西藏牦牛奶渣中优势乳酸菌产胞外多糖及其耐受性

从分离自西藏牦牛奶渣的113株乳酸菌中筛选出4株优势菌株(GY-L003、GY-L004、GY-L055、GYL112),对其产胞外多糖(exopolysaccharide,EPS)能力、耐酸能力、耐胆酸盐能力、耐渗透压能力及抑菌能力进行了比较研究。结果表明:4株乳酸菌产EPS能力不尽相同,其中性能最优的菌株为GY-L003,为379.94 mg/L;4株菌株表现出不同的耐受能力,其中GY-L003和GY-L004在pH 1.5条件下仍能存活;当胆酸盐质量分数高于0.4%时,GY-L003和GY-L004亦能生存,GY-L055和GY-L112则受到抑制;在耐渗透压方面,GY-L003和GY-L004性能较优,9%Na Cl溶液中仍能生长;4株菌均具较好的抑菌特性,对金黄色葡萄球菌抑制最强的为GY-L004,抑菌圈可达(15.94±0.31)mm;GY-L003对大肠杆菌和沙门氏菌的抑制效能最强,抑菌圈分别为(18.21±0.65)、(16.27±0.50)mm;GY-L112对单增李斯特菌抑菌效果佳,抑菌圈为(15.24±0.35)mm。综上,GY-L003和GYL004产EPS、耐受性、抑菌能力等性能俱佳,具有较好的应用潜力,为工业化利用提供了参考依据。

Exopolysaccharide (EPS)-Producing Ability and Tolerance of Dominant Lactic Acid Bacteria (LAB) Strains from Yak Milk Dreg in Tibet

A total of 113 strains of lactic acid bacteria (LAB) were isolated from yak milk dreg in Tibet. Out of these, four dominant LAB stains were screened and compared for their exopolysaccharide (EPS)-producing ability, acid, bile and osmotic pressure tolerance, and antimicrobial activity. Results demonstrated that the EPS-producing abilities were different for the 4 selected strains, with strain GY-L003 producing the highest yield of EPS (379.94 mg/L). The LAB strains exhibited different levels of tolerance to three environmental factors and strains GY-L003 and GY-L004 could survive at extremely acidic pH of 1.5. At a bile concentration of higher than 0.4%, GY-L003 and GY-L004 could grow while GY-L055 and GY-L112 were inhibited. In terms of osmotic tolerance, GY-L003 and GY-L004 were superior, being able to grow when NaCl concentration was up to 9%. All four LAB strains had strong antimicrobial activity, among which GY-L004 had the strongest inhibitory effect against Staphylococcus aureus, with an inhibition zone diameter of (15.94 ± 0.31) mm, GY-L003 had the strongest inhibitory effect against both E. coli and Salmonella, with an inhibition zone circle of (18.21 ± 0.65) and (16.27 ± 0.50) mm, respectively, and GY-L112 exhibited the strongest inhibitory effect against Listeria monocytogenes with an inhibition zone diameter of (15.24 ± 0.35) mm. Taken collectively, our results suggested that both GY-L003 and GY-L004 had high EPS-producing ability, good tolerance to acid, bile and osmotic pressure, and strong antimicrobial activity. Accordingly, these strains have a good application potential and can provide a reference basis for application in the production of fermented dairy products.