甘南藏族传统发酵乳中高产胞外多糖菌株筛选及发酵特性研究

Screening and fermentation characteristics of exopolysaccharidesproducing strains from Tibetan traditional fermented milk in Gannan

采用苯酚-浓硫酸法检测胞外多糖含量,对从甘南藏族传统发酵乳中分离的20株乳酸菌进行筛选。结果表明,菌株MN-002为高产菌株,在12%脱脂乳中产生的胞外多糖为(502.92±17.46)μg/mL。综合培养形态、显微形态、生理生化指标和16S rRNA基因序列分析,鉴定其为嗜热链球菌(Streptococcus thermophilus)。发酵结果显示,在12%脱脂乳中发酵5 h后pH即降至4.6以下,发酵6 h后活菌数达到7.8×10^8 cfu/g,菌株产酸速度快,为产黏菌株,发酵风味突出,且后酸化弱;稳定性研究结果表明,发酵乳在4℃贮藏21 d后,其中的乳酸菌活菌数仍保持在3.2×10^8 cfu/g,在43℃条件下发酵12%脱脂乳7 d后,pH值降至3.65,酸度为140°T,活菌数保持在4.7×10^7 cfu/g,揭示该菌株在酸性发酵乳中具有较好的稳定性。综上,菌株MN-002为一株性能优良、具有良好稳定性的菌株,可作为乳酸菌发酵剂进行进一步开发。

Strain MN-002 with high exopolysaccharide production was screened from 20 lactic acid bacteria isolated from Gannan Tibetan traditional fermented milk.The yield of exopolysaccharide in 12%skim milk medium was(502.92+17.46)μg/mL by phenol-sulfuric acid method.Strain MN-002 was identified as Streptococcus thermophilus by comprehensive analysis of culture morphological,physiological,biochemical characteristics and 16S rRNA gene sequence.The pH value dropped below 4.6 after 5 hours of fermentation in 12%skim milk,and the number of viable bacteria reached up to 7.8×10^8 cfu/g after 6 hours of fermentation.The results of stability study showed that the number of lactic acid bacteria remained at 3.2×10^8 cfu/g after 21 days storage at 4℃.After fermenting 12%skim milk at 43℃for 7 days,the pH value dropped to 3.65,the acidity was 140°T,and the number of live bacteria remained at 4.7×10^7 cfu/g,which indicated that the strain had good stability in acidic fermented milk.In conclusion,strain MN-002 is a strain with excellent performance and good stability,which can be further used as an industrial strain.