Covalent bonds formed in proteins during milk sterilization: studies on caseins and casein peptides.

Formation of covalent bonds at milk sterilization temperatures was studied using caseins and casein peptides. At 120 degrees C lysinoalanyl residues produced even at pH 7.0 were derived from intra-molecular interactions between phosphoserine and lysine; the conditions of formation were determined. It was also found that the formation fo isopeptidic cross-links was significant with conditions more severe than those used for milk sterilization.