Effect of whey protein addition and pH on the acid gelation of heated skim milk

The impact of pH and whey protein addition on protein distributions and the properties of acid gels prepared from heated milk was studied. Adding whey protein to milk at its natural pH before heating (80 °C/30 min) increased serum-phase κ-casein and whey protein levels and produced acid gels with higher stiffness, yield stresses and yield strains. For skim milk and skim milk with added whey protein, samples heated at pH 6.5 had low levels of serum-phase protein; however, the level increased as the pH increased to 7.1. At each pH, lower levels of serum-phase proteins were in skim milk than in those with added whey protein. Acid gels had higher stiffness and yield strains as the pH of the milk at heating increased. At each milk pH, the acid gels from milk with added whey protein had higher gel stiffness and yield stresses than those without added whey protein.