Optimization of medium constituents for ε-poly-L-lysine fermentation with response surface methodology

ε-Poly-L-lysine (ε-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 ε-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 ɛ-PL production were glucose, carbon source; peptone, organic nitrogen source; and (NH(4))(2)SO(4), inorganic nitrogen source. The optimum fermentation medium for ɛ-PL production of S. violaceusniger consisted of (g/L) glucose, 62.49; peptone, 5.71; (NH(4))(2)SO(4), 11.19; MgSO(4), 0.5; FeSO(4), 0.03; ZnSO(4), 0.04; KH(2)PO(4), 1.36; and Na(2)HPO(4).12H(2)O, 3.58. When cultured in the optimum medium, the ε-PL production was an average of 0.349 ± 0.025 mg/mL, which was 1.75 times higher than the initial medium.