体细胞组成对Cheddar干酪蛋白质水解及品质的影响

摘要

近年来,我国的干酪消费量迅速增加.小规模牧场的手工挤奶方式可能会导致体细胞混入原料奶中,从而影响终产品干酪的品质.但是,体细胞组成及相应酶的活力对干酪品质的影响尚未阐明.该研究分别从牛乳房表面、乳房炎牛乳和正常牛乳收集体细胞.通过将体细胞分离再与脱脂乳混合,原料乳质量的一致性得到保证.将含不同体细胞组成的牛乳用于Cheddar干酪制作,分别为干酪A,B和C.3种干酪的原料乳中,上皮细胞质量分数最高组为干酪A的原料乳(65.41%),巨噬细胞和淋巴细胞质量分数最高组为干酪B的原料乳(分别为78.15% 和12.15%),而多核中性粒细胞在干酪C的原料乳中质量分数最高(34.23%).结果表明,成熟过程中各干酪的蛋白酶活性和蛋白水解程度差异显著(P < 0.05).成熟90d后,干酪C中的血纤维蛋白溶酶和组织蛋白酶B活性显著高于其他组.此外,在整个成熟过程中,干酪中αs1-, αs2-和β-酪蛋白的存留率,以及pH 值4.6的可溶性氮和12%三氯醋酸可溶性氮的质量分数均为C组< B 组< A组.另外,3组试验干酪中干酪A的硬度最高,B和C之间无显著性差异.综上所述,体细胞对干酪品质的影响与体细胞的类型有关.体细胞中上皮细胞的增加对干酪品质的影响较小,而多核中性粒细胞的增加对干酪品质有显著影响.%Cheese consumption in China has largely increased in recent years. Manual milking manner in small-scale dairy farms may induce the mixing of somatic cells (SCs) into raw milk, which would exert an effect on the final quality of cheese. However, the effect of different SC compositions and related protease activities on cheese quality has not yet been elucidated. In this study, three sources of SCs were recovered and re-introduced into skim milk to ensure the same initial milk quality. SCs A were obtained directly from the udder of healthy cows, and SCs B and C were isolated from milk of healthy cows and cows with mastitis, respectively. Three SCs isolates were then mixed with the skim milk to obtain milks with different SCs compositions for cheese manufacture. Among the three experimental cheeses, the highest epithelial cell count was found in cheese A (65.41%), the highest macrophage and lymphocytes counts was in cheese B (78.15% and 12.15%, respectively), and the highest polymorphonuclear neutrophil count (PMN) was in cheese C (34.23%). The results indicated that there were differences in protease activity and proteolysis level among the cheese samples during ripening. The activity of plasmin and cathepsin B was significantly higher in cheese C than in other cheese samples after 90 d of ripening. In addition, the retention rate of intact αs1-, αs2- and β-CN, and the levels of pH value 4.6 soluble nitrogen and 12% trichloroacetic acid soluble nitrogen were in the order of C