一株酸奶发酵嗜热链球菌的筛选及特性研究

Identification and Characterization of a Streptococcus thermophiles Strain for Yogurt Fermentation

为获得能发酵鲜奶产生酸奶的嗜热链球菌菌种,采用50℃高温及MC选择性培养基为筛选条件,从自然发酵的酸奶中分离、筛选菌株,采用形态学观察、生理生化特征鉴定、16SrDNA基因序列测定及系统发育树同源性分析进行鉴定,并对该菌发酵酸奶特性及微生物学特性进行研究。筛选出一株能发酵产生酸奶的菌株LCM46,鉴定为嗜热链球菌(Streptococcus thermophilus)。该菌以鲜奶为基质,在42℃、发酵11h可产生风味俱佳、口感脆嫩的凝固型酸奶,酸度为(80.77±0.17)°T,菌落总数(11.71±0.20)×108 cfu/mL。该菌对数生长期为2~12h,最适生长基质为牛乳、温度40℃、pH 6.0,适合生长温度为10~60℃、pH 4.3~7.5,耐受pH临界值为3.5,自凝集率为19.28%,对大肠杆菌DH5α凝集率为12.32%。该菌有望与高黏附型菌种混合发酵提高发酵乳品质及口感。

To screen and identify Streptococcus thermophiles strain cultivated in fresh milk as the medium for potential use in the yogurt industry,the strains were isolated from traditional fermented milk via inoculated in MC selective medium at 50℃.The morphological,physiological characteristics and 16SrDNA gene sequence analyses were used to identify the strain of interest.Characteristics were analyzed using spectrophotometry and plate counting assays.The result showed that an isolate LCM46 consistently produced fermented yogurt was identified as Streptococcus thermophilus LCM46（Accession No.KR105939）and was thus selected for further study.When fermented by strain LCM46 at 42℃ for 11 hours,good flavor and crisp tastes would be observed in fermented yogurt with the acidity of（80.77±0.17）°T and the viable count of（11.71±0.20）×10~8 cfu/mL.The strain LCM46 reached the logarithmic growth phase after 2 hours,and the stationary phase after 12 hours.The optimal growth medium was milk,the temperature for the fermentation was 40℃,while the initial pH was 6.0.Its suitable growth temperature and pH were 10-60℃ and pH 4.3-7.5 respectively.The tolerance of critical pH value was 3.5.The auto-aggregation rate was 19.28% after 24 h of incubation,while the co-aggregation with E.coli DH5α was 12.32%.These studies indicate that the strain LCM46 represented a good strain with broad development potential in the yogurt industry,also it could be mixed fermented with high adhesion type strains to improve the yogurt quality and taste.