Pellet diameter and morphology of European Ganoderma pfeifferi in a repeated-batch fermentation for exopolysaccharide production

Abstract

The pellet diameter and morphology of an underutilized European Ganoderma pfeifferi (EGP) mycelium was studied in a repeated-batch fermentation (RBF) for exopolysaccharide (EPS) production. In preliminary fermentation, growth screening was performed for initial pH, glucose concentration, and agitation speed. At 30 degrees C, the favourable conditions for EPS production (0.58 g/L) and EPS productivity (0.058 g/L day(-1)) were 15 g/L glucose, initial pH 6, and 100 rpm, while the highest dry cell weight (DCW; 3.63 g/L) was achieved at 9 g/L glucose, initial pH 4, and 120 rpm. Morphologically verified, large, compact pellets (diameter: 40 mu m lt d lt 40.67 mu m) were associated with high DCW while small dispersed pellets (diameter: 11.67 mu m lt d lt 14.67 mu m) were associated with high EPS production. In RBF, EGP mycelium exhibited the ability to self-immobilize and high stability for repeated use with increasing smooth pellet diameter from RBF1 (7.33 mu m lt d lt 7.67 mu m) to RBF4 (16.67 mu m lt d lt 18.33 mu m). The fermentation period was subsequently shortened from 48 (batch) to 24 days in four consecutive cycles of RBF, and the productivity of EPS increased from 0.053 g/L day(-1) to 0.108 g/L day(-1). In an FTIR analysis, crude EPS of EGP showed the presence of beta-glucan characteristics at 1075 cm(-1) and 891 cm(-1) wavelengths, similar with European G. lucidum BCCM 31549. In addition, H-1 NMR showed similar beta-glycosidic linkages when compared with laminarin standard. The proposed strategy demonstrated that G. pfeifferi pellet morphology can withstand extended fermentation cycles for efficient EPS production.