牦牛乳清粉的功能特性

Functional Properties of Yak Whey Powder

为掌握牦牛乳清粉的组成特性和功能性质,分别利用酸沉淀得到的牦牛乳清液制取牦牛原乳清粉(nativeyak whey powder,NYW),利用加工牦牛乳干酪排出(即酶凝法)的乳清废液制取牦牛甜乳清粉(sweet yak wheypowder,SYW),测定NYW和SYW的总蛋白质、乳糖、灰分含量和pH值等指标以及溶解性、持水性、持油性、起泡性、乳化性和热稳定性等功能性质。结果表明:SYW和NYW的总蛋白质含量有显著差异(P<0.05),差值为3.433%,乳糖含量差异不显著(P>0.05),NYW的灰分含量高达11.188%,较SYW高3.156%,有显著差异(P<0.05),NYW和SYW溶液均呈酸性,pH值分别为4.837和5.410,差异显著(P<0.05);NYW(27.079%)和SYW(34.207%)的溶解性差异显著(P<0.05);NYW的持水率显著高于SYW,但持油率显著低于SYW(P<0.05);SYW的起泡能力、泡沫稳定性、乳化活性和乳化稳定性均显著高于NYW(P<0.05);NYW和SYW在60℃热处理时开始有沉淀产生,75℃以后沉淀量显著增加(P<0.05),85℃时沉淀率达最大值,说明牦牛乳清粉85℃时最不稳定,而市售荷斯坦乳清粉(Holstein whey powder,HW)在80℃最不稳定,牦牛乳清粉热稳定性优于HW。研究结果表明,酸沉淀和酶凝法获得的乳清粉主要成分和功能特性不同。

To provide insights into the chemical composition and functional properties of yak whey powder, in this experiment, native yak whey powder (NYW) from the supernatant of acid precipitated yak milk and sweet yak whey powder (SYW) from waste cheese whey (resulting from enzymatic milk coagulation) for measurement of their total protein, lactose and ash contents, pH values and functional properties such as solubility, water-holding capacity, oil-holding property, foaming capacity, emulsifying capacity and thermal stability. The results showed that the difference between the total protein contents of SYW and NYW was 3.433% which was significant (P < 0.05) while the difference in lactose content was not significant (P > 0.05). The ash content of NYW was 11.188%, which was 3.156% higher than that of SYW, with a significant difference being found between them (P < 0.05). The pH values of NYW and SYW solutions were 4.837 and 5.410, respectively, with the difference being significant (P < 0.05). The difference in solubility was significant (P < 0.05), 34.207% for SYW versus 27.079% for NYW. The water-holding capacity of NYW was significantly higher than that of SYW, but the oil-holding capacity was significantly lower than that of SYW (P < 0.05). The foaming ability, foam stability, emulsifying activity and emulsion stability of SYW were significantly higher than those of NYW (P < 0.05). When NYW and SYW were heat treated at 60 ℃, precipitation began to occur. When the temperature exceeded 75 ℃, the amount of precipitation increased significantly (P < 0.05), and the maximum value occurred at 85 ℃, indicating yak whey powder to be the least stable at 85 ℃. On the other hand, yak whey powder was more thermos-stable commercial Holstein whey powder (HW), the most unstable at 80 ℃. The findings from this study show that the main components and functional properties of the yak whey powders obtained by acid precipitation and enzymatic coagulation are different.