Role of oxygen supply in submerged fermentation of Ganoderma lucidum for production of Ganoderma polysaccharide and ganoderic acid

The effects of oxygen supply on the submerged fermentation of Ganoderma lucidum, a famous traditional Chinese medicinal mushroom, for simultaneous production of bioactive compounds-Ganoderma polysaccharide and ganoderic acid (GA) were studied. An initial volumetric oxygen transfer coefficient (K(L)a) value within the range of 16.4-96.0 h(-1) had a significant effect on the cell growth, cellular morphology and metabolites biosynthesis. At an initial K(L)a of 78.2 h(-1), a maximal cell concentration of 15.62 gl(-1) by dry weight was obtained, as well as a maximal intracellular polysaccharide (IPS) production of 2.19 g l(-1) and its maximal productivity of 217 mg l(-1) per day. An increase of initial K(L)a led to a bigger size of mycelia aggregates and a higher production and productivity of GA. The GA production and productivity at an initial K(L)a of 96.0 h(-1) was 1.8-fold those at an initial K(L)a of 16.4 h(-1). Dissolved oxygen tension (DOT) also affected the fermentation process. The cell growth of G. lucidum was significantly inhibited when DOT was controlled similar to10% of air saturation, which was due to the oxygen limitation in mycelia aggregates. The production of extracellular polysaccharide (EPS) and contents of IPS and GA similar to10% of DOT were higher than those similar to25% of DOT. However, the total production and productivity of IPS and GA at a low DOT were lower than those at a high DOT. The fundamental information obtained in this study will be useful for submerged fermentation of G. lucidum on a large scale. (C) 2002 Elsevier Science Inc. All rights reserved.