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Cell envelope proteases (CEPs) can break down milk protein into peptides with different functions, which are of great benefit to human health. Therefore, the high-yield CEPs of Lactobacillus plantarum have the potential to produce functional dairy products. In previous experiments, we found that Na2HPO4, inulin, casein peptone and leucine have significant effects on CEP production by Lactobacillus plantarum LP69. So we proceeded to optimize the composition of the CEP-producing culture medium of L. plantarum through Box-Behnken design and response surface methodology. The protease activity, protein content and specific activity of CEPs produced by L. plantarum by inulin (0.2, 0.3, 0.4 %), casein peptone (0.4, 0.6, 0.8 %), Na2HPO4 (0.50, 0.52, 0.54 %) and leucine (14, 16, 18 mg/L) were evaluated. The optimal ratio of medium is 0.4 % inulin, 0.66 % casein peptone, 0.5 % Na2HPO4 and 14.04 mg/L Leucine. The final enzyme activity reached (24.46±0.81) U/mL, and the specific activity reached (1.41±0.46) U/mg.

Cell-envelope proteinases (CEPs) can hydrolyze casein into functional peptides, which is beneficial to the health of the host. The single factor experiment screened out that the optimal conditions for CEP production by Lactobacillus plantarum LP69 were 37°C, 20h, initial pH of 7, and optimal inoculation amount of 5%. The best conditions for this experiment were obtained by orthogonal experiment: time 22h, temperature 39°C, initial pH value of 6, and inoculation amount of 5%. Under this culture condition, the target protease activity of Lactobacillus plantarum LP69 reached 22.31±0.82U/mL, the protein content was 19.07±0.36mg/mL, and the specific activity was 1.17±0.06U/mg. The specific activity significantly increased by 15.8% compared with the control (p

In present study, the effects of carbon sources (glucose, lactose, sucrose, galactose, maltose and soluble starch) and nitrogen sources (casein peptone, whey protein, soy peptone, yeast, tryptone, beef extract and peptone) on activity of cell envelope proteinases (CEP), specific activity, protein content, OD600 value and pH in MRS broth fermented by Lactobacillus plantarum LP69 were investigated by individual factor experiment. The results indicated that carbon and nitrogen sources have significant influence on the activity of CEP and specific activitys of L. plantarum LP69, glucose, maltose, casein peptone and peptone are superior to other selected carbon and nitrogen sources. The optimum concentrations of glucose, maltose, casein peptone and peptone for L. plantarum LP69 are 2%, 2%, 1% and 1%; the activity of CEP are 19.52U/mL, 21.13U/mL, 13.49U/mL and 20.61U/mL, respectively.

The objective of the present study was to obtain the optimum proportion of the carbon source and prebiotics for Bifidobacterium bifidum BB01 by the central composite design (CCD). The effect of carbon source (lactose) and two prebiotics (inulin and fructooligosaccharides) on the BB01 were observed by measuring the OD600 value, pH value and the viable counts at 18h. The final optimized concentrations of carbon source and prebiotics were: lactose 1.6%, inulin 0.26%, and fructooligosaccharides 0.22%. The result indicates that the growth of B. bifidum BB01 shows an significant increase in the optimized culture medium (p < 0.05), the OD600 value reached 1.434 at 18h, which increased 6.58% compared to the control. And the viable counts of B. bifidum BB01 increased 24.36% and reached (2.17±0.06) ×109cfu/mL. The results show that the optimization of the carbon source and prebiotics using CCD in this study is workable and necessary.