INFLUENCE OF HEATING REGIME AND PH ON THE PRIMARY PHASE OF RENNETING OF WHOLE MILK

The rate and extent of the chymosin-catalysed hydrolysis of kappa-case in, together with the extent of denaturation of individual and total w hey, proteins, has been determined in whole milk heated on a pilot pla nt-scale apparatus for periods of 15 s to 5 min at temperatures betwee n 72 and 140 degrees C. Denaturation of about 10% of the total whey pr otein resulted in partial inhibition of the reaction. Additional denat uration (up to about 60% of the total whey proteins) had no further ef fect on the reaction until the heating conditions were sufficiently se vere to cause chemical damage to the casein(s), Inhibition of the chym osin-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 kappa-casein which has been reported to occur under these conditions.