Rheology and texture of hen's egg protein heat-set gels as affected by pH and the addition of sugar and/or salt

Gelation properties of whole egg, white and yolk proteins were measured with and without the addition of sugar and/or salt at varying pH values (2, 5 and 8). Sodium chloride levels varied between 6% (w/w) in the absence of sucrose and 3% (w/w) in the presence of 3% (w/w) sucrose. Increasing pH and the addition of sugar and particularly salt resulted in elevated gelation temperatures. Whole egg gels exhibited higher levels of firmness as compared to yolk and white. A linear relationship between whole egg and yolk gel strength and pH was observed. Cohesion strength was higher for all egg samples at pH 5 and pH 8 than at pH 2 with white demonstrating the highest increase. Adhesiveness was highest at pH 5 for whole egg and white, whereas it remained relatively constant for yolk at all pH. The effect of sugar and salt on the cohesion strength and adhesiveness of egg gels was not pronounced. Nevertheless, significant differences of gel hardness were detected for egg yolk and white, which were attributed to the addition of sugar and/or salt. Native PAGE indicates that when heated, both yolk and white proteins unfold and interact to form high-molecular weight aggregates.