Optimization of medium composition for nisin fermentation with response surface methodology.

Nisin is an effective food biopreservative widely used in food industry. However, 1 problem of concern is limited production rate and final nisin concentration. A nisin-producing strain, L. lactis Lac2, a mutant strain with high yield of nisin, was obtained in our laboratory recently. In the present study, a fractional factorial design was applied to investigate the main factors that affect the yield of L. lactis Lac2. Central composite experimental design and response surface methodology were adopted to derive a statistical model for optimizing the composition of the medium. The results showed that the optimum medium for nisin production of L. lactis Lac2 was composed of 2.68% sucrose (w/v), 0.5% tryptone (w/v), 1% yeast extract (w/v), 0.3% Tween-80 (w/v), 0.02% MgSO4.7H2O (w/v), 0.81% NaCl (w/v), 1.91% K2HPO4 (w/v), 0.05% ascorbic acid (w/v), and 2% agar (w/v) (if necessary) at pH 6.5. When cultured in the optimum medium, the nisin yield is an average of 3381.81 IU/mL, which nearly doubled the yield when incubated in the initial medium. Also, the concentration of tryptone was decreased while that of the sucrose was increased when compared with CM broth, which means a reduction of the fermentation cost.