Study On Fermentation Conditions Affacting The Mycelial Growth And Polysaccharide Biosynthesis Of Grifola Frondosa

The fermentation conditions affect significantly the mycelial growth, morphology, and target metabolites of edible（medicinal） fungi during submerged culture process. The morphological changes of these fungi possibly lead to the structures of produced polysaccharides, and further influence their bioactivities. The well-known edible mushroom Grifola frondosa belongs to the order Aphyllopherales and family Polyporeceae. As one of the bioactive compounds of Grifola frondosa, the polysaccharides have recently attracted considerable attention for its physiological activities such as anti-tumor, hypoglycemic and immuno-stimulating properties. However, previous studies mainly focused on the process optimization of submerged fermentation to maximumly produce Grifola frondosa mycelia and mycelial（exo-） polysaccharide, while few references are available about relationship between polysaccharide biosynthesis and morphological changes of G. frondosa. Hence, based on our previous researches, the present study will aim to investigate effects of agitation, aeration and addition of microparticles on the mycelial growth and polysaccharide production of G. frondosa, and find a clue of the relationship between polysaccharide biosynthesis and morphological changes.The main obtained results are listed as follows:（1） The relationship between agitation and aeration, morphology and polysaccharide production by G.frondosa GF9801 in a 20 L fermentor was studied. The results showed that the agitation of 90 rpm yielded a highest mycelial biomass of 22.49 g/L and maximum mycelia polysaccharide production of 0.12 g/g, the pellets occupied for 52.23% in the broth. The agitation of 120 rpm benefited the exo-polysaccharide（EPS） production for 2.19 g/L and the EPS productivity was 0.31 g/L·d whereas the percentages of filaments and clumps were almost 20% ethither. High aeration of 1.0 vvm resulted in more clumps and maximum mycelial biomass of 24.75 g/L. The aeration of 0.75 vvm benefited the polysaccharide production for 2.32 g/L and 0.32 g/g. Hence, the middle agitation and aeration resulted in high mycelial biomass and pellets benefited the biosynthesis of polysaccharides.（2） Different concentrations varying from 0 to 20 g/L of Al₂O₃（48⁷5 μm） and Talc（45 μm） were added in the culture medium of G. frondosa GF9801. Results showed that the addition of Al₂O₃ decreased the diameter of the pellets, the percentage of S mycelia increased with the increasing of the concentration. The concentration of 3 g/L benefited the maximum mycelial biomass for 20.33 g/L, and the concentration of 10 g/L and 6 g/L yielded the highest EPS and mycelial polysaccharide production of 3.38 g/L and 0.26 g/g, respectively. Maximum mycelial biomass and EPS production was achieved at 6 g/L of Talc. The concentration of 3 g/L of Talc resulted in highest mycelial polysaccharide production of 0.24 g/g. The addition of Al₂O₃ showed superior effect on the mycelial growth and polysaccharide production of G. frondosa.（3） The monosaccharide composition of polysaccharide of G.frondosa under different fermentation conditions was studied. The glucose dominated the ratios of 95⁹8% in the EPS under different agitation and aeration. Glucose and mannose were the main component in the mycelial polysaccharide. The maximum mannose percentage of 51.05% was achieved at 60 rpm. The aeration of 0.75 vvm had the maximum percentage of arabinose for 14.02%. For the EPS, with the addition of microparticles, percentage of glucose was lower than that in the control. The concentration of 6 g/L of Al₂O₃ and Talc resulted in the lowest glucose percentage. With the addition of Talc, the maximum galactose percentage of 16.77% was achieved at 6 g/L. For mycelial polysaccharide, the percentage of glucose decreased while the percentage of galactose increased with increase of microparticle concentration. The minimum glucose and maximum galactose percentage were 12.70% and 31.19%, achieved at 20 g/L Al₂O₃ and Talc, respectively.（4） Effect of fermentation conditions on enzymes activities associated G. frondosa mycelial polysaccharides and exo-polysaccharide was investigated. Results showed that the percentages of glucose, mannose and galactose in G. frondosa polysaccharides showed the similar trends with activities of the polysaccharide-synthesis associated enzymes under various fermentation conditions. The agitation of 60 rpm had the maximum GDP-mannose pyrophosphorylase（GMPPB） activity of 82 mU/mg. The minimum UDP-glucose pyrophosphorylase（UGPG） and maximum UDP- Glucose-4-epimerase（UGE） activity of 68 mU/mg and 165 mU/mg were achieved at 20 g/L Al₂O₃ and Talc, respectively.The results suggested that PGI/GMPPB might be closely repated to mannose synthesis and UGPG /UGE could affect the percentages of glucose and galactose within the biosynthetic pathways of G. frondosa mycelial polysaccharides, respectively.