Screening of lactobacillus delbruekii subsp. bulgaricus with weak post-acidification capacity by natural and induced mutation

To derive new starter culture strains with weak post-acidification capacity, Lactobacillus delbruekii subsp. bulgaricus LY were screened by natural screening and inducing screening treated with ultraviolet and diethyl sulfate. Then treated strains were inoculated into low pH MRS medium and skim milk at 37°C for 24h, respectively. The mutants that could grow in skim milk but did not grow in low pH MRS medium were selected strains with weak post-acidification capacity. The mutants were preserved and their generation stabilities were tested. The natural screening, diethyl sulfate and ultraviolet treated mutants showed 5.1%, 5.9% and 11.9% lower post-acidification capacity than original strain at 25°C, respectively. The mutants showed genetically stable post-acidification capacity.