - ISBN 9789058086402 - 140
    geurstoffen en smaakstoffen - absorptie - verpakkingsmaterialen - voedselverpakking - eiwitten - koolhydraten - vetten - membraanpermeabiliteit - smaakpanels - modellen - flavour compounds - absorption - packaging materials - food packaging - proteins - carbohydrates - fats - membrane permeability - taste panels - models

    Keywords: flavour absorption, scalping, packaging, food matrix, lldpe, ldpe, pp, pc, pet, pen,b-lactoglobulin, casein, pectin, cmc, lactose, saccharose, oil, modelling, storage, oxygen permeability, taste perception, sensory quality.

    Absorption of flavour compounds by linear low-density polyethylene (LLDPE) was studied in model systems representing differences in composition of the food matrix. Proteins,b-lactoglobuline and casein, were able to bind flavours, resulting in suppression of absorption of flavour compounds. Polysaccharides, pectin and carboxymethylcellulose, increased viscosity, and consequently decreased absorption. Disaccharides, lactose and saccharose, increased absorption, probably caused by a "salting out" effect of less apolar flavour compounds. The presence of a relative small amount of oil (50 g/l) decreased absorption substantially. Combined oily model systems, oil/casein and oil/pectin, showed a similar effect. The extent of absorption of flavour compounds by LLDPE was influenced by food components in the order: oil or fat >> polysaccharides and proteins > disaccharides. A model based on the effect of the polarity (log P) of flavour compounds and on their partitioning coefficients between food(matrix) and packaging material was developed. The model is able to predict absorption of flavour compounds from foods into LLDPE when lipids in the food matrix are the determining factor in flavour absorption. Results show that the model fits nicely with experimental data of real foods skim and whole milk.

    LLDPE, polypropylene (PP), polycarbonate (PC), polyethylene terephthalate (PET film and PET bottle) and polyethylene naphthalate (PEN) were immersed in a model flavour solution at different temperatures up to 14 days. The absorption rate and/or total amount of absorbed compounds increased considerably with increasing temperature. Depending on temperature, the total absorption of flavour compounds by the polyolefins (LLDPE and PP) was up to 2400 times higher than by the polyesters (PC, PET and PEN).

    The effect of absorbed flavour compounds on the oxygen permeability of low-density polyethylene (LDPE), PP, PC and PET was studied. Due to swelling of the polymers as a result of absorption of flavour compounds, LDPE and PP showed a significant increase of oxygen permeability of 21% and 130%. The oxygen permeability of PC showed a significant decrease of 11% due to occupation or blockage of the "micro-cavities" by the absorbed flavour compounds. Flavour absorption by PET did not affect the oxygen permeability significantly.

    The influence of flavour absorption LDPE, PC and PET on the taste perception of a flavour model solution and orange juice stored in glass bottles was studied with and without pieces of the respective plastic films. Although the content of flavour compounds between controls and polymer treated samples decreased substantially due to absorption, no significant effect on the taste perception of the model solution and orange juice were observed by triangular taste panel tests.

    The role of sludge retention time in the hydrolysis and acidification of lipids, carbohydrates and proteins during digestion of primary sludge in CSTR systems
    Miron, Y. ; Zeeman, G. ; Lier, J.B. van; Lettinga, G. - \ 2000
    Water Research 34 (2000)5. - ISSN 0043-1354 - p. 1705 - 1713.
    afvalwaterbehandeling - rioolslib - anaërobe behandeling - koolhydraten - lipiden - eiwitten - verzuring - hydrolyse - waste water treatment - sewage sludge - anaerobic treatment - carbohydrates - lipids - proteins - acidification - hydrolysis
    CSTR systems: completely stirred tank reactor systems
    Physiology of exopolysaccharide biosynthesis by Lactococcus lactis
    Looijesteijn, E. - \ 2000
    Agricultural University. Promotor(en): J.A.M. de Bont; J. Hugenholtz. - S.l. : S.n. - ISBN 9789058082862 - 197
    lactococcus lactis - industriële microbiologie - biosynthese - biochemie - fysiologie - oligosacchariden - koolhydraten - melkzuurbacteriën - lactococcus lactis - industrial microbiology - biosynthesis - biochemistry - physiology - oligosaccharides - carbohydrates - lactic acid bacteria

    Several lactic acid bacteria (LAB) produce exopolysaccharides (EPS). EPSs produced by LAB are a potential source of natural additives and because LAB are food grade organisms, these EPSs can also be produced in situ . The amount of EPS in milk fermented with strain NIZO B40, which produces an anionic EPS composed of glucose, rhamnose, galactose and phosphate, is very low. This relatively low concentration could be increased by optimising the culture conditions and medium composition. Using pH-controlled fermentations and a chemically defined medium, the total EPS production was highest at pH 5.8 and 25 °C. Glucose was demonstrated to be the most efficient sugar source for EPS production by L. lactis NIZO B40. With fructose as the sugar source only a minor amount of EPS was produced. The intracellular levels of sugar nucleotides, the EPS precursors, were much lower in fructose- than in glucose-grown cultures. The activity of the enzymes involved in the biosynthesis of the sugar nucleotides were however unaffected by the source of sugar but the activity of fructose-1,6-bisphosphatase (FBPase) was very low. FBPase catalyses the conversion of fructose-1,6-diphosphate into fructose-6-phosphate, an essential step for the biosynthesis of sugar nucleotides from fructose but not from glucose. Overexpression of the fbp gene resulted in increased EPS synthesis on fructose.

    Most culture conditions influenced growth as well as EPS formation and EPS synthesis itself was also influenced by the growth rate. EPS production by strain NIZO B40 starts at the exponential growth phase but continues during the stationary phase in batch cultures, indicating that EPS biosynthesis and growth are not strictly coupled. Indeed we found that non-growing cultures were still able to produce EPS, making it possible to study the influence of different culture conditions on EPS biosynthesis independent of growth.

    The amounts of EPS produced by L. lactis NIZO B40 and NIZO B891 were comparable under glucose and leucine limitation. The efficiency of EPS production, the quantity of EPS produced per quantity of glucose consumed, was however much higher under conditions of glucose limitation. The production of phosphorylated B40 EPS and of unphosphorylated B891 EPS was strongly reduced under conditions of phosphate limitation. The sugar composition of both B40 and B891 EPS and the phosphate content of B40 EPS were unaffected by the type of limitation but surprisingly, glucose limitation resulted in the production of EPSs with strongly reduced molecular masses.

    Anionic B40 EPS in suspension and a cell-associated layer of this EPS protected the bacteria against toxic copper ions and nisin, probably due to charge interactions. Furthermore, cell-associated EPS resulted in a decrease in the sensitivity of the bacteria to bacteriophages and lysozyme, most likely by masking the targets for the phages and the enzyme. The protection of EPS against nisin and bacteriophages could be a competitive advantage in mixed strain dairy starter cultures. Unfortunately, the EPS yields were not increased in the presence of copper, bacteriophages, nisin or lysozyme.

    Prebiotic effects of non-digestible oligo- and polysaccharides
    Hartemink, R. - \ 1999
    Agricultural University. Promotor(en): F.M. Rombouts; M.J.R. Nout. - S.l. : S.n. - ISBN 9789058080516 - 205
    koolhydraten - oligosacchariden - polysacchariden - darmmicro-organismen - carbohydrates - oligosaccharides - polysaccharides - intestinal microorganisms

    This thesis is the result of work carried out within a four-year multi-disciplined program, entitled ' Non-digestible oligosaccharides in foods and feed'. Within the project, four Ph.D. students were employed at the Food Chemistry, Food Microbiology, Human Nutrition and Animal Nutrition groups of the Wageningen Agricultural University. This thesis describes the studies carried out at the Food Microbiology group.

    Oligosaccharides are carbohydrates, with an average chain length of 2-10 sugar residues. Most oligosaccharides cannot be digested by the enzymes in the upper gut, nor can these compounds be absorbed. These oligosaccharides are considered non-digestible, and reach the large intestine unaltered. Non-digestible oligosaccharides (NDOs) are mainly of vegetable origin and are a normal part of the human diet. Some of the natural NDOs are now produced commercially using enzymatic methods.

    Most NDOs are completely or partially degraded and fermented by the bacterial populations in the large intestine. Some of the NDOs are considered to have a beneficial effect on the health of the host, due to the specific fermentation by two groups of intestinal bacteria, the bifidobacteria and lactobacilli. Commercial NDOs are marketed as a healthy ingredient, due to this selective fermentation, in several Western countries.

    Chapter 1 describes the gastrointestinal tract and the bacterial composition in each part thereof. The same chapter gives an overview of the current knowledge of the fermentation of NDOs by intestinal bacteria and the effects on the host health, as far as known.

    Chapters 2 and 3 describe the effect of the two types of NDOs, currently available on the Dutch market, on the etiology of dental caries. When consumed, residues of NDOs in foods may remain in the oral cavity. In the oral cavity many different bacteria are capable of degrading and fermenting carbohydrates, which results in the formation of acid and, possibly, dental lesions and caries. NDOs, being carbohydrates, may thus be fermented and are, in theory, a risk factor for dental caries.

    In Chapter 2 the degradation and fermentation of fructooligosaccharides (FOS) by the oral microflora is described. It can be concluded that this class of NDOs can be fermented by the most common bacterial species. These NDOs can be considered cariogenic, in vitro , but in vivo studies have to be carried out to determine the actual risk for dental caries.

    In Chapter 3, the degradation and fermentation of transgalactosyl-oligosaccharides (TOS) by the oral microflora is described. It was concluded that this class of NDOs is not, or very slowly, degraded and fermented. These NDOs are not considered a risk factor for dental caries.

    Within the framework of the project, the Food Chemistry group synthesized and purified a large number of oligosaccharide mixtures from plant cell walls. As these purifications are laborious and the total quantities of pure oligosaccharides are very small, it was decided to determine the fermentation of plant cell wall compounds by intestinal bacteria. These plant cell wall compounds are available in large quantities and thus could be used for screening studies.

    Chapter 4 describes the degradation and fermentation of such a plant cell wall polysaccharide, xyloglucan. Xyloglucan is present in many edible plants, but it is commercially prepared from tamarind seeds. The more (chemically) complex the compound the more enzymes are necessary for degradation, and the less bacteria are capable of fermenting the compound. Xyloglucan has a relatively simple chemical structure, but, surprisingly, only very few intestinal bacteria were capable of degrading this compound. The second remarkable conclusion was that most of the bacteria capable of degrading xyloglucan, belonged to the genus Clostridium . Previously, this genus has not been considered of major importance for polysaccharide degradation in the intestine.

    Chapter 5 describes the degradation of a second plant cell wall polysaccharide, guar gum, a galactomannan. Like xyloglucan, galactomannans are part of the cell wall of many plants. Guar is commercially produced from the seeds of the Cyamopsis tetragonoloba tree and used as a thickening agent in many foods. Guar also has a relatively simple structure. Nevertheless, only three different bacterial species, capable of degrading guar, could be isolated from human and animal faeces. One of these, Bifidobacterium dentium was considered to be mainly an oral species, but, using guar, could also be isolated from faeces. The same species could also be isolated from samples of saliva from 19 out of 20 volunteers. A second species, Streptococcus bovis could only be isolated from animal faeces, whereas the third species, Clostridium butyricum was present in human and animal faeces. The latter species produced large amounts of gas, and can thus be considered responsible for the increased flatulence observed after the ingestion of guar.

    Chapter 6 describes the differences in the fermentation of different oligosaccharides by human faecal inocula. In addition three polysaccharides were used in these studies. All donors had received the same diet and four samples were taken from each volunteer. The results show large differences between test compounds within the same volunteer, and large differences between volunteers on the same test compound. It can be concluded that the fermentation is largely dependent on host (genetic) factors, and not on dietary factors. It was also concluded that formation of gas is correlated with the formation of butyric acid. Butyric acid is considered to be important for the health of the intestinal wall. Gas production can thus be used as a simple screening method for butyrate production.

    Within the project the variations in the bacterial composition of human and pig faeces have been studied. It was concluded in the early stages of the project that no methods existed for the reliable quantification of two major intestinal bacterial groups, bifidobacteria and lactobacilli. Two new methods had to be developed for the quantification of these bacterial groups.

    Chapter 7 describes the development of a new medium for bifidobacteria, the RB medium. Selectivity is based on raffinose, propionate and lithiumchloride. The medium is not yet an ideal medium for the isolation and quantification for bifidobacteria but, compared with media currently used, it is more selective.

    Chapter 8 describes the development of a new medium for lactobacilli, the LAMVAB medium. Selectivity is based on vancomycin and a low pH (5.0). The combination of vancomycin and low pH inhibits practically all other intestinal bacteria. LAMVAB has successfully been employed to isolate lactobacilli from faeces from a large number of animals.

    The two newly developed media were compared with two other media, that are used regularly. The results of this comparison is described in Chapter 9 . The media were used to isolate bifidobacteria and lactobacilli in human and cat faeces and pig small intestinal contents. The three media for bifidobacteria performed equally well for human faeces, but for the other two kinds of samples, the RB medium performed better. For lactobacilli, LAMVAB performed better for all three types of samples tested.

    Chapter 10 discusses the results of this thesis and some recommendations for further research are given.

    As conclusion it can be stated that very few NDOs are degraded and fermented selectively by bifidobacteria. This was confirmed in Chapters 2 and 6, in which degradation and fermentation of FOS by other bacterial groups is described.

    Although FOS and TOS are found to be possibly cariogenic, it is not likely that either oligosaccharide will cause caries under normal conditions.

    Xyloglucan and guar are degraded only by a limited number of bacteria. Unexpectedly, clostridia played a major role in the degradation of both substrates. Both substrates may be a good substrate for the production of new NDOs, but considering the results it is unlikely that these oligosaccharides are a good substrate for lactobacilli or bifidobacteria.

    RB and LAMVAB are new media, which are suitable for the quantitative isolation of bifidobacteria and lactobacilli from human faeces. LAMVAB is also suitable for animal faeces. Both media are more selective than the media used at present.

    Verwijdering oligosachariden uit reactor verhoogt opbrengst.
    Boon, M.A. ; Janssen, A.E.M. - \ 1998
    Voedingsmiddelentechnologie 25 (1998). - ISSN 0042-7934 - p. 11 - 13.
    oligosacchariden - koolhydraten - opbrengsten - enzymprecursors - kinematica - lactose - disacchariden - oligosaccharides - carbohydrates - yields - enzyme precursors - kinematics - disaccharides
    De enzymatische productie en toepassing van oligosachariden uit lactose. Resultaten van modelberekeningen zijn belicht
    Seed development and carbohydrates
    Wittich, P.E. - \ 1998
    Agricultural University. Promotor(en): M.T.M. Willemse; A.A.M. van Lammeren; C.J. Keijzer. - Wageningen : Wittich - ISBN 9789054858553 - 178
    zaadzetting - zaden - formatie - plantenfysiologie - plantenontwikkeling - vruchten - rijp worden - planten - embryologie - metabolisme - plantenvoeding - assimilatie - koolhydraten - vicia faba - gasteria verrucosa - organische scheikunde - seed set - seeds - formation - plant physiology - plant development - fruits - ripening - plants - embryology - metabolism - plant nutrition - assimilation - carbohydrates - vicia faba - gasteria verrucosa - organic chemistry

    Seeds assure the plant the onset of a next generation and a way of dispersal. They consist of endosperm and an embryo (originating from gametophytic tissue), enveloped by a seed coat (sporophytic tissue). Plants generate different types of seeds. For instance, the endosperm may either be consumed by the embryo during seed development or retained for use by the embryo during germination. Differences in timing of endosperm digestion can be illustrated with broad bean ( Vicia faba ) and Gasteria verrucosa . Broad bean forms seeds in which the endosperm has been consumed by the fully developed embryo, while the embryo of Gasteria is less developed and surrounded by a large amount of endosperm for use during germination.

    An important factor in seed development is the distribution, storage, and utilization of carbohydrates, since carbohydrates are a major source of energy for cell growth. In this thesis the carbohydrate distribution is studied in developing ovules and seeds of maize ( Zea mays ) and Gasteria , by identifying the cells and tissues in which sucrose is degraded. Sucrose is the main carbohydrate supplied by these plants in the developing seeds. The sucrose degrading activity of the enzymes sucrose synthase and invertase indicates the destination of the sucrose transport (Chapters 9 and 10). Immunocytochemical and histochemical techniques are used for the localization of these enzymes in situ .

    The results obtained in this study on maize (Chapter 2 and 3) and Gasteria seed development (Chapters 4 and 5) show a general pattern of carbohydrate transport. First, the greatest amount of carbohydrates is applied for the development of the seed coat and nucellus (sporophytic tissues). An example of such a carbohydrate consuming process is the deposition of phytomelan in the seed coat of Gasteria . Phytomelan is a black cell wall component and chemically very inert. Histochemical and electron microscopy observations (Chapters 6 and 7) show that callose forms a mould for the deposition of phytomelan. The breakdown products of callose (glucose monomers and polymers) seem to be used for the synthesis of the phytomelan. Chemical analysis reveals that phytomelan is a complex polyphenolic polymer, and not a melanin (Chapter 8). Second, carbohydrate transport to the sporophytic tissues is followed by transport of most carbohydrates into the endosperm. These carbohydrates will be used for endosperm growth and for storage. Finally the main carbohydrate flow will go to the embryo. The pattern of carbohydrate usage observed in maize and Gasteria was used to generate a general model for angiosperm seed development (Chapter 10). The model explains differences between seeds by relating carbohydrate distribution during seed development to the timing of seed dispersal.

    Qualitätsbestimmung bei Lagerkartoffeln
    Hak, P.S. ; Oosterhaven, J. - \ 1997
    Der Kartoffelbau 48 (1997)11. - ISSN 0022-9156 - p. 418 - 420.
    opslag - chemische samenstelling - planten - chemische analyse - koolhydraten - aldehyden - ketonen - zetmeel - cellulose - kwaliteit - prestatieniveau - fabrieksaardappelen - storage - chemical composition - plants - chemical analysis - carbohydrates - aldehydes - ketones - starch - quality - performance - starch potatoes
    Onderzoek naar oorzaken van veroudering bij het bewaren van fabrieksaardappelen. De balans tussen het zetmeel- en suikergehalte is een indicator voor de kwaliteit van frieten
    Wheat bran glucuronoarabinoxylans : biochemical and physical aspects
    Schooneveld - Bergmans, M.E.F. - \ 1997
    Agricultural University. Promotor(en): A.G.J. Voragen; G. Beldman. - S.l. : Schooneveld-Bergmans - ISBN 9789054857167 - 125
    graansoorten - maling - Triticum aestivum - tarwe - hexaploïdie - voedsel - voedingsmiddelen - koolhydraten - zetmeel - vezel - polysacchariden - structuur - chemische reacties - cereals - milling - Triticum aestivum - wheat - hexaploidy - food - foods - carbohydrates - starch - fibre - polysaccharides - structure - chemical reactions

    Arabinoxylans are present in cereal cell walls and in vitro they have interesting physicochemical properties, such as viscosity and gelation. Although many studies on these properties were reported for wheat flour arabinoxylan, not much research has been directed towards exploitation of these polysaccharides as food gum. For that purpose glucuronoarabinoxylans of wheat bran, a cheap by-product of the cereal industry, were studied with regard to their extractability, their structural and physicochemical properties.

    Approximately 50% of the glucuronoarabinoxylans of wheat bran cell wall material were recovered in high purity by barium hydroxide extraction at 70 to 95°C. Delignification or other treatments to open up the cell wall structure were not effective in increasing the yield. The extracted glucuronoarabinoxylans were very diverse in chemical structure and physicochemical properties. About 30% of them had a low degree of substitution, were easily degradable by xylanolytic enzymes and hardly influenced the viscosity of the solvent as a result of extensive aggregation. Over 50% of them had a high degree of substitution, were supposed to contain dimeric branches of arabinose and xylose, were scarcely degradable by xylanolytic enzymes, gave moderate viscosity to solutions and were very effective in stabilizing emulsions. The structure of these glucuronoarabinoxylans could only be speculated upon and it could not be enzymatically modified as a consequence of its complexity and the lack of appropriate enzymes. The remaining glucuronoarabinoxylans either had an intermediate or very high degree of substitution, of which the latter was presumed to be connected to lignin-fragments.

    Gel-forming glucuronoarabinoxylans were recovered only in low yield by dilute alkali extraction and subsequent purification was necessary. These feruloylated glucuronoarabinoxylans gelled upon addition of oxidative agents, of which peroxide - peroxidase, glucose - glucoseoxidase - peroxidase and ammonium persulphate were investigated. In comparison with wheat flour arabinoxylans, those of wheat bran appeared to give less flexible networks at high concentration, which was ascribed to their high degree of substitution and high ferulic acid content. Of the dimers formed upon cross-linking, the generally known diferulic acid, being a 5-5 coupled dimer, was only present in relatively low amounts. Dimers, in which the 8-position of the ferulic acid residue is involved were preponderant. The distribution of the dimers was not affected by the type of cross- linking agent or the type of arabinoxylan. However, the presence of lignin fragments in the bran extract was presumed to cause a low ferulic acid recovery upon cross-linking.

    Physiological effects of consumption of resistant starch
    Heijnen, M.L. - \ 1997
    Agricultural University. Promotor(en): A.C. Beynen; P. Deurenberg; J.M.M. van Amelsvoort. - S.l. : Heijnen - ISBN 9789054856511 - 163
    voeding - zetmeel - voedingsmiddelen - voedsel - koolhydraten - vezel - nutrition - starch - foods - food - carbohydrates - fibre

    Resistant starch (RS) is defined as the sum of starch and products of starch degradation not absorbed in the small intestine of healthy individuals. Thus, RS enters the colon where it may be fermented. In this respect, RS resembles some types of dietary fibre. Three types of RS are being discerned: RS 1 , physically entrapped starch; RS 2 , uncooked starch granules; RS 3 , retrograded starch. The estimated current mean per capita RS intake in the Netherlands is 5 g/d. The amount of RS in foods can be manipulated by the choice of raw products and food processing techniques. This is of potential interest if an increased RS consumption would be beneficial for human health. In this thesis several of the hypotheses concerning putative positive effects of RS consumption on human physiology are studied. Daily consumption of up to 32 g RS 2 or RS 3 was tolerated well by healthy individuals and increased colonic fermentative activity and stool weight. Replacement of 27 g digestible starch by RS 2 reduced diet-induced thermogenesis and postprandial glucose and insulin responses proportionally to the amount of indigestible carbohydrate consumed. When compared with an equivalent amount of glucose, daily supplementation of 30 g RS 2 or RS 3 for 3 wk did not affect serum lipid concentrations in healthy subjects, and daily supplementation with 32 g RS 2 or RS 3 for 1 wk did not affect putative risk factors for colon cancer, subjective feelings of hunger, faecal ammonia excretion and apparent absorption of magnesium, calcium and phosphorus in healthy individuals. No differences were observed between RS 2 and RS 3 , in the parameters studied. In piglets, dietary RS 3 , but not RS 2 , shifted nitrogen excretion from urine to faeces, and RS 2 reduced apparent magnesium and calcium absorption. In rats, dietary RS 2 , but not RS 3 , increased apparent, but not true magnesium absorption. It was concluded that daily consumption of up to 32 g RS 2 or RS 3 , is not unfavourable for healthy individuals, but it also does not have great beneficial effects on human physiology, at least for the parameters and time span studied in this thesis. Especially the significance for human health of increased activity and site of fermentation in the colon, and the possible role of the various types of RS in the prevention of colon cancer should be studied further.

    Influence of the enchytraeid worm Buchholzia appendiculata on aggregate formation and organic matter decomposition.
    Marinissen, J.C.Y. ; Didden, W.A.M. - \ 1997
    Soil Biology and Biochemistry 29 (1997)3-4. - ISSN 0038-0717 - p. 387 - 390.
    organische verbindingen - bodem - bodemchemie - aardwormen - cellulose - koolhydraten - decompositie - organic compounds - soil - soil chemistry - earthworms - cellulose - carbohydrates - decomposition
    Enchytraeid worms were kept in <0.3 mm sieved sandy loam subsoil mixed with ground wheat, for 6 weeks at 16°C. Sieved soil with organic matter but without worms was also incubated. The soil was then allowed to air-dry slowly during 6 weeks. Enchytraeid casts were collected from the surface of the soil with worms, and the remaining soil was separated into three size fractions by dry sieving. All size fractions were analysed for stability and %C, and mineralisation potential. The amount of soil in the fraction > 0.3 mm (including the casts) was larger in the presence of enchytraeid worms, at the cost of soil from the fraction 0.3 0.03 mm. The %C in both soils was highest in the fraction < 0.03 mm. Activity of enchytraeids significantly decreased the %C in the fraction > 0.3 mm. Fresh excrements, representing 0.5% of the soil, were very high in organic matter content. Mineralisation (expressed as percentage of C that was mineralised) was highest in the fraction <0.03 and lowest in the 0.3-0.03 fraction. Excrements showed very high mineralisation rates. Enchytraeid activity enhanced mineralisation in the fraction > 0.3 ram. Aggregates > 0.3 mm from the treatment with worms dispersed less clay after shaking with water than those from the treatment without worms. Although the influence of enchytraeid worms on total C-content and mineralisation was small, the changes in C of the different size fractions showed that enchytraeids influenced the active fraction of the C in the soil considerably by consuming litter, thereby locating it inside soil aggregates and linking the organic matter to clay particles.
    Isolation and characterisation of starch biosynthesis genes from cassava (Manihot esculenta Crantz)
    Munyikwa, T.R.I. - \ 1997
    Agricultural University. Promotor(en): E. Jacobsen; R.G.F. Visser. - S.l. : Munyikwa - ISBN 9789054858416 - 128
    koolhydraten - polysacchariden - biosynthese - genen - genomen - manihot esculenta - cassave - carbohydrates - polysaccharides - biosynthesis - genes - genomes - manihot esculenta - cassava

    Cassava (Manihot esculenta Crantz) is a tropical crop grown for its starchy thickened roots, mainly by peasant farmers, in the tropics, for whom it is a staple food. There is an increasing demand for the use of cassava in processed food and feed products, and in the paper and textile industries amongst others. This thesis describes research on the cloning of the genes encoding ADP-glucose pyrophosphorylase small and large subunits (AGPase B and S, respectively) and granule bound starch synthase II (GBSSII). These genes and their products were extensively characterised to determine their role in starch biosynthesis in cassava. Functional verification of the genes was carried out by transforming potato and cassava followed by analysis of the starch produced by the transgenic plants.

    In Chapter 1 cassava production in the world in general and in Zimbabwe in particular is examined against the backdrop of new cloning and transformation strategies to improve starch quality and quantity. The development of cassava cultivars whose starches have novel physico-chemical properties by genetic modification of the process of starch biosynthesis is examined therein. The main criteria for these new cultivars to emerge are set forth as being: the availability of cloned and characterised starch biosynthesis genes, a universally applicable transformation and regeneration procedure for cassava, transfer to appropriate cassava cultivars, and biosafety analysis of transgenic cassava plants before disbursement to farmers.

    The cloning of the cassava starch biosynthesis genes encoding granule bound starch synthase II (GBSSII) and the large and small subunits of ADP-glucose pyrophosphorylase (AGPase) is described in Chapters 2 and 3. The cloning of GBSSII reveals that there is indeed a second isoform of this enzyme in cassava as in other plants species. While sharing very little amino acid sequence homology with cassava GBSSI the GBSSII isophorm shares high amino acid sequence homology to other GBSSII genes from pea and potato. Cassava GBSSII seems to be more important in leaf tissue where it is more highly expressed than in tuber tissue where GBSSI predominates. Mapping of GBSSII revealed that this is a single copy gene located on the male derived linkage group T of the cassava mapping population.

    Cloning of the cassava genes coding for the small (B) and large subunit (S) of AGPase revealed interesting aspects about the cassava enzyme. The cassava AGPase is likely to be heterotetrameric in constitution as had been found in other plant species. Comparison of the cassava AGPase sequences with those of already cloned AGPases revealed that AGPase B is more similar to small subunit genes from other plants than to cassava AGPase S coding for the large subunit (Chapter 3). Segregation analysis of a cassava mapping population revealed that AGPase S is a single copy gene that is localised on the female derived linkage group E of the cassava genetic map. Both genes are expressed in all cassava tissues but AGPase B was shown to have a higher steady state mRNA level than AGPase S especially in leaf and tuber tissue. Post-transcriptional control of small subunit polypeptide levels could be inferred from the discrepancy between AGPase B mRNA and polypeptide levels. The AGPase enzyme activity was much higher in young cassava leaves than older leaves and tubers. Cassava leaf AGPase activity was increased 3 fold by the addition of 3-PGA (3-phospho-glycerate) and inhibited by up to 90% in the presence of inorganic phosphate (Pi). The tuber enzyme was relatively unaffected by 3PGA, but was highly inhibited by Pi.

    In order to verify the biological role of the AGPase B gene antisense constructs were made of the cassava AGPase B behind a CaMV35S promoter (chapter 3). This was transferred into potato plants by Agrobacterium tumefaciens. While the 224 transgenic antisense AGPase B potato plants did not differ in appearance from normal potato plants, 45 transgenic plants, however, had more numerous and smaller tubers than control plants. Antisense plants with reduced AGPase B mRNA levels had 1.5 to 3 times less starch than tubers from the control plants. The levels of the soluble sugars in the antisense plants increased significantly (up to 10 times more glucose, 6 times the amount of fructose, and 5 times the amount of sucrose) when compared to those found in control plants. These results show that a heterologous gene from cassava can have an antisense effect in potato, but that the number of plants required to find plants exhibiting maximum antisense effect has to be very large. This is probably due to sequence homology differences between the cassava AGPase B and potato AGPase B genes which share only 68% amino acid sequence homology.

    Chapter 5 describes the further development of an efficient, time and labour saving protocol for transforming cassava based on stringent selection of the luciferase (firefly) marker gene. In addition the first reported transformation of cassava with a gene (AGPase B) other than a marker gene is described. An antisense construct was made for transforming cassava. This consisted of the cassava AGPase B gene which was placed in antisense orientation behind the CaMV35S promoter. This was then coupled to the luciferase gene driven by another CaMV35S promoter. After particle bombardment of cassava FEC transgenic tissue was selected using three different selection regimes: non stringent luciferase selection, stringent luciferase selection and combined chemical (phosphinothrycin) and luciferase selection. Stringent luciferase selection whereby luciferase positive FEC units were precisely pinpointed, isolated and cultured was found to be the most effective and time saving method. It was possible to generate cultures having more than 90% luciferase positive FEC tissue after 12 weeks of stringent LUC selection, compared to 45% and <1 % for combined selection and non stringent selection respectively. The number of luciferase positive mature embryos generated was directly proportional to the percentage of luciferase positive tissue in the original FEC culture. Stringent luciferase selection enabled the time taken for production of transgenic cassava plants to be reduced to 28-36 weeks as compared to 8 months to a year with no stringent selection or LUC/PPT selection.

    Cassava plants carrying the AGPase B antisense gene had extremely low levels of starch, compared to control plants, as shown by iodine staining of in vitro induced thick stems. In plants exhibiting the highest AGPase B antisense effect, starch formation was limited only to the epidermal layer. These results functionally confirm the identity of cassava AGPase B as well as emphasising the critical role of AGPase in starch formation in cassava.

    A discussion about the significance and implications of cloning cassava genes and producing transgenic cassava for culture in developing countries is carried out in Chapter 6. While there are clearly many economic and nutritional benefits to producing transgenic cassava, for resource poor farmers, many people in the South are not aware of the biosafety implications of growing transgenic crops. It is further emphasised that discussions and debate should be initiated to make local communities aware of the issues surrounding transgenic crops and their products. In addition it is recommended that some form of international legal framework be set up to ensure that resource poor farmers are not disadvantaged by the patenting of material originating from their communities by individuals and companies in the North. This thesis clearly demonstrates how it will be possible in the near future to produce new cassava cultivars carrying the appropriate genes to affect pronounced changes on tuber productivity and starch quality.

    Samenstelling koolhydraatfractie in partijen aardappelstoomschillen, ontsloten aardappelzetmeel, tarwe-indampconcentraat en tarwezetmeel
    Smits, B. ; Gelder, A.H. van; Cone, J.W. - \ 1996
    Lelystad : ID-DLO (Rapport / ID-DLO no. 96.013) - 34
    diervoeding - voer - diervoedering - varkens - koolhydraten - zetmeel - animal nutrition - feeds - animal feeding - pigs - carbohydrates - starch
    Preservation of plant residues in soils differing in unfilled protective capacity
    Hassink, J. ; Whitmore, A.P. - \ 1996
    Soil Science Society of America Journal 60 (1996)2. - ISSN 0361-5995 - p. 487 - 491.
    koolhydraten - cellulose - decompositie - organische verbindingen - bodem - bodemchemie - carbohydrates - cellulose - decomposition - organic compounds - soil - soil chemistry
    Enzymic modification of cellulose - xyloglucan networks : implications for fruit juice processing = Enzymatische modificatie van cellulose - xyloglucaan netwerken
    Vincken, J.P. - \ 1996
    Agricultural University. Promotor(en): A.G.J. Voragen; G. Beldman. - S.l. : Vincken - ISBN 9789054855101 - 159
    appels - malus - koolhydraten - aldehyden - ketonen - zetmeel - cellulose - apples - malus - carbohydrates - aldehydes - ketones - starch - cellulose

    Xyloglucans play an important role in connecting cellulose microfibrils in the primary coli wall of plants, and the resulting cellulose-xyloglucan network is thought to determine the strength of these walls. Xyloglucans were isolated from apple fruit and potato tuber cell wall material by alkaline extraction and their primary structures were determined. Major differences between these two polysaccharides were their degree of backbone branching and the presence of fucosyl and arabinosyl residues.

    The substrate specificity of three ondoglucanases from Trichoderma viride (endol, endolV and endoV) was investigated. The target substrate of endol is cellulose, that of endolV xyloglucan, whereas endoV is the most versatile endoglucanase having the ability of degrading both substrates. EndolV and endoV differ in their mode of action towards potato xyloglucan. Further, strong indications were obtained that xyloglucanase activity is related to a long array of substrate-binding sites.

    The degradation of the cellulose-xyloglucan network in isolated coli wall material from apple fruit involves several glucanase activities. Xyloglucanase activity is important to make cell wall embedded cellulose more accessible to true cellulolytic enzymes such as endol and cellobiohydrolase. Extensive degradation is required because xyloglucan fragments having a backbone of 20 glucosyl residues (five building units) still bind to cellulose surfaces. These results might explain why fungi excrete so many different kinds of endoglucanases.

    When the cell walls of living apple fruit tissue were treated with pectin lyase and a mixture of glucanases from Trichoderma viride (liquefaction), the ease with which the apple tissue disintegrated, seemed to depend on the maturity of the fruit. The disintegration of apple fruit tissue during liquefaction correlates to the level of (ripeningrelated) xyloglucan endotransglycosylase activity in apple fruit. An hypothesis for the synergism of fungal and plant glucanases is put forward. Under certain circumstances (controlled liquefaction) the cellulose-xyloglucan network can be modified in such a way, that a stable cellulose-based cloud is formed in the resulting apple juice. The significance of these observations for juice manufacturing is discussed.

    NVVL-Workshop: Vezel, het belang voor de gezonde mens.
    Olthof, M. - \ 1996
    Voeding 57 (1996)12. - ISSN 0042-7926 - p. 21 - 23.
    koolhydraten - cellulose - spijsvertering - effecten - vezel - voedsel - voedingsmiddelen - gezondheid - darmen - voeding - zetmeel - voedingsvezels - welzijn - carbohydrates - digestion - effects - fibre - food - foods - health - intestines - nutrition - starch - dietary fibres - well-being
    Verslag van een workshop, georganiseerd door de werkgroep Voeding van de NVVL. Ingegaan is op de aspecten: fermentatie in de dikke darm; invloed op bloedlipidenconcentraties; invloed op de absorptie van mineralen
    Interaction between carbohydrates and fat in pigs : impact on energy evaluation of feeds
    Bakker, G.C.M. - \ 1996
    Agricultural University. Promotor(en): M.W.A. Verstegen; A.W. Jongbloed. - S.l. : Bakker - 193
    voer - voedingswaarde - koolhydraten - vetten - varkens - feeds - nutritive value - carbohydrates - fats - pigs

    In marketing pigs, nearly 50% of the costs are those of the feed. Therefore, it is necessary to know the nutritional value as accurately as possible.

    In the Netherlands, pigs receive in general (99%) compound feeds, containing all the nutrients they require. Cereals used to be the major ingredients. However, their proportion was reduced from 40% in 1970 to 15% in the eighties. The use of ingredients other than cereals or tapioca in compound feeds affected the chemical composition of the pig diet: from feeds with a large amount of starch towards feeds containing less starch but more fibrous polysaccharides, that are often called non-starch polysaccharides (NSP). Starch and NSP differ in many aspects: in chemical structure; in the type of nutrients they supply and their effect on other nutrients in the digestion process; efficiency of utilization for energy gain; and other, non-nutritional, aspects.

    In order to have maximum benefit of their potential nutrient supply, most nutrients need to be digested and absorbed before reaching the terminal ileum. These nutrients are: amino acids from protein, fatty acids from lipids, and glucose from starch and sugars. If they disappear from the large intestine, the energy value of the nutrients will be lower, resulting in a reduced feeding value of the total feed. On the other hand, NSP are fermented mainly in the hindgut, supplying energy to the pig in the form of volatile fatty acids.

    In general, the energy of pig feeds is evaluated by considering the differential contribution of digestible nutrients to energy supply. Energy evaluation is based on three assumptions: (1) that both the chemical composition and the digestibility coefficients of ingredients in a feed are known and can be derived from feedstuff tables; (2) that the amounts of digestible nutrients in the different ingredients are additive and that there are no interactions between ingredients; and (3) that after digestion the contribution of each nutrient to energy supply is independent of the amounts of other nutrients. Because NSP have a relatively low energy density, they are often supplemented with fat to maintain a certain energy density in the diet. Hence it is assumed that the feeding values are additive. It was found, however, that the combination of NSP rich by-products and fat resulted in less energy gain in pigs than an iso-energetic combination of cereals and fat or by-products separately. It was concluded that the NSP and fat interacted on energy supply to the pigs.

    It is important to know whether the interactive effect between fat and fermentable carbohydrates takes place prior to the terminal ileum or in the hindgut of the pig. To be able to measure this, a new technique of ileo-cecal cannulation was developed: the steered ileo-cecal valve (SICV). In contrast to other techniques, in this technique the gut remains intact. After testing it with high fibrous diets, it was concluded that both ileal and total tract digestibility can be measured in the same pig. For this, the use of a marker is recommended.

    To investigate the interaction between NSP and fat, an experiment was performed with 12 diets, in a 4 x 3 factorial arrangement with four amounts of animal fat and three sources of carbohydrate. The amounts of animal fat added to the diets were : 0 (o), 35 (1), 70 (m) and 105 (h) g per kg. The three sources of carbohydrate were maize starch (M), purified cellulose (C) and toasted soya bean hulls (S). The cellulose was. used as a source of poorly fermentable carbohydrate and the soya bean hulls as a source of easily fermentable carbohydrate. These diets were given to pen-housed pigs from 30 to 105 kg live weight, which period is the growing-finishing period in practice. In these pigs both digestibility of the diets and the energy gain were measured. In a separate set of pigs, the digestibility of nutrients at the terminal ileum was measured.

    All the measured digestibility coefficients were lower than expected from the feedstuff table. This effect was partly attributed to differences in techniques for estimating digestibility between the present experiment (practical conditions) and the experiments supplying data for the feedstuff table. Most of the tabulated values are obtained under well-controlled laboratory conditions. It was found that housing pigs in groups in pens, as in common practice, reduced the digestibility of organic matter with 1.5 %-units, compared to pigs housed in metabolism crates. For protein this difference was larger: on average 3.7 %-units. Feeding high fibrous diets tended to increase these differences.

    In addition, the assumption of additivity of digestible nutrients in ingredients within a diet was not correct, especially when high fibrous ingredients were used. When cellulose or soya bean hulls were included in the diet, digestibility of protein and fat was worse. It was concluded that intake of dry matter or fibrous material increased endogenous secreted protein with 36.5 g/d per kg NSP consumed, which reduced apparent digestibility. In addition, microbial protein synthesis of 116.6 g/d per kg fermented NSP also reduced apparent protein digestibility. Moreover, the added fat was less digestible at the terminal ileum when combined with cellulose or soya bean hulls in a diet, than when they were all fed separately. The total tract digestibility of the added fat was 91 % with the low fibre diet, but 83% when combined with cellulose and 87% when combined with soya bean hulls.

    The energy gain predicted from the measured digestible nutrients was compared with the net energy gain as actually achieved. It was concluded that the utilization of energy from fermentable carbohydrates was relatively low: 0.43. This was partly ascribed to energy losses in methane and energy losses in volatile fatty acids in faeces. Of the digestible energy from fermentable carbohydrates 0.81 to 0.90 was available for energy gain in the form of volatile fatty acids. In addition, increased weight of the empty gastrointestinal tract was found, which may have required a large part of the available energy for maintenance, leaving less energy for growth.

    It is concluded, that digestibility of nutrients should be measured both at the terminal ileum as over the total tract, when large amounts of fermentable carbohydrates are included in the diet. They should be measured under practical conditions. The variation in energy gain between pigs, however, remains relatively large.

    Goed verteerbaar en smakelijk rantsoen noodzakelijk voor roze-vleeskalveren
    Schans, F.C. van der - \ 1995
    Praktijkonderzoek / Praktijkonderzoek Rundvee, Schapen en Paarden (PR), Waiboerhoeve 8 (1995)5. - ISSN 0921-8874 - p. 25 - 26.
    kalveren - koolhydraten - karkassamenstelling - samenstelling - ontwikkeling - voer - groei - voedingswaarde - smakelijkheid - calves - carbohydrates - carcass composition - composition - development - feeds - growth - nutritive value - palatability
    Aan roze-vleeskalveren zijn krachtvoeders met variërende gehaltes aan verschillende koolhydraten gevoerd. Deze verschillende gehaltes aan zetmeel, suiker en ruwe celstof hadden geen effect op de voeropname, groei of slachtkwaliteit van de kalveren.
    A molecular analysis of L-arabinan degradation in Aspergillus niger and Aspergillus nidulans
    Flipphi, M.J.A. - \ 1995
    Agricultural University. Promotor(en): A.J.J. van Ooyen; J. Visser. - S.l. : Flipphi - ISBN 9789054853923 - 165
    aspergillus - celwanden - koolhydraten - cellulose - celmembranen - fermentatie - voedselbiotechnologie - glycosidasen - polysacchariden - genexpressie - pleiotropie - moleculaire genetica - aspergillus - cell walls - carbohydrates - cellulose - cell membranes - fermentation - food biotechnology - glycosidases - polysaccharides - gene expression - pleiotropy - molecular genetics

    This thesis describes a molecular study of the genetics ofL-arabinan degradation in Aspergillus niger and Aspergillus nidulans. These saprophytic hyphal fungi produce an extracellular hydrolytic enzyme system to depolymerize the plant cell wall polysaccharideL-arabinan. Chapter 1 surveys the occurrence, properties and applications ofL-arabinanolytic enzymes (arabinases). The A.niger system, which constitutes an endolytic endo-1,5-α-L-arabinase (ABN A) and two distinct α-L-arabinofuranosidases (ABF A and ABF B), has been a frequent subject of investigation in the past and represents the best characterizedL-arabinanolytic system to date. These three enzymes are all glycosylated. Current knowledge on the induction of fungal arabinase expression is summarized in this Chapter. Furthermore, the structure of the polysaccharide substrate and its function in the plant cell wall matrix are introduced.

    In Chapters 2 to 5, the cloning and characterization of the structural genes coding for the three glycosyl hydrolases from the A. nigerL-arabinan-degrading complex are described. A. niger abf A and abf B ar e the first eukaryotic ABF-encoding genes to be isolated and sequenced, abn A is the first ABN-encoding gene published. Chapter 2 reports on the isolation of the abf A gene encoding ABF A, the minor extracellular ABF. This gene could be cloned by utilizing ABF Aspecific cDNA as the probe. This cDNA was immunochemically identified from a cDNA library generated fromL-arabitol-induced myceliurn of an A. nigerD-xylulose kinase mutant. This mutant is unable to grow onL-arabitol and features enhanced expression of all three arabinases when transferred to medium containing this pentitol as sole carbon source. In Chapter 3 , the cloning of the ABN A-encoding gene (abn A) is described. This gene was isolated following the same strategy as with abf A, although a second cDNA library had to be generated first. The induction process was immunochemically monitored in order to establish the proper induction conditions for the new library. The abn A gene and the gene product were characterized by DNA sequence analyses of the cloned genomic DNA and the cDN A. The N-terminal amino acid sequences of ABN A and a CNBr-derived peptide were determined. Several transcription initiation sites and one polyadenylation site could be identified. The structural region codes for a protein of 321 amino acids and is interrupted by three introns. Extracellular ABN A consists of 302 amino acid residues with a deduced molecular weight of 32.5 kDa and a theoretical pl of 3.5. For the protein, an apparent pl of 3.0 and an apparent molecular weight of 43 kDa, determined upon SDS-PAGE, were previously reported. Chapter 4 documents the isolation and characterization of the abf B gene, coding for the major extracellular ABF. The determination of N-terminal amino acid sequences from ABF B and CNBr-generated peptides allowed the design of deoxyoligonucleotide mixtures which enabled the cloning of abf B. When utilized as primers in a polymerase chain reaction (PCR), ABF B-specific amplification products emerged, one of which was used to probe the gene. The abf B gene and the gene product were characterized by DNA sequence analyses of the cloned genomic DNA and of ABF B- specific cDNA isolated from the library described in Chapter 3. Several transcription initiation sites and one polyadenylation site could be identified. The structural region is a single open reading frame and codes for a protein of 499 amino acids. The mature enzyme consists of 481 amino acid residues with a deduced molecular weight of 50.7 kDa and a theoretical pl of 3.8. An apparent pl of 3.5 and an apparent molecular weight of 67 kDa, determined upon SDS-PAGE, were previously reported. The abf B gene product was suggested to be identical to the ABF purified and characterized by Kaji and Tagawa (Biochim Biophys Acta 207 : 456-464 (1970)). Considering the non-amino acid content of the latter protein, a molecular weight of 64 kDa could be deduced for ABF B. In Chapter 5 , the abf A gene and its gene product were characterized by DNA sequence analyses of the genomic DNA and of the cDNA for which the isolation was described in Chapter 2. The N-terminal amino acid sequences of ABF A and a CNBr-derived peptide were determined. One transcription initiation site and two polyadenylation sites could be identified. The structural region is interrupted by seven introns and codes for a protein of 628 amino acids. Mature ABF A consists of 603 amino acid residues with a deduced molecular weight of 65.4 kDa and a theoretical pl of 3.7. For this ABF, an apparent pi of 3.3 and an apparent molecular weight of 83 kDa, determined upon SDS-PAGE, were previously documented.

    Although the three enzymes are all active against (1->5)-α-glycosidic bonds betweenL-arabinofuranosides, ABF A, ABF B and ABN A are genetically unrelated. ABF A was found to be N -glycosylated whereas ABF B and ABN A were not - these enzymes are only O -glycosylated. For each gene, arabinaseoverproducing strains were generated by introducing multiple gene copies in A.niger or in A.nidulans uridine auxotrophic strains through co-transformation. Transformants were isolated upon primary selection for uridine prototrophy. Subsequent overproduction of the genes introduced was demonstrated in these recombinant strains upon growth on sugar beet pulp, both immunochemically and by assaying enzyme activity. abf A was shown to be expressed in the heterologous host A.nidulans, despite the absence of an abf A gene equivalent in this organism. High-copy number A.niger abf B transformants featured impaired secretion of other extracellular proteins upon growth on sugar beet pulp. ABN A overproduction was found to be limited to approximately five times the wild-type level in A.niger abn A transformants, but not in A.nidulans transformants. Such a limitation was not observed in case of the ABFs.

    In Chapters 5 and 6, the regulation ofL-arabinan degradation is addressed. The structural genes seem to be regulated mainly at the transcriptional level. Additional copies of either A13F-encoding gene in A.niger were shown to result in a reduction, but not in total silencing of the expression of the wild-type ABN Aencoding gene upon induction with either sugar beet pulp orL-arabitol ( Chapter 5 ). The reduction of the expression level of abn A correlated with the abf gene dosage. The repression effected by extra abf B gene copies was more stringent and more persistent than that elicited by additional abf A copies. Although observed with both inducers, these phenomena were more outspoken and more persistent on sugar beet pulp. Similar, but more moderate effects were observed towards the expression of the other abf gene in multiple copy abf A- and abf B-transformants. It was proposed that the abf genes titrate two distinct gene activators both involved in coordination of arabinase gene expression. However, the three genes were shown to respond differently upon a mycelial transfer toL-arabitol-containing medium, indicating that gene-specific factors are also involved. Four distinct sequence motifs were found in common in the promoter regions of the three genes. One of these elements is identical to the A.nidulans CREA-motif, which has been shown to mediate carbon catabolite repression on several A.nidulans enzyme systems. Arabinase expression in A.niger is known to be repressed in the presence ofD-glucose. Two other motifs are highly homologous to cAMP-responsive elements described in other organisms. For the fourth motif no functional analogues could be found, but the element was found to be present in several other fungal genes which are not involved inL-arabinan degradation at all. It is therefore likely that none of these common elements confer system-specific regulation.

    The presumed involvement ofL-arabitol in the induction process of fungal arabinases was further emphasized by the induction characteristics of an A. nidulans mutant unable to grow on the end-product ofL-arabinan degradation,L-arabinose, nor onL-arabitol ( Chapter 6).L-Arabitol is an intermediate ofL-arabinose catabolism in Aspergilli. This mutant was shown to lack NAD +-dependentL-arabitol dehydrogenase activity resulting inL-arabitol accumulation, both intracellularly and in the culture medium, wheneverL-arabinose is present. Upon submerged growth on various carbon sources in the presence ofL-arabinose, the mutant featured enhanced expression of the enzymes involved in extracellularL-arabinan degradation, and of those of the intracellularL-arabinose catabolism. The co-substrates on which the mutant secreted large amounts of arabitol simultaneously exhibited high arabinase expression and featured reduced growth.L-Arabitol secretion and enzyme production were also observed on a mixed carbon source ofD-glucose andL-arabinose, resulting in normal growth. Hence, in the presence ofL- arabinose, the carbon catabolite repression conferred byD-glucose in the wild-type, is overruled in the mutant.

    In Chapter 7 , ABN A is shown to have remote sequence similarity with four bacterial xylanolytic glycosyl hydrolases (three β-D-xylosidases and an endo-1,4-β-D-xylanase), three of which feature activity against para -nitrophenyl-α-L-arabinofuranoside. This synthetic compound is commonly utilized to assay potential ABF activity, whereas it is known to be an inhibitor of the fourth enzyme. The homology became evident only after multi pie-sequence alignments and hydrophobic cluster analysis. It was proposed that these enzymes share a binding site for a terminal non-reducing α-linkedL-arabinofuranosyl residue and that they all belong to glycosyl hydrolase family 43. Implications from these suggestions were discussed. The ABFs could not be assigned to an established glycosyl hydrolase family.

    Based on theL-arabinolytic system of the brown-rot fungus Monilinia fructigena, the sequence similarity found amongst ABF A and bacterial pullulan-degrading enzymes, and ABF expression levels under carbon starvation conditions and onD-glucose as the carbon source, distinct functions inL-arabinan and plant cell-wall degradation were proposed for ABF A and ABF B. ABF A would be essentially cell-wall associated and act to degradeL-arabinan fragments generated by ABN A. ABF B activity would be important for the primary release of small amounts ofL-arabinose which initiate induction of various endolytic systems to degrade plant cell walls, and thus function in substrate sensing. In line with these considerations, the involvement of other, not yet identified glycosyl hydrolases inL-arabinan degradation by A.niger was suggested.

    Induction and repression of arabinase gene expression are further discussed in Chapter 7 . The results of the studies in A.niger (Chapter 5) and A.nidulans (Chapter 6) were interpreted in a mutual context. The identity of the lowmolecular-weight compound directly responsible for induction of arabinase gene expression, was addressed. BothL-arabinose andL-arabitol are likely candidates to fulfil such a role. However, it was not possible to weigh the actual inductive capacities ofL-arabinose andL-arabitol due to their in vivo convertibility and the carbon catabolite repression elicited by the pentose. Competition for such a compound provides an alternative explanation for the phenomena observed in Chapter 5. The involvement of the transcriptional repressor CREA in arabinase gene expression is not limited to the direct repression of structural and regulatory genes of theL-arabinan-degrading system. It also plays a role in inducer exclusion and end-product repression, two processes shown to be eminently involved in the regulation ofL-arabinan degradation in wild-type A.nidulans. Fungal growth rate was suggested to be related to derepression of theL-arabinan-degrading system. The possible involvement of cAMP in arabinase gene expression, as suggested by the presence of potential cis -acting cAMP-responsive elements in the structural genes, was considered. Various ways by which cAMP might modulate arabinase synthesis were surveyed.

    Rhizosphere carbon fluxes in field-grown spring wheat : model calculations based on 14C partitioning after pulse-labelling
    Swinnen, J. ; Veen, J.A. van; Merckx, R. - \ 1994
    Soil Biology and Biochemistry 26 (1994)2. - ISSN 0038-0717 - p. 171 - 182.
    koolhydraten - koolstof-stikstofverhouding - cellulose - decompositie - modellen - onderzoek - bodem - carbohydrates - carbon-nitrogen ratio - cellulose - decomposition - models - research - soil
    Knowledge on the quantity and dynamics of rhizodeposition under ecologically realistic conditions may elucidate various aspects of soil organic matter dynamics. Data from a field experiment with 14C pulse-labelling of spring wheat at different development stages, were used to estimate rhizosphere carbon fluxes. Not only the flux of C to the roots was assessed but also the fluxes of organic and inorganic release of root-derived material. C fluxes were calculated from curves fitted to data on shoot and root biomass and to data on 14C distribution at different development stages. The 14C distribution curves were extrapolated from the first labelling date (elongation stage) down to crop emergence and from the last labelling date (dough ripening stage) up to crop harvest, using different extrapolation procedures. The results show that while the maximum shoot growth rate occurred around ear emergence, the flux of C to the roots had a maximum around tillering. Over the entire growing season, shoot growth amounted to 5730 kg Cha−1 and 2310 ± 90 kg C ha−1 was translocated belowground. Of this 920± 150 kg C ha−1 was lost in root respiration and 500 ±120 kg C ha−1 was released as young photosynthate rhizodeposits, which are defined as organic materials released from the roots within 19 days after assimilation. Root growth amounted to 940 ±40 kg C ha−1, of which, however, 370 ±40 kg C ha−1 was lost again through root decay. Root turnover during the growing season, defined as root decay divided by root growth, was therefore 37–42%. Most of the organic input to soil (56–64%) occurred through rhizodeposition, while 36–44% was comprised in root biomass at crop harvest. The model used for the calculation of the carbon fluxes is discussed.
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