Title: Degradation of Casein Fractions by Rennet Extract
Abstract: The proteolytic activity of commercial rennet on purified fractions of a,-and flcasein was studied.Products of proteolysis, soluble in 5% trichloroacetie acid, were examined by gel-filtration and by absorbancy at 280 mt~.Residual casein fractions were determined by polyacrylamidc-gel electrophoresis.Rennet enzymes appear to preferentially degrade a~-casein, fl-casein evidently is more resistant to rennet proteolysis th~n a~-casein.These findings confirm results of our studies with whole casein and suggest that successful rennet substitutes need to have the delicate differential proteolytie characteristics of rennet.Rennet extract enzymes are active proteolytieally in addition to catalyzing clot formations in most milk fermentations.Recently, polyaerylamide-gcl eleetrophoresis ( P A E ) of residual casein fractions in cheese indicated the nature of the proteolytic function of rennet in cheese ripening (3).During Cheddar cheese ripening, a~-casein was degraded earlier than fl-casein.This prompted further work on the differential proteolytie activity of commercial rennet by studying proteolysis of purified casein fractions.