Optimization of Antioxidant Activities and Intracellular Polysaccharide Contents Using Agaricus bisporus Extract as Elicitor in Submerged Fermenting Ganoderma lucidum

Ganoderma lucidum is one of the medicinal fungi frequently used as supplement. The intracellular polysaccharides of this fungus include high molecular weights and help strengthen the immune system. Furthermore, these polysaccharides act as antioxidants by inhibiting free radicals and enhancing activity of the enzymes. Addition of various elicitors to the fungi submerged culture media affects the cell growth and metabolite production. Fungal extracts are one of these elicitors.

In this study, Ganoderma lucidum was first cultured in various culture media to investigate the base media. Using three various methods (soaking the fruit body in water, disintegrating the fruit body with a blender and boiling the fruit body), Agaricus bisporus fruit body extract was prepared as elicitor and the extract with the highest sugar content was used. For the optimization of growth and antioxidant activity of the intracellular polysaccharides, effects of six independent factors were investigated using Placket-Burman method, including Agaricus bisporus extract, peptone, maltose, pH, vitamin B1 and CaCl2. Response surface method was used to optimize three factors of vitamin B1, Agaricus bisporus extract and maltose. Then, stirred tank bioreactor was used to culture Ganoderma lucidum.

The YPG culture medium was selected as the base medium based on mycelial growth and antioxidant activity of the intracellular polysaccharides (IC50). Sugar content of the Agaricus bisporus extract was 30.66 μg.ml-1. Placket-Burman method revealed that the extracts of Agaricus bisporus, maltose and vitamin B1 significantly increased antioxidant activity of the intracellular polysaccharides. After optimizing these factors using RSM, the IC50 was reported as 1.047 mg.ml-1. Ganoderma lucidum cultivation in bioreactor significantly increased the cell growth (5.29 g.l-1). Intracellular polysaccharides included an IC50 of 1.14 mg.ml-1, which was significantly higher than that the intracellular polysaccharides included in YPG culture media.