黄酒麦曲中产凝乳酶菌株的分离鉴定

Isolation and identification of rennet-producing strains from wheat Qu of Chinese rice wine

本研究利用梯度稀释法和划线纯化法对黄酒麦曲中的微生物进行初筛,再利用酪蛋白平板法和液态培养基发酵法进行复筛,最终得到了两株产凝乳酶的优良细菌菌株LB-1和LB-2。通过形态学特征观察、生理生化实验以及16S rDNA序列分析鉴定,这两株菌分别确定为甲醇芽孢杆菌(Bacillus methanolicus)和枯草芽孢杆菌(Bacillus subtilis)。根据凝乳活力曲线发现,这两株菌在发酵24 h时其发酵液的凝乳活力最高,分别为269.66±0.78 SU/m L和187.50±1.4 SU/m L,此时的蛋白水解活力分别为1.476±0.49 U/m L和1.29±1.41 U/m L,凝乳活力与蛋白水解活力比值(C/P)分别为187.50和145.34。通过凝乳效果评价,其发酵液所形成的凝块组织结构、质构参数和风味物质均与商品凝乳酶形成的凝块相当,适用于干酪的加工。

In this study, the microbes in the rice wine ＂wheat Qu＂ were screened by gradient dilution method and scribing method, fol- lowed by casein plate method and liquid culture medium fermentation. Two excellent bacterial strains of LB-1 and LB-2 producing rennet were obtained, which were further identified as Bacillus methanolicus and Bacillus subtilis by morphological observation, physiological and bio- chemical experiments and 16S rDNA sequence analysis. According to the enzyme activity curve, the highest milk clotting activity of the en- zymes from the two strains were 269.66 ± 0.78 SU/mL and 187.50± 1.4 SU/mL at 24 h fermentation, while the proteolytic activity were 1.476 ±0.49 U/mL and 1.29 ±1.41 U/mL, respectively. The ratio of milk clotting activity and proteolytic activity （C/P） were 187.50 and 145.34, respectively. Through the curd effect evaluation, the organization structure, texture parameters and flavor substances of the clots formed by the fermentation broth of the strains LB-1 and LB-2 had comparable milk-clotting effect with that of a commercial rennet, and they were suitable for cheese processing.