Influence of heating regime and pH on the primary phase of renneting of whole milk

ABSTRACT The rate and extent of the chymosin-catalysed hydrolysis of κ-casein, together with the extent of denaturation of individual and total whey proteins, has been determined in whole milk heated on a pilot plant-scale apparatus for periods of 15 s to 5 min at temperatures between 72 and 140 °C. Denaturation of about 10% of the total whey protein resulted in partial inhibition of the reaction. Additional denaturation (up to about 60% of the total whey proteins) had no further effect on the reaction until the heating conditions were sufficiently severe to cause chemical damage to the casein(s). Inhibition of the chymosin-catalysed hydrolysis milk heated at pH values between 6.2 and 8.5 and subsequently hydrolysed at pH 6.7, was greater at pH values above about 7.0. This may be due to the solubilization of micellar κ-casein which has been reported to occur under these conditions.