Study On Fermentation Technology Of Nisin

Nisin is an antimicrobial peptide produced by some strains of Lactococcus lactis. It is composed of 34 amino acids and has a molecular mass of 3500 Da. Nisin is widely used as a natural food pre-servative since it shows antimicrobial activity against most Gram-positive bacteria.To ferment Nisin by Lactococcus lactis is the only way to obtain Nisin. Base the single-factor experiment, uniform design was applied to optimize fermentation medium by MELN105 which preserved in our laboratory. The medium composition of the fermentation medium was: sucrose 2.93%, soy peptone1.0%, yeast extract 0.43%, Na₂HPO₄ 1.89%, MgSO₄·7H₂O 0.02%. Then the single-factor experiments were utilize to optimize the fermentation condition. And the optimized fermentation condition was determined as following, pH of medium was adjusted to 7.5 before sterilization and 20mL broth was incubated at 30℃for 24h 150mL Erlenmeyer flask. Compared the batch fermentation at natural pH and the optimum pH6.5, To avoid growth inhibition by a decrease of pH, caused by the accumulation of lactic acid in the lactic acid fermentation process, pH was controlled at 6.5. The titre of Nisin was increased 21.9% compared with the batch fermentation at natural pH. A higher initial sucrose concentration leads to the repression of catabolism and inhibits Nisin biosynthesis in batch culture. Fed-batch culture can eliminate substrate inhibition and control the substrate concentration at the appropriate level. Then two feeding strategies which can shorten the fermentation cycle were investigated. The Nisin titer reached its maximum, 4673 IU/mL, by addition of sucrose at a feeding rate of 10 g/L in two times; an increase in 19.2% over that of the batch culture at pH6.5.The Lactococcus lactis ATCC11454 fermentation process at pH6.5 in all cases were described by logistic model et al. The kinetic parameters were estimated by Genetic Algorithm. The mathematical kinetic models describing the course of Nisin fermentation were established. The experimental data showed that the model could describe Nisin fermentation quite well. This will provide the theoretical foundation for the further study and forecast of the Nisin fermentation process in future.