Needs E C, Stenning R A, Gill A L, Ferragut V, Rich G T
Institute of Food Research, Reading Laboratory, UK.
J Dairy Res. 2000 Feb;67(1):31-42. doi: 10.1017/s0022029999004021.
High isostatic pressures up to 600 MPa were applied to samples of skim milk before addition of rennet and preparation of cheese curds. Electron microscopy revealed the structure of rennet gels produced from pressure-treated milks. These contained dense networks of fine strands, which were continuous over much bigger distances than in gels produced from untreated milk, where the strands were coarser with large interstitial spaces. Alterations in gel network structure gave rise to differences in rheology with much higher values for the storage moduli in the pressure-treated milk gels. The rate of gel formation and the water retention within the gel matrix were also affected by the processing of the milk. Casein micelles were disrupted by pressure and disruption appeared to be complete at treatments of 400 MPa and above. Whey proteins, particularly beta-lactoglobulin, were progressively denatured as increasing pressure was applied, and the denatured beta-lactoglobulin was incorporated into the rennet gels. Pressure-treated micelles were coagulated rapidly by rennet, but the presence of denatured beta-lactoglobulin interfered with the secondary aggregation phase and reduced the overall rate of coagulation. Syneresis from the curds was significantly reduced following treatment of the milk at 600 MPa, probably owing to the effects of a finer gel network and increased inclusion of whey protein. Levels of syneresis were more similar to control samples when the milk was treated at 400 MPa or less.
在添加凝乳酶并制备奶酪凝块之前，对脱脂牛奶样品施加高达600兆帕的高静水压力。电子显微镜揭示了由经过压力处理的牛奶制成的凝乳酶凝胶的结构。这些凝胶含有细密的网络结构，与未处理牛奶制成的凝胶相比，这些网络在更大的距离上是连续的，未处理牛奶制成的凝胶中的纤维更粗，间隙空间更大。凝胶网络结构的改变导致流变学差异，经过压力处理的牛奶凝胶的储能模量值要高得多。凝胶形成速率和凝胶基质中的保水率也受到牛奶加工过程的影响。酪蛋白胶粒在压力作用下被破坏，在400兆帕及以上的处理条件下，破坏似乎是完全的。随着压力的增加，乳清蛋白，尤其是β-乳球蛋白会逐渐变性，变性的β-乳球蛋白会融入凝乳酶凝胶中。经过压力处理的胶粒会被凝乳酶迅速凝结，但变性β-乳球蛋白的存在会干扰二次聚集阶段并降低整体凝结速率。在600兆帕压力下处理牛奶后，凝块的脱水收缩明显减少，这可能是由于更细密的凝胶网络和乳清蛋白掺入增加的影响。当牛奶在400兆帕或更低压力下处理时，脱水收缩水平与对照样品更相似。
