Physical properties of heat-induced whey protein aggregates formed at pH 5.5 and 7.0

Abstract

Effects of pH on the physical properties of heat-induced whey protein aggregates were investigated using atomic force microscopy. At pH 5.5 and a protein concentration of 0.3% (w/w), micrometer-sized aggregates were formed within 1 min of heating at 80℃, while it took more than 30 min for aggregates to reach similar sizes at pH 7.0 and a protein concentration of 2.0% (w/w). The surface roughness of air-dried aggregates evaluated based on cross-sectional height data decreased by a factor of 2 with increasing pH from 5.5 to 7.0. Young’s modulus values of whey protein aggregates evaluated based on force-indentation curve measurements without drying decreased by a factor of 3 with increasing pH from 5.5 to 7.0. The present results suggest that heat-induced whey protein aggregates became mechanically weaker with increasing pH due to increased inter-/intra-molecular electrostatic repulsions.