Effect of Starter Cultures on the Ripening Properties of Yak Milk Cheese

Three batches of yak milk cheese were made using lactococcal culture (L culture) (Batch L), sour yak milk culture (S culture) (Batch 5), as well as the mixed L and S cultures (1:1) (LS culture) (Batch LS). The effects of these starter cultures on cheese ripening (90 d) properties, including proteolysis, texture, and volatile production, as well as the sensory characteristics of cheese were evaluated. The results showed that cheese composition was not significantly affected by the different cultures. Batch S and LS cheeses had higher proteolytic activity with a softer and less chewy structure than Batch L cheese. More volatile compounds were detected in Batch LS cheese than in the other two batches and the former was the only one to contain decanoic acid, 2-ethyl-1-hexanol, ethylbenzene, and styrene. However, 4-methylphenol with cowy aroma, which was observed in Batches L and S cheeses, was not detected in Batch LS cheese. Bacterial identification of S culture revealed a complex microbial composition, including 22 different strains from seven lactic acid bacterial species. The presence of several proteolytic and autolytic strains (Enterococcus durans etc.) in S culture might be important in the proteolytic activity, formation of texture, and characteristic volatiles of yak milk cheeses. In the sensory evaluation, Batch LS cheese was the most acceptable with the highest scores among the three batches. The results of this study suggested that a combination of commonly used lactococcal culture with traditional sour yak milk culture may be suitable for producing yak milk cheese with good acceptability.