INFLUENCE OF HEAT TREATMENTS ON WHEY PROTEIN DENATURATION AND RENNET CLOTTING PROPERTIES OF COWS AND GOATS MILK

摘要

Effect of heat treatments (65-85 degrees C for 5-35 min) an the rennet clotting properties and whey protein denaturation of cow's and goat's milk was investigated. The rennet clotting time (RCT) of raw cow's milk was longer than that of goat's milk. Although heat treatments increased the RCT of cow's milk samples, this parameter was not affected when goat's milk was heated up to 85 degrees C for 30 min. Heat treatments higher than 70 degrees C for 15 min rendered a very weak curd from cow's milk, however the consistency of curd from goat's milk was slightly affected by heat treatments. Whey proteins from goat's milk were more denatured than those from cow's milk on samples heated at temperatures higher than 75 degrees C. A good relationship was established between whey protein denaturation and RCT in cow's milk. Dialysis of cow's milk against an excess of goat's milk decrease the RCT of raw and heated samples; goat's milk was not affected by dialysis treatment against cow's milk. The influence of CaCl2 concentration on RCT was higher on cow's than on goat's milk for heat treatments up to 80 degrees C for 30 min.