Screening of a lactic acid bacterium with high-yield protease and optimization of its enzyme-producing conditions

In this study, lactic acid bacteria with high-yield protease was isolated and screened from feces of breastfed infants within 6 months of age by hydrolytic ring preliminary screening and protease rescreening. The screened strains were identified by morphological observation, physiological and biochemical tests and molecular biology techniques. The protease production conditions were optimized by single factor test, Plackett-Burman test, steepest climbing tests and response surface tests using protease as evaluation index. The results showed that a strain mys-01 with high-yield protease capacity was obtained and identified as Lacticaseibacillus rhamnosus. The optimal conditions for protease production of Lacticaseibacillus rhamnosus mys-01 were fermentation temperature 38 ℃, time 24 h, initial pH 6, whey powder addition 4%, inoculum 8.5%, malt extract addition 3%. Under the optimized conditions, the protease activity was 70.59 U/ml, which was 84.07% higher than before optimization.