Selection Of Microbial Strains And Optimization Of Its Fermentation Conditions For High Yield Nisin Production

Effects of pre-conditioning concentration of penicillin, pre-treatment time, concentration of lysozyme, enzymolysis time and enzymolysis temperature on the production and reproduction rate of protoplast of lactococcus lactis were investigated. Optimum conditions of preparation and reproduction of lactococcus lactis'protoplast were studied. After adding 0.6ug/ml ampicillin for pre-treatment during appropriate growing season of lactococcus lactis, selecting 6mg/ml enzyme solution and enzymolysis for 30min at 37℃, the highest product of production rate and reproduction rate can reach 46%.Mutagenesis of protoplast was conducted by ultraviolet radiation. HU17 was screened through agar block method and agar diffusion method. The genetic stability of HU17 was proven to be better through genetic stability test. After five generations, the potency of nisin was still around 3200IU/ml. Therefore, HU17 was screened as the lipstatin of nisin through ultraviolet mutagenesis.Concentration of corn steep liquor, corn mash, KH2PO4 and NaCl which affect the potency of nisin was investigated through one-factor experiment. The results showed that the ratio of the volume of corn steep liquor and corn mash was 8:2, the optimum concentration of KH2PO4 and NaCl were 14g/L and 2g/L. Concentration of corn steep liquor, corn mash, KH2PO4 and NaCl was optimized through Box-Behnken method and response surface methodologyrsm to show that the optimum components of fermention medium of nisin were: corn steep liquor: 0.88L/L, corn mash: 0.12L/L, KH2PO4: 15.6g/L,NaCl:2.5g/L. The potency of nisin was 5590IU/ml under optimum conditions.Scale-up cultivation of HU17 was performed in 5L fermentor. Effects of the inoculum age, inoculum dose, dissolved oxygen and initial PH of the medium on the potency and biomass of nisin were studied. The results showed that the potency and biomass of nisin were 6200IU/ml and 1.45g/L when the optimum inoculum age was 8h, the optimum inoculum dose was 3%, the optimum dissolved oxygen was 40%, initial PH of the medium was 7.