Lipase Production By Rhizopus Arrhizus

The lipase from Rhizopus has1,3-regioselectivity, so it can selectively catalyze the hydrolysis of triacylglycerol to produce some specific industrial products.The effects of feeding carbon sources and nitrogen sources on the lipase production by Rhizopus arrhizus were studied.A strategy for Rhizopus arrhizus lipase production enhancement by feeding oleic acid was developed. The oleic acid was proved to have strong inducing effect on lipase production, but high concentration oleic acid could repress lipase production. Our feeding strategy based on the decrease rate of oleic acid, which was a new feeding method, showed excellent performance. The maximum lipase activity was obtained by feeding dilute oleic acid every12h starting at60h, which maintained the oleic acid content in ferment liquor around18mg·L, and the lipase activity was31%higher than that without feeding. Compared with other nitrogen sources, whole-fat soybean flour has strong ability on the enhancement of lipase production, and the highest lipase activity370U·mL-1was gained at the optimum feeding condition:feeding0.5%soybean flour from60h every12h.Adding soybean hull during fermentation could not only prevent mycelia to form pellets just like the effect of polyurethane, but also makes fermentation scale-up easy. Inoculating5%36h-flask-inoculums and reducing the initial carbon concentration to5%can reduce the fermentation time and enhance the lipase productivity. Based on these conditions, feeding peanut oil when pH rebounded can boosted the lipase productivity to6233U·h-1(187U·mL-1at60h), which was three times as high as that of batch fermentation (2000U·h-1). Total nitrogen content in5L fermentor was analyzed and the lipase activity was enhanced by62%with the feeding strategy according to the variation of nitrogen source.Production of lipase by Rhizopus arrhizus was studied in a rotating biological contactor (RBC) with polyurethane foam (PUF), as a porous biomass support, fixed on both sides of the RBC disks. The effects of aeration rate, rotating rate of discs, volume of broth and the number of discs on the lipase activity were studied in the6L RBC, and the optimum fermentation condition was:4L·min-1aeration rate,100rpm, and3.5L medium with three discs in6L RBC. Repeated batch fermentation by immobilized mycelium was tested and it was found that immobilized cells showed high stability for repeated use. Five repeated batches could be carried out in6L RBC and the lipase productivity increased from3125 U·h-1in batch fermentation to9512U·h-1in repeated batch fermentation, which was3times as high as that in batch fermentation.Separation and purification of lipase in ferment liquor were studied. The fermented broth was concentrated greatly by polyethylene glycol during the purification process which can reduce the dosage of acetone. Using higher molecular weight of polyethylene glycol gave higher purity of lipase power, and had no reverse effect on the yield. Lipase yield could be enhanced when the purification process was carried out at low temperature or by adding surfactant (such as span85).