Food Science, University of Guelph, Guelph, OntarioN1G 1W5, Canada.
GayLea Foods, Research and Development, Speedvale Avenue, Guelph, OntarioN1H1J5, Canada.
J Dairy Res. 2020 May;87(2):248-254. doi: 10.1017/S0022029920000345. Epub 2020 May 14.
Using membrane filtration it is possible to selectively concentrate proteins and, in the case of microfiltration, concentrate casein micelles. During filtration, water is often added and this practice, called diafiltration, causes further release of permeable components and maintains filtration efficiency. Filtration causes changes in composition of the protein as well as the soluble phase, including soluble calcium, which is a critical factor controlling the gelation properties of the casein micelles in milk. It was hypothesized that concentrates obtained using membrane filtration with or without diafiltration would have different gelation behavior. To test this hypothesis, two concentrates of similar casein micelle volume fraction were prepared, using spiral wound polymeric microfiltration membranes with a 800 kDa molecular weight cutoff, with or without diafiltration. The concentrates showed a gelation behavior comparable to that of skim milk, with a similar gelation time and with a higher firmness, due to the higher number of protein linkages in the network. In contrast, the hydrolysis of κ-casein by chymosin and casein aggregation were inhibited in diafiltered casein micelle suspensions. When the concentrates were recombined with the original skim milk to a final concentration of 5% protein, which re-established a similar soluble phase composition, differences in gelation behavior were no longer observed: both treatments showed similar gelation time and gel firmness. These results confirmed that membrane filtration can result in concentrates with different functionality, and that ionic environmental conditions are critical to the aggregation behavior of casein micelles. This is of particular significance in industrial settings where these fractions are used as a way to standardize proteins in cheese making.
使用膜过滤可以选择性地浓缩蛋白质，并且在微滤的情况下，可以浓缩酪蛋白胶束。在过滤过程中，通常会添加水，这种做法称为渗滤，会导致更多的可渗透成分释放，并保持过滤效率。过滤会导致蛋白质以及可溶性相（包括可溶性钙）的组成发生变化，而可溶性钙是控制乳中酪蛋白胶束胶凝性质的关键因素。有人假设，使用膜过滤（无论是否渗滤）获得的浓缩物将具有不同的胶凝行为。为了验证这一假设，使用具有 800 kDa 分子量截止值的螺旋缠绕聚合物微滤膜制备了两种类似酪蛋白胶束体积分数的浓缩物，无论是否渗滤。浓缩物的胶凝行为与脱脂乳相似，具有相似的胶凝时间和更高的硬度，这是由于网络中蛋白质键的数量更多。相比之下，在渗滤的酪蛋白胶束悬浮液中，凝乳酶水解 κ-酪蛋白和酪蛋白聚集受到抑制。当将浓缩物与原始脱脂乳重新组合至 5%蛋白质的最终浓度时，恢复了类似的可溶性相组成，胶凝行为的差异不再明显：两种处理均显示出相似的胶凝时间和凝胶硬度。这些结果证实，膜过滤可以导致具有不同功能的浓缩物，并且离子环境条件对酪蛋白胶束的聚集行为至关重要。这在工业环境中尤为重要，在这些环境中，这些级分被用作奶酪制造中标准化蛋白质的一种方式。
