Abstract: In order to achieve value-added utilization of burdock root waste, the solid-state fermentation of low-quality burdock root by a high-yield polysaccharide-producing strain of Ganoderma lucidum (Leyss. ex. Fr.) Karst was optimized for improved production of mycelial polysaccharide and the in vitro antioxidant activity of the polysaccharide was assessed. The fermentation conditions including amount of medium contained in culture flasks, degree of pulverization and liquid-tosolid ratio were optimized by combined use of one-factor-at-a-time method and response surface methodology. The mycelial polysaccharide from G. lucidum was extracted by water extraction and ethanol precipitation and was quantified by the phenol-sulfuric acid method. After being deproteinized and decolorized by dialysis, the polysaccharide was characterized by infrared spectroscopy and was determined for its monosaccharide composition by high performance liquid chromatography (HPLC). Besides, the in vitro antioxidant activity was evaluated by 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH), superoxide anion and hydroxyl radical scavenging assays. The results showed that the optimal fermentation conditions were as follows: liquid-to-solid ratio 0.4 mL/g, medium-to-culture flask ratio 0.2 g/mL, and use of particles passing through a 6-mesh sieve. The polysaccharide content of the mycelia harvested under the optimized conditions was 24.85 mg/g. Fourier-transform infrared spectroscopy (FTIR) analysis showed that the product had the characteristic absorption peaks of polysaccharide. The monosaccharide composition analysis showed that the polysaccharide was composed of mannose, ribose, rhamnose, glucose and galactose, with mannose being the most abundant monosaccharide, which was 7.6 times as high as glucose. Each of the free radical was over 70% scavenged by the polysaccharide, and the effect increased with increasing its concentration. Hence, the polysaccharide had good antioxidant activity in vitro.

Key words: Arctium lappa L., Ganoderma lucidum, solid-state fermentation, polysaccharide, antioxidant activity