INTERACTION OF BETA-LACTOGLOBULIN WITH KAPPA-CASEIN IN MICELLES AS ASSESSED BY CHYMOSIN HYDROLYSIS - EFFECTS OF ADDED REAGENTS

The effect of lysozyme, ovalbumin, retinol, sucrose, l-anilino-8-naphthalenesulfonate (ANS), sodium sulfite, sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and cetylpyridinium chloride (CPC) on heat-induced interaction of β-lactoglobulin (β-Lg) with K-casein (k-C) on intact micelles was studied by following the kinetics of chymosin hydrolysis. Heating of β-Lg with casein micelles in Jenness-Koops buffer (pH 6.8) inhibited chymosin hydrolysis, resulting in decreased ini tial velocity (Vi) and glycomacropeptide (GMP) release. Lysozyme (0.4%), CTAB (2.6 X 10-3M), and CPC (2.6 X 10-3M) prevented the inhibition of chymosin hydrolysis, possibly by neutralizing the overall negative charge on casein micelles. On the other hand, SDS (5.2 X 10-3M), ovalbumin (0.5%), and ANS (1.04 X 10-3M) caused a further inhibition of chymosin hydrolysis. SDS and ovalbumin might have increased the net negative charge of the casein micelles, resulting in an increased electro static repulsion between the enzyme and substrate. Sodium sulfite (5.0 x 10-3M) and sucrose (6.67%) prevented the inhibition of chymosin hydrolysis to some extent, whereas retinol (7.2 X 10-4M) did not have any influence on hydrolysis. A concentration of 0.4% lysozyme prevented the inhibition of chymosin hydrolysis in heated skim milk and mixtures of casein micelles and β-Lg and restored the rennet clotting time of heated milk. © 1990, American Chemical Society. All rights reserved.