School of Biomolecular Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom.
Research School of Chemistry, The Australian National University, Acton, ACT 2601, Australia.
J Dairy Sci. 2024 Aug;107(8):5259-5279. doi: 10.3168/jds.2024-24779. Epub 2024 Mar 22.
Novel insights into the stability of milk and milk products during storage and processing result from describing caseins near neutral pH as hydrophilic, intrinsically disordered, proteins. Casein solubility is strongly influenced by pH and multivalent ion binding. Solubility is high at a neutral pH or above, but decreases as the casein net charge approaches zero, allowing a condensed casein phase or gel to form, then increases at lower pH. Of particular importance for casein micelle stability near neutral pH is the proportion of free caseins in the micelle (i.e., caseins not bound directly to nanoclusters of calcium phosphate). Free caseins are more soluble and better able to act as molecular chaperones (to prevent casein and whey protein aggregation) than bound caseins. Some free caseins are highly phosphorylated and can also act as mineral chaperones to inhibit the growth of calcium phosphate phases and prevent mineralized deposits from forming on membranes or heat exchangers. Thus, casein micelle stability is reduced when free caseins bind to amyloid fibrils, destabilized whey proteins or calcium phosphate. The multivalent-binding model of the casein micelle quantitatively describes these and other factors affecting the stability of milk and milk protein products during manufacture and storage.
描述等电点附近的酪蛋白为亲水的、固有无序的蛋白质，为理解乳和乳制品在储存和加工过程中的稳定性提供了新的见解。酪蛋白的溶解度强烈受 pH 值和多价离子结合的影响。在中性 pH 值或更高时，溶解度很高，但随着酪蛋白净电荷接近零，溶解度降低，允许形成浓缩的酪蛋白相或凝胶，然后在较低 pH 值时增加。对于接近中性 pH 值时的酪蛋白胶束稳定性特别重要的是胶束中游离酪蛋白的比例（即，不直接与磷酸钙纳米簇结合的酪蛋白）。游离酪蛋白比结合酪蛋白更易溶解，并且更能充当分子伴侣（以防止酪蛋白和乳清蛋白聚集）。一些游离的酪蛋白高度磷酸化，也可以充当矿物质伴侣，以抑制磷酸钙相的生长并防止在膜或热交换器上形成矿化沉积物。因此，当游离酪蛋白与淀粉样纤维、不稳定的乳清蛋白或磷酸钙结合时，酪蛋白胶束的稳定性会降低。酪蛋白胶束的多价结合模型定量描述了这些以及其他影响乳和乳蛋白产品在制造和储存过程中稳定性的因素。
