Heat-Induced Changes in the Proteins of Whey Protein Concentrate

Three-level fractional factorial experiments were used to study effects of heating conditions (pH, time, temperature, solids content, calcium addition) on whey protein concentrate. Increasing pH and temperature led to lower solubility at pH 4.6 and 7.0, lower sulfhydryl content, higher hydroxymethylfurfural, generally darker color, lower DNBS-available lysine and altered pepsin pancreatin digestion profiles. Mercaptoethanol and SDS demonstrated relative importance of disulfide and hydrophobic bonds on solubility loss. Polyacrylamide gel electrophoresis indicated heat stability of proteose peptones; susceptibility was greatest at pH 8.0, 95°C for β-lactoglobulin and α-lactalbumin, and pH 4.6, 95°C for bovine serum albumin. HPLC gel filtration showed that heating rendered a high molecular weight fraction undissociable by mercaptoethanol.