冻融处理对牦牛乳酪蛋白胶束组成和稳定性的影响

Effect of freeze-thaw treatment on the composition and stability of yak milk casein micelles

冷冻贮藏是克服牦牛乳生产的季节性、产量低、泌乳期短等问题的重要手段,本研究探究了冻融处理条件对牦牛乳酪蛋白胶束组成和胶体稳定性的影响。将脱脂后的牦牛和荷斯坦牛原料乳于-18℃和-80℃冷冻贮藏210 d后,分别在4℃、25℃和50℃条件下解冻,通过超高速离心法(135000 g,2 h,25℃)分离牦牛乳中的胶束相和乳清相。监测胶态钙和磷酸根、4种酪蛋白在两相中的分布;通过动态光散射检测酪蛋白胶束直径和直径分布,通过Turbiscan法测试样品经过冻融前后的物理稳定性变化规律。冻融处理促进了牦牛乳溶解相中的钙离子、磷酸根离子、αs1-酪蛋白、αs2-酪蛋白和β-酪蛋白迁移到胶束相中,导致胶束直径和直径多不分散指数增加,物理稳定性降低。冻藏温度相同的条件下,解冻温度越高,胶束相中钙和磷酸根、αs1-酪蛋白、αs2-酪蛋白和β-酪蛋白的含量越大,导致胶束的稳定性越低。在解冻温度相同的条件下,-18℃和-80℃冷冻贮藏条件产生的2种牦牛乳酪蛋白胶束的性质无显著差异。冻融处理对牦牛乳酪蛋白胶束的组成和稳定性有不利影响,低温解冻对牦牛乳酪蛋白胶束组成和稳定性的影响最小。

Frozen storage is an important means to overcome the problems of seasonality,low yield,and short lactation period in yak milk production.The purpose of this study was to clarify the effect of freeze-thaw treatment conditions on the composition and colloidal stability of yak milk casein micelles.The defatted yak and Holstein raw milks were frozen and stored at-18°C and-80°C for 210 days,then thawed at 4°C,25°C and 50°C respectively,and the micellar and whey phases were separated by ultracentrifugation(135000 g,2 h,25℃).The distribution of colloidal calcium,phosphate,and four kinds of casein in two phases was monitored,the diameter and diameter distribution of casein micelles were detected by dynamic light scattering,and the changes law of physical stability of samples before and after freezing and thawing was tested by Turbiscan method.Freeze-thaw treatment promotes the migration of calcium ions,phosphate ions,αs1-casein,αs2-casein andβ-casein from the dissolved phase of yak milk into the micellar phase,resulting in increased micelle diameter and diameter polydispersity index,and physical stability reduced.Under the same freezing temperature,the higher the thawing temperature,the higher the content of calcium and phosphate,αs1-casein,αs2-casein andβ-casein in the micelle phase,resulting in lower stability of the micelles.Under the same thawing temperature,the properties of the two yak milk casein micelles produced at-18°C and-80°C were not significantly different.Freeze-thaw treatments have adverse effects on the composition and stability of yak milk casein micelles,and low temperature thawing has the least effect on the composition and stability of yak milk casein micelles.