流式细胞术分析与评价酸奶菌种对模拟胃酸和胆汁盐的耐受力

研究传统酸奶菌种对人体胃酸和胆汁盐的耐受性，对评价酸奶的益生性具有重要意义。实验选取普通酸奶中的嗜热链球菌和保加利亚乳杆菌作为研究对象，模拟胃肠环境以探讨所选两种菌株在不同pH 值和不同质量浓度脱胆盐下的耐受力，用流式细胞仪(FCM)结合羧基荧光素二醋酸酯(5-(6)-carboxyfluorescein diacetate，5(6)-cFDA)和碘化丙锭(propidium iodide，PI)两种荧光染料评价其活力。结果表明：pH2.0 时，菌体细胞活性较低，其活细胞标记率仅为41.8%，在pH3.0、4.0、5.0、6.0、7.0 时，活细胞标记率越来越高，对其抑制性的影响逐渐减弱；在1g/100mL 的脱胆盐(DBS)中，活细胞标记率为48.7%，而在0.5、0.25、0.1、0.05g/100mL 的DBS 中时，活细胞的标记率越来越高；同时比较FCM 与平板菌落计数法检测菌体细胞的耐受水平。实验证实酸奶菌种能耐受pH 值为5.0～7.0 的胃酸和0.05～0.5g/100mL 的DBS；FCM 检测的菌体细胞的状况更能恰当地反映发酵酸奶品质的优劣。

Tolerability of Yogurt Strains to Mimic Gastric Acid and Bile Salt as Analyzed by Flow Cytometry

Studies on the tolerability of traditional yogurt strains to gastric acid and bile salt are very important to evaluate probiotic strains in yogurt. The Streptococcus thermophilus and Lactobacillus bulgaricus in yogurt were evaluated for their olerance to different pH and different concentrations of bile salt in mimic gastrointestinal environment using flow cytometry (FCM) combined with double-fluorescence dye staining by 5(6)-cFDA and PI. The cell viability was very small, and the percentage of labeled viable cells was only 41.8% at an exposure pH of 2.0 and became higher and higher as the exposure pH increased from 3.0 to 7.0 (3.0, 4.0 through 7.0), and the inhibitory effect on viable cells showed a progressive reduction. The percentage of labeled viable cells exposed to 1 g/100mL deconjugated bile salt (DBS) was 48.7%, and those of labeled viable cells exposed to 0.5 g/100mL, 0.25 g/100mL, 0.1 g/100mL and 0.05 g/100mL DBS displayed an increasing pattern. Flow cytometry and plate counts were comparatively used to determine cell viability. The above two species of strains exhibited strong tolerance at the conditions of pH 5.0－7.0 gastric acid and 0.05－0.5 g/100mL deconjugated bile salt. Flow cytometry count was superior to plate count.