关键词: 牦牛乳；酪蛋白；酸和热处理；功能特性

Abstract: Caseins were separated from the fresh milk of grazing yak cows in Tianzhu county, Gansu province by microfiltration to investigate changes in their heat stability, hydrophobicity, particle sizes and molecular weights after different pH treatments (pH 6.4, 6.6, 6.8 and 7.0) and heat treatments (80, 100, 120 and 140 ℃). The results showed that functional properties of yak milk caseins at pH 6.8 revealed the most significant deterioration after each heat treatment. At a temperature far below the denaturing temperature the caseins exhibited good retention of functional properties. Both acid and heat treatments caused molecular polarization of the caseins, destroyed the hydrophobic force, which contributes to maintaining the spatial structure of the protein molecules, and accordingly induced their dissociation or aggregation, causing changes in their molecular structure and in turn affecting their functional properties.

Key words: yak milk; casein; acid and heat treatments; functional properties