Abstract: Response surface methodology was employed to optimize the solid-state fermentation process of Fusarium oxysporum LD105, isolated from maca rhizosphere soil in Kunming, Yunnan Province, for improved production of antibacterial polysaccharides. Polysaccharide yield and antibacterial activity were used as response variables. Using one-factor-at-a-time method, fermentation time, initial moisture content, sucrose and KH2PO4 concentration were identified as main factors that significantly influence the responses. The three-dimensional response surfaces were generated to study the interaction among the four factors. The results showed that the optimal fermentation conditions were as follows: fermentation time 5 d; sucrose concentration 3%; fermentation temperature 28 ℃, initial moisture content 54%, KH2PO4 concentration 0.3%, inoculum size 10%, initial medium pH 6, peptone concentration 1.5%, and 10 g of medium contained in a 250 mL conical flask. Under these conditions, the percentage inhibition of Escherichia coli and the polysaccharide yield were 37.6% and 30.2 mg/g, which were increased by 2.8 and 2.5 folds as compared to that obtained using the unoptimized medium, respectively.

Key words: antimicrobial polysaccharide, solid-state fermentation, response surface optimization, Fusarium oxysporum LD105