Characterization of fat globules and milk fat globule membrane proteins in milk of different yak breeds

The objective of this work was to characterize the fat globule and milk fat globule membrane (MFGM) proteins in Maiwa (n = 6), Gannan (n = 4) and Zhongdian yak whole milks (n = 4). Fat globule size distribution and specific fat surface area of whole yak milk were determined using a laser diffraction particle size analyzer. The average specific fat surface area of Gannan yak milk (2.05 m(2).mg(-1)) and Zhongdian yak milk (2.01 m(2).mg(-1)) was higher (P < 0.05) than that of Maiwa yak milk (1.92 m(2).mg(-1)). The total protein content of MFGM and surface protein coverage of fat globule in Maiwa yak milk (11.12 mg.g(-1) fat and 5.67 mg.m(-2), respectively) and Gannan yak milk (12.24 mg.g(-1) fat and 5.97 mg.m(-2), respectively) were higher (P < 0.05) than that of Zhongdian yak milk (9.72 mg.g(-1) fat and 4.81 mg.m(-2), respectively). Protein components in the MFGM of yak milk were analyzed using an Ultrascan XL laser densitometer and an LKB 2400 GelScanXL software program. No major differences (P > 0.05%) in the protein patterns on the SDS gel were observed among the MFGM of Maiwa yak, Gannan yak and Zhongdian yak, with the exception of mucin 1 and butyrophilin which were significantly lower (P < 0.05) in the MFGM of Zhongdian yak milk.