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.

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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.

Foam properties of proteins, low molecular weight surfactants and their complexes
Lech, F.J. - \ 2016
Wageningen University. Promotor(en): Harry Gruppen; Peter Wierenga; Marcel Meinders. - Wageningen : Wageningen University - ISBN 9789462576247 - 122 p.
surfactants - proteins - bovine serum albumin - beta-lactoglobulin - lysozyme - foams - chemical properties - stability - mixtures - food chemistry - oppervlaktespanningsverlagende stoffen - eiwitten - runderserumalbumine - bèta-lactoglobuline - lysozym - schuim - chemische eigenschappen - stabiliteit - mengsels - voedselchemie

This thesis shows the effects that the addition of low molecular weight surfactants (LWMS) to proteins has on the foam stability of the mixture. For this, the bulk, interfacial, thin liquid films and foam properties are determined for different protein-LWMS mixtures at different molar ratios (MR). It was shown that the MR as well as the charge of the protein and LMWS determine the foam stability of the mixtures. For all mixtures it was found that the proteins have a select number of high affinity binding sites. So, the concentration of free LMWS in the solution is 0 until a critical MR (MRcr), at which all high affinity binding sites are saturated. Above this MRcr, part of the LMWS binds to low affinity binding sites of the proteins. The low affinity binding sites have a binding ratio < 1, which determines the concentration of bound and free LMWS. For similarly charged protein-LMWS mixtures (i.e. b-lactoglobulin (BLG) and sodium dodecyl sulphate (SDS) and bovine serum albumin (BSA) and SDS at pH 7) the foam stability typically decreases from the foam stability of the pure protein solution (MR 0) until MRcr is reached. At MR > MRcr the foam stability is dominated by the amount of free LMWS. For oppositely charged protein-LMWS mixtures, the binding of the LMWS to the proteins can be described in a similar way, although the number of high affinity sites and low affinity binding ratio are different. There is also a regime of MRs in which the protein-LMWS complexes form large aggregates. These aggregates were in some cases found to increase foam stability (lysozyme (LYS) and SDS and BLG-SDS at pH 3), while in another case (BLG and cetyltrimethylammonium bromide (CTAB)) they lead to decreased foam stability. Still, in all cases it was found that above MRD the aggregates dissociate and the foam stability becomes dominated by free surfactants, equivalent to what was observed for similarly charged protein-LMWS mixtures.

A multi-scale model was developed to describe the stability of thin liquid films in terms of rupture time and thickness. Initially, the model was used to predict the stability of surfactant free films of water and electrolyte solutions. Later, it was used to predict the foam stability in LYS-SDS mixtures. For that purpose, the model was combined with a foam drainage model to provide theoretical estimations of foam stability. This model is the basis to understand coalescence of bubbles in foam. Finally, the concept of the critical MRs and the free LMWS was introduced. Using this, the foam properties of protein-LMWS mixtures can partly be predicted by relative charge of the components and the binding to both high and low affinity binding sites.

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 - 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.

Schuimvorming op mest : eindrapportage
Starmans, D.A.J. ; Blanken, K. ; Kupers, G.C.C. ; Timmerman, M. - \ 2009
Lelystad : Wageningen UR, Livestock Research (Rapport / Wageningen UR, Livestock Research 288) - 40
varkenshouderij - varkens - mest - ontschuimen - schuim - mestverwerking - pig farming - pigs - manures - defoaming - foams - manure treatment
This report deals with the chemistry behind foam formation on liquid manure and the abatement of this foam in practical farm operations
Glasschuim evenaart productie in steenwol
Bouwman-van Velden, Pieternel ; Blok, C. - \ 2009
Onder Glas 6 (2009)9. - p. 5 - 7.
proeven op proefstations - teelt onder bescherming - schuim - substraten - voedingsstoffen - groenteteelt - pythium - siliciummeststoffen - glastuinbouw - groenten - station tests - protected cultivation - foams - substrates - nutrients - vegetable growing - silicon fertilizers - greenhouse horticulture - vegetables
Proeven bij Wageningen UR Glastuinbouw hebben aangetoond dat planten op glasschuim de productie op steenwol evenaren. Glasschuim bevat onder alle groeiomstandigheden 40% lucht en weinig vrij water. Naast een sterk generatieve groei heeft dit ook gevolg voor minder Pythium bij komkommers en minder neusrot bij tomaat
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
Mechanical and conformational aspects of protein layers on water
Martin, A.H. - \ 2003
Wageningen University. Promotor(en): Martien Cohen Stuart, co-promotor(en): M.A. Bos; Ton van Vliet. - [S.I.] : S.n. - ISBN 9058088103 - 126
bovenlagen - moleculaire structuur - schuim - eiwitten - schuifsterkte - reologie - surface layers - molecular conformation - foams - proteins - shear strength - rheology
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 9058089045 - 145
zonnebloemeiwit - fysicochemische eigenschappen - denaturatie - oplosbaarheid - schuimen - schuim - emulgeren - emulsies - sunflower protein - physicochemical properties - denaturation - solubility - foaming - foams - emulsifying - emulsions
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 0854048715 - p. 156 - 164.
sojaeiwit - schuim - schuimen - soya protein - foams - foaming
Failure behaviour of adsorbed protein Layers: consequences for emulsion and foam stability
Vliet, T. van; Aken, G.A. van; Bos, M.A. ; Martin, A.H. - \ 2003
In: Food Colloids, Biopolymers and Materials. - Cambridge UK : Royal Society of Chemistry - ISBN 0854048715 - p. 176 - 191.
schuim - emulsies - eiwitten - reologische eigenschappen - foams - emulsions - proteins - rheological properties
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 0854048715 - p. 192 - 199.
emulsies - schuim - schuimen - eiwitten - caseïnaten - grensvlak - mechanische eigenschappen - emulsions - foams - foaming - proteins - caseinates - interface - mechanical properties
Colloids and interfaces in life sciences
Norde, W. - \ 2003
New York; Basel : Marcel Dekker - ISBN 0824709969 - 433
colloïden - colloïdale eigenschappen - grensvlak - oppervlaktespanning - emulsies - schuim - reologische eigenschappen - studieboeken - oppervlaktechemie - colloids - colloidal properties - interface - surface tension - emulsions - foams - rheological properties - textbooks - surface chemistry
Biochemical and functional characterisation of casein and whey protein hydrolysates : a study on the correlations between biochemical and functional properties using multivariate data analysis
Ven, C. van der - \ 2002
Wageningen University. Promotor(en): A.G.J. Voragen; Harry Gruppen; D.B.A. de Bont. - S.l. : S.n. - ISBN 9789058086532 - 155
melkeiwitten - caseïnehydrolysaat - wei-eiwit - eiwithydrolysaten - peptiden - multivariate analyse - vloeistofchromatografie met omgekeerde fase - gelfiltratiechromatografie - infraroodspectroscopie - molecuulgewicht - emulsies - schuim - oplosbaarheid - bitterheid - milk proteins - casein hydrolysate - whey protein - protein hydrolysates - peptides - multivariate analysis - reverse phase liquid chromatography - gel filtration chromatography - infrared spectroscopy - molecular weight - emulsions - foams - solubility - bitterness
<p>Whey protein and sodium caseinate were hydrolysed with commercially available enzyme preparations. The resulting hydrolysates were characterised using several analytical characterisation methods and by determination of several functional properties. Subsequently, correlations between the biochemical characteristics themselves and between biochemical and functional properties were studied using multivariate regression analysis.</p><p>Biochemical characteristics of hydrolysates were determined using unifactorial methods like the degree of hydrolysis, and by multifactorial methods, <em>i.e</em> . reversed phase (RPC) and size exclusion chromatography (SEC), and Fourier transform infrared (FTIR) spectroscopy. FTIR spectroscopy appeared to discriminate most effectively between hydrolysates made from different protein sources and classes of proteolytic enzymes, followed by RPC and SEC.</p><p>Emulsion and foam properties of hydrolysates were similar or inferior to those of the parental proteins. Casein hydrolysates generally showed better emulsion and foam forming ability than whey protein hydrolysates. Foam forming ability of whey protein hydrolysates was correlated to the molecular weight distribution (MWD) of the peptides, showing that especially peptides with MW of 3-5 kDa contributed to foam forming ability.</p><p>Concerning prevention of emulsion instability due to coalescence it was shown that peptides with a molecular weight larger than 2 kDa are needed. Foam stabilising ability of casein hydrolysates also depended on the MWD of hydrolysates, but higher molecular weight peptides, <em>i.e.</em> larger than 7 kDa, were needed to obtain good foam stability.</p><p>The ability of the three multifactorial characterisation methods (SEC, RPC, FTIR spectroscopy) to predict functional properties was investigated. It appeared that SEC profiles were able to predict emulsion and foam stability of all hydrolysates, as well as foam forming ability, Angiotensin Converting Enzyme (ACE) inhibiting ability and bitterness of whey hydrolysates. RPC profiles were also able to predict these properties and additionally predicted solubility and bitterness of casein hydrolysates. FTIR spectra were best suited to predict a variety of hydrolysate properties, since apart from the before-mentioned properties, the spectra can also be used to predict emulsion forming ability and to improve prediction of bitterness of hydrolysates.</p><p>Finally, the influence of hydrolysis process conditions on ACE inhibiting ability of whey hydrolysates was investigated, showing that ACE inhibiting activity could be optimised by using process optimisation techniques like experimental design and response surface optimisation.
Anaerobic digestion of domestic sewage al low temperature
Elmitwalli, T.A. ; Zeeman, G. ; Lettinga, G. - \ 2001
Water Science and Technology 44 (2001)4. - ISSN 0273-1223 - p. 33 - 40.
afvalwaterbehandeling - anaërobe behandeling - rioolwater - anaërobe afbraak - polyurethanen - schuim - temperatuur - waste water treatment - anaerobic treatment - sewage - anaerobic digestion - polyurethanes - foams - temperature
The results of research concerning the feasibility of anaerobic treatment of domestic sewage at low temperature are summarized in this article. The batch tests demonstrated a high biodegradability of domestic sewage at 20°C (74Ž Both batch and continuous experiments for the treatment of domestic sewage showed that the removal of SS prior to anaerobic treatment of domestic sewage not only provides a stable reactor performance but also improves the removal of both colloidal (CODcol) and dissolved COD (CODdis). The results of the pre-treatment of domestic sewage in an anaerobic filter (AF) and an anaerobic hybrid (AH) reactor showed that the AF reactor is an efficient process for the removal of suspended COD (CODss), viz. 82°at an HRT of 4 h and 13°C. The novel AF reactor consists of vertical sheets of reticulated polyurethane foam with knobs, where the biomass was only in attached form. For the treatment of pre-settled sewage at 13°C, the AH reactor, with granular sludge, showed a higher total COD (CODt) removal than the UASB reactor as a result of higher CODcol removal. Therefore, the performance of a two-step system, AF AH (with granular sludge) reactor, was investigated with different HRTs at 13°C. For optimization of CODss and CODdis an HRT of 4 4 h is needed, while for optimization of CODcol removal an HRT of 4 8 h is required. A CODt removal of 71 as achieved with 60␌onversion to methane from the removed CODt when the AF AH system was operated at an HRT of 4 8 h at 13°C.
De veelzijdige aardappel
Oosterhaven, J. ; Schijndel, R. van; Soest, J. van; Tuil, R. van - \ 2000
Aardappelwereld 54 (2000)8. - ISSN 0169-653X - p. 21 - 23.
aardappelen - solanum tuberosum - industriële gewassen - kunststoffen - verwerking - technologie - schuim - verfsoorten - afdeklagen - potatoes - industrial crops - plastics - foams - paints - coatings - processing - technology
Perspectieven voor agrificatie van de aardappel. Van de aardappel worden al gemaakt: lijmen, schuimen, coatings, bindmiddel of verdikkingsmiddel in watergedragen verf en bio-afbreekbare luiers
Static and dynamic properties of proteins adsorbed at liquid interfaces
Benjamins, J. - \ 2000
Agricultural University. Promotor(en): J. Lyklema; E.H. Lucassen-Reynders. - S.l. : S.n. - ISBN 9789058083173 - 212
colloïdale eigenschappen - eiwitten - adsorptie - schuim - emulsies - colloidal properties - proteins - adsorption - foams - emulsions
<p>The aim of the investigation described in this thesis was to increase the level of understanding of the role that proteins play in the preparation and subsequent stabilisation of foams and emulsions. One aspect of this role is facilitation of break-up, due to surface tension lowering. A second aspect is the formation of a viscoelastic interfacial layer, which affects both the short-term and long-term stability of the dispersion. Therefore, a systematic study of the changes in static and dynamic interfacial properties induced by proteins was carried out.</p><p>For part of this study, dealing with the interfacial rheology, several experimental techniques were used. These techniques were either properly modified existing techniques (Chapter 3, modified longitudinal wave set-up) or newly developed (Chapter 4, Dynamic Drop Tensiometer; Chapter 5, Concentric Ring Surface Shear Rheometer) to meet the requirements for measuring the rheology of adsorbed protein layers at liquid/liquid interfaces. These requirements are (i) isotropic deformation, without leakage of the interfacial layer, for the dilational modulus measurements at air/water and oil/water interfaces and (ii) shear modulus measurements at small oscillatory deformation.</p><p>The proteins chosen for this study wereβ-casein,β-lactoglobulin (BLG), bovine serum albumin (BSA), ovalbumin and lysozyme. This set of proteins was chosen, because they differ considerably in relevant aspects, such as molecular weight, molecular structure and iso-electric point.</p><p>In Chapter 1 the scope and context of this study are given including a brief introduction into (i) the molecular properties of these proteins, that are relevant to the adsorption, (ii) protein adsorption and interfacial rheology, and (iii) the relation between interfacial properties and the properties of emulsions and foams.</p><p>Chapter 2 deals with the adsorption of proteins at the air/water interface. The adsorption was determined by ellipsometry, a method by which not only the adsorbed amount but also the layer thickness and protein concentration in the adsorbed layer could be determined. The ellipsometric studies were combined with surface tension measurements at the same surface.</p><p>All proteins examined show high affinity adsorption, i.e. strong adsorption at low concentration in solution. The initial rate of adsorption of all proteins is well described by a simple diffusion equation. For all proteins examined, the value of the surface pressure (Π) are protein-specific, but otherwise unique, time-independent functions of the adsorption (Γ). Time independence of theΠ(Γ) curve was concluded from the finding thatΠandΓpairs measured at different bulk concentrations and at different stages of adsorption, all collapse into one single curve. In other words, each protein has a unique surface equation of state indicated by its measuredΠ(Γ) curve. This curve reflects the relative rigidity of the protein molecule. For flexible molecules likeβ-casein and PVA ,Γ <sub>min</sub> (=ΓwhereΠstarts to deviate measurably from zero) is low and from this point onward the surface pressure increases gradually with increasingΓ. For rigid globular proteins (BSA, ovalbumin and lysozyme)Γ <sub>min</sub> is higher and with further increase of the surface concentration the surface pressure increases steeply. At high protein concentration and long adsorption times, for most proteins multilayer adsorption takes place.</p><p>For ovalbumin, in the pH range 4-8 the effect of pH on theΠ-Γcurve is small, which indicates that electrostatic intermolecular forces do not contribute much to the surface pressure.</p><p>In Chapter 3 a longitudinal wave technique, modified to ensure isotropic surface deformation, was used to determine the dilational modulus,ε, of adsorbed protein layers, at the air/water interface. This modification fully eliminated the complicating shear effects that became apparent in dilational modulus measurements with adsorbed layers of proteins in a conventional set-up.</p><p>For all proteins examined at frequencies in the range from 0.01 to 1 rad/s, the initial part of theε(Π) plot is a straight line through the origin. The slope of this initial part ranges between +4 and +12 . No clear relationship between the slope and the rigidity of the protein molecule was found. However, the extent of this linear range is smaller for the flexible molecules (β-casein and PVA). From the fact that this slope significantly exceeds the ideal value of +1, it must be concluded that the behaviour of the adsorbed layer is far from ideal. In the linear range, the measured moduli coincide with the limiting moduli,ε <sub>0</sub> , calculated from theΠ(Γ) curve. This indicates that the surface pressure adjusts "instantaneously" to the changing adsorption during a compression-expansion cycle in time-scales ranging from 1 to 100 s. This also means that the modulus is purely elastic, i.e. the effect of relaxation processes is negligible. In this elastic range, differences between individual proteins are related to different degrees of non-ideality, reflected in the surface equation of state.</p><p>At higher surface concentrations a relaxation mechanism becomes operative, which is most probably not caused by diffusional exchange between surface and solution. This conclusion is based on calculations of the diffusional transport rate and the theoretical frequency spectrum of the modulus. Relaxation due to conformational changes is plausible. In the visco-elastic regionε≥ε <sub>0</sub> for all proteins examined. This is an extra argument against diffusional exchange.</p><p>The modulus increases in the order: PVA &lt;β-casein &lt;BSA &lt; ovalbumin &lt;κ-casein. For the first four molecules the flexibility of the molecule decreases in the same order. The high modulus in the case ofκ-casein cannot be attributed to the rigid molecular structure.</p><p>Chapter 4 describes a new method, the Dynamic Drop Tensiometer, especially suitable for determining the dynamic properties of proteins adsorbed at oil/water interfaces. According to this method, a small drop is subjected to sinusoidal oscillations of its volume. The corresponding area changes produce interfacial tension changes, which are evaluated from measurements of the fluctuating shape of the drop, using the Young-Laplace equation. Compared to the conventional Langmuir trough set-up, this method is particularly suited for liquid/liquid interfaces, because (i) interfacial leakage is fully eliminated and (ii) uniform deformation is ensured even if one of the liquids is a viscous oil. An additional advantage of the method is its short response time. The dynamic properties of adsorbed protein layers at three interfaces (TAG (triacylglycerol)-oil/water, tetradecane/water and air/water) were compared. At the three interfaces, at low protein concentration, the conformation change upon adsorption is fairly fast, occurring within 1 min.. However, at high protein concentration (&gt; 1g/l), during the first minutes after adsorption a situation exists that differs from the equilibriumΠ(Γ) curve. At low interfacial pressures, during a modulus measurement, the adaptation of the conformation is faster (&lt; 1 s.). Non-ideality of the adsorbed layer increases in the sequence TAG-oil &lt; tetradecane &lt; air, which is probably related to a decrease of solution quality for the more hydrophobic amino acids, which decreases in the same sequence. At each of the different interfaces non-ideality increases with increasing rigidity of the protein molecule (β-casein&lt;β-lactoglobulin&lt;BSA&lt;ovalbumin). Collapse-type effects and conformation-related relaxation are most pronounced at TAG-oil/water, especially with BSA, but absent at all interfaces with ovalbumin.</p><p>The surface shear properties of adsorbed protein layers are described in Chapter 5. These properties were determined with a newly developed concentric ring surface shear rheometer. The technique allows measurements over a wide range of frequencies and deformations. As the magnitude of the shear deformation markedly affects the shear modulus,μ <sub>s</sub> , an extrapolation to zero deformation is required to asses the shear properties of the undisturbed surface. Because the surface dilational modulus and the surface shear modulus both increase in the sequence PVA&lt; Na-caseinate &lt;BSA &lt;ovalbumin, it is plausible that essentially the same molecular properties are responsible for the magnitude of both moduli. These properties are intermolecular interactions and the intramolecular structure. The low shear modulus for casein can be ascribed to relatively strong interactions between flexible, easily deformable molecules. With BSA and ovalbumin the interacting bonds are the weaker part of the network. So, for both moduli the rigidity of the molecule is the dominating characteristic. The finding that for most systemsε/μ <sub>s</sub> ≥3 indicates that the adsorbed protein layer can be modelled as a thin homogeneous gel layer. Such a model points to a significant ideal monolayer contribution toεat low to medium surface concentrations.</p><p>In Chapter 6 models describing the surface equation of state of adsorbed macromolecules were applied to the experimentalΠ(Γ) curves. These models were also applied to understand the dynamic behaviour of these layers. Statistical models, in which it is assumed that the macromolecules adsorb with all segments in direct contact with the surface, e.g. Singer equation, only explain the very low pressure part of the experimental curves of PVA andβ-casein. To explain the higher pressure part, progressive loop formation and molecular interaction must be accounted for. For rigid globular proteins, simple statistical models are unable to fit any part of the experimental curves, because such molecules only slightly change their conformation upon adsorption and consequently, will adsorb with only a small fraction of the segments at the surface, even at very low pressures.</p><p>A 2-D solution model, which accounts to first order for both entropy and enthalpy, is used to describe the non-ideal behaviour of adsorbed protein layers. This non-ideality was deduced from the highΓneeded to produce a measurableΠand the steep initial slopes of theε(Π) curves.</p><p>All above models need modification to describe the S-shaped part of theΠ(Γ) curves at high surface concentrations. This part of the curve can be described by the Soft Particle concept, which is a modification of the surface equation of state of a 2-D hard sphere fluid. The S-shape is attributed to a decrease of the molecular cross-sectional area with increasing surface concentration. This effect appears to be more pronounced for flexible molecules like PVA andβ-casein than for globular rigid molecules like BSA, ovalbumin and lysozyme. Experimentalε(Π) curves are within the limits that are predicted by this concept. A promising option is combining a molecular compressibility as used in the Soft Particle concept with the 2-D solution model.</p><p>In Chapter 7 it is shown that interfacial properties typical for proteins predict a larger drop size and a lower stability against recoalescence during production compared to low molecular weight (LMW) surfactants.</p><p>In the presence of both types of surfactant, concentrations and conditions can be chosen such that the LMW surfactant determines the dispersion efficiency, while the protein determines the long-term stability. A comparison between the different proteins reveals that, in the production stage, a higher dilational modulus at short times correlates with a faster build-up of stability against recoalescence. For a good long term stability a high dilational modulus of adsorbed protein layers at longer times is more important. In foams, retardation of Ostwald ripening, i.e. the growth of large bubbles at the expense of small ones, is probably the major factor. This mechanism depends on the ratio of the modulus to the surface tension, which ratio is considerably higher for proteins than for LMW surfactants in relevant cases.</p><p>For a measurable shear modulus a high surface concentration is required. Therefore, shear properties may only affect long term stability of emulsions and foams, but not break-up and stability against recoalescence during production.</p>
Liever inweken met schuim dan met water
Roelofs, P. ; Plagge, G. - \ 1998
Praktijkonderzoek varkenshouderij 12 (1998)6. - ISSN 1382-0346 - p. 11 - 13.
varkensstallen - stallen - schoonmaakgereedschap - schoonmaken - schuim - water - watertarieven - arbeidskunde - arbeid (werk) - pig housing - stalls - cleaning equipment - cleaning - foams - water costs - work study - labour
Inweken van varkensstallen met een schuimend inweekmiddel bespaart water en tijd ten opzichte van inweken met alleen water. Als de mest moet worden afgezet is de besparing op water en mestafzetkosten voldoende om de kosten van het inweekmiddel te betalen. Bovendien is het reinigingsresultaat beter.
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
The influence of spreading particles on the stability of thin liquid films
Bisperink, C.G.J. - \ 1997
Agricultural University. Promotor(en): A. Prins; H.J. Bos. - S.l. : Bisperink - ISBN 9789054857174 - 214
oppervlakten - grensvlak - dispersie - gassen - schuim - oppervlakteverschijnselen - surfaces - interface - dispersion - gases - foams - surface phenomena
<br/>The influence of spreading particles on the stability of thin liquid films was investigated. Due to the spreading of a particle, i.e. an oil droplet, over a surface of a thin liquid film the latter becomes thinner and may rupture. The following steps in the whole process were distinguished: 1) transport of the particle to the film surface, 2) dewetting of the particle ensuring physical contact between the particle surface and the film surface, 3) spreading of the particle over the film surface and 4) movement of the film bulk liquid induced by the surface movement due to spreading material.<p>An attempt was made to develop a theory that describes the spreading process quantitatively. It describes the film thinning process as a result of the liquid drag due to the surface motion initiated by the spreading material by using the parameters film thickness, droplet radius, liquid bulk viscosity, liquid bulk density and the surface rheological properties of the oil droplet and the film liquid.<p>Model systems of foaming liquid and lipid material were used to study this spreading process. The latter was done on a relative macroscopic scale over bulk surfaces which is different compared to the dimensions and conditions which are valid for spreading particles on a foam film. It was assumed that the developed theory could be applied to both dimensions. The experimental results pointed in this direction. This was verified by the experimental results of introducing small spreading emulsion droplets on thin liquid films. A clear correlation between the above mentioned parameters and film rupture initiated by the spreading droplets was found.
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