Origin of water loss from soy protein gels

Exploring changes in aggregation and gel network morphology of soybean protein isolate induced by pH, NaCl, and temperature in view of interactions

The texture of soybean protein-based products is primarily influenced by the aggregation and gel morphology of the protein, which is modulated by manufacturing factors. Interactions involved in protein morphology changes include disulfide bonds, hydrophobic interactions, electrostatic interactions, and hydrogen bonds. Notably, an interaction perspective probably provides a new way to explaining the aggregation and gel morphology, which could help overcome the hurdle of developing a textured product. Based on the interaction perspective, this review provides detailed information and evidence on aggregation, conformational stability, and gel network morphology of soybean protein and its components induced by pH, NaCl, and temperature. pH-induced electrostatic interactions and hydrogen bonds, NaCl-induced electrostatic interactions, and temperature-induced hydrophobic interactions and disulfide linkages are the main motivations responsible for changes in soybean aggregation and gel morphology. By reducing the proportion of strong-interactions, such as disulfide linkages and hydrophobic interactions, and increasing the proportion of weak-interactions, such as electrostatic interactions and hydrogen bonds, the protein total surface area expands, indicating increased conformational stretching and decreased cohesion. This possibly results in reduced hardness and increased toughness of textured proteins. The opposite effect can be observed when the proportion of strong interactions is increased and that of weak interactions is decreased.

Insight into the mechanism of the decrease in mechanical strength and water-holding capacity of gels made from oxidized gelatin

The purpose of this study was to investigate the effect of oxidation on the physicochemical properties of gelatin and gelatin gels. Porcine skin gelatin was oxidized with different concentrations of H2O2 (0-30 mM). Upon oxidation of gelatin, a significant modification of amino acid residues including glycine, proline, hydroxyproline, and hydroxylysine occurred. Zeta-potential, ordered secondary structure and the fraction of triple-helix decreased, while particle size and surface hydrophobicity increased. Gels made from oxidized gelatin showed a looser network structure indicated by scanning electron microscope, and the gels had a weakened mechanical strength and water-holding as compared to non-oxidized gelatin gels. Based on these results, a mechanism of how oxidation affects the gelatin gel properties was proposed: Oxidation-induced increase of hydrophobicity and decrease of net charges promoted aggregation between gelatin molecules, thereby limiting the formation of triple-helix, which subsequently leads to a loose network structure and eventually a weakened gel strength and water-holding capacity.

Single Ultrasonic-Assisted Washing for Eco-Efficient Production of Mackerel (Auxis thazard) Surimi

This study highlights a promising single washing method for producing dark-fleshed mackerel surimi aided by ultrasonication in conjunction with cold carbonated water containing 0.6% NaCl and mixed antioxidants (0.5% EDTA/0.2% sodium erythorbate/0.2% sodium tripolyphosphate) (CSA). Different washing periods (5, 10, and 15 min) with and without ultrasound were tested. Unwashed mince (A1) and conventional water-washed surimi (10 min/cycle, 3 cycles) (A2) were used as controls. A3, A4, and A5 were subjected to ultrasound-assisted washing for 5, 10, and 15 min, respectively, whereas A6, A7, and A8 had non-ultrasound-assisted washing for 5, 10, and 15 min. Results showed that the surimi yield decreased as the ultrasonic treatment time increased from 5 to 15 min (p < 0.05). Increased ultrasonic time resulted in greater protein denaturation, protein oxidation, myoglobin removal, and lipid oxidation in surimi (p < 0.05). Surimi produced by CSA ultrasonication for 5 min (A3), on the other hand, had a comparable overall quality to A2 surimi (p > 0.05). The correspondence gel (A3) outperformed the control gel (A2) in terms of gel strength, whiteness, and water-holding capacity (p < 0.05). The formation of regularly continuous, more organized, and smooth network structures in surimi gel was observed in A2 and A3 gels, whereas sparse and larger pore sizes were noticed in surimi gels produced by longer ultrasonic treatment. All of the surimi gels had identical FTIR spectra, indicating that the functional groups of the protein gel were consistent throughout. As a result, a single 5 min CSA-ultrasonic washing could potentially yield surimi of comparable quality to conventional washing. This could pave the way for the development of dark-fleshed fish surimi, which would require less washing time and produce less waste water.

Quantifying techno-functional properties of ingredients from multiple crops using machine learning

Food ingredients with a low degree of refining consist of multiple components. Therefore, it is essential to formulate food products based on techno-functional properties rather than composition. We assessed the potential of quantifying techno-functional properties of ingredient blends from multiple crops as opposed to single crops. The properties quantified were gelation, viscosity, emulsion stability, and foaming capacity of ingredients from yellow pea and lupine seeds. The relationships were quantified using spline regression, random forest, and neural networks. Suitable models were picked based on model accuracy and physical feasibility of model predictions. A single model to quantify the properties of both crops could be created for each techno-functional property, albeit with a trade-off of higher prediction errors as compared to models based on individual crops. A reflection on the number of observations in each dataset showed that they could be reduced for some properties.

Optimising Soy and Pea Protein Gelation to Obtain Hydrogels Intended as Precursors of Food-Grade Dried Porous Materials

Dried porous materials based on plant proteins are attracting large attention thanks to their potential use as sustainable food ingredients. Nevertheless, plant proteins present lower gelling properties than animal ones. Plant protein gelling could be improved by optimising gelation conditions by acting on protein concentration, pH, and ionic strength. This work aimed to systematically study the effect of these factors on the gelation behaviour of soy and pea protein isolates. Protein suspensions having different concentrations (10, 15, and 20% w/w), pH (3.0, 4.5, 7.0), and ionic strength (IS, 0.0, 0.6, 1.5 M) were heat-treated (95 °C for 15 min) and characterised for rheological properties and physical stability. Strong hydrogels having an elastic modulus (G') higher than 10³ Pa and able to retain more than 90% water were only obtained from suspensions containing at least 15% soy protein, far from the isoelectric point and at an IS above 0.6 M. By contrast, pea protein gelation was achieved only at a high concentration (20%), and always resulted in weak gels, which showed increasing G' with the increase in pH and IS. Results were rationalised into a map identifying the gelation conditions to modulate the rheological properties of soy and pea protein hydrogels, for their subsequent conversion into xerogels, cryogels, and aerogels.

Understanding the differences in heat-induced gel properties of twelve legume proteins: A comparative study

This study aimed to investigate the rheological and textural properties of heat-induced gels from twelve legume protein isolates at pH 3.0 and 7.0, including black kidney bean (BKPI), speckled kidney bean (SKPI), panda bean (PDPI), cowpea (CPPI), mung bean (MPI), adzuki bean (API), rice bean (RPI), black soybean (BPI), soybean (SPI), chickpea (CPI), broad bean (BRPI) and pea (PPI). SDS-PAGE revealed that 7S globulin was prominent protein in BKPI, SKPI, PDPI, CPPI, MPI, API and RPI, the main protein fraction of CPI was 11S globulin, and BPI, SPI, BRPI and PPI contained both 7S and 11S globulins as major components. Based on the gel's Power Law constant (K') and hardness, twelve legume proteins were divided into three categories with high, medium and low gel strength. BKPI, SKPI and PDPI with Phaseolin being the major protein fraction showed high gel strength regardless of pH. Electrostatic interactions, hydrophobic interactions and hydrogen bonds were the most important intermolecular forces in the formation of legume protein gel networks, of which gel strength at pH 3.0 and pH 7.0 was significantly affected by electrostatic interactions and hydrogen bonds, respectively. Moreover, gel strength was also remarkably negatively influenced by the non-network proteins. SEM observation indicated that the microstructure of gels at pH 7.0 was denser and more homogeneous than that at pH 3.0, leading to better water holding capacity. These findings would be of great importance for understanding the differences in legume protein gels, and also laid the scientific support for expanding applications of legume proteins in gel-based foods.

The Comprehensive Utilization of Bean Dregs in High-Fiber Tofu

A large quantity of bean dregs is produced by the production of tofu and treated as animal feed or plant fertilizer, which could cause environmental pollution. The purpose of this study was to use commercially available lactone tofu to compare the effects of innovative preparation methods of high-fiber tofu, where the innovative methods used partial de-slagging followed by the addition of soybean residue cellulose to prepare high-fiber tofu. The results showed that there were no significant differences among lactone tofu samples made with 5% cellulose, 10% cellulose, or 15% cellulose and the commercially available lactone tofu during the water-holding capacity and chroma analysis. Texture indices showed that lactone tofu with 10% cellulose was similar to the commercially available lactone tofu in chewiness and hardness, and lactone tofu with 15% cellulose was similar to the commercially available lactone tofu in adhesiveness and chewiness. Magnetic resonance imaging displayed that lactone tofu with 10% cellulose had better water retention and higher moisture content. Gel electron microscopy showed that lactone tofu with 10% cellulose achieved a better gel network, and the bean dreg cellulose had less influence to a certain extent. Volatile organic compound testing by GC-IMS method indicated that the lactone tofu with 10% cellulose had more volatile organic compound content. In conclusion, these results demonstrated that lactone tofu with 10% cellulose had the best market competitiveness in ensuring the quality of high-fiber tofu.

Effect of dry heating on egg white powder influencing water mobility and intermolecular interactions of its gels

BACKGROUND

Dry heat processing remains the most promising and simple approach for achieving better gelling properties of spray-dried egg white powder (EWP). Water mobility and intermolecular interactions in gels derived from EWP were investigated after subjecting EWP to various dry heating times (0-21 days).

RESULTS

The gel hardness and water-holding capacity significantly increased with an increase in dry heating time (P < 0.05), and both parameters were positively correlated with gel transparency. In contrast to the coarser structure of untreated EWP gel, the gel of EWP corresponding to 15 days of dry heating time had a fine-stranded and orderly network structure with smaller pores. An increase in the binding force between the gel and water was observed with an increase in dry heating time due to the formation of more 'protein-water' hydrogen bonds. Increasing the dry heating time resulted in an increase in the contribution of disulfide bonds, which in turn made a significant contribution to the rigidity of the EWP gels. By contrast, a decrease in the contribution of ionic bonds and hydrophobic interactions upon increasing the dry heating time promoted the formation of orderly networks.

CONCLUSIONS

Overall, gel corresponding to EWP dry heating for 15 days had better gel properties, the highest transparency and water-holding capacity, as well as a fine-stranded and orderly network structure. These results provide more information on improvement of the gel properties of EWP through dry heat treatment. © 2020 Society of Chemical Industry.

Soy/whey protein isolates: interfacial properties and effects on the stability of oil-in-water emulsions

BACKGROUND

The adsorption of proteins at oil/water interfaces can reduce interfacial tension and increase emulsion stability. However, emulsions stabilized by soy protein isolate (SPI) are not sufficiently stable. Using SPI as a control, a theoretical basis for the adsorption behavior of mixed SPI and whey protein isolate (WPI) at the oil/water interface was established and the effects of the protein ratio and content on the emulsion stability were studied.

RESULTS

Compared to SPI solution, SPI-WPI mixed solutions were found to reduce the size distribution of emulsion droplets and significantly improve the emulsion stability. Among the studied protein contents and ratios, the protein content of 0.2 g kg^-1 and SPI/WPI mass ratio of 1:9 offered the lowest creaming stability index (15%), the smallest droplet size (278 nm), and the largest absolute value ζ-potential (35 mV), i.e. the emulsion stability was excellent. The largest dilatational modulus (10.08 mN m^-1 ), dilatational elasticity (10.01 mN m^-1 ), and dilatational viscosity (1.18 mN m^-1 ), were observed with a protein content of 0.15 g kg^-1 (SPI/WPI ratio of 1:9), along with a high interfacial protein adsorption capacity (47.33%). SPI-WPI complexes form a thick adsorption layer around oil droplets, resulting in an increase of the expansion modulus of the interfacial layer.

CONCLUSION

SPI-WPI complexes can form a thick adsorption layer around oil droplets, resulting in increased expansion modulus of the interfacial layer, which improves emulsion stability. © 2020 Society of Chemical Industry.

Soy Protein Pressed Gels: Gelation Mechanism Affects the In Vitro Proteolysis and Bioaccessibility of Added Phenolic Acids

In this study, a model system of firm tofu (pressed gel) was prepared to study how the coagulation mechanism-acidification with glucono δ-lactone (GDL) or coagulation with magnesium sulphate (MgSO₄)-affected the physical properties of the gels along with their in vitro proteolysis (or extent of proteolysis). The two types of gels were also fortified with 3.5 mM protocatechuic (PCA) and coumaric acid (CMA) to test whether they can be used as bioactive delivery systems. Texture analysis showed that all MgSO₄-induced gels (fortified and control) had a higher hydration capacity and a weaker texture than the GDL-induced gels (p < 0.05). MgSO₄ gels had almost double proteolysis percentages throughout the in vitro digestion and showed a significantly higher amino acid bioaccessibility than the GDL gels (essential amino acid bioaccessibility of 56% versus 31%; p < 0.05). Lastly, both gel matrices showed a similar phenolic acid release profile, on a percentage basis (~80% for PCA and ~100% for CMA). However, GDL gels delivered significantly higher masses of bioactives under simulated intestinal conditions because they could retain more of the bioactives in the gel after pressing. It was concluded that the coagulation mechanism affects both the macro- and microstructure of the soy protein pressed gels and as a result their protein digestibility. Both pressed gel matrices are promising delivery systems for bioactive phenolic acids.

Relationship between gel properties and water holding of ovalbumin-carboxymethylcellulose electrostatic complex hydrogels

The relationship between the water holding (WH) and gel properties of protein-based hydrogels is important for designing and regulating the texture and sensory properties of foods. Herein, the relation among WH and heat-set gel properties of ovalbumin (OVA)-carboxymethylcellulose (CMC) electrostatic complexes was explored. The results showed that the gels exhibited homogeneous and dense structure and good WH compared with pure OVA at pH 4.6, while Young's modulus decreased significantly (P < 0.05). This was closely related to the inhibition of the electrostatic interaction on the formation of large protein aggregates during heat treatment (90 °C, 30 min). Specially, the CMC1.2 (the degree of substitution was 1.2) with higher charge density showed stronger interference than CMC0.7 (the degree of substitution was 0.7) for the gel network structure and properties. Moreover, the addition of salt ions could enhance the gel strength. Meanwhile, the coarseness and microstructure pore size were also increased with enhancing of ionic strength, resulting in a significant decrease in the WH. The effective permeability coefficient (k₁) and water flux coefficient (k₂) of gels have a significant positive correlation with their network pore size, indicated that the regulation of WH of hydrogel mainly depended on controlling the pore size of its microstructure.

Properties of β-Lactoglobulin Aggregates and Gels as Affected by Ternary Emulsifier Mixtures of Tween 20, Lecithin, and Sucrose Palmitate

The influence of sucrose palmitate, Tween 20, and lecithin on the properties of heat-induced aggregates and cold-set gels of β-lactoglobulin was studied based on an experimental mixture design with a fixed total emulsifier concentration. Emulsifiers were added to the protein solution before heating. Aggregate size and absolute values of ζ potential increased with the addition of emulsifiers, among which lecithin had the most pronounced effect. The water retention of the aggregates correlated positively with the aggregate size. Gels had reduced fracture stress and strains with increasing sucrose palmitate and decreasing Tween 20 contents. The fracture properties correlated with the ζ potentials of the aggregates, and larger aggregates led to gels with higher water-holding capacities. The emulsifiers hence influenced the gel properties indirectly via the aggregate properties. The impact of emulsifiers on food structures should therefore be considered when a food product is designed.

Composite Gels Containing Whey Protein Fibrils and Bacterial Cellulose Microfibrils

In this study, we investigated the gelation of WPI fibrils in the presence of bacterial cellulose (BC) microfibrils at pH 2 upon prolonged heating. Rheology and microstructure were investigated as a function of BC microfibril concentration. The presence of BC microfibrils did not influence the gelation dynamics and resulting overall structure of the WPI fibrillar gel. The storage modulus and loss modulus of the mixed WPI‐BC microfibril gels increased with increasing BC microfibril concentration, whereas the ratio between loss modulus and storage modulus remained constant. The WPI fibrils and BC microfibrils independently form two coexisting gel networks. Interestingly, near to the BC microfibrils more aligned WPI fibrils seemed to be formed, with individual WPI fibrils clearly distinguishable. The level of alignment of the WPI fibrils seemed to be dependent on the distance between BC microfibrils and WPI fibrils. This also is in line with our observation that with more BC microfibrils present, WPI fibrils are more aligned than in a WPI fibrillar gel without BC microfibrils. The large deformation response of the gels at different BC microfibril concentration and NaCl concentration is mainly influenced by the concentration of NaCl, which affects the WPI fibrillar gel structures, changing form linear fibrillar to a particulate gel. The WPI fibrillar gel yields the dominant contribution to the gel strength.

Mixed gels from whey protein isolate and cellulose microfibrils

Whey proteins can form different gel structures ranging from fine-stranded to particulate when appropriate conditions are applied. By incorporating polysaccharides, the gelation of WPI can be influenced. We investigated the heat-induced gelation of whey protein isolate (WPI) in the presence of bacterial cellulose (BC) microfibrils at pH 7 at different concentrations of NaCl. Our results showed that WPI and BC microfibrils form a homogeneous dispersion at pH 7. Upon heating, the WPI gel was formed independently in the presence of the BC microfibril gel, resulting in the formation of a composite gel. The gel structure and gelation dynamics of WPI was not influenced by the presence of BC microfibrils. However, the presence of BC microfibrils increased the storage modulus of the WPI gel, with an increase being negligible when the strength of the WPI gel is above a certain value. With an increase of NaCl concentration, the WPI gel structure changes from fine-stranded to a particulate gel, while the BC microfibril gel structure remains unchanged. No macroscopic phase separation could be observed in the WPI-BC microfibril gels. Our results showed that the rheological properties and water holding capacity of the WPI-BC microfibril mixed gels are mainly dominated by the WPI.

Bolus matters: the influence of food oral breakdown on dynamic texture perception

This review article focuses on design of food structure, characterisation of oral processing by boli characterisation and dynamic texture perception. Knowledge of the food properties governing bolus formation and bolus properties determining temporal changes in texture perception is of major importance. Such knowledge allows academia to better understand the mechanisms underlying texture perception and food industry to improve product texture. For instance, such knowledge can be used for developing foods with desired texture perception that fit in a healthy diet or that are customized to specific consumer groups. The end point of oral processing is the formation of a safe-to-swallow bolus. The transitions of solid and soft solid foods into bolus are accompanied by tremendous modifications of food properties. The review discusses dynamic changes in bolus properties resulting in dynamic changes of texture perception during oral processing. Studies monitoring chewing behaviour are discussed to complement the relationships between bolus properties and dynamic texture perception. We conclude that texture perception evolves over mastication time and depends on food properties, such as mechanical properties, mainly in the beginning of oral processing. Towards the middle and end of oral processing, bolus properties depend on food properties and explain texture perception better than food properties.

Formation and functional properties of protein-polysaccharide electrostatic hydrogels in comparison to protein or polysaccharide hydrogels

Protein and polysaccharide mixed systems have been actively studied for at least 50years as they can be assembled into functional particles or gels. This article reviews the properties of electrostatic gels, a recently discovered particular case of associative protein-polysaccharide mixtures formed through associative electrostatic interaction under appropriate solution conditions (coupled gel). This review highlights the factors influencing gel formation such as protein-polysaccharide ratio, biopolymer structural characteristics, final pH, ionic strength and total solid concentration. For the first time, the functional properties of protein-polysaccharide coupled gels are presented and discussed in relationship to individual protein and polysaccharide hydrogels. One of their outstanding characteristics is their gel water retention. Up to 600g of water per g of biopolymer may be retained in the electrostatic gel network compared to a protein gel (3-9g of water per g of protein). Potential applications of the gels are proposed to enable the food and non-food industries to develop new functional products with desirable attributes or new interesting materials to incorporate bioactive molecules.

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.

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.

Calcium Binding Restores Gel Formation of Succinylated Gelatin and Reduces Brittleness with Preservation of the Elastically Stored Energy

To better tailor gelatins for textural characteristics in (food) gels, their interactions are destabilized by introduction of electrostatic repulsions and creation of affinity sites for calcium to "lock" intermolecular interactions. For that purpose gelatins with various degrees of succinylation are obtained. Extensive succinylation hampers helix formation and gel strength is slightly reduced. At high degrees of succinylation the helix propensity, gelling/melting temperatures, concomitant transition enthalpy, and gel strength become calcium-sensitive, and relatively low calcium concentrations largely restore these properties. Although succinylation has a major impact on the brittleness of the gels formed and the addition of calcium makes the material less brittle compared to nonmodified gelatin, the modification has no impact on the energy balance in the gel, where all energy applied is elastically stored in the material. This is explained by the unaffected stress relaxation by the network and high water-holding capacity related to the small mesh sizes in the gels.

Characterization of heat-set gels from RuBisCO in comparison to those from other proteins

To anticipate a future shortage in functional proteins, it is important to study the functionality of new alternative protein sources. Native RuBisCO was extracted from spinach, and its gelation behavior was compared to other native proteins from animal and plant origins. Protein gels were analyzed for their mechanical gel properties during small and large deformation and for their microstructure. Heat-induced aggregation and network formation of RuBisCO resulted in gels with unique characteristics compared to, for example, whey protein and egg white protein. Having a very low critical gelling concentration and low denaturation temperature, RuBisCO readily forms a network with a very high gel strength (G', fracture stress), but upon deformation it has a brittle character (low critical strain, low fracture strain). This breakdown behavior can be explained by the dominant role of hydrophobic and hydrogen bonds between RuBisCO molecules during network formation and by the coarse microstructure. RuBisCO was shown to exhibit high potential as a functional ingredient giving opportunities for the design of new textures at low protein concentration.