The Study On The Fermentation Technology Of Lactococcus Lacits Subsp. Lactis To Produce The Nisin

Nisin, a polypeptide produced by Lactococcus lactis, restrains most Gram-positive bacteria , especially spores of bacterium. Nisin is cosidered as a safe preservative because of its non-toxic and stability at low pH. The study on Nisin began at 1950s and there are more than 50 countries which permit Nisin as preservative. The standard of Nisin was issued in China these years.The industrial wastes were used as the medium components in the fermentation of Lactococcus lacits subsp.Lactis CGMCC1.2030. It is shown that Nisin productivity was mainly influenced by corn steep liquor, molasses,K2HPO4 and MgSO4 with single factor experiment and the optimal levels were 200 g/L, 30 g/L, 9 g/L and 1 g/L respectively. Box-Behnken design and response surface analysis methods were applied to confirm optimum concentration of mainly effect factor.The results showed that the optimum medium culture was corn steep liquor 243.35 g/L,molasses 26.77 g/L,K2HPO4 8.56 g/L,MgSO4 0.44 g/L.The predictive Nisin productivity is 1334 IU/mL with optimal medium. The validation experiments with optimal medium were conducted 5 times and the average Nisin productivity is 1315.6IU/mL, which confirm the model could fit the fermentation conditions. The cost could be decreased significantly by the industrial waste as medium components to produce Nisin.With the Plackett-Burman method , the factors affected the Nisin titer were studied , and three important components were got , which are glucose , yeast extract and K2HPO4. Box-Behnken experiment were used to optimize the medium , the optimal medium were got as : glucose 24.80 g/L , yeast extract 22.35 g/L,K2HPO4 13.65 g/L. Under the optimal condition , the max predicted Nisin titer is 2157 IU/mL ,while the experimental results 2115 IU/mL .The effects of the medium pH,temperature,rotate speed,inoculum size were studied in this work . The result suggests the optimal culture condition as : medium pH 7 , temperature 36℃, rotate speed 160 r/min , inoculum size 5 %.The pilot-scale fermentation was carried in the Biomate 10 L fermenter . Anaerobic and aerobic batch fermentation was studied. The biomass and Nisin titer were higher in aerobie fermentation. The biomass with aerobic batch fermentation were 4.92 times compared with anaerobic fermentation,while the Nisin titer of aerobic batch fermentation was little higher than that of anaerobic fermentation.