Gross composition and nutrient profiles of Chinese yak (Maiwa) milk.

Yaks are a major source of livelihood for the high landers where agriculture does not exist. This multipurpose animal has remained a subject of studies since the second half of 18th century. However, there is limited data available on the chemistry of yak milk in China. The objective of this study was to analyze the chemical composition and nutrient profiles of Chinese yak milk. Fresh milk samples from 7 mid-lactating yaks (Maiwa breed) in Hongyuan county of Sichuan Province in China were collected, pooled, lyophilized and stored at -20 °C before use. Gross composition (total solids, protein, fat, ash, and lactose), minerals, and profiles of fatty acids, amino acids and proteins of the milk samples were examined. The average values of gross composition were 14.35% total solids, 3.51% protein, 5.80% fat, 3.90% lactose, and 0.58% ash in the yak milk. The levels of Ca, Na, K, Mg, Zn, and Fe were 1149.4, 276.8, 1066.1, 105.3, 6.9, and 1.5 mg/L, respectively. Gas liquid chromatography analysis of milk fat showed that major fatty acids in yak milk were C16:0, C18:1, C18:0, and C14:0. There was a small amount (2.68 mg/g fat) of conjugated linoleic acid in yak milk. Results of amino acid analysis indicated that glutamic acid (183.79 mg/g protein) was the most abundant amino acid in yak milk. The mean values of lysine and methionine were 81.01 and 30.61 mg/g protein, respectively. The total essential amino acid percentage is 46.36% which suggests that the yak milk may be a good supply of essential amino acids. SDS-PAGE and densitometry results demonstrated that, similar to cow's milk, the major proteins in yak milk are caseins, which accounts for over 60% relative percentage of total proteins. The relative percentage of α-lactalbumin in yak milk was significantly lower (P < 0.05) compared to bovine milk. As information about yak milk chemistry is limited, especially in China, more systematic studies in this area are needed in order to utilize this valuable resource. [ABSTRACT FROM AUTHOR]