嗜热链球菌发酵剂的筛选及其发酵特性研究

Screening and Fermentation Properties of Streptococcus thermophilus

嗜热链球菌作为发酵剂菌株,其发酵特性直接影响着酸奶质地和风味。本研究采用选择性平板、形态观察和16S rDNA基因序列分析,从发酵乳制品和植物制品样品中共鉴定出10株嗜热链球菌;并通过测定菌株生长曲线、pH值及乳酸产量,从中筛选出S.thermophilus ST-M-03和ST-P-07两株性能较好的菌株。培养14h发现,ST-M-03和ST-P-07的OD_(600)为1.75,pH值分别为4.44和4.47,乳酸含量为241.63和238.17μmol/mL;两株菌株在5h内均可使酸奶的pH值达到4.5;贮藏期结束S.thermophilus ST-M-03和ST-P-07发酵的酸度分别增加了7.64和10.13 T,活菌数为8.74和8.78 lg CFU/g,黏度为3602.78和20140.38mPa·s,离心沉淀率为57.18%和49.99%。表明S.thermophilus ST-M-03和ST-P-07菌株均具有良好的生产性能,其产酸能力、弱后酸、稳定性和低离心沉淀率均与商品化发酵剂菌株相当,是两株性能优良的酸奶发酵剂菌株。

The fermentation properties of Streptococcus thermophilus as a starter is a major factor in yogurt's texture and flavor characteristics.In this study,S.thermophilus were isolated and screened from dairy products and plant materials.The strains were identified by bacterium morphology and the 16S rDNA gene.By analyzing the growth curve,pH curve,and lactic acid content,strains with excellent growth performance and high acidification capacity were obtained.Fermentation properties of the strains in yogurt were assessed by assessing the acidity,microbial counts,viscosity,and centrifugal sedimentation rate during the storage period after the strains had fermented the milk.The results revealed that among the 10 S.thermophilus,ST-M-03,and ST-P-07 had a growth rate with an OD_(600) of 1.75 and pH values of 4.44 and 4.47,respectively,after 14 hours of incubation.The lactic acid contents were 241.63 and 238.17μmol/mL,respectively.Both strains were capable of reducing the pH of yogurt to 4.5 within 5 hours.Upon completion of the storage period,ST-M-03 and ST-P-07 exhibited a significant increase in acidity with an increment of 7.64 and 10.13°T,respectively.The viable bacterial counts were observed to be 8.74 and 8.78 lg CFU/g,and the viscosities were found to be 3602.78 and 20140.38 mPa·s,respectively;The centrifugal sedimentation rates were recorded to be 57.18%and 49.99%,respectively.These findings suggest that S.thermophilus ST-M-03 and ST-P-07 possess high acidification capacity,weak post-acidification,good strain stability,and low centrifugal sedimentation rates,thereby demonstrating their potential as a starter for the dairy industry.