Optimization of Medium Constituents for ε-Poly-L-Lysine Fermentation with Response Surface Methodology

epsilon-Poly-L-lysine (epsilon-PL) is a novel food biopreservative with broad antimicrobial activity. In the present study, single-factor experiments were applied to screen optimal carbon and nitrogen sources that affect the yield of a epsilon-PL-producing strain, Streptomyces violaceusniger, which was obtained in our laboratory recently. Box-Behnken design and response surface methodology (RSM) were adopted to derive a statistical model for optimizing the composition of the fermentation medium. The results showed that the main factors that affect e-PL production were glucose, carbon source; peptone, organic nitrogen source; and (NH4)(2)SO4, inorganic nitrogen source. The optimum fermentation medium for e-PL production of S. violaceusniger consisted of (g/L) glucose, 62.49; peptone, 5.71; (NH4)(2)SO4, 11.19; MgSO4, 0.5; FeSO4, 0.03; ZnSO4, 0.04; KH2PO4, 1.36; and Na2HPO4 center dot 12H(2)O, 3.58. When cultured in the optimum medium, the e-PL production was an average of 0.349 +/- 0.025 mg/mL, which was 1.75 times higher than the initial medium.