Influence of pH and calcium chloride on the high-pressure-induced aggregation of a whey protein concentrate

Protein denaturation and aggregation of a whey protein concentrate (WPC) as induced by pressure (400 MPa for 30 min) at a protein concentration of 2.2%, has been studied at; pH 5, 6, and 7 and at calcium concentrations ranging from 0 to 7.0 mM. Protein modifications were studied by solubility assays, HPLC, and SDS-PAGE of the soluble protein fraction at pH 4.6. Whey proteins remained most soluble after pressurization at pH 6; the lowest solubility was encountered at pH 5. An increase in calcium concentration reduced overall solubility of whey proteins after pressurization at pH 6 and 7 but not at pH 5. HPLC and SDS-PAGE measurements of the soluble protein fraction at pH 4.6 demonstrated that the amount of native beta-lactoglobulin was reduced significantly after pressurization, in contradiction to alpha-lactalbumin, for which no significant changes were noticed.