Gelling and emulsifying properties of soy protein hydrolysates in the presence of a neutral polysaccharide.

Soy protein hydrolysates (SPH) with different degrees of hydrolysis (DH 0-16%) were obtained by varying the time of hydrolysis with bromelain. The objective of this study was to evaluate how selected techno-functional properties (gelation, emulsification) of SPH were affected by the presence of a non-gelling polysaccharide. A slight hydrolysis was beneficial to increase gel strength. Also, the emulsifying activity was improved for low DHs, whereas hydrolysis was detrimental for emulsion stability. Under certain conditions the presence of the non-gelling polysaccharide was beneficial to improve SPHs' functional properties, but the effect was in general complex and strongly dependent on both biopolymers' concentration and molecular weight. Nevertheless, it was demonstrated that by using SPH and galactomannan mixtures and controlling the biopolymers' concentration and molecular weight, improved functionalities can be obtained with useful applications in food formulation.

Effect of the molecular weight of a neutral polysaccharide on soy protein gelation.

The effects of galactomannans with different molecular weights on the heat-induced gelation characteristics of soybean protein were investigated using dynamic small-strain rheometry, under conditions where the proteins carry a net negative charge (pH7). Microstructure of the resulting gels was investigated by confocal laser scanning microscopy. Phase-separated systems were obtained with different morphologies and degree of phase separation, depending on both biopolymer concentrations and polysaccharide molecular weight. In general, a gelling enhancing effect on soy proteins was verified, despite extensive phase-separation processes observed at the higher polysaccharide molecular weight. This effect was demonstrated by an increase of the gelation rate, a decrease in the temperature at the onset of gelation, and an increase of gel stiffness and elastic character, with the length of polysaccharide chains. Overall, the results obtained established that the judicious selection of the galactomannan molecular weight may be used to modify the structure and gelation properties of soy proteins, originating a diversity of rheological characteristics and microstructures that will impact on the design of novel food formulations.

Influence of galactomannans with different molecular weights on the gelation of whey proteins at neutral pH.

The effect of locust bean gum, a galactomannan, with different molecular weights on the microstructure and viscoelastic properties of heat-induced whey protein gels has been studied using confocal laser scanning microscopy and small-deformation rheology. The results obtained clearly showed that differences in the molecular weight of the polysaccharide have a significant influence on the gel microstructure. Homogeneous mixtures and phase-separated systems, with dispersed droplet and bicontinuous morphologies, were observed by changing the polysaccharide/protein ratio and/or the molecular weight. At 11% whey protein, below the gelation threshold of the protein alone, the presence of the nongelling polysaccharide induces gelation to occur. At higher protein concentration, the main effect of the polysaccharide was a re-enforcement of the gel. However, at the higher molecular weight and concentration of the nongelling polymer, the protein network starts to lose elastic perfection, probably due to the formation of bicontinuous structures with lower connectivity.