Action of Rennin and Pepsin on β-Casein: Insoluble and Soluble Products

Abstract

β-Casein was hydrolyzed to a considerable extent by the enzymes pepsin and rennin at pH 6.4. Pepsin hydrolyzed β-casein more extensively than rennin when given sufficient time. Hydrolysis of β-casein was evidenced by an increase in solubility at pH 4.7, and an increase in solubility in 2% trichloroacetic acid (TCA). Solubility in 12% TCA was about the same before and after enzyme treatment; hence, it was not a suitable reagent for demonstrating hydrolysis. The insoluble portion (pH 4.7; 2% TCA) of β-casein after enzyme treatment was heterogeneous, containing at least three components. The soluble fraction was very heterogeneous and contained ten or more components. The major products released by rennin and pepsin have similar electrophoretic behavior, but there were differences among the minor products.