山羊脱脂乳于25 ℃超离心,分为乳清和胶束,后者复溶于脱脂乳超滤液,于4 ℃超离心,分为乳清和胶束,探究4 ℃诱导解离对胶束结构的影响。4 ℃下超离心和超滤液复溶2次后,胶束态酪蛋白的解离达平衡,总酪蛋白的解离达36.5%,其中β-、κ-、αs-酪蛋白的解离达60.4%、31.4%、11.8%;25 ℃下游离β-酪蛋白以2P、3P和4P的低磷酸化形式存在,4 ℃下胶束钙的解离导致5P和6P的高磷酸化β-酪蛋白的解离;4 ℃诱导解离后,胶束钙相对含量从72.0%减少至50.2%,胶束中钙与酪蛋白物质的量之比从21.8减少至19.4,胶束仍保持完整的球状形貌,胶束均方回转半径Rg、流体力学半径Rh、重均分子质量均减小,胶束形状因子Rg/Rh、水合率和内源荧光强度均增加,胶束内部结构中酪蛋白空间分布的非均一性降低,表明低温诱导解离后胶束内部组分发生了重排,骨架结构变得更加松散。该研究为羊乳酪蛋白配料的分离提供参考。
Caprine skim milk was ultracentrifuged at 25 ℃ and divided into whey and micelles.The latter was dissolved in the caprine skim milk ultrafiltration fluid, was ultracentrifuged at 4 ℃, and divided into whey and micelles.The effects of dissociation induced by 4 ℃ on caprine casein micelle structures were investigated.The dissociation of micellar casein reached equilibrium after ultracentrifugation at 4 ℃ and reconstitution in ultrafiltration fluid two times.The dissociation rate of total casein was 36.5% and the dissociation rate of β-, κ-, and αs-casein were 60.4%, 31.4%, and 11.8% separately.Soluble β-casein at 25 ℃ existed in the form of low phosphorylation containing 2P, 3P, and 4P.The dissociation of colloidal calcium at 4 ℃ led to the dissociation of high-phosphorylated β-casein containing 5P and 6P.After dissociation induced by 4 ℃, the relative calcium content of caprine micelle decreased from 72.0% to 50.2%.The molar ratio of calcium to casein decreased from 21.8 to 19.4.Casein micelles remained in complete spherical morphology.The mean square radius of gyration (Rg), hydrodynamic radius (Rh), and weight average molecular weight of micelles all decreased.Micelle shape factor Rg/Rh, hydration rate, and endogenous fluorescence intensity all increased.The local protein inhomogeneity within the micelles reduced, suggesting that the internal components reorganized and the frame structure became looser.This study provides a reference for the separation of caprine casein ingredients.
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