INFLUENCE OF PH ON CHYMOSIN ACTION IN SOLUTIONS OF DIFFERENT KAPPA-CASEIN VARIANTS

Chymosin hydrolysis of kappa-casein variants A, B, or AB or heated (85 degrees C x 10 min) mixtures of kappa-casein variants plus beta-lactoglobulin A, B, or AB in buffers at pH 6.7, 6.4, 6.0, 5.6, or 5.3 were monitored spectrophotometrically at 420 nm by reaction with 2,4,6-trinitrobenzenesulfonic acid. The genetic type of kappa-casein and pH of the medium influenced the rate and extent of hydrolysis. At pH 5.3 and 5.6 kappa-casein B was most extensively hydrolyzed, but at pH 6.0-6.7 the hydrolyses of the three variants were identical. kappa-Casein A was most susceptible to hydrolysis (at pH 5.3) in heated solutions containing different genetic combinations of kappa-casein plus beta-lactoglobulin.