Ana M. R. Pilosof

Functional properties of soy protein isolates as affected by heat treatment during isoelectric precipitation

Research was carried out on the influence of heat treatment during isoelectric precipitation on the functionality of the resulting isolates prepared from “low-heated”, undenatured, defatted soy flour. The isoelectric dispersions were heated at 50°C, 60°C, 65°C or 70°C for 30 min and characterized for solubility, water absorption capacity, oil absorption capacity, viscosity and gel properties. The effect of heat treatment during isoelectric precipitation was reflected by all the functional properties. The soy isolated heated at 60°C showed remarkably different flow characteristics. It yielded the most viscous dispersions and the strongest gels and also the highest water absorption capacity value. Simple and multiple lineal regression models were used to provide a description of the relationship between the different properties studied. Significant correlations were found between gel viscosity and water absorption capacity. Gel characteristics also correlated significantly with viscosity of 20% dispersions. Viscosity of dispersions correlated to solubility or to water absorption capacity, depending on protein concentration. That dependence was quantified and a highly significant multiple correlation was found between viscosity and the independent variables of log solubility and water absorption capacity.