Department of Food Science, Cornell University, Ithaca, NY 14853, USA.
J Dairy Sci. 2012 Nov;95(11):6339-50. doi: 10.3168/jds.2012-5706. Epub 2012 Sep 7.
The increased interest in using micellar casein concentrates (MCC) obtained by microfiltration in the manufacture of shelf-stable high-protein beverages creates a need to understand the effect of sterilization treatments on the stability of this ingredient. The goals of this work were to (1) elucidate the effects of pH and heat treatment temperatures in the sterilization range on the stability of MCC, and (2) use the generated knowledge to develop solutions for stabilizing the MCC during sterilization treatments. Micellar casein concentrate powders were reconstituted, and the resulting casein dispersions were adjusted to pH values of 6.5 to 7.3. Subsequently, the MCC samples were heated in an oil bath to 110 to 150°C. The treated samples were evaluated for particle size, soluble minerals, and casein dissociation. At pH <6.7, all heat-treated samples were visibly aggregated or coagulated. At pH 6.9, higher temperatures led to increased particle size, whereas at pH >6.9, few or no changes were observed after heat treatment. Casein dissociation increased with increasing pH for all caseins, at all temperatures, with dissociation of κ-casein and β-casein being the most pronounced. At higher pH, the levels of dissociated α(s)-casein decreased after heat treatment, suggesting aggregation of α(s)-casein in the presence of Ca and protection lost by κ-casein. It was concluded that increased stability of MCC requires increasing the pH or lowering the processing temperature. After applying these modifications, MCC was submitted to both retorting and UHT sterilization, at equivalent lethality. A significant reduction in particle size was obtained and no coagulation or aggregation occurred after retorting or UHT under the modified conditions as compared with the controls. The knowledge generated in this study will allow the effective stabilization of MCC in practical applications, such as the production of high-protein, shelf-stable beverages.
人们对使用微滤法获得的浓缩胶束酪蛋白（MCC）来生产货架稳定高蛋白饮料的兴趣日益浓厚，这就需要了解灭菌处理对该成分稳定性的影响。本工作的目的是：（1）阐明灭菌处理范围内 pH 值和热处理温度对 MCC 稳定性的影响；（2）利用所获得的知识，找到在灭菌处理过程中稳定 MCC 的解决方案。MCC 粉末经复水后，将得到的酪蛋白分散液的 pH 值调节至 6.5 至 7.3。随后，将 MCC 样品在油浴中加热至 110 至 150°C。处理后的样品用于评估粒径、可溶性矿物质和酪蛋白解离情况。在 pH <6.7 时，所有热处理后的样品均可见聚集或凝结。在 pH 6.9 时，较高的温度会导致粒径增大，而在 pH >6.9 时，热处理后几乎没有或没有观察到变化。对于所有的酪蛋白，在所有温度下，κ-酪蛋白和 β-酪蛋白的解离程度最大，随着 pH 值的增加，酪蛋白的解离程度也随之增加。在较高的 pH 值下，热处理后 α(s)-酪蛋白的解离水平降低，这表明在 Ca 存在下 α(s)-酪蛋白的聚集以及 κ-酪蛋白丧失保护作用。结论是，增加 MCC 的稳定性需要提高 pH 值或降低加工温度。在应用这些改进措施后，MCC 分别进行了高温瞬时灭菌和超高温灭菌，致死率相同。与对照相比，在改性条件下进行高温瞬时灭菌或超高温灭菌后，粒径显著减小，且未发生凝结或聚集。本研究获得的知识将有助于在实际应用中有效稳定 MCC，例如生产高蛋白、货架稳定的饮料。
