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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    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
    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.

    Spontaneous, non-enzymatic breakdown of peptides during enzymatic protein hydrolysis
    Butre, C.I. ; Buhler, S. ; Sforza, S. ; Gruppen, H. ; Wierenga, P.A. - \ 2015
    Biochimica et Biophysica Acta. Proteins & Proteomics 1854 (2015)8. - ISSN 1570-9639 - p. 987 - 994.
    beta-lactoglobulin - cleavage - bond - specificity - identification - selectivity - kinetics - isolate - water
    It is expected that during the hydrolysis of proteins with specific enzymes only peptides are formed that result from hydrolysis of the specific cleavage sites (i.e. specific peptides). It is, however, quite common to find a-specific peptides (i.e. resulting from a-specific cleavage), which are often ignored, or explained by impurities in the enzyme preparation. In recent work in a whey protein isolate (WPI) hydrolysate obtained with the specific Bacillus licheniformis protease (BLP), 13 peptides of 77 identified were found to be the result of a-specific cleavage. These were formed after degradation of 6 specific peptides, after 5 different types of amino acids. The fact that other peptides were not hydrolyzed after these 5 amino acids suggests that the cleavages were not the result of a contamination with a different enzyme. In other systems, certain peptide sequences have been described to degrade chemically, under relatively mild conditions. This process is referred to as spontaneous cleavage. To test if the a-specific peptides observed in the WPI hydrolysis are the results of spontaneous cleavages, the parental peptides were synthesized. Surprisingly, 4 of the 5 synthesized peptides were indeed spontaneously cleaved under the mild conditions used in this study (i.e. 40 °C and pH 8) showing that peptides are less stable than typically considered. The rate of cleavage on the a-specific bonds was found to be enhanced in the presence of BLP. This suggests that the formation of a-specific peptides is not due to side activity but rather an enhancement of intrinsic instability of the peptides.
    Towards predicting the stability of protein-stabilized emulsions
    Delahaije, R.J.B.M. ; Gruppen, H. ; Giuseppin, M.L.F. ; Wierenga, P.A. - \ 2015
    Advances in Colloid and Interface Science 219 (2015). - ISSN 0001-8686 - p. 1 - 9.
    in-water emulsions - random sequential adsorption - equation-of-state - beta-lactoglobulin - light-scattering - latex-particles - quantitative description - exposed hydrophobicity - globular-proteins - diffusing wave
    The protein concentration is known to determine the stability against coalescence during formation of emulsions. Recently, it was observed that the protein concentration also influences the stability of formed emulsions against flocculation as a result of changes in the ionic strength. In both cases, the stability was postulated to be the result of a complete (i.e. saturated) coverage of the interface. By combining the current views on emulsion stability against coalescence and flocculation with new experimental data, an empiric model is established to predict emulsion stability based on protein molecular properties such as exposed hydrophobicity and charge. It was shown that besides protein concentration, the adsorbed layer (i.e. maximum adsorbed amount and interfacial area) dominates emulsion stability against coalescence and flocculation. Surprisingly, the emulsion stability was also affected by the adsorption rate. From these observations, it was concluded that a completely covered interface indeed ensures the stability of an emulsion against coalescence and flocculation. The contribution of adsorption rate and adsorbed amount on the stability of emulsions was combined in a surface coverage model. For this model, the adsorbed amount was predicted from the protein radius, surface charge and ionic strength. Moreover, the adsorption rate, which depends on the protein charge and exposed hydrophobicity, was approximated by the relative exposed hydrophobicity (QH). The model in the current state already showed good correspondence with the experimental data, and was furthermore shown to be applicable to describe data obtained from literature.
    Comparison of Heat-Induced Aggregation of Globular Proteins
    Delahaije, R.J.B.M. ; Wierenga, P.A. ; Giuseppin, M.L.F. ; Gruppen, H. - \ 2015
    Journal of Agricultural and Food Chemistry 63 (2015)21. - ISSN 0021-8561 - p. 5257 - 5265.
    laser-light scattering - beta-lactoglobulin - ionic-strength - induced denaturation - reaction-kinetics - whey proteins - neutral ph - in-situ - ovalbumin - gels
    Typically, heat-induced aggregation of proteins is studied using a single protein under various conditions (e.g., temperature). Because different studies use different conditions and methods, a mechanistic relationship between molecular properties and the aggregation behavior of proteins has not been identified. Therefore, this study investigates the kinetics of heat-induced aggregation and the size/density of formed aggregates for three different proteins (ovalbumin, ß-lactoglobulin, and patatin) under various conditions (pH, ionic strength, concentration, and temperature). The aggregation rate of ß-lactoglobulin was slower (>10 times) than that of ovalbumin and patatin. Moreover, the conditions (pH, ionic strength, and concentration) affected the aggregation kinetics of ß-lactoglobulin more strongly than for ovalbumin and patatin. In contrast to the kinetics, for all proteins the aggregate size/density increased with decreasing electrostatic repulsion. By comparing these proteins under these conditions, it became clear that the aggregation behavior cannot easily be correlated to the molecular properties (e.g., charge and exposed hydrophobicity).
    Comparing foam and interfacial properties of similarly charged protein–surfactant mixtures
    Lech, F.J. ; Meinders, M.B.J. ; Wierenga, P.A. ; Gruppen, H. - \ 2015
    Colloids and Surfaces. A: Physicochemical and Engineering Aspects 473 (2015). - ISSN 0927-7757 - p. 18 - 23.
    sodium dodecyl-sulfate - bovine serum-albumin - air-water interfaces - beta-lactoglobulin - titration calorimetry - binding - sds - adsorption - rheology - layers
    The foam stability of protein–surfactant mixtures strongly depends on the charge of the protein and the surfactant, as well as on their mixing ratio. Depending on the conditions, the mixtures will contain free proteins, free surfactants and/or protein–surfactant complexes. To be able to compare different protein–surfactant mixtures, generic knowledge about the occurrence of each of these states and their relative contribution to foam stability is essential. In this work, the foam stability and interfacial properties of bovine serum albumin (BSA) mixed with sodium dodecyl sulphate (SDS) as well the binding of SDS to BSA as are studied at different molar ratios (MR). A comparison is made with ß-lactoglobulin (BLG) mixed with SDS. Both proteins and SDS are negatively charged at pH 7. The foam stability in the presence of small amounts (up to MR 1) of SDS is half the value of the pure protein solutions. The foam stability for both protein surfactant mixtures reaches a minimum at MR 20. A further increase of the MR leads to an increase of foam stability. The foam stability of BLG–SDS at MR >20 follows the foam stability of pure SDS solutions at equivalent concentrations, while BSA–SDS mixtures have an offset and begin to increase from MR >50. This behaviour was also reflected in the surface pressure and complex dilatational elastic moduli, and could be linked to the binding of the surfactant to the proteins. Both proteins bind SDS at high and low affinity binding sites. BSA's high affinity binding sites have a binding stoichiometry of 5.5 molSDS/molprotein, and BLG's high affinity binding site has a stoichiometry of 0.8 molSDS/molprotein (determined by isothermal titration calorimetry). Binding to the low affinity binding sites, occurs with a binding ratio, leading to an accumulation of free surfactants. While the basic mechanisms underlying the foam properties of mixed systems are not explained in detail by this approach, the foam stability plots of both protein surfactant mixtures could be superimposed using the concentration of free SDS.
    Determination of the influence of the pH of hydrolysis on enzyme selectivity of Bacillus licheniformis protease towards whey protein isolate
    Butre, C.I. ; Sforza, S. ; Wierenga, P.A. ; Gruppen, H. - \ 2015
    International Dairy Journal 44 (2015). - ISSN 0958-6946 - p. 44 - 53.
    differential scanning calorimetry - beta-lactoglobulin - peptides - endopeptidases - kinetics
    Enzymatic protein hydrolysis is typically described by the degree of hydrolysis and by the enzyme specificity. While the specificity describes which cleavage sites can potentially be cleaved, it does not describe which are preferred. To identify the relative rate at which each individual cleavage site is hydrolysed, enzyme selectivity has recently been introduced. To test the effect of pH on selectivity, whey protein isolate (WPI) was hydrolysed with Bacillus licheniformis protease (BLP) at pH 7.0, 8.0 or 9.0. At all pH values, large differences in the enzyme selectivity (from
    Pickering Emulsions for Food Applications: Background, Trends, and Challenges
    Berton-Carabin, C.C. ; Schroën, C.G.P.H. - \ 2015
    Annual Review of Food Science and Technology 6 (2015). - ISSN 1941-1413 - p. 263 - 297.
    in-water emulsions - protein-stabilized emulsions - quinoa starch granules - colloidal particles - oxidative stability - lipid oxidation - o/w emulsions - silica nanoparticles - beta-lactoglobulin - physicochemical characteristics
    Particle-stabilized emulsions, also referred to as Pickering emulsions, have garnered exponentially increasing interest in recent years. This has also led to the first food applications, although the number of related publications is still rather low. The involved stabilization mechanisms are fundamentally different as compared to conventional emulsifiers, which can be an asset in terms of emulsion stability. Even though most of the research on Pickering emulsions has been conducted on model systems, with inorganic solid particles, recent progress has been made on the utilization of food-grade or food-compatible organic particles for this purpose. This review reports the latest advances in that respect, including technical challenges, and discusses the potential benefits and drawbacks of using Pickering emulsions for food applications, as an alternative to conventional emulsifier-based systems.
    The effect of calcium on the composition and physical properties of whey protein particles prepared using emulsification
    Westerik, N. ; Scholten, E. ; Corredig, M. - \ 2015
    Food Chemistry 177 (2015). - ISSN 0308-8146 - p. 72 - 80.
    beta-lactoglobulin - aggregation - gelation - supplements - droplets - chloride - gels
    Protein microparticles were formed through emulsification of 25% (w/w) whey protein isolate (WPI) solutions containing various concentrations of calcium (0.0–400.0 mM) in an oil phase stabilized by polyglycerol polyricinoleate (PGPR). The emulsions were heated (at 80 °C) and the microparticles subsequently re-dispersed in an aqueous phase. Light microscopy and scanning electron microscopy (SEM) images revealed that control particles and those prepared with 7.4 mM calcium were spherical and smooth. Particles prepared with 15.0 mM calcium gained an irregular, cauliflower-like structure, and at concentrations larger than 30.0 mM, shells formed and the particles were no longer spherical. These results describe, for the first time, the potential of modulating the properties of dense whey protein particles by using calcium, and may be used as structuring agents for the design of functional food matrices with increased protein and calcium content.
    Preparation, structure and stability of sodium caseinate and gelatin micro-particles
    Ince, A.E. ; Saglam, D. ; Venema, P. ; Linden, E. van der; Scholten, E. - \ 2015
    Food Hydrocolloids 45 (2015). - ISSN 0268-005X - p. 291 - 300.
    glucono-delta-lactone - whey-protein particles - light-scattering - physical-properties - beta-lactoglobulin - swelling behavior - phase-separation - ionic-strength - high-pressure - mixed gels
    Protein particles are promising candidates for texturing food products and can be produced in several ways. Here, we produced protein particles using a two-step emulsification method. This method is suitable to change the size of the particles and to control the protein concentration inside the particles. In this study, we prepared protein particles from two different protein sources, sodium caseinate (NaCas) and gelatin, that are gelled by acidification and cooling, respectively. The size and the internal protein concentration of the particles, their stability against heating and pH changes were studied. Although similar emulsification conditions were used to prepare the particles, NaCas particles were found to be 10 times smaller (average diameter 400 nm) than the gelatin particles (average diameter 4 µm). The internal protein concentration of the NaCas particles (16.8% w/w) is approximately twice as high compared to that of gelatin particles (7.6% w/w) (using an initial protein concentration of the solution of 10% (w/w)). The NaCas particle dispersions were found to be stable between pH 3 and pH 4. The particles disintegrated at pH values further away from the iso-electric point. Upon heating the dispersions at 90 °C, the NaCas particles were shown to be heat stable. Dispersions of gelatin particles were stable against aggregation at all pH values studied, except at pH 6, while the particles melted above 40 °C. Swelling of both particles was observed for both acidic and alkaline pH values. We conclude that emulsification method is robust for different protein sources used.
    Effect of crosslink density on the water-binding capacity of whey protein microparticles
    Peters, J.P.C.M. ; Luyten, H. ; Alting, A.C. ; Boom, R.M. ; Goot, A.J. van der - \ 2015
    Food Hydrocolloids 44 (2015). - ISSN 0268-005X - p. 277 - 284.
    microbial transglutaminase - statistical-mechanics - beta-lactoglobulin - moisture transport - gels - particles - genipin - isolate - meat - disulfide
    The ability of whey protein microparticles (MPs) to bind water and consequently to swell is, amongst others, determined by the crosslink density of the MPs. The Flory-Rehner model states that a decrease in crosslink density should lead to an increased swelling of the MPs. Decreasing the crosslink density of MPs with dithiothreitol (DTT) decreased the amount of disulphide bridges and increased the water-binding capacity (WBC) from 6 to 9 g water/g protein. Increasing the crosslink density with transglutaminase or genipin resulted in a decreased number of primary amino groups, although the WBC did not change significantly. The WBC of the MPs was determined using a centrifugation method that resulted in the formation of a pellet, so water inside and between the MPs was measured simultaneously. Therefore, additional microscopy and swelling tests were performed, which suggested that an increased WBC of the pellet of MPs was not only related to an increased swelling of the MPs, but also to an increased amount of water between the MPs.
    Effect of interfacial properties on the reactivity of a lipophilic ingredient in multilayered emulsions
    Chaprenet, J. ; Berton-Carabin, C.C. ; Elias, R. ; Coupland, J. - \ 2014
    Food Hydrocolloids 42 (2014)part1. - ISSN 0268-005X - p. 56 - 65.
    in-water emulsions - whey-protein isolate - solid lipid nanoparticles - oxidative stability - beta-lactoglobulin - surfactant micelles - delivery-systems - chemical-stability - oil - droplets
    The aim of this work was to investigate the location and reactivity of a lipophilic spin probe, 4-phenyl- 2,2,5,5-tetramethyl-3-imidazoline-1-oxyl nitroxide (PTMIO) in multilayered, biopolymer-based emulsions stabilized with a primary anionic layer (sodium caseinate) and a secondary cationic layer (lysozyme or diethylaminoethyl (DEAE) dextran). A broad range of ¿-potential values, from ca. -55 mV to 35 mV, was achieved. Emulsions with good physical stability were achieved when the magnitude of the net charge on the droplets was sufficiently great, otherwise some physical destabilization (flocculation) could be observed, especially in the case of caseinate-lysozyme-stabilized emulsions. The analysis of electron paramagnetic resonance (EPR) spectra of PTMIO in emulsion systems showed that probe molecules partitioned between the oil droplet core (ca. 73%) and the aqueous phase (ca. 27%), independently of the interfacial composition. Surprisingly, the rate of reduction of the nitroxide group of PTMIO by ascorbate anions remained unchanged when secondary interfacial layers were added, showing that the droplet surface charge was not the prevalent factor controlling the interactions between lipophilic compounds and aqueous phase reagents. Instead we argue that the reduction of PTMIO occurs in the aqueous phase.
    Quantitative description of the parameters affecting the adsorption behaviour of globular proteins
    Delahaije, R.J.B.M. ; Gruppen, H. ; Giuseppin, M.L.F. ; Wierenga, P.A. - \ 2014
    Colloids and Surfaces. B: Biointerfaces 123 (2014). - ISSN 0927-7765 - p. 199 - 206.
    air-water-interface - bovine serum-albumin - beta-lactoglobulin - rheological properties - air/water interface - surface rheology - kinetics - ovalbumin - charge - denaturation
    The adsorption behaviour of proteins depends significantly on their molecular properties and system conditions. To study this relation, the effect of relative exposed hydrophobicity, protein concentration and ionic strength on the adsorption rate and adsorbed amount is studied using ß-lactoglobulin, ovalbumin and lysozyme. The curves of surface elastic modulus versus surface pressure of all three proteins, under different conditions (i.e. concentration and ionic strength) superimposed. This showed that the interactions between the adsorbed proteins are similar and that the adsorbed proteins retain their native state. In addition, the adsorption rate (kadsorb) was shown to scale with the relative hydrophobicity and ionic strength. Moreover, the adsorbed amount was shown to be dependent on the protein charge and the ionic strength. Based on these results, a model is proposed to predict the maximum adsorbed amount (Gmax). The model approximates the adsorbed amount as a close-packed monolayer using a hard-sphere approximation with an effective protein radius which depends on the electrostatic repulsion. The theoretical adsorbed amount was in agreement with experimental Gmax (±10%).
    Changes in protein conformation and surface hydrophobicity upon peroxidase-catalyzed cross-linking of apo-a-lactalbumin
    Saricay, Y. ; Wierenga, P.A. ; Vries, R.J. de - \ 2014
    Journal of Agricultural and Food Chemistry 62 (2014)38. - ISSN 0021-8561 - p. 9345 - 9352.
    secondary structure analyses - high hydrostatic-pressure - microbial transglutaminase - horseradish-peroxidase - circular-dichroism - whey proteins - beta-lactoglobulin - maillard reaction - oxygen radicals - dairy-products
    In this study, we explore the effect of peroxidase-catalyzed cross-linking on the molecular conformation of apo-a-lactalbumin (apo-a-LA) and the resulting changes in protein surface hydrophobicity. In studying conformational changes, we distinguish between early stages of the reaction (“partial cross-linking”), in which only protein oligomers (106 Da > Mw = 104 Da) are formed, and a later stage (“full cross-linking”), in which larger protein particles (Mw = 106 Da) are formed. Partial cross-linking induces a moderate loss of a-helical content. Surprisingly, further cross-linking leads to a partial return of a-helices that are lost upon early cross-linking. At the same time, for partially and fully cross-linked apo-a-LA, almost all tertiary structure is lost. The protein surface hydrophobicity first increases for partial cross-linking, but then decreases again at full cross-linking. Our results highlight the subtle changes in protein conformation and surface hydrophobicity of apo-a-LA upon peroxidase-catalyzed cross-linking.
    Modification of Ovalbumin with Fructooligosaccharides: Consequences for Network Morphology and Mechanical Deformation Responses
    Munialo, C.D. ; Ortega, R.G. ; Linden, E. van der; Jongh, H.H.J. de - \ 2014
    Langmuir 30 (2014)46. - ISSN 0743-7463 - p. 14062 - 14072.
    protein gels - rheological properties - beta-lactoglobulin - maillard reaction - pea protein - neutral ph - mixed gels - gelation - aggregation - perception
    The Maillardation of proteins has been used as a natural alternative to improve its functionality by covalent coupling of proteins with saccharides. However, the impact of Maillard reaction on the structural aspects of protein networks and, as a consequence, the mechanical breakdown properties of the gel networks has not been reported. The objective of this study was to evaluate how the attachment of linear oligo-sugar moieties onto ovalbumin affects its aggregation, network morphology, and consequently the mechanical deformation properties including the ability of the networks to elastically store energy in this material. To potentially alter the morphology of the network structure, ovalbumin was modified by conjugating some of its amino groups with fructooligosaccharide (FOS) moieties via the Maillard reaction. It was demonstrated that the attachment of FOS to ovalbumin does not affect the integrity of the secondary and tertiary structure as characterized using circular dichroism and tryptophan fluorescence. Differences in the network morphology were observed by scanning electron microscopy for FOS-modified ovalbumin variants. Upon increased modification, the microstructure of the gels had more and larger pores and had thinner strands than nonmodified variants. Evaluation of the large deformation properties of the gels demonstrated that FOS-modified gels were less strong and less brittle and showed lower stiffness than nonmodified variants. The recoverable energy (elastically stored energy) of gels reduced with an increase in the degree of modification. The results show that the attachment of FOS to ovalbumin alters the structural and mechanical (large) breakdown properties of the protein gels. The consequences of the alteration of the network structure and large deformation properties of FOS-modified ovalbumin offer opportunities to efficiently design food materials with desirable techno-functional applications
    Design, properties, and applications of protein micro- and nanoparticles
    Saglam, D. ; Venema, P. ; Linden, E. van der; Vries, R.J. de - \ 2014
    Current Opinion in Colloid and Interface Science 19 (2014)5. - ISSN 1359-0294 - p. 428 - 437.
    microparticulated whey proteins - beta-lactoglobulin - phase-separation - heat-stability - gelatin/maltodextrin mixtures - polysaccharide complexes - rheological properties - functional-properties - biopolymer particles - controlled delivery
    The design of protein particles with tailored properties has received an increased attention recently. Several approaches, from simple heat treatment in dilute systems to the combination of heat and mechanical treatments in concentrated protein solutions, have been used to obtain protein particles with varying functional properties. Control of particle size, morphology, surface- and internal properties is crucial for obtaining protein particles with the necessary properties for emerging applications. The latter include not only the use of protein particles in foods, where they can improve the stability of foods at high protein content, but also as food-grade particles for the delivery of bio-actives. By tuning the morphology and size of protein particles, protection or controlled release of various bio-active components may be obtained. We review the various methods that have been used to prepare protein particles and discuss the behavior of the particles in dispersed systems and their possible applications.
    Determination of the Influence of Substrate Concentration on Enzyme Selectivity Using Whey Protein Isolate and Bacillus licheniformis Protease
    Butré, C.I. ; Sforza, S. ; Gruppen, H. ; Wierenga, P.A. - \ 2014
    Journal of Agricultural and Food Chemistry 62 (2014)42. - ISSN 0021-8561 - p. 10230 - 10239.
    beta-lactoglobulin - functional-properties - mass-spectrometry - hydrolysis - peptide - endopeptidase - sequence - casein - model
    Increasing substrate concentration during enzymatic protein hydrolysis results in a decrease in hydrolysis rate. To test if changes in the mechanism of hydrolysis also occur, the enzyme selectivity was determined. The selectivity is defined quantitatively as the relative rate of hydrolysis of each cleavage site in the protein. It was determined from the identification and quantification of the peptides present in the hydrolysates. Solutions of 0.1–10% (w/v) whey protein isolate (WPI) were hydrolyzed by Bacillus licheniformis protease at constant enzyme-to-substrate ratio. The cleavage sites were divided into five groups, from very high (>10%) to very low selectivity (
    Separation of Whey Proteins using Cascaded Ultrafiltration
    Patil, N.V. ; Janssen, A.E.M. ; Boom, R.M. - \ 2014
    Separation Science and Technology 49 (2014)15. - ISSN 0149-6395 - p. 2280 - 2288.
    tangential flow filtration - membrane cascades - nanofiltration cascades - monoclonal-antibody - bed chromatography - beta-lactoglobulin - fractionation - purification - oligosaccharides - configuration
    Whey protein isolate, containing a-Lactalbumin and ß-Lactoglobulin, was separated by using a continuous three-stage ultrafiltration cascade system. Single-stage experiments were optimized to enable good and stable cascade operation. Three different cascade configurations, a non-constrained ideal system (Configuration A), and adapted version (Configuration B), and a countercurrent cascade (Configuration C) were experimentally tested and compared. The countercurrent cascade system showed the traditional trade-off between yield and purity. Both the adapted cascade system and the non-constrained ideal cascade gave better performance in terms of recovery and purity and show potential for application, albeit for different purposes.
    Improved emulsion stability by succinylation of patatin is caused by partial unfolding rather than charge effects
    Delahaije, R.J.B.M. ; Wierenga, P.A. ; Giuseppin, M.L.F. ; Gruppen, H. - \ 2014
    Journal of Colloid and Interface Science 430 (2014). - ISSN 0021-9797 - p. 69 - 77.
    in-water emulsions - protein-exposed hydrophobicity - beta-lactoglobulin - drop size - adsorption - flocculation - interface - stabilization - ph - dependence
    This study investigates the influence of succinylation on the molecular properties (i.e. charge, structure and hydrophobicity) and the flocculation behavior of patatin-stabilized oil-in-water emulsions. Patatin was succinylated to five degrees (0% (R0) to 57% (R2.5)). Succinylation not only resulted in a change of the protein charge but also in (partial) unfolding of the secondary structure, and consequently in an increased initial adsorption rate of the protein to the oil–water interface. The stability against salt-induced flocculation showed two distinct regimes, instead of a gradual shift in stability as expected by the DLVO theory. While flocculation was observed at ionic strengths > 30 mM for the emulsions stabilized by the variants with the lowest degrees of modification (R0–R1), the other variants (R1.5–R2.5) were stable against flocculation ¿ 200 mM. This was related to the increased initial adsorption rate, and the consequent transition from a protein-poor to a protein-rich regime. This was confirmed by the addition of excess protein to the emulsions stabilized by R0–R1 which resulted in stability against salt-induced flocculation. Therefore, succinylation of patatin indirectly results in stability against salt-induced flocculation, by increasing the initial adsorption rate of the protein to the oil–water interface, leading to a shift to the protein-rich regime.
    Controlled formation of protein nanoparticles by enzymatic cross-linking of a-lactalbumin with horseradish peroxidase
    Dhayal, S.K. ; Gruppen, H. ; Vries, R.J. de; Wierenga, P.A. - \ 2014
    Food Hydrocolloids 36 (2014). - ISSN 0268-005X - p. 53 - 59.
    field-flow fractionation - beta-lactoglobulin - foaming properties - interfacial properties - light-scattering - separation - emulsions - transglutaminase - stability
    Inorganic and organic colloidal particles are known to impart much higher stability to foams and emulsions than proteins, heat-induced protein aggregates or low molar mass surfactants. In this study we show that a-lactalbumin can be enzymatically cross-linked by horse-radish peroxidase to produce nanoparticles with controlled size and meso-scale structure. Furthermore, the effects of process parameters, such as the protein concentration (10–30 g L-1), total dosed amount of hydrogen peroxide (0–10 mM), the time gap between each dosage of hydrogen peroxide (120–600 s) and ionic strength (100–200 mM), on the sizes of the nanoparticles have been investigated. The cross-linked protein nanoparticles varied in size (radius of gyration, Rg) and weight averaged molar mass (Mw), ranging between monomeric protein (~2 nm, 14.2 kDa) and nanoparticles (200 nm, 100 MDa). The speed of particle formation increased with increasing ionic strength, but their meso-scale structure remained similar. The Rg of these nanoparticles scaled as Mw0.6, indicating similar meso-scale structure (conformation) at all length scales but variation of density with size. The apparent density (internal protein concentration) of the nanoparticles was between 104 and 10 kg m-3 for Rg ~ 20 nm and Rg > 100 nm respectively.
    The ability to store energy in pea protein gels is set by network dimensions smaller than 50 nm
    Munialo, C.D. ; Linden, E. van der; Jongh, H.H.J. de - \ 2014
    Food Research International 64 (2014). - ISSN 0963-9969 - p. 482 - 491.
    globular protein - beta-lactoglobulin - large-deformation - particulate gels - heat-treatment - whey-protein - mixed gels - gelation - ph - dissociation
    The objective of this study was to identify which length scales set the ability to elastically store energy in pea protein network structures. Various network structures were obtained frompea proteins by varying the pH and salt conditions during gel formation. The coarseness of the network structure was visualized by the use of confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) and ranked from least coarse to most coarse networks. Least coarse networks were formed at a pH away from the isoelectric point (IEP) of pea proteins, and at a low ionic strength, whereas more coarse networks were formed at pH values close to the IEP and at a high ionic strength during gel formation. Mechanical deformation properties of the gels such as elastically stored (recoverable) energy, Young's moduli (stiffness of gels), fracture stress (gel strength), and fracture strain (brittleness of the gels) were measured by the use of a texture analyzer and correlated to the coarseness of the networks structure. The influence of coarseness on the ability of the networks to elastically store energy was observed for length scales below 50 nm. The findings show that elastically stored energy of pea protein gels can be modulated via the creation of different network structures below 50 nm length scales. The results from this study contribute to a better understanding of the dimensions that set the ability to elastically storage in pea protein gels. If the ability of pea proteins to store energy can be understood, products can be better tailored for consumers.
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