凝乳酶添加量对牦牛乳硬质干酪蛋白质降解的影响

Effect of Calf Chymosin Dose on Protein Degradation in Hard Cheese Made from Yak Milk

通过测定不同可溶性氮含量以及采用尿素凝胶电泳法,研究了不同小牛皱胃酶添加量对牦牛乳硬质干酪3个月成熟过程中蛋白质降解的影响,并对干酪苦味进行了感官评价。研究表明:凝乳酶添加量对干酪p H 4.6SN和12%TCASN影响显著(P<0.05),在成熟1个月时,不同凝乳酶添加量干酪p H 4.6SN之间差距较大,且凝乳酶添加量与干酪p H 4.6SN间存在较强线性关系。凝乳酶添加量对5%PTASN和游离氨基酸影响不显著(P>0.05)。尿素凝胶电泳显示:干酪中αs-酪蛋白降解依赖于凝乳酶添加量,且降解程度大于β-酪蛋白。凝乳酶添加量对干酪苦味影响显著(P<0.05),且随着凝乳酶添加量的增多,其苦味程度逐渐加重,但是大部分干酪苦味属于轻微苦味和中等程度苦味之间。干酪苦味与12%TCASN、αs-酪蛋白和β-酪蛋白降解率之间具有较强相关性(Spearman相关系数>0.7,P<0.01)。

The effect of calf chymosin supplementation on degradation of protein in hard cheese made from yak milk during the three-month ripening process was studied by measuring content of various types of soluble nitrogen. Additionally, urea-polyacrylamide gel electrophoresis and sensory evaluation regarding bitterness in the cheese was conducted. The results showed that chymosin dosage had significant impact on content of soluble nitrogen in p H 4.6 acetate buffer and 12% trichloroacetic acid(p < 0.05). After one month of ripening, there were significant differences in soluble nitrogen content in p H 4.6 acetate buffer between samples with different chymosin dosages, and a strong linear correlation was found between chymosin dosage and soluble nitrogen content. However, chymosin dose had no significant effect on the content of soluble nitrogen in 5% phosphotungstic acid and free amino acid content(p > 0.05). Results of urea-polyacrylamide gel electrophoresis showed that degradation of αs-casein in cheese was dependent on chymosin dosage and was more extensive than that of β-casein. Chymosin dosage had a significant impact on cheese bitterness as well, which increased in intensity with increasing amount of chymosin, with most cheeses ranging from slightly to moderately bitter. The degree of cheese bitterness strongly correlated with soluble nitrogen content in 12% trichloroacetic acid as well as degree of αs-casein and β-casein degradation(Spearman correlation coefficient > 0.7, p < 0.01).