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

摘要： 选择甘肃天祝牧区的鲜牦牛乳为研究对象，采用微滤的分离方法获得牦牛乳酪蛋白，研究了在pH 6.4、6.6、6.8、7.0及80、100、120、140℃处理后牦牛乳酪蛋白的热稳定性、疏水性、粒径大小和分子质量的变化。结果表明：在pH 6.8时，不同温度处理后各个功能性质均为最差，而在远离变性温度（140℃）的条件下，酪蛋白具有良好的功能特性。在酸诱导和热处理后，蛋白质分子发生了极化，维持空间结构的疏水作用力遭到破坏，引起蛋白分子的解离或聚集，导致蛋白分子自身结构发生改变，从而影响其性质的优劣。

关键词: 牦牛乳；酪蛋白；酸和热处理；功能特性