The usage of rice straw as a major substrate for the production of surfactin by Bacillus amyloliquefaciens XZ-173 in solid-state fermentation.

Agro-industrial byproducts, especially rice straw, are potential resources. This work was aimed to utilize raw materials to produce value-added biosurfactant in solid-state fermentation (SSF). Rice straw and soybean flour were found efficient and selected as major substrates for surfactin production. The results of Plackett-Burman design indicated that glycerol, water content, inoculum size and temperature were the significant variables identified in the screen of nine total variables. The optimum values for the four significant variables were determined by the Box-Behnken design. The optimal surfactin production was obtained when the medium contained 5 g soybean flour, 4 g rice straw, 2% (w/w) maltose and 2.65% (w/w) glycerol, pH 7.0. The ideal growth conditions for surfactin production consisted of a moisture content of 62.8% (v/w) and growth supplemented with 15.96% inoculum size in 250 mL flasks at 26.9 °C for 48 h. Under optimal conditions, a surfactin yield of 15.03 mg/gds was attained in 1000-fold scale-up fermentation in a 50 L fermenter, thereby validating the accuracy of this approach. This study proposed an eco-friendly and economical way to convert agro-industrial byproducts into biosurfactant.