Optimization studies to develop a low-cost medium for production of the lipases of Rhizopus microsporus by solid-state fermentation and scale-up of the process to a pilot packed-bed bioreactor

Abstract

Abstract A low-cost lipase preparation is required for enzymatic biodiesel synthesis. One possibility is to produce the lipase in solid-state fermentation (SSF) and then add the fermented solids (FS) directly to the reaction medium for biodiesel synthesis. In the current work, we scaled up the production of FS containing the lipases of Rhizopus microsporus. Initial experiments in flasks led to a low-cost medium containing wheat bran and sugarcane bagasse (50:50 w/w, dry basis), supplemented only with urea. We used this medium to scale-up production of FS, from 10 g in a laboratory column bioreactor to 15 kg in a pilot packed-bed bioreactor. This is the largest scale yet reported for lipase production in SSF. During scale-up, the hydrolytic activity of the FS decreased 57%: from 265 U g−1 at 18 h in the laboratory bioreactor to 113 U g−1 at 20 h in the pilot bioreactor. However, the esterification activity decreased by only 14%: from 12.1 U g−1 to 10.4 U g−1. When the FS produced in the laboratory and pilot bioreactors were dried and added directly to a solvent-free reaction medium to catalyze the esterification of oleic acid with ethanol, both gave the same ester content, 69% in 48 h.