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Characteristics of Insoluble Pepsin Used in a Continuous Milk-Clotting System

Department of Food Science, University of Wisconsin, Madison 53706

ABSTRACT

Skimmilk acidified to pH 5.6 or 5.9 was passed through a column of pepsin-glass at 15 C, warmed to 30 C and allowed to coagulate. A typical skimmilk curd was formed. No soluble pepsin was detected in whey from such milk or in Jenness and Koops' salts solution after passage through the column. Passage of skimmilk through the column slowly inactivated the insoluble enzyme. Plowing whey at pH 5.9 inactivated the enzyme at more than twice the rate of skimmilk at pH 5.9 but Jenness and Koops' solution at pH 5.9 caused no inactivation. Nitrogen bound to pepsin-glass increased markedly when skimmilk was passed through the enzyme bed. Passage of skimmilk through 5.5-cm columns at 6.0 ml per minute or through 50-cm columns of enzyme at 50 ml per minute resulted in the same rate of inactivation of pepsin-glass. Dilute HC1, but not 4 M urea, fully reactivated pepsin-glass which had been previously inactivated with skimmilk. However, pepsin-glass reactivated or pretreated with dilute HC1 lost its enzymic activity much more rapidly than untreated pepsin-glass. Treatment with .05 M H₂0₂ sterilized pepsin-glass with no significant loss in enzymic activity.