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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    Microbubble stability and applications in food
    Rovers, T.A.M. - \ 2015
    Wageningen University. Promotor(en): Erik van der Linden, co-promotor(en): Marcel Meinders; Guido Sala. - Wageningen : Wageningen University - ISBN 9789462574755 - 138
    microbubbles - eiwit - stabiliteit - karakterisering - voedsel - voedseladditieven - oppervlaktespanningsverlagende stoffen - zuurbehandeling - reologische eigenschappen - sensorische evaluatie - tribologie - druk - verwarming - koelen - microbubbles - protein - stability - characterization - food - food additives - surfactants - acid treatment - rheological properties - sensory evaluation - tribology - pressure - heating - cooling

    Aeration of food is considered to be a good method to create a texture and mouthfeel of food products that is liked by the consumer. However, traditional foams are not stable for a prolonged time. Microbubbles are air bubbles covered with a shell that slows down disproportionation significantly and arrests coalescence. Protein stabilized microbubbles are seen as a promising new food ingredient for encapsulation, to replace fat, to create new textures, and to improve sensorial properties of foods. In order to explore the possible functionalities of microbubbles in food systems, a good understanding is required regarding the formation of protein stabilized microbubbles as well as their stability in environments and at conditions encountered in food products. The aim of this research was to investigate the key parameters for applications of microbubbles in food systems. In Chapter 1 an introduction to this topic is given.

    In Chapter 2, the effect of the microbubble preparation parameters on the microbubble characteristics, like the microbubble yield, size and stability, was investigated. The protein Bovine Serum Albumin (BSA) and the method sonication was used to manufacture the microbubbles. The manufactured number and stability of microbubbles was highest when they were prepared at a pH around 5 to 6, just above the isoelectric point, and at an ionic strength of 1.0 M. This can be related to the protein coverage at the air/water interface of air bubbles formed during sonication. At a pH close to the isoelectric point the BSA molecules is in its native configuration. Also the repulsion between the proteins is minimized at these pH values and ionic strength. Both the native configuration and the limited repulsion between the proteins result in an optimal protein coverage during the first part of sonication. Also a high protein concentration contributes to a higher surface coverage. The surface coverage is proportional to the protein concentration up to a concentration of 7.5% after which an increase in protein concentration did not lead to a substantial increase in the number of microbubble . In the second part of sonication the protein layer around the air bubble becomes thicker and stronger by heat induced protein-protein interactions. We found that and at a preheating temperature of 55-60°C, about 5 °C below the BSA denaturation temperature, and a final solution temperature of 60-65°C most microbubbles were obtained, while at higher temperatures mainly protein aggregates and (almost) no microbubbles are formed. This suggests that at temperature of around 60°C to 65°C protein aggregated mostly at the air-water interface creating a multi-layered shell, while at higher temperature, they also aggregated in bulk. These aggregates cannot form microbubbles. We found that optimal preparation parameters strongly depend on the protein batch. We hypothesize that the differences in microbubble formation between the protein batches is due to (small) differences in the protein molecular and denaturation properties that determine the temperature at which the molecules start to interact at the air-water interface. Microbubbles made with different protein concentration and preheating temperatures shrunk in time to a radius between 300 nm and 350 nm, after which the size remained constant during further storage. We argue that the driving force for the shrinkage was the Laplace pressure, resulting in an air flux from the bubbles to the solution. We argue that the constant final size can be explained by a thickening of the microbubble shell as a result of the microbubble shrinkage, thereby withstanding the Laplace pressure.

    In Chapter 3 and Chapter 4, microbubble stability at environments and conditions representative for food products were studies. In Chapter 3 we investigated the stability upon addition of surfactants and acid, When surfactants or acid were added, the microbubbles disappeared in three subsequent steps. The release of air from the microbubble can be well described with the two-parameter Weibull process. This suggests two processes are responsible for the release of air: 1) a shell-weakening process and 2) a random fracture of the weakened shell. After the air has been released from the microbubble the third process is identified in the microbubble disintegration: 3) the shell disintegrated completely into nanometer-sized particles. The probability of fracture was exponentially proportional to the concentration of acid and surfactant, meaning that a lower average breaking time and a higher decay rate were observed at higher surfactant or acid concentrations. For different surfactants, different decay rates were found. The disintegration of the shell into monomeric proteins upon addition of acid or surfactants shows that the interactions in the shell are non-covalent and most probably hydrophobic. After surfactant addition, there was a significant time gap between complete microbubble decay (release of air) and complete shell disintegration, while after acid addition the time at which the complete disintegration of the shell was observed coincided with the time of complete microbubble decay.

    In Chapter 4 the stability of the microbubbles upon pressure treatment, upon fast cooling after heating and at different storage temperatures was studied. The microbubble stability significantly decreased when microbubbles were pressurized above 1 bar overpressure for 15 seconds or heated above 50°C for 2 minutes. Above those pressures the microbubbles became unstable by buckling. Buckling occurred above a critical pressure. This critical pressure is determined by the shell elastic modulus, the thickness of the shell, and the size of the microbubble. Addition of crosslinkers like glutaraldehyde and tannic acid increased the shell elastic modulus. It was shown that microbubbles were stable against all tested temperatures (up to 120°C) and overpressures (4.7 bar) after they were reinforced by crosslinkers. From the average breaking time at different storage temperatures, we deduced that the activation energy to rupture molecular bonds in the microbubbles shell is 27 kT.

    In Chapter 5, we investigated the effect of microbubbles on the rheological, tribological sensorial properties of model food systems and we compared this effect to the effect on food systems with emulsion droplets and without an added colloid. We investigated the effect in three model food systems, namely fluids with and without added thickener and a mixed gelatine-agar gel. In a sensory test panellists were asked whether they could discriminate between samples containing microbubbles, emulsion droplets or no added colloid. Emulsions could be sensorially well distinguished from the other two samples, while the microbubble dispersion could not be discriminated from the protein solution. Thus, we concluded that at a volume fraction of 5% of these BSA covered microbubbles were not comparable to oil-in-water emulsions. The good discrimination of emulsion might be ascribed to the fact that emulsion had a lower friction force (measured at shear rates form 10 mm/s to 80 mm/s) than that microbubbles dispersions and protein solutions. Upon mixing emulsions and microbubble dispersions the friction value approximated that of emulsions. This effect was already noticed at only 1.25% (v/v) oil, indicating that microbubbles had not a significant contributions to the friction of these samples. Also microbubble dispersions with and without protein aggregates were compared. The microbubble dispersions with and without thickener containing protein aggregates had a higher viscosity than the those samples without protein aggregates. Protein aggregates in the gelled microbubble sample yielded a higher Young’s modulus and fracture stress. The differences between the gelled samples could be well perceived by the panellists. We attribute this mainly to the fracture properties of the gel. In general we concluded that microbubbles, given their size of ~ 1 mm and volume fraction of 5%, did not contribute to a specific mouthfeel.

    Finally in Chapter 6, the results presented in the previous chapters are discussed and put in perspective of the general knowledge on microbubbles production, stability, and applications in food. We described the main mechanisms leading to microbubble formation and stability. We showed that the production parameters significantly influence the interactions in the microbubble shell, and the those interactions highly determine the stability of the microbubbles under several conditions. We reported about limitations of sonication as a method to produce microbubbles suitable for food applications and we provided some ways to overcome these limitations. The use of microbubbles in food systems has been explored and we clearly see possible applications for microbubbles in food. We reported about directions for possible further research.

    In this work we made significant progress in understanding the interactions in the microbubble shell and their relation to microbubble stability. We also advanced in comprehension towards possible applications of microbubbles in food.

    Autogenerative high pressure digestion : biogass production and upgrading in a single step
    Lindeboom, R.E.F. - \ 2014
    Wageningen University. Promotor(en): Jules van Lier, co-promotor(en): Jan Weijma; Caroline Plugge. - Wageningen : Wageningen University - ISBN 9789461738608 - 208
    biogas - spijsvertering - druk - methaanproductie - kooldioxide - zetmeel - hydrolyse - biogas - digestion - pressure - methane production - carbon dioxide - starch - hydrolysis
    Analyses of changes in spatial distribution of the beam trawl fleet and their effects on the plaice and sole stock, 1990 - 2005
    Quirijns, F.J. ; Rijnsdorp, A.D. ; Grift, R.E. - \ 2006
    IJmuiden : IMARES (Report / Wageningen IMARES C075/06) - 27
    visserij - visserijbeheer - beperkende factoren - effecten - vis vangen - druk - boomkorvisserij - visvangsten - vlootdynamica - fisheries - fishery management - limiting factors - effects - fishing - pressure - beam trawling - fish catches - fleet dynamics
    Management measures directed at limiting fishing effort may have had an influence on the behaviour of the beam trawl fleet that negatively affected the North Sea plaice and sole stocks. This study analyses trends in fleet behaviour and fishing pressure in relation to management measures proposed by the fishing industry.
    Mit reduzierten Druck spritzen
    Os, E. van; Michielsen, J. - \ 2005
    Gemüse 41 (2005)5. - ISSN 0016-6286 - p. 22 - 24.
    gewasbescherming - ziektebestrijding - bladbespuiting - druk - druppels - druppelgrootte - spuitvloeistoffen - verontreiniging - bodemverontreiniging - drift - verontreinigingsbeheersing - glastuinbouw - plant protection - disease control - foliar spraying - pressure - droplets - droplet size - sprays - pollution - soil pollution - drift - pollution control - greenhouse horticulture
    De toepassing van gewasbeschermingsmiddelen bij teelt onder glas. Onderzocht werden de effecten van druk en druppelgrootte op effectiviteit van bespuiting en belasting voor het milieu door verspilling
    Effect van spuitdruk : 5-10 bar is optimaal
    Os, E. van; Michielsen, J.M. - \ 2005
    Onder Glas 2 (2005)2. - p. 8 - 9.
    gewasbescherming - vruchtgroenten - tomaten - spuiten - druk - emissie - depositie - toedieningswijzen - spuitapparatuur - glastuinbouw - groenten - plant protection - fruit vegetables - tomatoes - spraying - pressure - emission - deposition - application methods - spraying equipment - greenhouse horticulture - vegetables
    In de glastuinbouw wordt bij de teelt van vruchtgroenten gespoten met werkdrukken tussen 5 en 15 bar. Daarmee wordt veel water verspoten en slijten de spuitdoppen sneller en het gewas wordt heel nat. Om effectiever te kunnen spuiten is bij tomaat onderzoek gedaan naar optimalisatie van de spuitdruk. Tijdens drie groeistadia is met een spuitmast gespoten bij vier verschillende spuitdrukken (2,5; 10 en 15 bar). In een kader wordt een schematisch overzicht gegeven van de proefopzet en de ligging van de collectoren in de verschillende groeistadia. In de proeven is gespoten bij een gewashoogte van 0,75 m, bij 2,25 m en bij 2,8 m
    Pneumat blaast onkruid weg
    Wijnker, J.P.M. ; Bleeker, P.O. - \ 2004
    BloembollenVisie 2004 (2004)52. - ISSN 1571-5558 - p. 26 - 26.
    onkruidbestrijding - mechanische methoden - bloembollen - wiedmachines - pneumatische kracht - lucht - druk - tests - biologische landbouw - weed control - mechanical methods - ornamental bulbs - rod weeders - pneumatic power - air - pressure - tests - organic farming
    Mechanische onkruidbestrijding in de bollenteelt is altijd moeilijk uit te voeren geweest. Dit komt vooral door de brede plantregels en weinig ruimte tussen de plantregels voor grondbewerking. Deze heeft veel minder ruimte tussen de regels nodig dan bijvoorbeeld een vingerwieder. Onderzoek dat afgelopen jaar is uitgevoerd door PPO in tulp toonde een goede onkruidbestrijding zonder neveneffecten op de opbrengst
    De voordelen van sterilisatie onder hoge druk voor de kwaliteit van voedingsmiddelen
    Matser, A.M. ; Krebbers, B. ; Berg, R.W. van den; Bartels, P.V. - \ 2004
    Elsevier Voedingsmiddelen Industrie 5 (2004)4. - ISSN 1570-6907 - p. 33 - 38.
    voedseltechnologie - houdbaarheid (kwaliteit) - druk - steriliseren - smaak - voedingsstoffen - food technology - keeping quality - pressure - sterilizing - taste - nutrients
    Indien toegepast bij verhoogde temperaturen en gebruikmakend van de temperatuurtoename door adiabatische compressie, kan verwerking onder hoge druk gebruikt worden voor de sterilisatie van voedingsmiddelen. Het is mogelijk om, via het kiezen van geschikte procescondities, zowel vegetatieve cellen als microbiële sporen volledig te inactiveren zodat er voedingsmiddelen ontstaan die stabiel blijven tijdens de opslag. De kwaliteit van producten die onder hoge druk gesteriliseerd zijn, is over het algemeen hoger dan bij producten die op een conventionele manier gesteriliseerd zijn met behulp van warmte. Dit geldt vooral voor de textuur, smaak en het vasthouden van nutriënten. Het effect van sterilisatie onder hoge druk op de kleur is afhankelijk van het product. Dit varieert van volledig behoud van de frisse kleur tot het optreden van dezelfde kleurverandering als bij conventionele technieken
    Door verlaging van de spuitdruk naar minder emissie en betere depositie van spuitvloeistof bij hoogvolume spuiten in tomaat
    Os, E.A. van; Michielsen, J.M.P.G. ; Corver, F.J.M. ; Berg, J.V. van den; Bruins, M.A. ; Porskamp, H.A.J. ; Zande, J.C. van de - \ 2004
    Wageningen : Agrotechnology & Food Innovations (Rapport / Agrotechnology & Food Innovations nr. 237) - ISBN 9789067548090 - 37
    spuiten - druk - spuitvloeistoffen - emissie - depositie - spuitapparatuur - tomaten - spraying - pressure - sprays - emission - deposition - spraying equipment - tomatoes
    Druppelgrootte en drift bij het Pulstec spuitsysteem : laboratorium- en modelonderzoek
    Holterman, H.J. ; Porskamp, H.A.J. ; Zande, J.C. van de - \ 2002
    Wageningen : IMAG (Nota / Instituut voor Milieu- en Agritechniek (IMAG) V 2002-07) - 10
    landbouwtechniek - spuitapparaten - veldspuiten - drift - druk - akkerbouw - druppelgrootte - proeven - agricultural engineering - sprayers - field sprayers - drift - pressure - arable farming - droplet size - trials
    Deze rapportage is een verslag van een laboratorium- en modelonderzoek naar het driftreducerend vermogen van een Pulstec spuitsysteem, toegepast op een veldspuit.
    Mechanische ventilatie in varkensstallen met uitloop biedt perspectief
    Leeuw, M. de; Wagenberg, V. van - \ 2002
    Praktijkkompas. Varkens 16 (2002)3. - ISSN 1570-8578 - p. 10 - 11.
    varkensstallen - varkens - ventilatie - kunstmatige ventilatie - klimaatregeling - mechanische methoden - luchtstroming - druk - scharrelhouderij - huisvesting, dieren - varkenshouderij - biologische landbouw - binnenklimaat - pig housing - pigs - ventilation - artificial ventilation - air conditioning - mechanical methods - air flow - pressure - free range husbandry - animal housing - pig farming - organic farming - indoor climate
    De biologische en scharrelvarkenshouderij past veelal natuurlijke ventilatie toe. Deze manier van ventileren is echter minder beheersbaar dan mechanische ventilatie.
    Listeria monocytogenes - inactivation by essential oils and high pressure, and contribution of genetic variation to stress resistance
    Karatzas, K.A.G. - \ 2002
    Wageningen University. Promotor(en): F.M. Rombouts; M.H.J. Bennik. - S.l. : S.n. - ISBN 9789058086303 - 86
    voedselmicrobiologie - listeria monocytogenes - inactivatie - etherische oliën - druk - genetische variatie - stressreactie - food microbiology - listeria monocytogenes - inactivation - essential oils - pressure - genetic variation - stress response

    A variety of non-thermal mild preservation techniques have lately been introduced in food production, or are currently being investigated thoroughly for potential use in food processing. Two of these novel preservation techniques are the use of essential oil compounds isolated from plants and of High Hydrostatic Pressure (HHP) treatment. Applications of these preservation methods, alone or combined, have shown to reduce the viable numbers of microorganisms occurring in foods, and in addition, are able to preserve the nutritional and sensory characteristics of the product. The objectives of this thesis were to asses the antimicrobial potential of these combined processing techniques against the foodborne bacterium Listeria monocytogenes , which can cause serious disease with a relatively high mortality rate. In addition, to get more insight in the primary cellular targets that are affected upon HHP treatment of L. monocytogenes , we examined the mechanism underlying increased HHP tolerance of an isolate of this organism.

    Chapter 1 gives a short introduction on L. monocytogenes. Furthermore, mild and novel preservation techniques in food processing are addressed, with special emphasis on the use of essential oil compounds from plants, and the use of High Hydrostatic Pressure (HHP). General characteristics and the mode of action of these preservation techniques are described, followed by resistance mechanisms that bacteria use to counteract their potentially lethal action. This chapter is concluded with the combined use of these preservation methods, and an outline of this thesis.

    In Chapter 2 , it is demonstrated that various plant-derived volatiles, namely, S-carvone, carvacrol, cinnamaldehyde, thymol, and decanal, have the ability to reduce the viable numbers of L. monocytogenes if used in combination with mild heat treatment, while these treatments alone were not affecting the viability of this pathogen. These findings show that essential oil compounds can play an important role in minimally processed foods, and can be used in the concept of Hurdle Technology to reduce the intensity of heat treatment or possibly other individual hurdles.

    In Chapter 3 , the combined antimicrobial action of carvacrol or thymol in combination with HHP was investigated at different temperatures. These treatments showed a synergistic action, with greater antimicrobial effects upon pressurisation at 1 oC than at 8°C or 20°C. Furthermore, addition of carvacrol to cells after exposure to sub-lethal HHP treatment showed reductions in viable numbers that were similar to those using simultaneous treatment with carvacrol and HHP. Synergism was also observed between carvacrol and HHP in semi-skimmed milk that was artificially contaminated with L. monocytogenes . The study demonstrates the synergistic antimicrobial effect of essential oils in combination with HHP. Together with the results described in Chapter 2, these data indicate the potential of essential oils to be employed in food processing if combined with other techniques.

    A major problem that successful application of HHP treatment faces is the variable piezotolerance of bacterial species, strains within a species, and even cells within pure cultures that are not homogenous. In Chapter 4 , we investigated the characteristics of a L. monocytogenes ScottA isolate, named AK01, that was derived from a wild type (wt) culture after a single pressurisation treatment. The survival of exponential and stationary phase cells of AK01 was at least 2 logs higher than that of the wt over a broad range of pressures (150-500 MPa), while both strains showed higher piezotolerance in the stationary than in the exponential phase of growth. In semi-skimmed milk, exponential phase cells of both strains showed lower reductions upon pressurisation than in buffer, but again, AK01 was more piezotolerant than the wt. The piezotolerance of AK01 was retained for at least 40 generations in rich medium, suggesting a stable phenotype. Interestingly, cells of AK01 lacked flagella and were elongated, and this strain showed slightly lower maximum specific growth rates at 8°C, 22°C and 30°C than the wt. Moreover, the piezotolerant strain AK01 showed increased resistance to heat, acid, and H 2 O 2 compared with the wt. The difference in HHP tolerance between the piezotolerant strain and the wt strain could not be attributed to differences in membrane fluidity, since strain AK01 and the wt had identical in situ lipid melting curves, as determined by Fourier Transfer Infrared spectroscopy.

    In Chapter 5 , the mechanisms underlying the altered phenotypic characteristics of AK01 are further examined. In this chapter, high piezotolerance, immobility, and reduced virulence were conclusively linked to a single amino acid deletion in the highly conserved glycine-rich region of the regulatory protein CtsR ( C lass t hree s tress gene r epressor). CtsR negatively regulates the expression of Class III heat shock genes ( clpP , clpE and the clpC operon). The Clp proteins prevent the accumulation of misfolded proteins that might be toxic to the cell. In the mutant strain AK01, expressing the CtsRΔGly protein, we observed upregulation ofclpP , which demonstrates the involvement of Class III heat shock genes in increased survival upon HHP treatment and other stresses. Replacement of the wt ctsR gene with the ctsRΔGly gene in a wt background resulted in a mutant strain that also lost its motile character, and importantly, also showed attenuated virulence. The deletion of three base pairs in the region of ctsR that normally encodes four glycines is seemingly not an isolated incident, since we detected the same mutation in the majority of other spontaneous piezotolerant isolates of L. monocytogenes . This suggests a functional role for this mutation in L. monocytogenes to survive unforeseen events that do not allow for adaptation of normal cells, but require genetic diversity.

    In conclusion, this work demonstrated some of the potentials that novel techniques, like the use of essential oils and HHP, can offer alone or combined with other novel or traditional techniques, like heat treatment. We furthermore investigated risks that could emerge from the use of those novel techniques. The occurrence of the piezotolerant strain AK01 of L. monocytogenes demonstrated the existence of bacterial heterogeneity within a supposedly pure wt population with regard to HHP resistance. The variance of piezotolerance within a microbial population, but also between different strains, is an important parameter that determines successful application of HHP treatment. This will be an important aspect for risk assessment of HHP treated foods that are, or will become, available on the market. Tailored HHP treatments, possibly in combination with additional mild preservatives, will be required for different products, and increased knowledge about the effects of these treatments will enable the food industry to produce safe foods at minimal costs.

    Vloeistof- en grondwaterdruk bij mestkelders
    Braam, C.R. - \ 2000
    Agrabeton 10 (2000)1. - ISSN 0167-3246 - p. 8 - 9.
    opslagloodsen - mest - bouwconstructie - sterkte - statica - berekening - grondwater - vloeistoffen (fluids) - druk - stores - manures - building construction - strength - statics - calculation - groundwater - fluids - pressure
    Nieuwe eigenschappen met bekende ingrediënten door ultrahoge druk: Trends in ingrediënten deel 5
    Matser, A.M. ; Bartels, P.V. - \ 1999
    Voedingsmiddelentechnologie 32 (1999)13. - ISSN 0042-7934 - p. 30 - 32.
    voedselbewaring - druk - voedseltechnologie - voedselindustrie - voedingsmiddelen - organoleptische kenmerken - sensorische evaluatie - ingrediënten - food preservation - pressure - food technology - food industry - foods - organoleptic traits - sensory evaluation - ingredients
    De invloed van deze technologie op vitamines, kleur, smaak en textuur. Enzymen en micro-organismen kunnen geinactiveerd worden, terwijl vitamines, kleur en smaak intact blijven
    Mogelijkheden voor hogedruk mestinjecteur
    Hol, J.M.G. ; Huijsmans, J.F.M. - \ 1998
    Landbouwmechanisatie 49 (1998)6/7. - ISSN 0023-7795 - p. 22 - 23.
    injectie - kunstmeststoffen - bodeminjecteurs - druk - luchtverontreiniging - ammoniak - emissie - vervluchtiging - noorwegen - injection - fertilizers - soil injectors - pressure - air pollution - ammonia - emission - volatilization - norway
    In het buitenland is de ammomiakemissie ook actueel geworden. Zo is de Direct Ground Injection machine (DGI) ontwikkeld in Noorwegen. Het IMAG-DLO onderzocht deze techniek in Nederland
    Berekeningsmethoden voor de leidingweerstand van mengmest.
    Arts, M.W.M.F. ; Vliet, T. van; Telle, M.G. ; Have, P.J.W. ten - \ 1991
    Wageningen : IMAG-DLO - ISBN 9789054060048 - 35
    gesloten systemen - stalmest - stroming - stromingsweerstand - vloeistofmechanica - vloeistoffen (fluids) - frictie - hydrodynamica - vloeistoffen (liquids) - beweging - pijpen - druk - weerstand - drijfmest - slangen (buizen) - viscosimeters - viscositeit - closed systems - farmyard manure - flow - flow resistance - fluid mechanics - fluids - friction - hydrodynamics - liquids - movement - pipes - pressure - resistance - slurries - tubes - viscometers - viscosity
    Simulatiemodel van slibtransport in het IJsselmeer, IJslib.
    Verhagen, J.H.G. - \ 1988
    Wageningen : Landbouwuniversiteit Wageningen (Onderzoeksverslag / Landbouwuniversiteit, Vakgroep Hydraulica en Afvoerhydrologie 88) - 35
    kanalen - computersimulatie - stroming - stromingsweerstand - vloeistoffen (fluids) - geologische sedimentatie - hydrodynamica - wiskundige modellen - beweging - druk - onderzoek - weerstand - rivieren - simulatie - simulatiemodellen - waterlopen - water - ijsselmeer - canals - computer simulation - flow - flow resistance - fluids - geological sedimentation - hydrodynamics - mathematical models - movement - pressure - research - resistance - rivers - simulation - simulation models - streams - water - lake ijssel
    Glycoalkaloids and phenolic compounds in gamma irradiated potatoes; a food irradiation study on radiation induced stress in vegetable products
    Bergers, W.W.A. - \ 1980
    Landbouwhogeschool Wageningen. Promotor(en): W. Pilnik, co-promotor(en): J.H. Koeman. - Wageningen : Bergers - 49
    voedingsmiddelen - voedselbewaring - druk - fermentatie - solanum tuberosum - aardappelen - straling - effecten - deeltjes - bestraling - ioniserende straling - landbouw - glycoalkaloïden - foods - food preservation - pressure - fermentation - solanum tuberosum - potatoes - radiation - effects - particles - irradiation - ionizing radiation - agriculture - glycoalkaloids
    Irradiation is a recent preservation method. With the aid of ionizing radiation microorganisms in food can be killed or specific physiological processes in vegetable products can be influenced.

    In order to study the effects of metabolic radiation stress on quantitative chemical changes in vegetable products, specific target compounds were investigated in stored irradiated potatoes. These target compounds, i.e. glycoalkaloids and phenolic compounds were choosen with a view to food toxicology and food sensoric quality.

    Much attention has been spent on quantitative analyses of the pre-selected target compounds in the potato samples. Enzymic changes of the polyphenolic compounds were kept to a minimum by the direct freezing of potato slices in liquid nitrogen, freeze-drying and extraction by boiling in 80% ethanol.

    A quantitative assay for solanidine potato glycoalkaloids was developed from a pre-existing method with minor changes, by which the rapidity of the assay is improved, without affecting its sensitivity. As a specific application, this method was used for the analysis of solanidine glycoalkaloids in industrial potato protein. Because of objections to the colour assays for glycoalkaloids, concerning their specificity (Fitzpatrick & Osman, 1974; Coxon et al., 1979), these quantitative reactions were investigated.

    Quantitative analyses of phenolics and coumarins were done, starting from the alcoholic extracts. Qualitative data were obtained by analysis of UV spectra and fluorescence of diluted extracts and TLC chromatography on cellulose plates. For quantitative analyses a method was developed by HPLC chromatography of alcoholic extracts. Evidence with respect to identification of scopolin and scopoletin in the alcoholic extracts was obtained by comparison of extracts with and without enzymic hydrolysis with B-glycosidase. Scopoletin was also directly identified by UV, IR and Mass Spectra.

    Results of glycoalkaloids, analyzed over several seasons, show no significant changes with regard to irradiation dose or storage time. On the other hand a change in phenolic compounds and coumarins was observed.

    A 10 to 30 fold accumulation of scopolin was found in irradiated (3 kGy) potatoes of the Eba variety after approx. one month's storage at 10 °C, 90% RH and also a decrease in the chlorogenic acid content. For irradiated (3 kGy) potatoes of the Bintje variety, the increase in fluorescent compounds was smaller. Several unidentified phenolic compounds increase in 3 kGy irradiated Eba potatoes, which were detected by UV absorbance at 310 nm.

    Chemical analyses of samples of irradiated Eba potatoes indicate a dose threshold for accumulation of fluorescent compounds. Below 0.5 kGy no increase is observed.

    By using the high fluorescence of the accumulated coumarins it was possible to detect accumulation of fluorescent compounds by simply examining potato halves under long wave UV light. The results agree with the chemical analyses of extracts of irradiated potatoes of the Eba and Bintje varieties. In this way potatoes of several varieties irradiated with a dose of 3 kGy and stored for at least 2 weeks at 10 °C could be examined. The results indicate pronounced differences between varieties. Further, a threshold for the accumulation of fluorescent compounds in irradiated Eba potatoes could be determined. In Eba potatoes irradiated above 0.5 kGy accumulation of fluorescent compounds could be seen. By fluorescence microscopy of sections of tubers it was observed that specific cells accumulate fluorescent coumarins. Examination of the fluorescent cells after plasmolysis, indicates a vacuolar origin of these compounds. Similar results have been reported for fungal infected potatoes (Clarke, 1973; Clarke & Baines, 1976). The increase in scopoletin can be explained by the increase in phenyl ammonia lyase, which has been shown to increase in irradiated citrus fruits (Riov et al., 1972) and irradiated potatoes (Pendharkar & Nair, 1975).

    In view of conflicting earlier reports of increases in mutagenic compounds in alcoholic extracts of irradited potatoes, glycoalkaloids and phenolic compounds as well as the alcoholic extracts of irradiated and control potatoes were examined using a bacterial mutagenicity test system. No increased mutagenicity of extracts or reference compounds were found. These results aqree with the negative findings of Levinsky & Wilson (1975) for mutagenic evaluation of extracts of irradiated potatoes and mutagenicity studies on irradiated potatoes and chlorogenic acid by Hossain et al. (1976).

    Radiation-induced increase in coumarins is to be expected primarily in vegetable products having a natural coumarin content. Chemical changes as a result of radiolytic processes in a theoretical foodstuff can be estimated. Diehl & Schertz (1975) calculated 55 mg/kg radiolytic decomposition products for a 5 kGy dose. In comparison, in this study an increase in scopolin content from 2 to 60 mg/kg was found in 3 kGy irradiated Eba potatoes after a month's storage at 10 °C caused by metabolic stress.

    Onderzoek naar verstoppend materiaal in een waterleidingbuis m.b.v. lichtmicroscopie, REM-EDAX en roentgendiffractie
    Bisdom, E.B.A. ; Jongerius, A. - \ 1979
    Wageningen : STIBOKA (Rapport / Stichting voor Bodemkartering no. 1471) - 15
    stroming - stromingsweerstand - vloeistoffen (fluids) - hydrodynamica - beweging - pedologie - druk - weerstand - bodemmicromorfologie - flow - flow resistance - fluids - hydrodynamics - movement - pedology - pressure - resistance - soil micromorphology
    Merkenonderzoek Westfalia vacuumregulateur type Vacurex
    Anonymous, - \ 1977
    Wageningen : I.M.A.G. (Bulletin / Instituut voor mechanisatie, arbeid en gebouwen no. 702) - 4
    lucht - verdunning - dynamometers - krachten - gassen - meting - mechanica - druk - drukmeters - pompen - vacuüm - vacuümpompen - werk - air - dilution - dynamometers - forces - gases - measurement - mechanics - pressure - pressure gauges - pumps - vacuum - vacuum pumps - work
    De kook - en verwerkingskwaliteit van met elektronenstralen behandelde aardappelen
    Buitelaar, N. - \ 1974
    Wageningen : [s.n.] (Mededelingen / Instituut voor bewaring en verwerking van landbouwprodukten no. 426) - 12
    cassave - fermentatie - voedselbewaring - voedingsmiddelen - huishoudkunde - aardappelen - druk - wortelgewassen als groente - solanum tuberosum - cassava - fermentation - food preservation - foods - home economics - potatoes - pressure - root vegetables - solanum tuberosum
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