Advanced Food Systems Research Unit, Institute for Sustainable Industries and Liveable Cities, College of Health and Biomedicine, Victoria University, Melbourne, VIC 8001, Australia.
FrieslandCampina, 3818 LE Amersfoort, The Netherlands.
Molecules. 2023 Sep 28;28(19):6847. doi: 10.3390/molecules28196847.
The present study investigated the effect of micellar calcium phosphate (MCP) content and pH of skim milk on heat-induced changes in skim milk. Four MCP-adjusted samples, ranging from 67 to 113% of the original MCP content, were heated (90 °C for 10 min) at different pH values (6.3, 6.6, 6.9, and 7.2), followed by determining changes in particle size, turbidity, protein distribution, and structure. The results demonstrate a strong effect of MCP level and pH on heat-induced changes in milk, with the MCP samples revealing the greatest thermal stability. Specifically, decreasing MCP content by 33% (MCP) led to a smaller increase in non-sedimentable κ-casein and a lower decrease in αs-casein concentrations after heating compared to other samples. Lower MCP content resulted in a moderate rise in the average particle size and turbidity, along with lower loading of β-turn structural component after heating at low pH (pH 6.3). Notably, MCP exhibited instability upon heating, with increased particle size, turbidity, and a significant decrease in non-sedimentable αs-casein concentration, along with a slight increase in non-sedimentable κ-casein concentration. The FTIR results also revealed higher loading of intermolecular β-sheet, β-turn, and random coil structures, as well as lower loading of α-helix and β-sheet structures in MCP-enhanced skim milk samples. This suggests significant changes in the secondary structure of milk protein and greater formation of larger aggregates.
本研究调查了胶束磷酸钙（MCP）含量和脱脂乳 pH 值对脱脂乳热诱导变化的影响。将 4 种 MCP 调节样品（MCP 含量分别为原始 MCP 含量的 67%、87%、103%和 113%）在不同 pH 值（6.3、6.6、6.9 和 7.2）下加热（90°C 加热 10 分钟），然后测定粒径、浊度、蛋白质分布和结构的变化。结果表明，MCP 水平和 pH 值对牛奶的热诱导变化有很强的影响，MCP 样品表现出最大的热稳定性。具体来说，与其他样品相比，MCP 含量降低 33%（MCP）导致加热后不可沉淀 κ-酪蛋白的增加较小，αs-酪蛋白浓度的降低较低。较低的 MCP 含量导致平均粒径和浊度适度升高，以及在低 pH 值（pH 6.3）下加热后β-转角结构成分的负载较低。值得注意的是，MCP 在加热时表现出不稳定性，粒径、浊度增大，不可沉淀的 αs-酪蛋白浓度显著降低，不可沉淀的 κ-酪蛋白浓度略有增加。傅里叶变换红外光谱（FTIR）结果还显示，MCP 增强的脱脂乳样品中，分子间β-折叠、β-转角和无规卷曲结构的负载增加，而α-螺旋和β-折叠结构的负载降低。这表明乳蛋白的二级结构发生了显著变化，形成了更大的聚集物。
