Alpha s1-casein, milk composition and coagulation properties of goat milk

Abstract

Amounts of alpha s1-casein (α s1-CN), protein, fat, SNF and total solids were measured in 125 goat milk samples. Coagulation time, coagulation rate and curd firmness were measured in 75 goat milk samples by dynamic mechanical analysis using a Bohlin VOR Rheometer. After adjustments were made for month, time of milk collection and animal age, it was confirmed that goat milk with high percent total solids, SNF, fat and protein coagulated faster (high coagulation rate) and formed a firmer curd than milk that had lower levels of milk components. Coagulation was delayed (long coagulation time) in milk with high protein but resulting curds were firmer than curds made from low protein milks. Amount of α s1-CN was positively correlated with milk components and coagulation time. Goat milk that lacked α s1-CN had lower percentages of milk components and poorer coagulation properties than milk that contained α s1-CN, suggesting that the presence of α s1-CN in milk should improve coagulation properties. However, percent total solids, SNF and protein were more highly correlated with coagulation properties than α s1-CN. Thus, measuring total solids, SNF or protein may be more practical in predicting cheese-making potential of goat milk than measuring α s1-CN, which is more tedious and expensive. Milk from Nubians and Nubian×Alpine crosses contained a higher amount of α s1-CN and other milk components, and exhibited higher coagulation rate and curd firmness than milk from Toggenburgs and Saanen×Alpine crosses. Selection of goats with high solids, particularly Nubians, is recommended if cheese-making is the objective.