【摘要】 以某单位保存的3份乳酸菌菌种进行分离纯化,根据菌落及细菌形态分离得到7株乳酸菌,分别命名为IV-1、IV-2、IV-3、ZK、G、ST和393。利用生化试验将393株初步鉴定为乳球菌,IV-1和IV-3株鉴定为乳杆菌,IV-2、ZK、G和ST株鉴定为链球菌。再用PCR扩增16SrDNA序列,将测得的序列进行同源性分析,结果显示IV-1株为嗜酸乳杆菌,IV-3株为保加利亚乳杆菌,393株为乳酸乳球菌,IV-2、ZK、G和ST株为嗜热链球菌。选择不同乳酸菌的代表菌株进行酸乳发酵试验,结果表明不仅不同种乳酸菌的凝乳时间、产酸速度、酸乳风味和质地等存在差异,而且同种不同株嗜热链球菌也存在显著差异;在所试的6株乳酸菌中,G和ST株嗜热链球菌的综合发酵性能指标较好,其他菌株具有一定的单方面优势。结果提示,基于16SrDNA序列的遗传进化树分析可用于乳酸菌的准确鉴定,但不能取代常规方法用于优良酸乳发酵性能菌株的筛选。更多还原

【Abstract】 Contamination and/or genetic variation may occur during passage and storage of lactic acid bacteria,and thus prompt rejuvenation and identification of the bacterial stocks are often needed.In this study,seven lactic acid bacterial strains were isolated by streaking 3lactic acid bacterial stocks on agar plates,which were named as IV-1,IV-2,IV-3, ZK,G,ST and 393.The seven bacterial strains were characterized as Lactococcus(strain 393),Lactobacillus(strains IV-1and IV-3)or Streptococcus(strains IV-2,ZK,G and ST)according to their biochemical reaction characteristics.To identify further the lactic acid bacterial strains,16Sribosomal DNA(rDNA)was amplified for sequence homology analysis,the seven lactic acid bacterial strains belonged to L.acidophilus(strain IV-1),L.bulgaricus(strain IV-3),L.lactis(strain 393)and S.thermophilus(strains IV-2,ZK,G and ST),respectively.Yogurt fermentation showed significant differences in milk clotting time,acidifiability,viscosity and dehydration shrinkage,flavor and texture of the acidophilus milks,not only between different lactic acid bacterial species,but also between different strains of S.thermophilus. Among 6lactic acid bacterial strains tested,S.thermophilus strain G and ST had better performance in yogurt fermentation,the other strains had some unilateral advantages.These data indicate that the 16SrDNA-based sequence analysis is valuable for accurate identification of lactic acid bacteria,but unable to replace the conventional methods for screening of the fine strains with excellent performance in yogurt fermentation.更多还原