Water holding of protein gels

Abstract Food products are typically multicomponent systems, where often the spatial volume is set by a protein continuous network. The ability of protein-based food products to entrap water and to prevent its exudation upon mechanical deformation is important for the texture and thus sensory perception of food products. Understanding of structural origins that determine gel water holding is therefore essential, and would allow designing foods with controlled sensory perception. Water removal from the gel (quantity, kinetics and mechanism) is related to the coarseness and deformation of the network. An understanding of the interplay between the effect of coarseness and stiffness on WH in fine and coarse gels allows one to take a better control and tune juiciness and the release of tastants from food products

Permeability of gels is set by the impulse applied on the gel

To better understand sensory perception of foods, water exudation studies on protein-based gels are of a high importance. It was aimed to study the interplay of gel coarseness and gel stiffness on water holding (WH) and water flow kinetics from the gel once force is applied onto the material. Ovalbumin heat-set gels were used as a model system, where protein volume fraction was kept constant and ionic strength was varied to obtain a range of different gel morphologies and stiffness. WH of gels was measured both as a function of time and force applied. From experimental data (i) an effective gel permeability coefficient and (ii) an effective water flux coefficient were obtained and related to gel coarseness and stiffness. Gel coarseness determined maximum amount of water removed from the gel at defined conditions, where lower (=0.1 µm) and upper (=0.4 µm) limiting scales for water removal were identified. Gel stiffness is the major determinant for water removal kinetics from the gel. The combination of gel coarseness and gel stiffness showed a cooperative effect on gel WH. The insights can be exploited in product development to predict and tune oral perception properties of (new) products

Protein Aggregates May Differ in Water Entrapment but Are Comparable in Water Confinement

Aggregate size and density are related to gel morphology. In the context of the water distribution in complex food systems, in this study, it was aimed to investigate whether protein aggregates varying in size and density differ in entrapped and confined water. Heat-set soy protein aggregates (1%, v/v) prepared in the presence of 3.5 mM divalent salts increased in size and decreased in apparent density following the salt type order MgSO4, MgCl2, CaSO4, and CaCl2. In the absence of applied (centrifugal) forces, larger and less dense aggregates entrap more water. When force is applied from larger and more deformable aggregates, more water can be displaced. Entrapped water of ∼8-13 g of water/g of protein is associated with (pelleted) aggregates, of which approximately 4.5-8.5 g of water/g of protein is not constrained in exchangeability with the solvent. The amount of confined water within aggregates was found to be independent of the aggregate density and accounted for ∼3.5 g of water/g of protein. Confined water in aggregates is hindered in its diffusion because of physical structure constraints and, therefore, not directly exchangeable with the solvent. These insights in the protein aggregate size and deformability in relation to water entrapment and confinement could be used to tune water holding on larger length scales when force is applied

Permeability of gels is set by the impulse applied on the gel

To better understand sensory perception of foods, water exudation studies on protein-based gels are of a high importance. It was aimed to study the interplay of gel coarseness and gel stiffness on water holding (WH) and water flow kinetics from the gel once force is applied onto the material. Ovalbumin heat-set gels were used as a model system, where protein volume fraction was kept constant and ionic strength was varied to obtain a range of different gel morphologies and stiffness. WH of gels was measured both as a function of time and force applied. From experimental data (i) an effective gel permeability coefficient and (ii) an effective water flux coefficient were obtained and related to gel coarseness and stiffness. Gel coarseness determined maximum amount of water removed from the gel at defined conditions, where lower (=0.1 µm) and upper (=0.4 µm) limiting scales for water removal were identified. Gel stiffness is the major determinant for water removal kinetics from the gel. The combination of gel coarseness and gel stiffness showed a cooperative effect on gel WH. The insights can be exploited in product development to predict and tune oral perception properties of (new) products

Origin of Water Loss from Soy Protein Gels

Water holding (WH) of soy protein gels was investigated to identify which length scales are most contributing to WH when centrifugal forces are applied. More specifically, it was attempted to differentiate between the contributions of submicron and supramicron length scales. MgSO4 and MgCl2 salt specificities on soy protein aggregation (submicron contribution) were used to create different gel morphologies (supramicron contribution). Obtained results showed that the micrometer length scale is the most important contribution to WH of gels under the applied deformation forces. WH of soy protein gels correlated negatively with Young?s modulus and positively with recoverable energy. The occurrence of rupture events had only a limited impact on WH. The ease by which water may be removed from the gel, but not the total amount, seemed to be related to the initial building block size. These insights could be exploited in product development to predict and tune oral perception properties of (new) products

Origin of Water Loss from Soy Protein Gels

Water holding (WH) of soy protein gels was investigated to identify which length scales are most contributing to WH when centrifugal forces are applied. More specifically, it was attempted to differentiate between the contributions of submicron and supramicron length scales. MgSO4 and MgCl2 salt specificities on soy protein aggregation (submicron contribution) were used to create different gel morphologies (supramicron contribution). Obtained results showed that the micrometer length scale is the most important contribution to WH of gels under the applied deformation forces. WH of soy protein gels correlated negatively with Young?s modulus and positively with recoverable energy. The occurrence of rupture events had only a limited impact on WH. The ease by which water may be removed from the gel, but not the total amount, seemed to be related to the initial building block size. These insights could be exploited in product development to predict and tune oral perception properties of (new) products

Water holding of soy protein gels is set by coarseness, modulated by calcium binding, rather than gel stiffness

This work aims to differentiate between the contributions to water holding (WH) by gel microstructure and network stiffness of soy protein (SP) gels. SP were succinylated to increase calcium binding affinity, and the presence of different calcium salts were used to generate gels with different morphologies while keeping ionic strength and protein concentration constant. It was found that not gel stiffness, but coarseness (gel microstructure inhomogeneity) is more dominant in setting the WH ability. A higher energy dissipation of applied stress onto the protein network was related to inability of a gel network to retain water.</p

Gelatin increases the coarseness of whey protein gels and impairs water exudation from the mixed gel at low temperatures

To understand the origin of water holding of mixed protein gels, a study was performed on water exudation from mixed whey protein (WP)-gelatin gels upon applied pressure. Mixed gels were prepared with varying WP and gelatin concentration and gelatin type to obtain gels with a wide range of gel properties. Gels were characterized for their water holding (maximum of exuded water, Amax, and ease with which water can be exuded, k), gel coarseness (from CLSM image analysis) and gel stiffness (Young's modulus) at 20 and 40 °C, below and above the melting temperature of gelatin. Gelatin caused an increase in gel coarseness of the WP network, as induced by phase separation between WP and gelatin. The effect of gel coarseness and gel stiffness on Amax was found to be intertwined but above all, dictated by the gelatin concentration and gelatin network. At 20 °C, a transition point in gelatin concentration was observed above which stiffness surpassed coarseness in importance for Amax. Above this concentration, gelatin dominates the mechanical response of the mixed system. At 40 °C, when gelatin is melted, coarser and less stiff networks, as set by the WP network, lead to higher Amax. Tailoring of the coarseness and stiffness and therefore Amax and k, can be achieved by selective mixing in terms of protein concentrations, and type of gelatin. By varying gelatin type from A to B, altered phase behavior leads to gels with higher coarseness and lower stiffness but similar Amax

Water holding as determinant for the elastically stored energy in protein-based gels

To evaluate the importance of the water holding capacity for the elastically stored energy of protein gels, a range of gels were created from proteins from different origin (plant: pea and soy proteins, and animal: whey, blood plasma, egg white proteins, and ovalbumin) varying in network morphology set by the protein concentration, pH, ionic strength, or the presence of specific ions.The results showed that the observed positive and linear relation between water holding (WH) and elastically stored energy (RE) is generic for globular protein gels studied. The slopes of this relation are comparable for all globular protein gels (except for soy protein gels) whereas the intercept is close to 0 for most of the systems except for ovalbumin and egg white gels. The slope and intercept obtained allows one to predict the impact of tuning WH, by gel morphology or network stiffness, on the mechanical deformation of the protein-based gel. Addition of charged polysaccharides to a protein system leads to a deviation from the linear relation between WH and RE and this deviation coincides with a change in phase behavior.<br/