Production of lipase by repeated batch fermentation with immobilized Rhizopus arrhizus

Lipase produced by immobilized mycelium from Rhizopus arrhizus in submerged fermentation was studied. The highest lipase activity of 315 u/mL was achieved at 26.5 °C, 130 rpm and 100 mL medium in 250 mL flask consisting of (%): soybean flour 4.0 (w/v), peanut oil 1.0 (v/v), MgSO4 0.1 (w/v), K2HPO4 0.5 (w/v), (NH4)2SO4 0.2 (w/v), after 96 h of cultivation. Repeated batch fermentation by immobilized mycelium was tested and the time to replace, the volume of the replaced medium and the optimal composition of the medium for replacing during the repeated batch fermentation were optimized. Immobilized cells showed high stability for repeated use. Nine repeated batches could be carried out in flasks for 140 h and six repeated batches in 5 L fermentor when the substitute culture medium consisted of (%): soybean flour 3.0 (w/v), peanut oil 0.5 (v/v) and the culture medium was replaced by 67–83%. The lipase productivity increased from 3.1 u/mL h in batch fermentation to 17.6 u/mL h in repeated batch fermentation, which was 5.6 times as high as that in batch fermentation.