Action of Rennet on Casein as Influenced by Hydrogen Peroxide–Catalase Treatment

The effect of hydrogen peroxide-catalase treatment upon the release o£ glycomacropeptide by rennet from casein in skimnfilk and caseinate-ultrafiltrate systems and on clotting time of these materials was investigated.The hydrogen peroxide-catalase treatment of skimmilk and caseinate-ultrafiltrate systems retarded the release o£ glycomacropeptide from K-casein by rennin.The peroxide-catalase treatment also reduced the rate and the completeness of casein clotting by rennin in skimmilk and caseinate-ultrafiltrate systems.The peroxide-catalase treatment of skimmilk reduced the methionine conten~ of isoelectric casein by about 19% but had no effect upon the methionine content of rennet curd prepared from skimmilk or caseinat e-ultrafiltrate systems.Peroxide oxidation of methionine, the ~-terminal amino acid in the glycomacropeptide moiety of ~-casein, was therefore implicated as a possible cause for retarding the primary action of rennin upon casein.Results indicate that the softness of cheese made from peroxide-catalase-treated milk may be due to the inhibitory effect of peroxide upon the primary action of rennin upon casein and on clot formation.