Rennet inactivation

Emmons (1970) experienced significant inactivation when commercial pepsin and pepsin-calf rennet mixtures were diluted with high-pH, hard water 10 min before adding them to the cheese vat. Mickelsen and Ernstrom (1972) reported that mixtures of porcine pepsin and calf rennet were stable between pH 5.0 and 6.0, but that pepsin activity was lost from the mixture aboire pH 6.0. This loss was shown to be entirely due to pepsin instability. Below pH 6.0 chymosin activity was destroyed by pepsin. 

Rennet is inactivated at the high cooking temperatures used in Swiss and Mozzarella but is still active in Cheddar curd cooked to 39 °C (Matheson 1981). Residual rennet activity has implications for the subsequent ripening of the cheese. 

However, conflicting results have been reported concerning the effect of shear on the activity of enzymes. Charm and Wong (1970) showed that the enzymes catalase, rennet, and carboxypeptidase were partially inactivated when subjected to shear in a coaxial cylinder viscometer. The remaining activity could be correlated with a dimensionless group gammatheta, where gamma and theta are the shear rate and the time of exposure to shear, respectively.10 In the case... 

Protein immunochemistry has been used also to verify the presence, the nature, and the origin of a number of enzymes currently used in the food industry, since immunochemical techniques allow detection of these additions even after the original activity of the enzyme is lost upon stabilization of the product (e.g., by heat treatment or by addition of enzyme-inactivating agents), or when measurement of the enzyme activity does not provide hints as for its origin (as is the case for many rennetting enzymes used in the dairy industry). 

---