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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    Intracellular & extracellular lipolysis : regulation by the PPAR targets ANGPTL4 & HILPDA
    Dijk, Wieneke - \ 2016
    Wageningen University. Promotor(en): Sander Kersten. - Wageningen : Wageningen University - ISBN 9789462579460 - 248
    foams - foaming - milk products - processing - aggregates - casein - micelles - physical properties - schuim - schuimen - melkproducten - verwerking - bodemdeeltjes - caseïne - micellen - fysische eigenschappen

    The body efficiently stores energy in the form of triglyceride (fat) molecules. However, triglycerides cannot directly enter or exit our cells, but first need to be degraded to so-called fatty acids before moving in or out a cell. This degradation process, called lipolysis, is crucial for human physiology and is tightly regulated to prevent the accumulation of fats either within organs or within the bloodstream - hallmarks of diseases such as obesity and cardiovascular disease.

    To allow for uptake by underlying organs, triglycerides in the circulation are efficiently broken down by an enzyme called lipoprotein lipase (LPL) that sits in the bloodstream of multiple organs (extracellular lipolysis). In this thesis, we characterized a protein named angiopoietin-like 4 (ANGPTL4) that potently inhibits LPL and, thereby, inhibits the breakdown of triglycerides in the bloodstream. Our data show that by adjusting the tissue expression levels of ANGPTL4, different organs collaborate to ensure that triglycerides are distributed to organs in need of energy. Moreover, we uncovered that, in the fat tissue, ANGPTL4 starts to inhibit LPL before LPL arrives in the bloodstream. By preventing the arrival of LPL in the bloodstream, ANGPTL4 is capable of rapidly adjusting the rates of triglyceride degradation and the concomitant uptake of fatty acids from the circulation to the energy requirements of the underlying organ.

    To exit our cells, stored triglycerides, such as present in our fat tissue, need to be broken down to fatty acids. Subsequently, the released fatty acids can fuel other organs in need of energy. To further clarify the mechanisms underlying this process of intracellular lipolysis, we investigated the role of a promising new protein called HILPDA. Our data show, however, that loss of HILPDA did not impact the release of fatty acids from the fat tissue, while a high abundance of HILPDA only had a mild attenuating effect on the release of fatty acids. This suggests that HILPDA is not a major physiological regulator of intracellular lipolysis in fat cells.

    In conclusion, in this thesis, we have clarified the regulation of intracellular and extracellular lipolysis by studying the respective roles of the proteins ANGPTL4 and HILPDA. Such efforts are clinically relevant, as regulators of lipolysis are potential therapeutic targets to lower cardiovascular disease risk.

    The role of casein micelles and their aggregates in foam stabilization
    Chen, Min - \ 2016
    Wageningen University. Promotor(en): Erik van der Linden; Toon van Hooijdonk, co-promotor(en): Marcel Meinders; Guido Sala. - Wageningen : Wageningen University - ISBN 9789462579842 - 124
    foams - foaming - milk - casein - micelles - physical properties - stabilization - schuim - schuimen - melk - caseïne - micellen - fysische eigenschappen - stabilisatie

    Many foam products derived from milk or specific dairy ingredients suffer from drainage, coalescence and/or disproportionation. Previous studies indicated that foam properties of milk are strongly influenced by the composition of the milk as well as by the processing conditions during foam production. The aim of this research was to get a better understanding of these two factors. Interestingly, the presence of aggregates of casein micelles was found to result in very stable foams. The interfacial properties (adsorption speed, adsorption energy, dynamical interfacial tension, interfacial dilatational moduli), thin film stability (rupture time) and foam properties (foamability, drainage, coalescence) of casein micelle dispersions were determined. Based on these data, the very stable foams were concluded to result from properties of the thin films in the foam, which were affected drastically by the presence of the large aggregates of casein micelles.

    Molecular assembly, interfacial rheology and foaming properties of oligofructose fatty acid esters
    Kempen, S.E.H.J. van - \ 2013
    Wageningen University. Promotor(en): Erik van der Linden, co-promotor(en): Leonard Sagis; Henk Schols. - S.l. : s.n. - ISBN 9789461737328 - 238
    vetzure esters - oppervlaktespanningsverlagende stoffen - estervorming - oppervlaktereologie - schuimen - fatty acid esters - surfactants - esterification - surface rheology - foaming

    Aerated food products consist of air bubbles that are surrounded by a matrix that can be either liquid or solid. Due to the large number of air bubbles that are generally present in aerated products, these systems contain a large interfacial area. Therefore, the properties of the interfaces are considered to contribute significantly to the macroscopic properties of the system. The properties of these interfaces are largely determined by the type of surfactant that adsorbs. Two major types of surfactants that are used within the food industry are proteins and low molecular weight (LMW) surfactants. Proteins are macromolecules consisting of hydrophilic and hydrophobic patches that adsorb at the interface, where they lower the surface tension and can unfold to create a two-dimensional network that can provide a high modulus. In contrast, LMW surfactants are molecules with a well-defined hydrophilic and hydrophobic part. They can form more compact surface layers than proteins, leading to lower surface tensions. They generally do not provide the interface with a high modulus, instead they stabilize the interface through the Gibbs-Marangoni mechanism that relies on rapid diffusion of surfactants after deformations of the interface. A molecule that can lower the surface tension considerably, like a LMW surfactant, and at the same time provide a high modulus, like a protein, has the potential to be an excellent foam stabilizer. In this thesis we focus on a series of molecules that obey these criteria: oligofructose fatty acid esters. We address the influence of changes in chemical fine structure (fatty acid chain length and degree of saturation, degree of esterification and size of the hydrophilic group) on the functional properties.

    These esters are synthesized by esterification of fatty acids to oligofructose, which is a mixture of oligomers with different degrees of polymerization. As we show in chapter 2, reasonable yields are obtained when using lipase as the catalyst in a mixture of DMSO and ButOH. The conversion into mono-esters increased with increasing fatty acid chain length and is consistent with the preference of the enzyme for more hydrophobic substrates. The crude reaction product consisted of a mixture of unreacted oligofructose and fatty acids, the main reaction products mono-esters and small amounts of di-esters. The crude product was fractionated using RP-SPE. MALDI-TOF MS and (2D) NMR were used to confirm the structure and purity of the esters; >90% for mono-esters and >80% for di-esters.

    Similar to typical LMW surfactants, the oligofructose esters formed spherical micelles in the bulk after a certain critical concentration. As we show in chapter 3, the CAC depended on the hydrophobicity of the molecules. The efficiency also increased with increasing hydrophobicity and the effectiveness was similar. The area occupied by a single molecule at the interface was determined by fitting the CAC curves with the Gibbs adsorption model and measured directly using ellipsometry. The area occupied at the interface was larger for oligofructose mono-esters compared to sucrose esters. Furthermore, oligofructose di-esters occupied slightly more area than sucrose esters. All esters occupied significantly more area than a single fatty acid chain. This shows that the oligofructose group dominates the area occupied at the interface.

    The rheological properties, as studied in chapter 4, were determined using a traditional approach, where the dependency of the surface dilatational modulus on surface pressure and frequency was determined, and using a novel approach, where we show how the surface dilatational modulus is dependent on deformation amplitude and temperature. Furthermore, we show how Lissajous plots of surface pressure versus deformation may be used to gain information about the correlation between surface rheological properties and interfacial microstructure. Sucrose esters behaved like typical LMW surfactants, with low surface dilatational moduli, scaling exponents in the frequency dependency close to 0.5, and fairly viscous Lissajous plots without significant asymmetries. In contrast, oligofructose mono-esters formed interfaces with high surface dilatational moduli, low scaling exponents in the frequency dependency and asymmetric Lissajous plot with strain hardening during compression and strain softening during expansion. We conclude that the oligofructose mono-esters form a two-dimensional soft glass. The oligofructose di-esters behaved like typical LMW surfactants at high surface pressures, showing that the presence of the second fatty acid chain prevent the formation of the glass by the oligofructose part.

    In chapter 5 we focus on the difference in functionality between the crude reaction product, the individual components that are present in the crude product and mixes of these products. Unreacted fatty acids migrated to the interface only in very small amount, due to the low solubility in the bulk. The addition of mono-esters slightly improved the amount of fatty acid that could migrate to the interface. Oligofructose was not surface active and its addition to the mono-ester only diluted the mono-ester which did not lead to significant changes in functional properties because the concentration of mono-ester was still close to the CMC. When mono-esters and di-esters were mixed, the rheological results showed that the ratio between mono-ester and di-ester was very important for the rheological profile. In both cases the results suggest the presence of islands of glass phase formed by the mono-esters surrounded by a viscous phase formed by the di-esters. When the surface concentration of mono-esters was high, the glassy patches dominated the interface, leading to a high modulus, low frequency dependency and Lissajous plots with a high degree of asymmetry. When the surface concentration of mono-esters decreased, the lower connectivity between the glassy patches lead to a low modulus, intermediate frequency dependency, and Lissajous plots with moderate asymmetry.

    To study the potential of oligofructose esters as food grade surfactants it is important to consider that many food products contain ingredients with the potential to be surface active. Therefore, in chapter 6 we have studied the functional properties of an oligofructose mono-ester in the presence of whey protein isolate, a commonly used food protein. Except for at the highest protein concentration, the surface was dominated by the oligofructose ester. The stabilization mechanisms of oligofructose ester and WPI were mutually exclusive, leading to interfaces with a low surface dilatational modulus. Since the foaming properties were not negatively affected, we conclude that the Gibbs-Marangoni mechanism occurred. Only at the highest protein concentration, the surface concentration of WPI was sufficiently high to interfere with this mechanism, leading to a significant decrease in foam stability. Oligofructose esters were also able to displace a fully developed WPI network.

    In chapter 7 we discuss the foaming properties of the esters. We show that only esters of intermediate hydrophobicity are able to form foams with small bubbles and a uniform bubble size distribution that lead to high foam stability. The affinity of esters with shorter fatty acid chains, up to 8 carbon atoms, for the interface was quite low as a result of the relatively hydrophilic nature of the molecules. Therefore, they were not effective foam stabilizers. The most hydrophobic components (mono-ester with a chain length of 18 carbon atoms and di-ester with a chain length of 12 carbon atoms) were too slow to migrate to the interface. Therefore, also these components were poor foam stabilizers. We show that the surface tension at short time scales is the most accurate predictor of foam stability. However, despite similar initial surface tension values, oligofructose esters lead to higher foam stability. This could be attributed to the oligofructose part that forms a two-dimensional glass phase and provides mechanical stability to the foam films.

    In the general discussion that is presented in chapter 8 we integrate the results from the different chapters. One of the factors that is persistent throughout the different chapters is the rheological profile of the interfaces. We have shown that by using amplitude sweeps and Lissajous plots, a lot more information on the interfacial microstructure can be extracted from rheological data than by using more conventional methods. In the last part of the general discussion improvements to the synthesis are discussed, as the optimization of the synthesis was not considered in this thesis. Furthermore, improvements for the functional experiments and additional applications were identified.

    Physico-chemical and techno-functional properties of proteins isolated from the green microalgae Tetraselmis sp.
    Schwenzfeier, A. - \ 2013
    Wageningen University. Promotor(en): Harry Gruppen, co-promotor(en): Peter Wierenga; Michel Eppink. - S.l. : s.n. - ISBN 9789461734532 - 132
    algen - eiwitten - functionele eigenschappen - schuimen - emulgeren - emulsies - algae - proteins - functional properties - foaming - emulsifying - emulsions

    In this thesis, the mild isolation of an algae soluble protein isolate (ASPI) and the characterisation of its techno-functional properties are described. The ASPI was isolated from the green microalgae Tetraselmis sp. by beadmilling and subsequent anion exchange adsorption. The isolate obtained contained 59 ± 7% (w/w) protein and 20 ± 6% (w/w) carbohydrates, the latter composed for approximately one fourth of uronic acids (4.8 ± 0.4% [w/w]). In the pH range 5.5 – 6.5, in which currently used legumin seed protein isolates (e.g. soy) show low solubility, ASPI retained high solubility independent of ionic strength. In the soluble pH range, the foam stability of ASPI is superior to the foam stabilities of whey protein isolate (WPI) and egg white albumin (EWA). At pH 7, ASPI stabilized foams are 1.7 times more stable than WPI stabilized foams. Further fractionation of APSI results in foams even 3 times more stable than WPI stabilized foams. In addition, emulsions stabilised with ASPI are stable against droplet aggregation around pH 5 at low ionic strength, while emulsions stabilised by WPI are not stable at this pH. The stability of ASPI emulsions at this pH is attributed to the co-adsorption of the charged polysaccharide fraction present in ASPI. The role of the charged polysaccharides on stabilisation of the emulsions was confirmed by fractionating ASPI into protein-rich and charged polysaccharide-rich fractions. The combination of charged polysaccharides and proteins in ASPI results in good techno-functional properties that are between that of pure proteins and that of the naturally occurring protein-polysaccharide hybrid gum arabic (GA). It is concluded that ASPI represents an attractive substitute for currently used high-value food protein isolates. Due to the combination of the positive interfacial properties of its protein fraction with the broad pH stability of its charged polysaccharide fraction, ASPI possesses the positive attributes of two types of techno-functional ingredients.

    Foaming behaviour of organic and regular milk
    Pijnenburg, J. ; Sala, G. ; Valenberg, H.J.F. van; Meinders, M.B.J. - \ 2012
    Wageningen : Wageningen UR - 23
    melk - biologische voedingsmiddelen - schuimen - stabiliteit - melkproducten - milk - organic foods - foaming - stability - milk products
    Organic milk is used more and more by consumers to froth milk that is used e.g. for the preparation of a capuccino. Frequently, organic milk turns out not to foam properly. This report describes a study to find the main couse of this bad foamability of organic milk. The focus of the research was to get insight in the foaming behaviour of a specific brand, indicated as A. The foamability and stability of different milk, both organic and regular, as well as skimmed, semi-skimmed, and full fat, were tested. The foamability of the different milk varieties appeared to be about equal. However, differences were observed for the foam stability. Foams made from A showed the lowest stability of all tested milk varieties. The reason for this is not yet clear, but the bad foam stability of this milk might be probably due to a higher fatty acid content.
    Ontwikkeling prototype residuverwijdering met VAM-Residuce : eindrapportage 1 Januari 2010- 15 Mei 2011
    Jong, P.F. de; Antwerpen, E. van; Berg-Somhorst, B.P.M. van de; Bastiaan-Net, S. - \ 2012
    Wageningen : Wageningen UR - Food & Biobased Research (Rapport / Wageningen UR Food & Biobased Research nr. 1310) - ISBN 9789461732583 - 13
    behandeling na de oogst - pesticidenresiduen - pesticiden - fruit - fruitteelt - reductiemiddelen - schuimen - meting - postharvest treatment - pesticide residues - pesticides - fruit - fruit growing - reducing agents - foaming - measurement
    Voor het succesvol implementeren van een residuverwijderingsprototype in de huidige sorteerlijnen is het belangrijk dat tijdens het sorteerproces niet te veel schuim ontstaat in het sorteerwater en dat de concentratie van het gebruikte reducerend middel (VAM-Residuce) in het sorteerproces op peil gehouden kan worden. Een tweetal titratiemethodes en een schuim-onderdrukkende techniek zijn ontwikkeld om respectievelijk de concentratie VAM-Residuce te controleren en overmatige schuimvorming tijdens het sorteerproces tegen te gaan.
    Onderzoek naar schuimproblemen in slibvergisters
    Grolle, K.C.F. ; Wierenga, P.A. ; Zeeman, G. - \ 2011
    H2O : tijdschrift voor watervoorziening en afvalwaterbehandeling 44 (2011)5. - ISSN 0166-8439 - p. 53 - 54.
    afvalwaterbehandeling - milieutechniek - slibzuivering - co-vergisting - schuimen - waste water treatment - environmental engineering - sludge treatment - co-fermentation - foaming
    Milieutechnisch onderzoek naar schuimproblemen heeft vaak als doel de schuimbepalende parameter te vinden om de ingrediënten te identifi ceren die de schuimproblemen veroorzaken. In de levensmiddelensector is uitgebreid fundamenteel onderzoek gedaan naar schuim en daar is die schuimbepalende parameter (nog) niet gevonden. In dit artikel worden suggesties gedaan voor milieutechisch onderzoek naar schuimproblemen in slibvergisters op basis van de kennis die opgedaan is in de levensmiddelentechnologie.
    Peroxidase-mediated cross-linking of bovine a-lactalbumin
    Heijnis, W.H. - \ 2010
    Wageningen University. Promotor(en): Harry Gruppen, co-promotor(en): Willem van Berkel; Peter Wierenga. - S.l. : s.n. - ISBN 9789085858324 - 120
    alfa-lactalbumine - peroxidase - schuimen - schuim - enzymatische cross-linking - alpha-lactalbumin - peroxidase - foaming - foams - enzymatic cross-linking
    The research presented in this thesis aimed at controlling the horseradish peroxidase-catalyzed cross-linking of bovine α lactalbumin and the implications of this cross-linking for the foam stabilizing properties. Attention is also given to microreactors and their potential to control the enzymatic cross-linking of proteins.
    The proportion of cross-linked α lactalbumin dimers, oligomers and polymers could be directed by variations in ionic strength, pH, H2O2, and temperature.
    Covalent α lactalbumin dimers were proteolytic digested. FTMS analysis of the peptide mixture resulted in the unambiguous identification of a Tyr18 Tyr50 dityrosine cross-link. Structural modeling of the α lactalbumin dimer indicated that favorite electrostatics direct the selectivity of the cross-linking reaction and, hence, the formation of an intermolecular cross-link. The formation of the Tyr18-Tyr50 cross-link suggests that further cross-linking of α lactalbumin dimers enables the formation of linear polymers.
    A microreactor system was set up to obtain control over the reaction conditions to cross-link proteins. The enzymatic cross-linking of α lactalbumin was analyzed as a function of enzyme and substrate(s) feed. The increase in absorption at 318 nm due to dityrosine formation was found to be directly correlated to the decrease in monomeric α lactalbumin and was shown to be a good tool to monitor the cross-linking reaction.
    The α lactalbumin oligomers produced were investigated for their foam stabilizing properties. Cross-linked α lactalbumin oligomers did not stabilize foams, whereas α lactalbumin polymers acted as an anti-foam, destabilizing other protein films.

    Bewaring lelie. Diverse aspecten tijdens de bewaring van leliebollen
    Kok, B.J. ; Aanholt, J.T.M. van - \ 2005
    Lisse : PPO Bloembollen - 155
    opslag - lilium - bloembollen - dompelen - schuimen - behandeling na de oogst - invriezen - gewaskwaliteit - houdbaarheid (kwaliteit) - forceren van planten - teelt - ventilatie - heetwaterbehandeling - schubben - storage - lilium - ornamental bulbs - dipping - foaming - postharvest treatment - freezing - crop quality - keeping quality - forcing - cultivation - ventilation - hot water treatment - scales
    Verslag van uitgebreid onderzoek naar diverse aspecten tijdens de bewaring van leliebollen waar op gelet moet worden.
    Branden, heet water en heet schuim: energieverbruik en capaciteit verschilt
    Kurstjens, D.A.G. - \ 2004
    Tuin en Park Techniek 11 (2004)1. - ISSN 1380-3212 - p. 28 - 29.
    onkruidbestrijding - bestrating - wegen - bestrijdingsmethoden - warmtebehandeling - heetwaterbehandeling - verbranden - schuim - schuimen - capaciteit - energiegebruik - brandstofverbruik - watergebruik - gebruiksefficiëntie - gebruikswaarde - weed control - pavements - roads - control methods - heat treatment - hot water treatment - burning - foams - foaming - capacity - energy consumption - fuel consumption - water use - use efficiency - use value
    Voor onkruidbestrijding op verhardingen is het vanuit milieuoverwegingen belangrijk om effectieve en betaalbare alternatieven voor chemische bestrijding te vinden. Wageningen UR vergeleek drie thermische methoden van onkruidbestrijding op energieverbruik, capaciteit en bestrijdingseffect (bij verschillende rijsnelheden). Een Hoaf Weedstar 100 onkruidbrander, een zelfrijdende heetwatermachine en een Herbifoam-installatie voor heet schuim werden ingezet op proefvelden ingezaaid met gele mosterd en Engels raaigras. Op gele mosterd was de brander het zuinigst en snelst; bij gras de heetwatermachine
    Physico-chemical and functional properties of sunflower proteins
    Gonzalez-Perez, S. - \ 2003
    Wageningen University. Promotor(en): Fons Voragen, co-promotor(en): Harry Gruppen; A.L.J. Vereijken. - [S.l.] : S.n. - ISBN 9789058089045 - 145
    zonnebloemeiwit - fysicochemische eigenschappen - denaturatie - oplosbaarheid - schuimen - schuim - emulgeren - emulsies - sunflower protein - physicochemical properties - denaturation - solubility - foaming - foams - emulsifying - emulsions
    Keywords: Sunflower protein, Helianthusannuus ,helianthinin, albumins, solubility, structure,denaturation, pH, temperature, ionic strength,phenoliccompounds,chlorogenicacid, foams, emulsions, functionality

    The research described in this thesis deals with the relation between specific sunflower proteins, their structure and their functional properties as a function of extrinsic factors as pH, ionic strength and temperature.

    Sunflower protein isolate (SI) devoid ofchlorogenicacid (CGA), the mainphenoliccompound present, was obtained withoutdenaturationof the proteins. Sunflower proteins were found to be composed of two main protein fractions: 2S albumins or sunflower albumins (SFAs) andhelianthinin. Subsequently, these protein fractions werebiochemicallyand structurally characterized under conditions relevant to food processing.

    Depending on pH, ionic strength, temperature and protein concentration,helianthininoccurs in the 15-18S (high molecular weight aggregate), 11 S (hexamer), 7S (trimer) or 2-3S (monomer) form. Dissociation into 7S from 11S gradually increased with increasing pH from 5.8 to 9.0. Enhancing the ionicstrengthresulted in stabilization of the 11S form. Heating and lowering the pH resulted in dissociation into themonomericform ofhelianthinin. The 11S and 7S form ofhelianthinindiffer in their secondary structure, tertiary structure, and thermal stability. With respect to solubilityas a function of pH,helianthininshows a bell shaped curve with a minimum at approximately pH 5.0 at low ionic strength. At high ionic strength,helianthininis almost insoluble at pH< 5.0.

    The second main sunflower fraction,SFAs, revealed to be very stable against pH changes (pH 3.0 to 9.0) and heat treatment (up to 100°C), and their solubility was only marginally affected by pH and ionic strength. The solubility of the SI as a function of pH seems to be dominated by that ofhelianthinin.

    Foam and emulsion properties of the sunflower isolate as well as those of purifiedhelianthinin,SFAsand combinations thereof were studied at various pH values and ionic strengths, and after heat treatment. Sunflower proteins were shown to form stable emulsions, with the exception ofSFAsat alkaline and neutral pH values. Increasing amount ofSFAsimpaired the emulsifying properties. Regarding foam properties, less foam could be formed fromhelianthininthan fromSFAs, but foam prepared withhelianthininwas more stable againstOstwaldripening and drainage than foam prepared withSFAs. Increasing amounts ofSFAshad a positive effect on foam volume and a negative one on foam stability and drainage. It was found that treatments that increase conformational flexibility improve the emulsion and foam properties of sunflower proteins.
    Effects of stress relaxation in soy glycinin films on bubble dissolution and foam stability
    Meinders, M.B.J. ; Bos, M.A. ; Lichtendonk, W.J. ; Vliet, T. van - \ 2003
    In: Food Colloids, Biopolymers and Materials / Dickinson, E., van Vliet, T., Cambridge UK : Royal Society of Chemistry - ISBN 9780854048717 - p. 156 - 164.
    sojaeiwit - schuim - schuimen - soya protein - foams - foaming
    Entering and spreading of protein-stabilized emulsion droplets at the expanding air-water interface
    Hotrum, N.E. ; Cohen Stuart, M.A. ; Vliet, T. van; Aken, G.A. van - \ 2003
    In: Food Colloids, Biopolymers and Materials / Dickinson, E., van Vliet, T., Cambridge : Royal Society of Chemistry - ISBN 9780854048717 - p. 192 - 199.
    emulsies - schuim - schuimen - eiwitten - caseïnaten - grensvlak - mechanische eigenschappen - emulsions - foams - foaming - proteins - caseinates - interface - mechanical properties
    Physico-chemical and functional properties of potato proteins
    Koningsveld, G.A. van - \ 2001
    Wageningen University. Promotor(en): P. Walstra; A.G.J. Voragen; M.A.J.S. van Boekel; H. Gruppen. - S.l. : S.n. - ISBN 9789058084446 - 147
    aardappelen - aardappeleiwit - chemische precipitatie - oplosbaarheid - chemische structuur - schuimen - emulgering - potatoes - potato protein - chemical precipitation - solubility - chemical structure - foaming - emulsification

    Key words: potato proteins, patatin, protease inhibitors, solubility, structure, pH, temperature, ethanol, ionic strength, phenolic compounds, foams, emulsions

    In potato starch manufacture an aqueous byproduct remains that is called potato fruit juice (PFJ). On a dry matter basis PFJ contains about 20-25 % protein and amino acids, 15 % sugars, 20 % minerals, 14 % organic acids and other components, such as phenolic compounds. Potato protein has a relatively high nutritional quality, comparable to that of whole egg, and it therefore has high potential for utilization in food applications. Protein recovery from industrial PFJ is presently achieved through heat coagulation by steam injection after pH adjustment. This method is very efficient in removing protein from solution. However, it leads to protein precipitates that exhibit a poor solubility, which hampers potential food applications.

    An economic method to efficiently recover soluble potato protein would considerably increase its possibilities for use in food and add to its commercial value. Therefore, the important question resulting in this study was: can potato proteins be recovered from PFJ in such a way that they retain their functional properties, most importantly their solubility? This recovery method should be applicable at a large scale and result in a high yield. Potato protein recovery was expected to be complicated by the presence of and the interactions with non-protein components in PFJ. The objective in this study was to examine how extrinsic factors like pH, ionic strength and temperature would influence the structure of potato proteins, this in relation to the functionality of the proteins in making and stabilizing foams and emulsions.

    Three groups of potato proteins can be distinguished in PFJ. Patatin, the major potato tuber protein, comprises 38 % of the protein in PFJ from cultivar Elkana . The protease inhibitors make up about 50 % and other proteins up to 12 % of total protein in PFJ from cultivar Elkana .

    In Chapter 2 the effects of pH and various additives on the precipitation and (re)solubility at pH 7 of potato proteins from industrial PFJ are studied. Addition of various strong and weak acids caused the same extent of protein precipitation, which comprised at the most 60 % of total protein at pH 3. The use of weak acids, however, resulted in an increase in the resolubility of the precipitates at pH 7, as compared to strong acids. At pH 5 addition of FeCl 3 or ZnCl 2 increased both precipitation and resolubility. The largest increase in precipitation and resolubility was achieved by using organic solvents, resulting in a maximum precipitation (pH 5) of 91 % of total protein and a maximum resolubility of 91 % of precipitated protein. The results described in Chapter 2 lead to the hypothesis that precipitation and resolubilization of potato proteins from PFJ is not so much determined by their isoelectric pH but by their interactions with low molecular weight components.

    In Chapter 3 it was shown, using DSC and both far-UV and near-UV CD spectroscopy, that potato proteins unfold between 55°C and 75°C. Increasing the ionic strength from 15 to 200 mM generally caused an increase in denaturation temperature. It was concluded that the dimeric protein patatin unfolds either in its monomeric state or that its monomers are loosely associated and unfold independently. Thermal unfolding of the protease inhibitors was correlated with a decrease in protease inhibitor activities and resulted in an ionic strength dependent loss of protein solubility. Potato proteins were best soluble at neutral and strongly acidic pH. At mildly acidic pH the overall potato protein solubility was dependent on ionic strength and the presence of unfolded patatin.

    In Chapter 4 a protein isolate with a high solubility at neutral pH prepared from industrial PFJ by precipitation at pH 5 in the presence of ethanol is described. The effects of ethanol itself and the effects of its presence during precipitation on the properties of various potato protein fractions were examined. The presence of ethanol significantly reduced the denaturation temperature of potato proteins, indicating that preparation of this potato protein isolate should be done at low temperature to retain a high solubility. In the presence of ethanol the thermal unfolding of the tertiary and the secondary structure of patatin were shown to be almost completely decoupled. Even at 4°C precipitation of potato proteins in the presence of ethanol induced significant conformational changes. These changes did, however, only result in minor changes in the solubility of the potato protein preparations.

    In Chapter 5 foam forming and stabilizing properties of potato proteins are described; whipping or sparging was used to make foam. The performed whipping tests showed that less foam could be formed from untreated patatin than from the protease inhibitors, but also that patatin foam was much more stable against coalescence, Ostwald ripening and drainage. The foam forming properties of patatin could be strongly improved by partial unfolding of the protein. Whipping tests, at both low (0.5 mg/ml) and high (10 mg/ml) protein concentrations, also indicated that foams made with an ethanol precipitated protein isolate (PPI) were more stable against Ostwald ripening and drainage than those made withβ-casein andβ-lactoglobulin. More generally it was concluded that when proteins are used as a foaming agent, a high concentration is required, because the available protein is inefficiently used. Also, the different methods used to make foam, result in changes in the mutual differences in foaming properties between the various protein preparations and may induce different instabilities to become apparent in foams made at the same conditions.

    In Chapter 6 emulsions made with various potato protein preparations were characterized with respect to average droplet size, plateau surface excess and the occurrence of droplet aggregation. The average droplet size of the emulsions made with potato proteins appeared to be determined by the lipolytic release of surface active fatty acids and monoglycerides from the tricaprylin oil phase during the emulsification process. It was concluded that only trace amounts of patatin, the lipase activity of which has been strongly underestimated in literature, sufficed to liberate significant amounts of these surfactants. The plateau surface excess of emulsions made with patatin was found to be 2.6 mg/m 2 , while emulsion droplets made with protease inhibitors showed a significantly smaller surface excess. Of the various solvent conditions and treatments applied only heat treatment resulted in a significant increase in surface excess. Droplet aggregation in emulsions made with potato protein preparations other than patatin, could in contrast to at pH 5 and at pH 7 be prevented at pH 3.

    In Chapter 7 the relations between potato protein structure, solubility and foam and emulsion forming and stabilizing properties are discussed. Also, the different mechanisms by which phenolic compounds may affect protein solubility are discussed in relation to the solubility and resolubility behavior of potato proteins in PFJ and when separated. A summary of the most important differences in the properties of patatin and protease inhibitors is also given.

    Proteins and protein/surfactant mixtures at interfaces in motion
    Boerboom, F.J.G. - \ 2000
    Agricultural University. Promotor(en): A. Prins; M.A. Cohen Stuart. - S.l. : S.n. - ISBN 9789058082817 - 213
    eiwitten - oppervlakten - oppervlaktespanningsverlagende stoffen - eigenschappen - surfaces - surfactants - foaming - properties

    The research described in this thesis covers a number of aspects of the relation between surface properties and foaming properties of proteins, low molecular surfactants and mixtures thereof. This work is the result of a question of the industrial partners if it is possible to understand the foaming properties of protein hydrolysates. As there are many aspects of the surface properties that can be responsible for the foaming behaviour a number of problems were defined by which we can obtain a better understanding of the relation between surface properties and foam formation and stability in relation to the type of surface active substance.

    In this thesis an important question a priori has been: How can we understand the foaming properties from the properties of the surface active species. We presumed that the molecular properties cannot be translated forthwith to foaming properties but that a number of translation steps are necessary. First of all the molecular properties need to be translated into surface properties which manifest themselves in mechanical properties of surfaces and films. In addition there is a relation between these mechanical properties and the foaming properties.

    An important consideration a priori was that the way in which the surface is deformed is important for finding the relevant relation between the mechanical properties and the foaming properties. Here we made a distinction in two types of deformation being deformations caused by forces applied parallel and perpendicular to the surface. A force that is applied perpendicular to the surface (pressure) generally leads to a homogeneous deformation of the surface. The properties of the surface change with time or time scale but at the surface there are no differences with respect to surface tension. surface concentration or relative rate of expansion. Forces applied perpendicular to the surface generally lead solely to enlargement or reduction in surface area. Forces applied parallel to the surface (shear forces) can also lead to enlargement or reduction in surface area. These forces are generally due to viscous friction with the surface. In addition to a change in surface area these forces also cause a redistribution of surface active material over the surface. Hence the surface concentration. the surface tension as well as the relative rate of expansion vary over the surface. This leads to a surface tension gradient that is necessarily equal to the viscous drag at the surface. It is striking that in literature only homogeneous deformations are studied in detail. This fact can be attributed to the difficult experimental accessibility of surfaces subjected to shear forces. Nevertheless shear forces may play a role in the foaming properties such as in drainage and bubble break-up. An important part of this thesis will be devoted to the relation between viscous friction and surface motion.

    A device which enables the quantification of the relation between viscous drag and motion of the surface in relation to the surface properties is the overflowing cylinder. This device consists of an inner cylinder surrounded by an outer cylinder with a larger diameter. In this inner cylinder liquid is pumped up which flows over the rim into the space between the inner and outer cylinder. At the top surface we find a continuously expanding surface of which the relative expansion rate remains approximately constant over the surface in the vicinity of the centre of the cylinder. The expansion rate of the surface can be influenced by changing the length of the falling film. Hence within certain limits the expansion rate at the top surface c5n be varied. If we consider the falling film at the leading edge of the inner cylinder the falling motion of the liquid in the film causes the deformation of the surface parallel to the surface. If we would be able to measure the properties of the falling film we could learn how the surface properties vary with distance. However the surface of the falling film is experimentally not accessible. Therefore in this thesis the changes in surface properties of the falling film have been studied by measuring the surface tension of the top and bottom surface at a fixed place. This provides a reasonable measure of the surface tension difference over the falling film of the overflowing cylinder.

    In order to interpret this difference, the conditions at the falling film have been approximated by means of simple hydrodynamic theory. From this approximation we could conclude that there is a relation between the relative expansion rate, the length of the falling film and the surface tension difference. The surface of the falling film is propelled by the falling motion of the liquid which causes a surface tension gradient at the surface as a consequence of the viscous drag. If we compare the calculations with experimental data we can find that this approach is in agreement with the experiments. Hence the difference in surface tension over the falling film can be considered to be a measure of the resistance to deformation of the surface to forces applied parallel to the surface.

    The surface tension gradients which could be generated by means of different surface active species appeared to differ significantly from each other. Especially the difference between low molecular surfactants and proteins could be shown to be large. This can be ascribed to the sensitivity of the surface tension of these substances to expansion and compression of the surface. Adsorbed layers of proteins have a high surface tension in expansion. This can be explained by the time required for unfolding at a surface of these substances. In compression low surface tensions are found for proteins due to the slow desorption of proteins. The surface tension of low molecular surfactants is less sensitive to compression and expansion. In expansion the relatively short diffusion length causes the surface tension to deviate much less from the equilibrium surface tension. In compression these substances desorb easily causing the surface tension to be close to the equilibrium surface tension as well. Hence the surface tension gradient that can be generated by proteins is much larger the for low molecular surfactants. If mixtures of low molecular surfactants and proteins (Tween 20 andβ-casein) are considered it is found that in expansion the surface tension is influenced by both species. In compression however the surface tension is around the equilibrium surface tension of the low molecular surfactant. From this we can conclude that the low molecular surfactant determines the surface tension in compression. Most probably there the affinity of the surface active substance for the surface is important which causes the preferential desorption of proteins. This means that the surfaces of these mixtures have a low resistance to deformation by forces applied parallel to the surface.

    Unfolding behaviour of proteins at interfaces

    The most important class of surface active substances which have been studied in this thesis are proteins due to the similarities in structure and properties with protein hydrolysates. Proteins consist of 20 different amino acids which vary in residual group. Despite the similarity in the basic structure of these substances the difference in foaming properties between proteins is large. In literature this difference in foaming properties is ascribed to the difference in unfolding rate during adsorption at air/water interfaces of these polymers. There are no reliable data on the unfolding rate of proteins however. The overflowing cylinder technique can be used to determine the unfolding rates of proteins since the top surface is in a steady state while the relative expansion rate is finite. The relative expansion rate can be seen as a characteristic time scale of the surface.

    In order to measure the unfolding rate of the proteins, at the top surface, the surface tension, the relative rate of expansion and the surface concentration were determined using the Wilhelmy plate technique, laser Doppler anemometry and ellipsometry respectively. With these three parameters the surface can be characterised completely. The reasoning behind the characterisation is as follows: If proteins need time for the unfolding at an interface, the relative expansion rate determines the mean degree of unfolding of the proteins at the interface. As a function of the relative rate of expansion and at equal adsorbed amounts the surface tension will vary due to a difference in the mean degree of unfolding.

    If we would know the surface tension and surface concentration for different bulk concentrations as a function of the relative rate of unfolding then we would be able to establish the influence of the unfolding rate of the protein on the surface tension. Since this is difficult to determine on the basis of the raw date, a simple model was used to express this influence of unfolding in an unfolding and a refolding parameter. In this model the transport to and the unfolding at the top surface of an overflowing cylinder has been described. The unfolding and refolding has been described by means of a first order reaction. In essence we assume that the degree of unfolding can be seen as an average over many stages of unfolding over a large number of molecules. By dividing the interface into a large number of concentric rings and by carrying out the calculations for the transport and unfolding for each concentric ring the surface properties can be calculated as a function of the distance to the centre. By varying the relative rate of expansion as a function of the distance to the centre in the same way as takes place at the top surface of the overflowing cylinder also the surface tension gradient can be determined. Since there is a fixed relation between the surface tension gradient and the maximum relative rate of expansion, the maximum relative rate of expansion can be determined by means of iteration.

    In this thesis the unfolding behaviour of the proteins:β-casein,β-lactoglobulin, BSA and lysozyme has been determined experimentally. In literature these proteins have been characterised well with respect to adsorption and unfolding behaviour. The unfolding rates of these proteins differ several orders of magnitude.β-Casein andβ-lactoglobulin were shown to unfold most rapid. The characteristic time scales of unfolding of these proteins is in the order of a tenth forβ-casein to a few tenths forβ-lactoglobulin. Lysozyme hardly unfolds within the time scale of the experiment which indicates that the unfolding takes more than 100 seconds. The model was shown not to apply for BSA since the change in surface tension proceeds in two steps. Nevertheless it could be calculated that the unfolding of BSA takes place in a time scale in the order of 20 seconds.

    The model and the overflowing cylinder technique have also been applied to mixtures of proteins and low molecular surfactants. The systemβ-casein/Tween 20 was chosen because in this system no complications are known such as aggregation in he bulk phase, or electrostatic interactions at the surface. At expanding interfaces these systems were shown to behave in a more or less additive manner. The surface tension of the mixture appeared to be lower than the addition of the decrease in surface tension of each species individually. This can be attributed to the fact that both species occupy part of the space at the interface. In static conditions it was found in literature that low molecular surfactants can displace proteins from the interface. This difference in behaviour is caused by the fact that in expansion the surface tension is controlled mainly by transport to and unfolding at the surface while in equilibrium time scale is irrelevant and the affinity of the substances to the surface determines the behaviour. Despite certain deviations the measured properties were indicated to be consistent with the calculations by the model. Higher order effects such as the presence of the surfactants in micelles and preferential adsorption were shown to have little effect of these mixtures at expanding surfaces.

    Foam formation and foam stability

    In order to quantify the experimental values and techniques of this research for practical situations, foaming experiments have been performed for a number of relevant systems. In these experiments, the bubble size and the drainage rate of the foams have been determined. Subsequently the results of these experiments were related to mechanical surface properties.

    The experiments indicated that the surface tension difference over the falling film in the overflowing cylinder correlated with the bubble size and the rate of drainage. For the formation of foam this means that not only the amount of energy supplied is important for the bubble size but that also characteristic properties of the surface being the maximal viscous drag that can be transferred is important for the break-up of foam bubbles. The explanation that can be given for this is that the shear stress generated at the surface provides the deformation that leads to an unstable shape of the bubbles which finally leads to break-up. Surface active species that enable the generation of a high shear stress therefore promote the generation of small bubbles.

    In addition it was demonstrated that there is a relation between drainage and viscous friction at the bubble surface. The rate of drainage expressed in the decrease of the characteristic film thickness decreases when a higher surface tension difference between top and bottom surface in the overflowing cylinder is present at a rather arbitrarily chosen relative rate of expansion of 1 s -1 .

    In chapter 6 the foaming properties of protein hydrolysates were discussed. The most important reason that protein hydrolysates have good foaming properties is that in these systems the low molecular components do not displace high molecular components. This causes the surface tension difference between a compressed and expanded surface to be high. This supports the creation of small bubbles and the resistance to drainage. It is possible that the good foamability of protein hydrolysates compared to proteins is caused by the lower surface tension in equilibrium.

    In general it can be said that surface tension gradients play a larger role in foam formation and foam stability than the attention in literature would suggest. More attention for the properties which determine the resistance against deformation of surfaces, parallel to the surface would lead to a better insight in the reasons why different surface active substances exhibit different foaming behaviour.

    Surface properties of proteins in relation to foaming behaviour.
    Kalsbeek, H.K.A.I. van; Prins, A. - \ 1997
    Industrial Proteins 4 (1997)2. - ISSN 1381-0022 - p. 12 - 14.
    eiwitten - schuimen - voedselindustrie - voedseltechnologie - reologie - fysica - vloeistofmechanica - oppervlakte-eiwitten - proteins - foaming - food industry - food technology - rheology - physics - fluid mechanics - surface proteins
    De schuimvormende en schuimstabiliserende werking van eiwitten
    Formation and stability of foam made from aqueous protein solutions.
    Prins, A. - \ 1997
    Industrial Proteins 4 (1997)2. - ISSN 1381-0022 - p. 3 - 5.
    eiwitten - peptiden - structuur - schuim - schuimen - reologie - fysica - vloeistofmechanica - reologische eigenschappen - moleculaire fysica - proteins - peptides - structure - foams - foaming - rheology - physics - fluid mechanics - rheological properties - molecular physics
    Onderzoek naar de relatie tussen moleculaire structuur van eiwitten en het schuimgedrag van de oplossing
    Physics of breadmaking
    Kokelaar, J.J. - \ 1994
    Agricultural University. Promotor(en): A. Prins; T. van Vliet. - S.l. : Kokelaar - ISBN 9789054852223 - 129
    broodbereiding - bakkwaliteit - deeg - vloeistofmechanica - reologie - visco-elasticiteit - schuim - schuimen - oppervlakteverschijnselen - breadmaking - baking quality - doughs - fluid mechanics - rheology - viscoelasticity - foams - foaming - surface phenomena

    Bread dough is a foam and the stability of the gas bubbles towards disproportionation and coalescence during the breadmaking process determines for a large part the final appearance of the baked bread with respect to crumb structure and loaf volume. Gas bubble behaviour in bread dough is determined by both surface and bulk rheological properties of dough (components). These properties were studied and their relevance to breadmaking was established.

    Surface dilational moduli of different dough components were determined. It appears that wheat lipids and added surfactants as SSL and DATEM can retard disproportionation to a large extent if these components are present in the right concentration and modification. Wheat proteins will hardly retard this foam instability mechanism.

    Dynamic measurements and biaxial extension tests on wheat and rye flour as well as wheat gluten doughs were performed. Both flour and gluten doughs show strain hardening at 20 and at 55°C. Wheat cultivars with good breadmaking performance exhibit stronger strain hardening properties than poor baking ones and rye. Next to strain hardening, biaxial stress and extensibility are important parameters determining bread quality.

    During mixing both the surface tension and the viscosity of the dough determine the (minimum) radii of the entrapped gas bubbles. Directly after mixing surface properties dominate primarily gas bubble behaviour by retarding disproportionation, especially if surfactants like SSL or DATEM are added. Already during first proof bulk properties, especially biaxial stress, extensibility and strain hardening, start to dominate gas bubble stability and this remains as such during almost the remainder of the breadmaking process. In the final stage of oven rise surface properties may contribute to the stability of some dough films that have become very thin.

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