Abstract: Native whey protein concentrate (NWPC) and sweet whey protein concentrate (SWPC) were prepared by spiral-wound membrane ultrafiltration of native yak whey and sweet yak whey followed by sequential dialysis through regenerated cellulose membranes with different molecular mass cutoffs (MMCOs), respectively, and their major components (lactose, pH and total protein) and functional properties (solubility, water-holding capacity, oil-holding capacity, foaming properties, emulsifying properties and thermal stability) were evaluated. The results showed that the total protein content of the whey protein concentrates (WPCs) obtained after dialysis through 10 000 Da MMCO cellulose membrane, which were found to contain no lactose, was over 80%. The solubility, water-holding capacity (WHC), oil-holding capacity (OHC), foaming properties, emulsifying properties and thermal stability were all significantly higher than those of the WPCs obtained after ultrafiltration through 3 500 Da MMCO rolled membrane and after dialysis through 5 000 Da MMCO cellulose membrane. The higher the protein content in WPC, the better the functional properties. After the same concentration treatment, the foaming capacity, foam stability, emulsifying capacity and emulsion stability of SWPCs were significantly (P < 0.05) higher than those of NWPCs. Yak WPC was the most unstable at 85 ℃, which was higher than 80 ℃ observed for Holstein cow milk WPC. The appropriate thermal treatment could improve the foaming properties, emulsifying properties and thermal stability of yak WPC. The yak WPC with high protein content obtained by membrane processing had good functional characteristics, making it having wide applications. It will play a key role in solving the problem of yak whey resource utilization, protecting the environment, and improving the economic benefits of enterprises.

Key words: yak native whey protein concentrate; yak sweet whey protein concentrate; main components; functional properties; protein content