The yak is a rare animal that predominantly lives on the Qinghai-Tibet Plateau. The production volume of yak milk is low, but it is rich in nutrients, containing higher contents of protein, fat and lactose compared with Holstein milk, as well as abundant amounts of other nutrients. Furthermore, it is found that yak milk has anti-hypoxia, anti-fatigue and antioxidant activities, among other, which may be attributed to the unique habitat of yaks. In this article, the lactation performance of yaks, as well as the nutritional components and functional characteristics of yak milk is reviewed, with a view to providing a theoretical reference for the development and utilization of yak milk.

To improve the fermentation performance of Lactobacillus helveticus, Streptococcus thermophilus as a potential starter culture for functional fermented milk was utilized together with L. helveticus to produce fermented milk. As results, the mixed culture fermentation shortened the curding time by 3.5 h, increased yogurt viscosity by 1.8 times and improved whey syneresis and texture properties as compared to L. helveticus alone. Interestingly, S. thermophilus weakened the postacidification of fermented milk containing L. helveticus, maintaining a pH value greater than 4.2 for 20 d of storage. To account for this finding, the number of living bacterial cells, lactose consumption and the activity of glutamate decarboxylase and β-galactosidase were measured. It was found that the activity of glutamate decarboxylase and β-galactosidase of the fermented milk containing the two strains was lower, resulting in a lower lactose consumption and consequently weakening yogurt postacidification. This study concluded that co-fermentation with S. thermophilus was an effective means to improve the fermentation performance of Lactobacillus helveticus.

The objective of this study was to explore and compare the effect of different heat treatments on the stability of buffalo milk. For this purpose, milk samples were subjected to different heat treatments for the comparative determination of pH buffer capacity, total dissolved solids (TDS) content, the amount of protein precipitation and apparent viscosity. The results showed that the pH buffering capacity, TDS, protein precipitation and apparent viscosity of buffalo milk were significantly changed after heat treatments. After treatment at 121 ℃ for 15 min, the pH buffering capacity, TDS, protein precipitation and apparent viscosity reached their maximum levels, while pH buffering capacity and TDS were minimized after treatment at 95 ℃ for 5 min. Therefore, it was concluded that the stability of buffalo milk was most affected by treatments at 121℃ for 15 min and at 95 ℃ for 5 min in the experimental range investigated.