Beijing Advanced Innovation Center for Food Nutrition and Human Health, Beijing Engineering and Technology Research Center of Food Additives, Beijing Technology and Business University, China 100048. Electronic address: [Email]
Yak is one of the few species of which the rennet-coagulated cheese making characteristics of its milk are still not well understood. This study investigated composition and rennet-induced coagulation properties of milk from 17 individual yak cows in comparison with milk from 32 individual Holstein cows. Yak cows produced milk with generally higher concentrations of milk components. The concentrations of fat, protein, solids-not-fat (SNF), and calcium in yak milk were 1.89-, 1.68-, 1.46-, and 2-fold those in Holstein milk, respectively. The hydrodynamic radii of casein micelles (187.25 nm) and chymosin-induced paracasein (1,620 nm) were about twice the sizes of those found in Holstein milk. Higher concentrations of calcium in yak milk, together with larger sizes of casein micelles, explains the reason for its fast rate of curd formation and firmer curd texture. Optical microrheology analysis also showed that Ca2+ concentration had greater influence on the coagulation of yak milk than on Holstein milk. Cheese making trials with yak and Holstein milk proved the higher cheese yield of yak milk: 1.67-fold that of Holstein milk. Therefore, yak milk could be a suitable source of milk for enzyme-coagulated cheese making.