为了筛选到适合酸奶生产的抗噬菌体菌株,采用双层平板法及自然选育的方法,从酸奶异常发酵液中分离到3种不同的噬菌体,并获得了4株具有抗这些噬菌体能力的非溶源性抗性菌株St1、St2、St3、St4,对这4株抗性菌株进行20次传代和酸奶发酵实验,结果表明其抗性稳定,其中St3发酵酸奶产酸可达110°T,凝乳时间与出发菌株基本相当,在高噬菌体浓度下发酵,产酸正常,黏度、硬度、口感较好,凝乳时间较短、乳清析出较少并且富集培养后菌体浓度可达1010CFU/mL,适宜于工业生产。

To select bacteriophage-resistant mutants suitable for yoghurt production,the method of double layer agar plate and natural selection were used. Three different phages were isolated from the abnormal fermentation broth of Streptococcus thermophilus St0 which producing yoghourt. Four bacteriophage-resistant mutants( St1,St2,St3,St4) were obtained and proved to be non-lysogen by Mitomycin induction. The resistance and the yoghourt fermentation ability of these mutants were stable after 20 subcultures. The mutant St3 produced total acids up to 110° T after fermentation and the yogurt curd time was as same as the origin strain. When the mutant strain was cultured under higher concentrations phage environment,the bacteria growth was normal,and its acid production,viscosity,hardness,taste were all better than those of original strain. In the meantime,shorter curd and less whey separation were obtained and bacteria concentration was up to 1010CFU/mL after enrichment culture. So it was suitable for industrial production.