Effect of Heat Treatments in Very Acidic Conditions on Whey Protein Isolate Properties

The effect of heat treatments of whey protein isolate was studied under very acidic conditions.Dispersions of whey protein isolate in .1 M HCl (PH 1.2 to 1.3) were heated at 90°C for 0 to 120 min, adjusted to pH 6.9, dialyzed, and freeze-dried.The resulting isolates were characterized for protein solubility at different pH and for the extent of protein deamidation.Electrophoretic and calorimetric behavior, light transmittance of heated dispersions, and gelling properties were also determined.Thermal treatments produced several protein alterations: protein denaturation, partial deamidation, and a decrease of 0-LG.a-LA, and BSA; protein species of low molecular weight and aggregates appeared at the same time.Gels prepared by dispersion of the isolate heated for 2 h in .1 M HCl exhibited very low elasticity, firmness, and water-holding capacity.However, texture characteristics of gels of whey protein isolate heated for 0 to 60 min in .lM HCl did not differ in spite of protein changes during treatment.