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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    Lubrication and perception of foods : tribological, rheological and sensory properties of particle-filled food system
    Liu, K. - \ 2016
    Wageningen University. Promotor(en): Erik van der Linden, co-promotor(en): Markus Stieger; Fred van de Velde. - Wageningen : Wageningen University - ISBN 9789462576803 - 236
    rheological properties - tribology - fat globules - particles - lubrication - sensory evaluation - simulation models - food - gels - rice - reologische eigenschappen - tribologie - vetbolletjes - deeltjes - smering - sensorische evaluatie - simulatiemodellen - voedsel - gels - rijst

    Background and aims

    Food structure is determined by its composition and the interaction between the compositional or structural elements. Both food structure and the texture perception of foods undergo dynamic changes during different phases of oral processing. During oral processing, both rheological and tribological properties of foods are relevant for sensory perception. The general aim of this thesis was to understand the relationship between the structural properties, rheological and tribological properties during food breakdown, and the sensory perception of foods. More specifically, this thesis aimed to link the properties of food particles in liquid and semi-solid matrices to the tribological and rheological properties, and in this way, understand the sensory perception of these systems.

    Methods

    Fat droplets and micro-particle fat replacers based on protein and starch were investigated. These particles varied in size, morphology, deformability and stability, as well as their interaction with the surrounding matrix. These particles were dispersed in liquid or semi-solid gel phases, forming the food model systems under consideration. The friction and microstructural evolution of food model systems under shear was determined using a mouth-mimicking tribometer connected to a confocal laser scanning microscopy. The viscosities of liquid systems were analyzed using a rheometer, and the large deformation properties of semi-solid gel systems were determined during uniaxial compression tests. The sensory perception of the food model systems were measured using quantitative descriptive analysis. The release and deposition of fat droplets on the tongue were determined using in vivo fluorescence.

    Results

    Food structural elements could be manipulated to control the tribological properties of food model systems. Morphology, size, and deformability of food particles determine the lubrication behavior of the food systems. Spherical particles with micrometer size were able to reduce friction through a ball bearing mechanism, while irregularly shaped particles increased friction by increasing apparent surface asperity contacts. Deformable particles could flatten the surface by filling asperities, thus reduced friction. Coalescence of unstable droplets could plate-out on the surface and form film patches, thus reduced friction. Other structural elements, such as emulsifiers and sticky molecules, also influenced tribological properties of the systems. Interactions between the food structural elements could influence the rheological properties of liquid and semi-solid food systems. These properties as well as tribological properties were inter-related and all of them affect sensory perception. The inter-relations between physical and sensory properties of food systems were influenced by oral processing, such as oral processing duration and temperature. Furthermore, several fat reduction and replacement strategies were suggested, including increasing the availability of fat that is in contact with oral surfaces, improving the lubrication by ball bearing of particles, and reducing perception of negative attributes such as roughness.

    Conclusions

    This thesis showed the importance of food particle properties in both the tribological properties and sensory perception of foods, and emphasized the different lubrication mechanisms of different structure elements and their relation to perception. The differences in behavior of food particles between liquid and semi-solid gel systems were highlighted. These findings would enable a better understanding of relationship between food structure and their physical and sensory properties, and this would allow designing or modifying food products with targeted texture and sensory perception.

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

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

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

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

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

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

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

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

    Quantitative analysis of the network structure that underlines the transitioning in mechanical responses of pea protein gels
    Munialo, C.D. ; Linden, E. van der; Ako, K. ; Jongh, H.H.J. de - \ 2015
    Food Hydrocolloids 49 (2015). - ISSN 0268-005X - p. 104 - 117.
    whey-protein - rheological properties - gelation properties - large-deformation - particulate gels - ionic-strength - isolate gels - mixed gels - set - ph
    The objective of this study was to analyze quantitatively the network structure that underlines the transitioning in the mechanical responses of heat-induced pea protein gels. To achieve this, gels were prepared from pea proteins at varying pHs from 3.0 to 4.2 at a fixed 100 mg/mL protein concentration. Gels were also prepared by varying the protein concentration from 100 to 150 mg/mL at a fixed pH 3.0. Mechanical deformation properties of the gels were determined. An increase in protein concentration at a fixed pH resulted in an increase in fracture stress and Young's modulus. Variation of the pH at a fixed protein concentration resulted in transitioning in mechanical responses such as fracture stress, fracture strain, and the recoverable energy. The network structures were visualized by the use of confocal laser scanning and scanning electron microscopy, and the characteristic length scales of these structures were quantitatively analyzed in terms of the pair correlation function. Variation of the protein concentration at a fixed pH did not significantly alter the microstructure of the gels, whereas variation of the pH at a fixed protein concentration resulted in significant changes in the gel structure. Structural transitioning was shown to occur around pH 3.7. The findings from this study show transitioning in rheological responses of pea protein gels occur as a result of structural changes. The results from this study offer opportunities to broaden the application of pea proteins in food products, as products with desirable rheological (textural) and structural properties can be designed from pea proteins.
    Understanding the role of oat ß-glucan in oat-based dough systems
    Londono, D.M. ; Gilissen, L.J.W.J. ; Visser, R.G.F. ; Smulders, M.J.M. ; Hamer, R.J. - \ 2015
    Journal of Cereal Science 62 (2015). - ISSN 0733-5210 - p. 1 - 7.
    rheological properties - celiac-disease - bread quality - pentosans - diet - formulations - yeast
    B-glucan is one of the components that differentiate oats from other cereals and that contribute to the health-related value of oats. However, so far oats cannot easily be applied in bread-like products without loss of product quality. Here we have studied how the content and viscosity of oat ß-glucan affect the technological properties of oat dough in both a gluten-free and a gluten-containing system. In both systems, increasing the ß-glucan concentration resulted in an increase of dough stiffness and in a reduction of dough extensibility. ¿-glucan negatively impacted the elastic properties that additional wheat gluten conferred to oat dough. This effect was smaller for medium-viscosity ß-glucan than for high-viscosity ß-glucan. Interestingly, dough made from low ß-glucan flour (
    Dynamic texture perception and oral processing of semi-solid food gels: Part 1: Comparison between QDA, progressive profiling and TDS
    Devezeaux de Lavergne, M.S.M. ; Delft, J.M. van; Velde, F. van de; Boekel, M.A.J.S. van; Stieger, M.A. - \ 2015
    Food Hydrocolloids 43 (2015). - ISSN 0268-005X - p. 207 - 217.
    emulsion-filled gels - sensory texture - rheological properties - mechanical-properties - temporal dominance - time - microstructure - sensations
    Texture perception of food is a dynamic phenomenon depending on food properties and oral processing. Several sensory techniques enable to measure texture perception over time. The aim of this study was to compare quantitative descriptive analysis (QDA), temporal dominance of sensation (TDS) and progressive profiling in the assessment of dynamic texture of emulsion filled gels varying in fracture stress (low/high), fracture strain (low/high) and oil release (oil droplets bound/unbound to the gel matrix). The QDA results revealed that the variation of mechanical properties led to significant differences in texture properties perceived at first bite (firmness and brittleness). Texture attributes perceived at later stages of mastication showed significant differences between gels depending on the first bite properties e.g. soft gels were perceived as more melting. Progressive profiling showed that creaminess increased over eating time while firmness decreased. TDS results were in agreement with the other methods and additionally conveyed information on the succession of perceived attributes over time. The TDS sensory trajectories demonstrated that for all gels dynamic perception evolved in a similar fashion but samples with a high or low fracture strain differed at the end of oral processing. We conclude that texture perception of semi-solid gels is dynamic and can be measured by either of the three sensory methods. The mechanical properties of the gels influence the perception of texture attributes at first bite and at later stages of mastication. QDA, TDS and progressive profiling gave matching and complementary results in the assessment of dynamic sensory texture.
    Modulating fracture properties of mixed protein systems
    Ersch, C. ; Laak, I. ter; Linden, E. van der; Venema, P. ; Martin, A. - \ 2015
    Food Hydrocolloids 44 (2015). - ISSN 0268-005X - p. 59 - 65.
    egg white gels - whey-protein - thermodynamic incompatibility - textural characteristics - rheological properties - structural-properties - large-deformation - phase-separation - milk gels - gelatin
    To design foods with desired textures it is important to understand structure build-up and breakdown. One can obtain a wide range of structures using mixtures of different structuring ingredients such as for example protein mixtures. Mixed soy protein isolate (SPI)/gelatine gels were analyzed for their linear rheological properties, fracture properties and microstructure. The two ingredients were found to form independent networks despite changes in the SPI microstructure, which were attributed to micro phase separation. It is shown that mixing of SPI and gelatine allows to arrive at a large variety of fracture properties. This provides opportunities for tailoring textures in foods using mixed independent gel networks. The fracture stress of mixed gels corresponded to the fracture stress of the strongest of the two gels. At constant fracture stress, increasing Young's modulus of the mixed independent gels resulted in reduced fracture strain.
    High internal phase emulsion gels (HIPE-gels) created through assembly of natural oil bodies
    Nikiforidis, C.V. ; Scholten, E. - \ 2015
    Food Hydrocolloids 43 (2015). - ISSN 0268-005X - p. 283 - 289.
    protein-stabilized emulsions - concentrated emulsions - rheological properties - sunflower-seed - body emulsions - maize germ - physicochemical stability - physical stability - ratio emulsions - yield-stress
    A natural emulsion was used to create a high internal phase emulsion (HIPE) gel with elastic properties, indicated by shear elastic moduli between 102 and 105 Pa. The elasticity of the gel network was provided from a 2D-gel network of proteins which were naturally adsorbed at the interface of an oil-in-water emulsion formed after aqueous extraction of oil bodies from sunflower seeds. Extensive centrifugation of the obtained emulsion resulted in a stable ultrahighly concentrated emulsion with an oil volume fraction of 0.91 and a protein content of 2.5 wt% only. This high volume fraction of the emulsion cream was achieved due to the large deformability (low rigidity) of the oil body surface. After formation of the HIPE, the rigidity of the interfacial network was increased by addition of small concentrations of Ca2+ and heating at 72 °C for 10 min. This led to aggregation of the interfacial proteins, thereby forming a 2D interfacial gel providing a space-spanning network. The behaviour of the self-supporting gel exhibited increased elastic behaviour, determined by the increased elastic modulus of the interfacial network. The balance between the low rigidity upon formation and the increased rigidity after formation offers a tempting strategy to produce structured solid matter that contains edible hydrophobic liquids. Additionally, the followed procedure is cost-effective and friendly to the environment.
    Incorporation of Mesoporous Silica Particles in Gelatine Gels: Effect of Particle Type and Surface Modification on Physical Properties
    Perez-Esteve, E. ; Oliver, L. ; Garcia, L. ; Nieuwland, M. ; Jongh, H.H.J. de; Martinez-Manez, R. ; Barat, J.M. - \ 2014
    Langmuir 30 (2014)23. - ISSN 0743-7463 - p. 6970 - 6979.
    gate-like scaffoldings - controlled-release - filled gels - drug-delivery - polymer nanocomposites - rheological properties - mechanical-properties - nanoparticles - deformation - fracture
    The aim of this work was to investigate the impact of mesoporous silica particles (MSPs) on the physicochemical properties of filled protein gels. We have studied the effect of the addition of different mesoporous silica particles, either bare or functionalized with amines or carboxylates, on the physical properties of gelatine gels (5% w/v). Textural properties of the filled gels were investigated by uniaxial compression, while optical properties were investigated by turbidity. The MSPs were characterized with the objective of correlating particle features with their impact on the corresponding filled-gel properties. The addition of MSPs (both with and without functionalization) increased the stiffness of the gelatine gels. Furthermore, functionalized MSPs showed a remarkable increase in the strength of the gels and a slight reduction in the brittleness of the gels, in contrast with nonfunctionalized MSPs which showed no effect on these two properties. The turbidity of the gels was also affected by the addition of all tested MSPs, showing that the particles that formed smaller aggregates resulted in a higher contribution to turbidity. MSPs are promising candidates for the development of functional food containing smart delivery systems, also being able to modulate the functionality of protein gels.
    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%).
    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.
    Physical characteristics of submicron emulsions upon partial displacement of whey protein by a small molecular weight surfactant and pectin addition
    Kaltsa, O. ; Paximada, P. ; Mandala, I. ; Scholten, E. - \ 2014
    Food Research International 66 (2014). - ISSN 0963-9969 - p. 401 - 408.
    in-water emulsions - protein/surfactant interfacial interactions - competitive adsorption - sodium caseinate - plus surfactant - rheological properties - stabilized emulsions - nonionic surfactant - chitosan complexes - milk-proteins
    O/W emulsions (6% wt olive oil) were prepared at pH 3.3 using different WPI:Tween 20 weight ratios (1:0, 3:1, 1:1, 1:3, 0:1) at 1% wt total concentration. The emulsion droplet size was found to decrease with an increase in Tween 20. A minimum droplet size of d3,2 300 nm was found for Tween systems alone, similar to that found (360 nm) for a 1:1 WPI:Tween 20 combination (p <0.05). This specific composition showed a value for the interfacial tension close to that of Tween 20 alone. However, the emulsions presented low stability regardless of the WPI:Tween 20 ratio. To increase their stability, pectin was added, in various concentrations (0.2, 0.4 and 0.6% wt), using the Layer by Layer technique. In the presence of pectin, the ¿-potential of the oil droplets became negative; indicating that negatively charged pectin was absorbed onto the positively-charged droplet surface forming a secondary layer. The additional layer resulted in a wide range of emulsion stability. For all pectin concentrations, the 1:1 ratio of WPI:Tween 20 showed the highest stability. In most emulsions, extensive aggregation of oil droplets was observed, and their viscosity increased. Insufficient amounts of pectin to form the secondary layers led to bridging flocculation phenomena of oppositely charged pectin and proteins, leading to aggregation of the oil droplets. The higher the concentration of pectin, the greater the stability of the emulsion due to higher viscosity. All in all, the addition of a second layer consisting of pectin can be used to increase the stability of an emulsion containing emulsion droplets in the sub-micron range.
    Characterization of an acetyl esterase from Myceliophthorathermophila C1 able to deacetylate xanthan
    Kool, M.M. ; Schols, H.A. ; Wagenknecht, M. ; Hinz, S.W.A. ; Moerschbacher, B.M. ; Gruppen, H. - \ 2014
    Carbohydrate Polymers 111 (2014). - ISSN 0144-8617 - p. 222 - 229.
    bacterial polysaccharide xanthan - xylan esterases - carbohydrate esterases - xanthomonas-campestris - rheological properties - plant polysaccharides - enzymatic-hydrolysis - gum - transition - families
    Screening of eight carbohydrate acetyl esterases for their activity towards xanthan resulted in the recogni-tion of one active esterase. AXE3, a CAZy family CE1 acetyl xylan esterase originating from Myceliophthorathermophila C1, removed 31% of all acetyl groups present in xanthan after a 48 h incubation. AXE3 activ-ity towards xanthan was only observed when xanthan molecules were in the disordered conformation.Optimal performance towards xanthan was observed at 53¿C in the complete absence of salt, a condi-tion favouring the disordered conformation. AXE3-deacetylated xanthan was hydrolyzed using cellulasesand analyzed for its repeating units using UPLC–HILIC–ELSD/ESI–MS. This showed that AXE3 specificallyremoves the acetyl groups positioned on the inner mannose and that acetyl groups positioned on theouter mannose are not removed at all. After a prolonged incubation at optimal conditions, 57% of allacetyl groups, representing 70% of all acetyl groups on the inner mannose units, were hydrolyzed.
    Whey protein particles modulate mechanical properties of gels at high protein concentrations
    Saglam, D. ; Venema, P. ; Vries, R.J. de; Berg, L. van den; Linden, E. van der - \ 2014
    Food Hydrocolloids 38 (2014). - ISSN 0268-005X - p. 163 - 171.
    stabilized emulsion gels - beta-lactoglobulin - viscoelastic properties - rheological properties - isolate gels - mixed gels - microstructure - behavior - gelation - ph
    We have studied the influence of dense whey protein particles on the mechanical properties of whey protein isolate (WPI) gels at high protein concentrations (16–22% (w/w)). Incorporation of dense whey protein particles in the gel, while keeping the total protein concentration constant, leads to a considerably lower storage modulus. By adding protein particles, the total protein concentration of the WPI gels could be increased by 25–55% (w/w), without increasing the storage modulus of the gel. The large deformation properties of the WPI gels were also influenced by the presence of dense protein particles. Gels containing protein particles fractured at a lower strain than pure WPI gels at the same protein concentration. We conclude that protein particles can be used to modulate mechanical properties of WPI gels and are promising candidates for the development of high protein foods with improved textural properties.
    Complex interfaces in food: Structure and mechanical properties
    Sagis, L.M.C. ; Scholten, E. - \ 2014
    Trends in Food Science and Technology 37 (2014)1. - ISSN 0924-2244 - p. 59 - 71.
    in-water emulsions - by-layer technique - polyelectrolyte capsules - rheological properties - air/water interfaces - dilatational rheology - pickering emulsions - droplet deformation - protein adsorption - liquid interfaces
    Multiphase food systems (emulsions, foam) often have interfaces with a complex microstructure, formed by interfacial self-assembly of proteins, lipids, or colloidal particles. The response of these interfaces to deformations tends to be highly nonlinear and far more complex than the response of interfaces stabilized by simple low molecular weight surfactants. In this review we present an overview of various types of complex interfaces encountered in food products, and discuss their microstructure and mechanical properties. We also discuss how to properly characterize the nonlinear behavior of these interfaces, using surface rheological techniques, droplet deformation studies, and structural characterization methods.
    The potential of aqueous fractionation of lupin seeds for high-protein foods
    Berghout, J.A.M. ; Boom, R.M. ; Goot, A.J. van der - \ 2014
    Food Chemistry 159 (2014). - ISSN 0308-8146 - p. 64 - 70.
    functional-properties - isoelectric precipitation - rheological properties - thermal-damage - albus - angustifolius - ultrafiltration - sustainability - isolate - sweet
    Aqueous fractionation of protein from lupin seeds was investigated as an alternative to the conventional wet fractionation processes, which make use of organic solvents. The effect of extraction temperature was studied and the consequences for downstream processing were analysed. Omitting the extraction of oil with organic solvents resulted in a protein isolate that contained 0.02–0.07 g oil g-1 protein isolate, depending on the exact extraction conditions. Nevertheless, the protein functionality of the aqueous fractionated lupin protein isolate was similar to the conventional lupin protein isolate. The protein isolate suspension could be concentrated to 0.25 g mL-1 using ultrafiltration, which provides a relevant concentration for a range of high-protein products. Based on the results, we conclude that aqueous fractionation can be a method to lower the environmental impact of the extraction of proteins from legumes that contain water- and dilute salt-soluble proteins.
    Self-assemblies of lecithin and a-tocopherol as gelators of lipid material
    Nikiforidis, C.V. ; Scholten, E. - \ 2014
    RSC Advances : An international journal to further the chemical sciences 4 (2014)5. - ISSN 2046-2069 - p. 2466 - 2473.
    edible oils - rheological properties - reverse micelles - drug-delivery - fatty-acids - organogels - gels - mixtures - agents
    Amongst the different mechanisms that have been proposed and used to structure organogels, self-assembly of the gelators into supramolecular structures linked through non-covalent bonds is the most interesting. The gelator activity of LMGOs is often found most effective when micellar or lamellar phases are obtained, which is dependent on the gelator geometry and the specific packing parameter. Gelation can therefore be induced by altering the packing parameter of different gelators, but due to the law restrictions there are only a few edible gelators that can be used to structure edible lipids. Here, we show that a combination of a-tocopherol and phosphatidylcholine (PC) can be used to alter the packing geometry to provide supramolecular structures needed for the organogelation. We have observed that when the gelators were combined at 1:1 ratio in sunflower oil, edible organogels were obtained. The firmness of the solid-like material was enhanced when 1.0 wt% of water was added. The proposed mechanism for this assembly is that most likely cylindrical micellar structures are formed, due to combined assembly of the a-tocopherol and phosphatidylcholine, stabilized through physical interactions. Since these interactions, and the accompanied packing geometry, depends on temperature and application of external stresses, the formation of the organogels showed reversibility when the organogels were subjected to shear or when the temperature was increased to values above 35 oC. Polarized microscopy along with small angle X-ray scattering were used to provide a hypothesis for the mechanism behind the gelation.
    Linear viscoelasticity of polyelectrolyte complex coacervates
    Spruijt, E. ; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2013
    Macromolecules 46 (2013)4. - ISSN 0024-9297 - p. 1633 - 1641.
    rheological properties - discrete relaxation - dynamic properties - core micelles - time spectra - stability - diffusion - polymers - model - ratio
    Two flexible, oppositely charged polymers can form liquid-like complex coacervate phases with rich but poorly understood viscoelastic properties. They serve as an experimental model system for many biological and man-made materials made from oppositely charged macromolecules. We use rheology to systematically study the viscoelastic properties as a function of salt concentration, chain length, chain length matching, and mixing stoichiometry of model complex coacervates of poly(N,N-dimethylaminoethyl methacrylate), PDMAEMA, and poly(acrylic acid), PAA. The dynamics of making and breaking ionic bonds between the oppositely charged chains underlie all linear viscoelastic properties of the complex coacervates. We treat (clusters of) ionic bonds as sticky points and find that there is a remarkable resemblance between the relaxation spectra of these complex coacervates and the classical sticky Rouse model for single polymer systems. Salt affects all relaxation processes in the same way, giving rise to a widely applicable time–salt superposition principle. The viscoelastic properties of the complexes are very different from those of the individual components. In the complexes with a chain length mismatch, the effect of the mismatch on the viscoelastic properties is not trivial: changing the length of the polycation affects the relaxation behavior differently from changing the length of the polyanion
    Modulation of the Gelation Efficiency of Fibrillar and Sherical Aggregates by Means of Thiolation
    Munialo, C.D. ; Jongh, H.H.J. de; Broersen, K. ; Linden, E. van der; Martin, A.H. - \ 2013
    Journal of Agricultural and Food Chemistry 61 (2013)47. - ISSN 0021-8561 - p. 11628 - 11635.
    whey-protein isolate - bovine beta-lactoglobulin - sulfhydryl-groups - rheological properties - succinylated caseins - gels - heat - stability - ph - temperature
    Fibrillar and spherical aggregates were prepared from whey protein isolate (WPI). These aggregates were thiolated to a substantial degree to observe any impact on functionality. Sulfur-containing groups were introduced on these aggregates which could be converted to thiol groups by deblocking. Changes on a molecular and microstructural level were studied using tryptophan fluorescence, transmission electron microscopy, and particle size analysis. The average size (nm) of spherical aggregates increased from 38 to 68 nm (blocked variant) and 106 nm (deblocked variant) after thiolation, whereas the structure of fibrillar aggregates was not affected. Subsequently, gels containing these different aggregates were prepared. Rheological measurements showed that thiolation decreased the gelation concentration and increased gel strength for both WPI fibrillar and spherical aggregates. This effect was more pronounced upon thiolation of preformed fibrillar aggregates. The findings suggest that thiolation at a protein aggregate level is a promising strategy to increase gelation efficiency.
    Probe mobility in native phosphocaseinate suspensions and in a concentrated rennet gel: effect of probe flexibility and size
    Salami, S. ; Rondeau-Mouro, C. ; Duynhoven, J.P.M. van; Mariette, F. - \ 2013
    Journal of Agricultural and Food Chemistry 61 (2013)24. - ISSN 0021-8561 - p. 5870 - 5879.
    diffusing wave spectroscopy - glucono-delta-lactone - nmr self-diffusion - casein micelles - skim milk - rheological properties - pfg-nmr - electron-microscopy - poly(vinyl alcohol) - induced aggregation
    Pulsed field gradient nuclear magnetic resonance and proton nuclear magnetic resonance relaxometry were used to study the self-diffusion coefficients and molecular dynamics of linear (PEGs) and spherical probes (dendrimers) in native phosphocaseinate suspensions and in a concentrated rennet gel. It was shown that both the size and the shape of the diffusing molecules and the matrix topography affected the diffusion and relaxation rates. In suspensions, both translational and rotational diffusion decreased with increasing casein concentrations due to increased restriction in the freedom of motion. Rotational diffusion was, however, less hindered than translational diffusion. After coagulation, translational diffusion increased but rotational diffusion decreased. Analysis of the T2 relaxation times obtained for probes of different sizes distinguished the free short-chain relaxation formed from a few monomeric units from (i) the relaxation of protons attached to long polymer chains and (ii) the short-chain relaxation attached to a rigid dendrimer core.
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