Staff Publications

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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    Photosynthetic efficiency in microalgal lipid production
    Remmers, Ilse M. - \ 2017
    Wageningen University. Promotor(en): R.H. Wijffels, co-promotor(en): P.P. Lamers. - Wageningen : Wageningen University - ISBN 9789463434607 - 200
    algae - biofuels - light - triacylglycerols - lipids - metabolism - algae culture - cultural methods - algen - biobrandstoffen - licht - triacylglycerolen - lipiden - metabolisme - algenteelt - cultuurmethoden

    Microalgae can contain large amounts of lipids which make them a promising feedstock for sustainable production of food, feed, fuels and chemicals. Various studies, including pilot-scale, have been performed and the knowledge on microalgal processes has advanced quickly. Unfortunately, current production costs for cultivation are still too high for bulk lipid production from microalgae.

    One of the major causes for the high costs of bulk lipid production is the reduced solar-to-lipid conversion efficiency. Current research, however, does not provide sufficient insight to identify optimization targets. Therefore, in this thesis we have studied the lipid production in microalgae in depth.

    Different TAG-accumulation strategies were investigated from a process engineering and metabolic point of view. The combination of all findings were used in the general discussion to thoroughly evaluate the microalgal lipid accumulation strategies. Current phototrophic microalgal lipid yields are still 10 times lower than the theoretical maximum. There is, however, still an enormous potential for further improvements. Future research should focus on (genetically) improved strains and advanced cultivation strategies, including adaptation to fluctuating outdoor weather conditions.

    This thesis was performed within the EU FP7 FUEL4ME project under grand agreement No 308938. Objective of this program is to develop a sustainable and scalable process for biofuels from microalgae and to valorize the by-products.

    Milk fat triacyglycerols : their variabiblity, relations with fatty acids, DGAT1, B polymorphs and melting fractions
    Tzompa Sosa, D.A. - \ 2016
    Wageningen University. Promotor(en): Toon van Hooijdonk, co-promotor(en): Hein van Valenberg; G.A. van Aken. - Wageningen : Wageningen University - ISBN 9789462577503 - 122
    milk fat - triacylglycerols - fatty acids - composition - polymorphism - dairy cows - cows - crystallization - fat crystallization - melting - calorimetry - maldi-tof - thin layer chromatography - melkvet - triacylglycerolen - vetzuren - samenstelling - polymorfisme - melkkoeien - koeien - kristallisatie - vetkristallisatie - smelten - calorimetrie - maldi-tof - dunnelaagchromatografie

    Milk fat (MF) triacylglycerol composition varies within a population of dairy cows. The variability of MF triacylglycerols and their structure was partially explained by the fatty acid (FA) composition of the MF, and by DGAT1 K232A polymorphism. The FA C16:0 and C18:1cis-9 play a major role in understanding the changes seen in triacylglycerol profile and structure because they are the most abundant FAs in MF and are negatively correlated. MFs with low ratio C16:0/C18:1cis-9 were decreased in triacylglycerols with 34 and 36 carbons and were increased in triacylglycerols with 52 and 54 carbons. These changes in MF composition greatly affected the crystallization behavior of MF by changing the types of polymorphs formed during its crystallization. MF with low ratio C16:0/C18:1cis-9 formed stable and metastable polymorphs (β and β’, respectively), whereas MF with high ratio C16:0/C18:1cis-9 formed exclusively metastable polymorphs (β’) when the fat was crystallized at 20°C. The changes in MF composition also affected the melting behavior of MF by changing the melting point of the MF fractions.

    Batch and repeated-batch oil production by microalgae
    Benvenuti, G. - \ 2016
    Wageningen University. Promotor(en): Rene Wijffels, co-promotor(en): Rouke Bosma; Maria Barbosa. - Wageningen : Wageningen University - ISBN 9789462576582 - 149
    algae - chlorella - arthrospira - dunaliella - nostoc - triacylglycerols - light - lipogenesis - photosynthesis - oil products - productivity - biomass conversion - economic analysis - algen - chlorella - arthrospira - dunaliella - nostoc - triacylglycerolen - licht - lipogenese - fotosynthese - olieproducten - productiviteit - biomassaconversie - economische analyse

    Microalgal triglycerides (TAGs) are promising feedstocks for the commodity markets (i.e. food, chemical and biofuel). Nevertheless, microalgal TAGs are not yet economically feasible due to the high production costs. To reduce these costs, TAG productivity needs to be maximized.

    The aim of this thesis was to increase microalgal TAG productivity by investigating the effects of biological and engineering parameters (i.e. production strain and operational strategy).

    We first screened seven marine species on their TAG productivity under nitrogen (N) starvation. Nannochloropsis sp. was identified as the most suitable species as it retained its photosynthetic activity while accumulating large amounts of TAGs ensuring the highest TAG productivity. Therefore, Nannochloropsis sp. was used in all following studies.

    Next, we aimed at optimizing TAG productivity by investigating the effect of initial-biomass-specific (IBS) light availability (i.e. ratio of light impinging on reactor ground area divided by initial biomass concentration per ground area) in batch outdoor cultivations carried out in horizontal and vertically stacked tubular reactors at different initial biomass concentrations at the start of the TAG accumulation phase, over different seasons. Based on the observed trends of TAG productivity for the Dutch climate, optimal initial biomass concentrations were suggested to achieve high areal TAG productivities for each reactor configuration and season.

    Subsequently, repeated-batch processes were investigated to further increase TAG productivity compared to batch processes. For this, repeated-batch cultivations were tested and compared to batch cultivations both at lab-scale under day/night cycles and in two identical, simultaneously operated, outdoor vertically stacked tubular reactors over different seasons. Although at lab-scale, batch and repeated-batch cultivations led to similar TAG productivities, outdoor repeated-batch processes were always outcompeted by the batch. It was concluded that repeated-batch processes require further optimization.

    For this, the physiological responses of Nannochloropsis sp. to N-starvation and N-replenishment were determined under continuous light in lab-scale batch and repeated-batch cultivations and condensed into a mechanistic model describing both cultivation strategies. Scenarios for improved TAG yields on light were simulated and, based on the optimized yields, a comparison of the two processes was performed. It was concluded that under continuous light, an optimized batch process will always result in higher TAG productivities than an optimized repeated-batch process.

    Finally, a techno-economic analysis for a two-step-continuous TAG production process (i.e. growth reactors are operated in continuous mode such that multiple batch-operated stress reactors are inoculated and sequentially harvested) is performed for a hypothetical 100 ha-scale plant in southern Spain using vertically stacked tubular reactors. Photosynthetic efficiencies based on outdoor pilot data were used as model input. By optimizing both photosynthetic efficiency and process technology, the production cost could be decreased from 7.4 to 3.0 €·kg-1 of TAG-enriched biomass. We believe to be on the right track to achieve an economically feasible TAG production platform provided that photosynthetic efficiency is further improved, the whole biomass is valorized and cheaper reactors are designed.

    The dynamics of oil accumulation in Scenedesmus obliquus
    Breuer, G. - \ 2015
    Wageningen University. Promotor(en): Rene Wijffels, co-promotor(en): Dirk Martens; Packo Lamers. - Wageningen : Wageningen University - ISBN 9789462572348 - 268
    algen - stikstof - uithongering - triacylglycerolen - productiviteit - fotosynthese - koolstof - tussenmuren - oliën - algae - nitrogen - starvation - triacylglycerols - productivity - photosynthesis - carbon - partitions - oils

    .Abstract long

    Global demands for food and biofuels increase rapidly, together with an increase of concerns for depleting fossil resources and climate change. New sustainable sources of vegetable oil, from now on referred to as triacylglycerol (TAG), are therefore highly desired. Arable land to produce these TAGs is however limited. Microalgae have the potential to achieve much higher TAG productivities than commonly used terrestrial plants and can be cultivated on non-arable land. Microalgae are therefore often considered as a promising alternative natural-source of TAGs. Microalgae can accumulate up to 50% of their weight as TAGs, but only do so in response to nitrogen starvation. At the same time, nitrogen starvation also affects many other cellular processes, including photosynthesis. At the start of the work presented in this thesis, little was known about the quantitative aspects of photosynthesis and TAG production during nitrogen starvation. This contributed to a large uncertainty in what could be expected from microalgae. This thesis therefore provides a quantitative understanding of the microalgal response to nitrogen starvation, that can be used to understand and optimize TAG production.

    The differences between microalgae species in their response to nitrogen starvation are characterized. It was found that the difference in the response to nitrogen starvation between microalgae could be characterized in 1) how long the species could retain their photosynthetic efficiency during nitrogen starvation, 2) how much the species could in increase in biomass concentration in the absence of a nitrogen source, and 3) which fraction of the newly made biomass constitutes of TAG. The microalga species S. obliquus was chosen as the most suitable species for TAG production and used in all further studies.

    It is quantified how process conditions, such as the light intensity, pH, and temperature, influence TAG production during nitrogen starvation in S. obliquus. It was found that TAG could be produced in the ranges pH 5-9, temperature of 20-35°C, and incident light intensity of 200-1500 µmol m-2 s-1. The light intensity did not affect the maximum TAG content. The light intensity did, however, have a major effect on the photosynthetic efficiency. Suboptimal pH values and temperatures resulted in both a reduction in photosynthetic efficiency and reduction in maximum TAG content.

    It was found that during nitrogen starvation, at best approximately half of the biomass produced during nitrogen starvation is TAG. Large amounts of starch were produced simultaneously. This simultaneous starch and TAG production was therefore investigated in more detail. It was investigated how the carbon partitioning ratio (the ratio between fatty acid and starch synthesis rates), and the photosynthetic efficiency during nitrogen starvation, are influenced by the light intensity during nitrogen starvation and by the photoacclimated state at the onset of nitrogen starvation. It was found that the ratio between starch and fatty acid synthesis strongly correlated to the extent of nitrogen starvation, quantified as the biomass nitrogen content. Immediately after nitrogen depletion, mostly starch was made, but when nitrogen starvation progressed, this ratio shifted in favour of fatty acid synthesis. When nitrogen starvation progressed further, only fatty acids were made. Hereafter, the initially accumulated starch was degraded while fatty acid synthesis continued. The effects caused by the photoacclimated state persisted during nitrogen starvation. This did however not affect the photosynthetic efficiency or the carbon partitioning ratio during nitrogen starvation. The light intensity during nitrogen starvation had a major impact on the photosynthetic efficiency, but only a minor impact on the carbon partitioning ratio.

    Because large amounts of starch are produced during nitrogen starvation in wild-type S. obliquus, it is investigated how starchless mutants of S. obliquus can be used to improve TAG production. The carbon-partitioning of the wild-type and the slm1 starchless mutant of S. obliquus are therefore compared. It was found that the starchless mutant diverted all photosynthetic capacity, that was used for starch synthesis in the wild-type, towards TAG synthesis. This resulted in much higher TAG accumulation rates during initial nitrogen starvation. Furthermore, it was found that the efficiency of photosynthesis was not negatively affected in this starchless mutant. Altogether, the TAG yield on light increased by 51%.

    Using these insights, a mechanistic model was developed that describes photosynthesis and carbon partitioning during nitrogen starvation. The model was validated using experimental data from both the wild-type and starchless mutant of S. obliquus. This model was used to investigate how TAG production could be improved by advances in reactor design and strain improvement. Projections are made for productivities that seem feasible when various technologies are implemented in the microalgal cultivation process, using S. obliquus as a case-study.

    Finally, the findings of this thesis are used to evaluate the outcomes of techno-economic and life cycle analysis (LCA) studies that investigated the cost-price and net energy ratio of microalgal products, mostly biodiesel. It was found that the biomass productivity and biochemical composition associated with the cultivation of microalgae are large uncertainties in the input values for these studies. Several scenarios for microalgal cultivation are therefore presented based on the findings of this thesis. For each scenario, productivities, biochemical compositions, and nutrient requirements are provided that can be used as more realistic input values for techno-economic and LCA studies. It was concluded that the TAG productivity is commonly overestimated by 3 to 6-fold. According to these studies, approximately half of the costs and energy are used in the cultivation step. It was therefore concluded that these techno-economic and LCA studies underestimate the cost-price and energy consumption by 2 to 3.5-fold. The future improvements in productivity that might seem feasible according to the model simulations, could potentially improve the productivity such that it approaches the productivity that is commonly assumed as the base-case in current techno-economic and LCA studies. These advances in productivity can help to reduce the cost-price and specific energy consumption, but in addition, a reduction in costs and energy consumption of photobioreactors is needed before microalgal TAG production can be commercialized.

    Lipid production in microalgae
    Klok, A.J. - \ 2013
    Wageningen University. Promotor(en): Rene Wijffels; Dirk Martens; Packo Lamers. - Wageningen : Wageningen University - ISBN 9789461737762 - 224
    algen - biobased economy - vet - triacylglycerolen - algenteelt - algae - biobased economy - fat - triacylglycerols - algae culture
    Een goed voorbeeld van een bulkproduct dat gewonnen kan worden uit microalgen is triacylglycerol (TAG), een vet dat bestaat uit een glycerol molecuul met daaraan 3 vetzuurketens. Om de productie van TAG te kunnen verhogen is begrip van het biologische mechanisme dat TAG vorming veroorzaakt onontbeerlijk. Het doel van dit onderzoek was dan ook om meer inzicht te krijgen in het mechanisme van TAG accumulatie in microalgen die blootgesteld zijn aan nadelige groeicondities, en om de verkregen kennis te vertalen naar optimale kweekcondities voor TAG productie.
    Continuous TAG production by the green microalga Neochloris oleoabundans under nitrogen limited conditions
    Klok, Anne - \ 2012
    algae - lipids - productivity - triacylglycerols - biofuels - biobased economy
    Triacylglycerol (TAG) accumulation in microalgae
    Breuer, Guido - \ 2012
    triacylglycerols - biochemistry - algae - biobased chemicals - biobased economy
    A moderate change in temperature induces changes in fatty acid composition of storage and membrane lipids in a soil arthropod
    Dooremalen, C. van; Ellers, J. - \ 2010
    Journal of Insect Physiology 56 (2010)2. - ISSN 0022-1910 - p. 178 - 184.
    orchesella-cincta collembola - thermal-reaction norms - biological significance - european populations - stress resistance - enzyme-activities - cold - growth - triacylglycerols - acclimation
    A moderate change in ambient temperature can lead to vital physiological and biochemical adjustments in ectotherms, one of which is a change in fatty acid composition. When temperature decreases, the composition of membrane lipids (phospholipid fatty acids) is expected to become more unsaturated to be able to maintain homeoviscosity. Although different in function, storage lipids (triacylglycerol fatty acids) are expected to respond to temperature changes in a similar way. Age-specific differences, however, could influence this temperature response between different life stages. Here, we investigate if fatty acid composition of membrane and storage lipids responds similarly to temperature changes for two different life stages of Orchesella cincta. Juveniles and adults were cold acclimated (15 °C ¿ 5 °C) for 28 days and then re-acclimated (5 °C ¿ 15 °C) for another 28 days. We found adult membranes had a more unsaturated fatty acid composition than juveniles. Membrane lipids became more unsaturated during cold acclimation, and a reversed response occurred during warm acclimation. Membrane lipids, however, showed no warm acclimation, possibly due to the moderate temperature change. The ability to adjust storage lipid composition to moderate changes in ambient temperature may be an underestimated fitness component of temperature adaptation because fluidity of storage lipids permits accessibility of enzymes to energy reserves.
    Fatty Acid Digestion and Deposition in Broiler Chickens Fed Diets Containing Either Native or Randomized Palm Oil
    Smink, W. ; Gerrits, W.J.J. ; Hovenier, R. ; Geelen, M.J.H. ; Lobee, H.W.J. ; Verstegen, M.W.A. ; Beynen, A.C. - \ 2008
    Poultry Science 87 (2008). - ISSN 0032-5791 - p. 506 - 513.
    metabolizable energy - digestibility - lard - triacylglycerols - absorption - saturation - tissues - lipids
    The hypothesis tested was that randomization of palm oil would increase its digestibility, especially that of its palmitic acid (C16:0) component, with subsequent changes in the fatty acid composition in body tissues. Broiler chickens were fed diets containing either native or randomized palm oil. Diets with either native or a 50/50 mix of native and hydrogenated sunflower oil were also fed. Randomization of palm oil raised the fraction of C16:0 at the sn-2 position of the glycerol molecule from 14 to 32%. Hydrogenation of sunflower oil reduced fat and total saturated fatty acid digestibility, whereas no change in digestibility of total unsaturated fatty acids was found. Randomization of palm oil raised the group mean apparent digestibility of C16:0 by 2.6 and 5.8% units during the starter and grower-finisher phase, respectively. On the basis of the observed digestibilities in the grower-finisher period, it was calculated that the digestibility for C16:0 at the sn-2 and sn-1,3 position was 90 and 51%, respectively. The feeding of randomized instead of native palm oil significantly raised the palmitic acid content of breast meat and abdominal fat and lowered the ratio of unsaturated to saturated fatty acids. It is concluded that randomized palm oil may be used as vegetable oil in broiler nutrition with positive effect on saturated fatty acid digestibility when compared with native palm oil and positive effect on firmness of meat when compared with vegetable oils rich in unsaturated fatty acids.
    Crystal network for edible oil organogels: Possibilities and limitations of the fatty acid and fatty alcohol systems
    Schaink, H.M. ; Malssen, K. van; Morgado-Alves, S. ; Kalnin, D.J.E. ; Linden, E. van der - \ 2007
    Food Research International 40 (2007)9. - ISSN 0963-9969 - p. 1185 - 1193.
    rheological properties - triacylglycerols - mixtures
    The textural and structural properties of organogels made by structuring liquid oil with mixtures of stearic acid (octadecanoic acid) and stearyl alcohol (octadecanol) have been studied. Optical, rheological and X-ray diffraction measurements have been used to investigate the influence of temperature, time and composition on the pseudo-binary system. The aim of these experiments is to relate the observed macroscopic behaviour of the organogels to the microscopic molecular ordering within the crystals that form a network. Oscillating strain measurements have been performed on mixtures with various acid to alcohol ratios. A synergetic effect in structuring was obtained by applying a 3:7 (acid:alcohol) ratio. Hardness and elastic modulus were significantly higher compared to samples with other ratios, at the same overall structurant concentration. Microscopy showed that the crystal habit of the structurant strongly depends on the composition of the mixture. X-ray diffraction experiments, which show that mixed crystals are formed when structurant mixtures are used, confirmed this result. The observed behaviour of the elastic modulus is likely the result of the difference in the microstructure of the interlinked crystals.
    Separation and direct detection of long chain fatty acids and their methylesters by the non-aqueous reversed phase HPLC and Silver Ion Chromotography, combined with CO laser pumped thermal lens spectrometry
    Bicanic, D.D. ; Mocnik, G. ; Franko, M. ; Niederlander, H.A.G. ; Bovenkamp, P. van de; Cozijnsen, J.L. ; Klift, E.J.C. van der - \ 2006
    Instrumentation Science and Technology 34 (2006)1-2. - ISSN 1073-9149 - p. 129 - 150.
    performance liquid-chromatography - beta-carotene - lipids - triacylglycerols - deflection - oils
    The potential of the CO laser pumped dual beam thermal lens spectrometer (TLS) used as the detector of infrared (IR) absorbance in non-aqueous reversed-phase high pressure liquid chromatography (NARP-HPLC) and argentation chromatography (Ag-HPLC-TLS) has been investigated. The linoleic acid C18:2 (9,11) cis, cis, the conjugated linoleic acid C18:2 (9,12) cis, cis, and (9,11) cis, cis and oleic acid C18:1 (9) cis free fatty acids present in the test mixture were separated and detected by NARP-HPLC-TLS directly, i.e., without a need for their prederivatization. The limit of detection (LOD) for the present NARP-HPLC-TLS set-up was determined using either oleic acid C18:1 (9) cis or linoleic acid C18:2 (9,12) cis, cis as the only analyte. The LOD obtained at 1750 cm-1 for C18:2 (9,12) cis, cis is 0.14% (v/v) with the standard deviation being 3.8% of the measured value. This is comparable to the LOD attainable by the bulk property refractive index detector (RID). For C18:1 (9) cis the LOD is 0.04% (v/v) with a standard deviation of 2.5%. The unique feature of the NARP-HPLC-TLS is its excellent selectivity; this was demonstrated experimentally by adding alcohols (octanol and decanol) that lack the C&dbnd;O carbonyl group to the aforementioned mixture of three fatty acids. In another experiment, the Ag-HPLC-TLS in IR was used to directly detect two different mixtures of five fatty acid methyl esters (FAMEs) after separation on the column. The results were compared to those achieved by the conventional UV absorbance detector. Despite more favourable excitation cross sections of FAMEs in the IR, the concentration LOD obtained for Ag-HPLC-TLS is inferior to that of the Ag-HPLC-UV. However, the mass LOD (11 µg) achieved by Ag-HPLC-TLS in IR for C18:3 FAME is two times better than that of the Ag-HPLC-UV absorbance detector. High IR absorption of eluent restricts, at present, the sensitivity of the Ag-HPLC-TLS and NARP-HPLC-TLS. Improved LOD's are anticipated by a judicious choice of the mobile phase and after materialising several modifications of the experimental set-up.
    Analysis of docosahexaenoic acid biosynthesis in Crypthecodinium cohnii by 13C labelling and desaturase inhibitor experiments
    Swaaf, M.E. de; Rijk, T.C. de; Meer, P. van der; Eggink, G. ; Sijtsma, L. - \ 2003
    Journal of Biotechnology 103 (2003)1. - ISSN 0168-1656 - p. 21 - 29.
    n-3 fatty-acids - marine microalgae - omega-3-fatty-acids - triacylglycerols
    The lipids of the heterotrophic microalga Crypthecodinium cohnii contain the omega-3 polyunsaturated fatty acid (PUFA) and docosahexaenoic acid (22:6) to a level of over 30&Eth;The pathway of 22:6 synthesis in C. cohnii is unknown. The ability of C. cohnii to use 13C-labelled externally supplied precursor molecules for 22:6 biosynthesis was tested by 13C NMR analysis. Furthermore, the presence of desaturases (typical for aerobic PUFA synthesis) was studied by the addition of specific desaturase inhibitors in the growth medium. The addition of 1-13C acetate or 1-13C butyrate in the growth medium resulted in 22:6 with only the odd carbon atoms enriched. Apparently, two-carbon units were used as building blocks for 22:6 synthesis and butyrate was first split into two-carbon units prior to incorporation in 22:6. When 1-13C oleic acid was added to the growth medium, 1-13C oleic acid was incorporated into the lipids of C. cohnii but was not used as a precursor for the synthesis of 22:6. Specific desaturase inhibitors (norflurazon and propyl gallate) inhibited lipid accumulation in C. cohnii. The fatty acid profile, however, was not altered. In contrast, in the arachidonic acid-producing fungus, Mortierella alpina, these inhibitors not only decreased the lipid content but also altered the fatty acid profile. Our results can be explained by the presence of three tightly regulated separate systems for the fatty acid production by C. cohnii, namely for (1) the biosynthesis of saturated fatty acids, (2) the conversion of saturated fatty acids to monounsaturated fatty acids and (3) the de novo synthesis of 22:6 with desaturases involved.
    Enzymatic acylglycerol synthesis in membrane reactor systems
    Padt, A. van der - \ 1993
    Agricultural University. Promotor(en): K. van 't Riet. - S.l. : Van der Padt - ISBN 9789054851264 - 151
    derivaten - alcoholen - glycerol - acylglycerolen - diacylglycerolen - triacylglycerolen - chemische reacties - membranen - omgekeerde osmose - ultrafiltratie - fermentatie - voedselbiotechnologie - vetzuren - carbonzuren - derivatives - alcohols - glycerol - acylglycerols - diacylglycerols - triacylglycerols - chemical reactions - membranes - reverse osmosis - ultrafiltration - fermentation - food biotechnology - fatty acids - carboxylic acids

    Up till twenty years ago, only chemical modifications of agricultural oils for novel uses were studied. Because of the instability of various fatty acids, enzymatic biomodifications can have advantages above the chemical route. Nowadays, enzymatic catalysis can be used for the modification of oils and fats. One way of biomodification is the enzymatic esterification of glycerol with fatty acid for the synthesis of mono- and triacylglycerols. Monoesters (monoacylglycerols) are used as emulsifiers in food and in cosmetics, tailor made triesters (triacylglycerols) are used to adjust the melting range of foods and cosmetics. This thesis describes a number of membrane reactor systems for the enzymatic esterification of glycerol with decanoic acid in hexadecane as solvent. Description and modelling of the kinetics and thermodynamic equilibrium have resulted in reactor concepts to reach the objective of mono- and triester synthesis.

    The basic reactor studied is a two-phase immobilized enzyme membrane reactor. In the membrane reactor, lipase from Candida ragosa is immobilized at the inner fibre side of a hydrophilic hollow fibre module. Decanoic acid in n-hexadecane is circulated at the same side, meanwhile a water-glycerol phase is circulated at the shell side. The glycerol diffuses through the membrane matrix allowing the synthesis to take place at the interface. The water produced diffuses backwards.

    Chapter 2 describes the enzymatic esterification of decanoic acid with glycerol for an emulsion system and for a hydrophilic membrane system. In a two-phase system, the enzyme activity is related to the oil-phase volume, the interface area and the enzyme load. The rate per unit interface area of the membrane system approximates the rate measured in an emulsion system. This implies that the cellulose membrane does not affect the esterification. Another consequence is that the activity per oil-phase volume is only specific surface area related, therefore a hollow fibre device is desirable. The optimum enzyme load in the membrane system is half of that in the emulsion system.

    The enzyme stability in glycerol-water mixtures is described in chapter 3. The activity of lipase from Candida rugosa with time can be described with a two-step model, assuming the native lipase reversibly altering its conformation to a form having no activity. The reversibility is experimentally verified. Both, the native and inactive form do inactivate irreversible at the same time to a completely inactive form. The inactivation is a function of the glycerol concentration. The activity of immobilized enzyme is reduced to the same level of activity as is found for free lipase.

    Not only activity and stability of the enzymatic system are of importance, also the equilibrium ester concentrations must be known in the non-ideal two-phase system. Chapter 4 presents the program TREP (Two-phase Reaction Equilibrium Prediction). With the use of measured thermodynamic activity based equilibrium constants, mass balances and the UNIFAC group contribution method, TREP predicts the equilibrium product and substrate concentrations for given initial amounts. Equilibrium predictions show that an excess of triesters can be obtained only at low water activity conditions, in this case an one-phase system is predicted. Predictions show that pure monoesters cannot be obtained in a two-phase system of decanoic acid-hexadecane phase and a glycerol-water phase, even with a high glycerol to fatty acid ratio. This is experimentally verified.

    From the knowledge gathered in these chapters, two membrane reactor systems are designed, one membrane reactor for the triester production and a second membrane reactor system equipped with an in-line adsorption column for the synthesis of monoesters.

    Chapter 5 describes a pervaporation system in which an excess of triesters can be synthesized at low water activity conditions. Lipase is immobilized onto the lumen side of a cellulose membrane where the organic phase is present. At the shell side, air circulates and the water activity is controlled with the use of a condenser. The lipase catalyzed esterification of decanoic acid with partial glycerides is studied in this reactor. In agreement with the predictions made in chapter 4, an excess of triacylglycerols, is obtained at low water activity conditions only.

    A second membrane reactor concept is described in chapter 6, the organic-phase is led over an adsorption column in order to adsorb the monoglycerides onto the adsorbate. When the column is saturated with monoesters, the column can be desorbed off-line in a continuous membrane/repeated batch column process. If a 5 % ethanol in hexane solution is used as desorption solvent, monoesters are desorbed selectively leading to a 90 % purity.

    Finally, in chapter 7, the potentials and limitations of the enzymatic esterification are discussed. To predict the steady-state concentration of a continuous reactor, the enzyme kinetics must be described. The membrane reactor is reaction limited, this could be overcome by placing a column packed with immobilized enzyme in the organic phase recirculation loop. Not only esterification can be performed in the pervaporation system, this system could also be suitable for interesterification or transesterification. Then the program TREP should be extended for reactions with different types of fatty acids.

    Botervet en gefraktioneerd botervet : overeenkomsten en verschillen in de vetzuur- en triglyceridesamenstelling
    Essers, M.L. ; Muuse, B.G. - \ 1987
    Wageningen : RIKILT (Rapport / Rijks-kwaliteitsinstituut voor Land- en Tuinbouwprodukten 87.43) - 13
    boterolie - fractionering - chemische samenstelling - vetzuren - triacylglycerolen - butter oil - fractionation - chemical composition - fatty acids - triacylglycerols
    Om de natuurlijke spreiding in de vetzuursamenstelling van botervet vast te stellen en om de mogelijkheden te onderzoeken voor het onderscheiden van ongemodificeerde en gefraktioneerde botervetten, zijn de volgende botervetten onderzocht op vetzuur- en triglyceridesamenstelling en getest op het kristallisatie gedrag in koude hexaan: 235 Nederlandse botervetten (uit de periode maart 1985 - febr. 1986), 37 winterbotervetten uit 1983/1984, 29 harde gefraktioneerde, 9 zachte gefraktioneerde en 29 ongemodificeerde botervetten die dienden als uitgangsmateriaal voor fraktionering.
    Butteroil RM 164 : assessment of purity of triglyceride calibrants
    Muuse, B.G. ; Kamp, H.J. van der; Herstel, H. - \ 1987
    Wageningen : RIKILT (Report / RIKILT 87.28) - 10
    boterolie - triacylglycerolen - vetzuren - butter oil - triacylglycerols - fatty acids
    Ten saturated and three unsaturated triglycerides have been controlled on their purity. Fatty acid and triglyceride analyses of the individual samples and of mixtures of the short chain respectively the long chain fatty acids have been clone. The gaschromatographic purity was judged to be acceptable for further use in the certification trial of BCR butterfat reference material RH 164. From the results of the mixtures it was concluded that none of the samples contains impurities of non-eluting materials. Some problems were found in preparing and handling the long chain fatty acid mixtures since some crystallization was observed, leading to increasing calibration factors.
    Onderzoek en analysemethoden voor het aantonen van gefraktioneerd botervet
    Kamp, H.J. van der; Muuse, B.G. - \ 1983
    Wageningen : RIKILT (Verslag / RIKILT 83.59) - 8
    boter - vet - vetzuren - cholesterol - triacylglycerolen - analytische methoden - analytische scheikunde - butter - fat - fatty acids - cholesterol - triacylglycerols - analytical methods - analytical chemistry
    Doel van dit onderzoek is: Ontwikkeling van een methode voor het aantonen van gefraktioneerd botervet. Voor het aantonen van gefraktioneerd botervet zijn de analysen van de vetzuursamenstelling, vetzuren in 2 positie, cholesterolgehalte en triglyceridesamenstelling onvoldoende. Een meer betrouwbare detektiemethode werd ontwikkeld, gebaseerd op de kristallisatie van vnl. de verzadigde hogere triglyceriden in hexaan bij 12,5°C. Normaal botervet geeft daarbij geen kristallisatie terwijl gefraktioneerd botervet tot 15% kristalmassa oplevert. Indien meer dan 0,5% kristallen worden gevonden dan is de aanwezigheid van gefraktioneerd botervet duidelijk aangetoond. Met in principe dezelfde methode is aantonen van de zachte fraktie mogelijk.
    Referentiemateriaal voor de bepaling van de vetzuursamen-stelling van melkvet
    Kamp, H.J. van der; Muuse, B.G. - \ 1982
    Wageningen : RIKILT (Verslag / RIKILT 82.42) - 9
    triacylglycerolen - gaschromatografie - boterzuur - melkvet - triacylglycerols - gas chromatography - butyric acid - milk fat
    Vaststellen van de vetzuursamenstelling van een monster botervet om te komen tot een in Nederland geaccepteerd referentiemonster. De samenstelling van enkele synthetische mengsels van triglyceriden werd berekend. De triglyceriden werden tevoren afzonderlijk gecontroleerd op zuiverheid aan de hand van correctiefactoren en gaschromatografische analysen. Met behulp van de triglyceride-mengsels werd de vetzuursamenstelling van een monster botervet vastgesteld. Dit resultaat werd vergeleken met de NIZO-uitkomst.
    Aantonen van gefraktioneerd botervet
    Muuse, B.G. ; Kamp, H.J. van der; Oortwijn, H. - \ 1982
    Wageningen : RIKILT (Verslag / RIKILT 83.3)
    melkvet - vetzuren - sterolen - triacylglycerolen - fractionering - voedselanalyse - analytische methoden - milk fat - fatty acids - sterols - triacylglycerols - fractionation - food analysis - analytical methods
    Doel van het onderzoek was het verkrijgen van methoden voor het aantonen van gefraktioneerd botervet, puur en na verwerking in levensmiddelen. In het kader van een ringonderzoek van de studiegroep gefraktioneerd botervet, werd in 5 x 3 monsters het gehalte c .q. de samenstelling bepaald van: vetzuren, 2 positie vetzuren, triglyceriden, sterolen. De ringtestmonsters bestonden uit normaal botervet (uitgangsmateriaal) en resp. de harde en zachte fraktie daarvan.
    Infrared spectra of monoacid triglycerides : with some applications to fat analysis
    Ruig, W.G. de - \ 1971
    Wageningen : Pudoc, Centre for Agricultural Publishing and Documentation (Agricultural research reports 759) - 143
    derivaten - alcoholen - glycerol - acylglycerolen - diacylglycerolen - triacylglycerolen - infraroodspectroscopie - analyse - chemie - analytische scheikunde - derivatives - alcohols - glycerol - acylglycerols - diacylglycerols - triacylglycerols - infrared spectroscopy - analysis - chemistry - analytical chemistry
    Increasing potato yield with glyceroltriacetate and glyceroldiacetate
    Kuiper, F. ; Kuiper, P.J.C. ; Aalderen, B.W. van - \ 1969
    Wageningen : Veenman (Mededelingen Landbouwhogeschool Wageningen 69-6) - 7
    plantenvoeding - kunstmeststoffen - mest - solanum tuberosum - aardappelen - plantengroeiregulatoren - derivaten - alcoholen - glycerol - acylglycerolen - diacylglycerolen - triacylglycerolen - plant nutrition - fertilizers - manures - solanum tuberosum - potatoes - plant growth regulators - derivatives - alcohols - glycerol - acylglycerols - diacylglycerols - triacylglycerols
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