RESULTS: The production medium was first optimized using a statistical optimization approach to increase pectinase production. A maximal enzyme concentration of 76.35 U/mL (a 2.8-fold increase compared with the initial medium) was produced in a medium composed of (g/L): pectin, 32.22; (NH4)2SO4, 4.33; K2HPO4, 1.36; MgSO4.5H2O, 0.05; KCl, 0.05; and FeSO4.5H2O, 0.10. The cultivations were then carried out in a 16-L stirred tank bioreactor in both batch and fed-batch modes to improve enzyme production, which is an important step for bioprocess industrialization. Controlling the pH at 5.5 during cultivation yielded a pectinase production of 109.63 U/mL, which was about 10% higher than the uncontrolled pH culture. Furthermore, fed-batch cultivation using sucrose as a feeding substrate with a rate of 2 g/L/h increased the enzyme production up to 450 U/mL after 126 h.
CONCLUSIONS: Statistical medium optimization improved volumetric pectinase productivity by about 2.8 folds. Scaling-up the production process in 16-L semi-industrial stirred tank bioreactor under controlled pH further enhanced pectinase production by about 4-folds. Finally, bioreactor fed-batch cultivation using constant carbon source feeding increased maximal volumetric enzyme production by about 16.5-folds from the initial starting conditions.
OBJECTIVES: This work focuses on the development of a simple cultivation strategy for exopolysaccharides (EPS) production using Ganoderma lucidum and submerged cultivation system.
METHODS: At first, the best medium supporting EPS production was chosen experimentally from the current published data. Second, like many EPS production processes, carbon and nitrogen concentrations were optimized to support the highest production of polysaccharides in the shake flask level. Furthermore, the process was scaled up in 16-L stirred tank bioreactor.
RESULTS: The results clearly demonstrated that the best cultivation strategy was cultivation under controlled pH conditions (pH 5.5). Under this condition, the maximal volumetric and specific yield of EPS production were, 5.0 g/L and 0.42 g/g, respectively.
CONCLUSION: The current results clearly demonstrate the high potential use of submerged cultivation system as an alternative to conventional solid-state fermentation for EPS production by G. lucidum. Furthermore, the optimization of both carbon and nitrogen sources concentration and scaling up of the process showed a significant increase in both volumetric and specific EPS production.