Effect of lactosylation on plasmin-induced hydrolysis of β-casein

The inhibition of the plasmin-induced hydrolysis of β-casein was explored by decreasing β-casein availability through lactosylation. As plasmin hydrolyses proteins on the carboxyl site of lysine and arginine residues, with a preference for lysine, the lysine residues on the β-casein backbone were targeted. The results indicated that modification of lysine affects plasmin-induced hydrolysis negatively in proportion to the increase in the lactosylation level and independent of the stages of the Maillard reaction. Early stages of the Maillard reaction, e.g., lactosylation, involve the attachment of lactose at the ε-amino group of lysine and advanced stages involve cross-linking, thus modifying lysine and making it unrecognisable to plasmin; in addition, the cross-linking may affect the release of plasmin-generated peptides. These results indicate that lactosylation can be used to control the plasmin-induced hydrolysis of milk proteins and the mechanism can be useful for generating a plasmin-resistant protein using different methods of protein modification.