To be competitive with common synthetic surfactants, the cost of production of rhamnolipid must be minimized by the fermentation process of non-foaming and low impurities. Herein, a novel solid-state fermentation process was developed for production of rhamnolipid by Pseudomonas aeruginosa SKY. The results were shown that high-density polyurethane foam is a satisfactory alternative to agro-industrial by-products for SSF of rhamnolipid. Palm oil and NaNO3 were promising carbon source and nitrogen source, respectively. Response surface methodology was employed to enhance the production of rhamnolipid. Palm oil, NaNO3 and liquid-to-solid ratios were significant factors. The optimal medium was developed as: 73.6 g/l palm oil; 3.0 g/l g NaNO3; 1.1 g NaCl; 1.1 g KCl; 3.4 g KH2PO4; 4.4 g K2HPO4; 0.5 g MgSO4·7H2O and 37.2 liquid-to-solid ratios. An overall 1.39-fold increase in rhamnolipid production was achieved in the optimized medium as compared with the unoptimized basal medium. Air pressure pulsation solid-state fermentation (APP-SSF) was applied to the experiment of scale-up for improving transfer efficiency of heat and mass. The yield of rhamnolipid reached 39.8 g/l in a 30 l APP-SSF fermenter. The crude extract of rhamnolipid lowered the surface tension of water to 28 mN/m and kept the critical micelle concentration at 50 mg/l. The work revealed the SSF with HPUF as an inert support was a promising fermentation system that could effectively produce rhamnolipid with low impurities, high productivity and low cost of production at a large scale.
Keywords: Air pressure pulsation solid-state fermentation; High-density polyurethane foam; Response surface methodology; Rhamnolipid; Solid-state famentation.