Increasing the hydrophobicity of the heat-induced whey protein complexes improves the acid gelation of skim milk

The formation of whey protein complexes during heating enhances the acid gelation of milk; hydrophobic interactions may play an important role in this acid gelation. To investigate this, the surface hydrophobicity of model heat-induced whey protein complexes was modified using acylation with various carbon chain lengths. It was determined that the size and thiol/disulfide distribution of the complexes were unaffected, and that the change in their apparent isoelectric point could be restricted within 0.5 pH unit. These complexes were added to whey protein-free skim milk systems and the resulting acid-gelation behaviour of the milk samples was measured. Increasing the hydrophobicity of the heat-induced whey protein complexes significantly increased the pH of gelation of the milk samples and strongly affected the final properties of the acid gels, demonstrating both the importance of the heat-induced complexes and the relevance of hydrophobic interactions in the acid-induced gelation of preheated milk.