乳清组分的波动对牛乳体系及其酶凝胶特性的影响

The Influence of Serum Composition on the Milk System and Its Rennet Coagulation Properties

为探讨牛乳乳清的组成成分对酪蛋白胶束酶凝胶特性的影响,采用超滤浓缩技术去除渗透液,并分别用去离子水、乳清蛋白和酪蛋白酸钠溶液取代所除掉的渗透液,进而改变乳清相的蛋白质组成和离子强度。研究表明,添加乳清蛋白和酪蛋白酸钠虽未对酪蛋白胶束的结构和电荷特性产生影响,但能显著阻碍蛋白质凝胶结构的形成。研究发现添加酪蛋白酸钠能够完全阻止酪蛋白凝胶结构的形成,主要是它通过疏水作用与酪蛋白胶束相结合,从而提高酪蛋白胶束间的静电和空间排斥作用。另外,添加去离子水的样品显著降低了体系的钙离子浓度。酪蛋白胶束的Zeta电势值从-20mV增到-33mV,同时粒径从163nm降到153nm。钙离子浓度的降低显著减缓了酶凝胶的形成过程,凝胶时间延长到93min,所得凝胶的弹性模量仅为1.5Pa。本研究发现乳清中的钙离子含量、蛋白质含量及种类都能显著影响酪蛋白胶束的酶凝集过程。酪蛋白酸钠具有强大的阻碍酪蛋白胶束聚集的能力。此外,钙离子浓度的降低也会对酪蛋白凝胶结构的形成及特性产生影响,乳清中足量的钙离子浓度(>330mg/L)是获得良好凝胶结构的必要条件。

The objective of this research was to investigate the influence of serum composition on the rennet coagulation properties of casein micelles. The ultrafiltration technique was adopted to remove the milk permeate, which was then replaced by deionised water, serum phase and sodium caseinate solution. The results showed that the addition of serum and sodium caseinate, which increased the soluble protein content in the system, has no influence on the structure and zeta potential of the casein micelles. However, the presence of higher amount of soluble proteins was detrimental to the coagulation properties of casein micelles. No aggregation of casein micelles was detected for the sample with the addition of sodium caseinate. The replacement of permeate with deionised water significantly reduced the calcium concentration in the serum phase. The zeta potential of casein micelles increased from -20 mV to -33 mV while the average size decreased from 163nm to 153nm. The reduction of calcium decreased the rennetability of casein micelles. The gelation point happened at a much longer time 93min and the resulted gel had a very weak structure with the strength value only 1.5 Pa. It can be concluded that the calcium concentration, protein composition and concentration have significant influence on the rennet coagulation behaviour of casein micelles. Sodium caseinate can strongly inhibit the aggregation capacity of casein micelles and the decrease of calcium concentration also influence the rennet gelation process. The presence of sufficient (>330 mg/L) calcium is essential to obtain good milk gel structure.