Optimization Of Active Exo-polysaccharides From Inonotus Obliquus In Submerged Fermentation Using Response Surface Methodology And Lignocellulose Decomposition

Inonotus obliquus is a rare edible and medicinal fungus. The fruit body and mycelium of Inonotus obliquus contain several kinds of bioactive substances. Polysaccharides in the fungus have antioxidative activity, immunomodulating, antitumor, and anti-caducity actions. In this thesis, the culture medium in submerged fermentation of Inonotus obliquus was optimized with statistical methods to obtain extracellular polysaccharides (EPS) with the strongest hydroxyl radical scavenging activity. On this basis, lignocellulose decomposition was employed to further enhance the EPS yield and hydroxyl radical scavenging activity.A two-level fractional factorial design was used to evaluate the effect of different components of medium. Corn flour, peptone, and KH₂PO₄ were important factors significantly affecting hydroxyl radical scavenging activity. These selected variables were subsequently optimized using path of steepest ascent (descent), a central composite design, and response surface analysis. The optimal medium composition was (% w/v): corn flour 5.30, peptone 0.32, KH₂PO₄ 0.26, MgSO₄ 0.02, and CaCl₂ 0.01. Under the optimal condition, the hydroxyl radical scavenging rate (49.4%) was much higher than that using either basal fermentation medium (10.2%) and single variable optimization of fermentation medium (35.5%).Improvement of EPS production and hydroxyl radical scavenging activity by Inonotus obliquus was further achieved by employing lignocellulose decomposition in corn straw-containing submerged fermentation. A significant stimulation of EPS production was obtained in corn straw-containing medium. A synchronized effect between lignocellulose decomposition rate and malondialdehyde (MDA) presenting hydroxyl radical concentration in fermentation broth was identified. A significant increase in the EPS production and hydroxyl radical scavenging activity from 1.09g/L and 72.3%, in a basal medium, to 1.38g/L and 82.7% in the presence of corn straw was obtained. The adding of thiourea, a hydroxyl radical scavenging reagent, in corn straw-containing medium suppressed MDA generation and lowered lignocellulose decomposition rate. The production and hydroxyl radical scavenging activity of the EPS decreased to 1.26g/L and 74%, respectively. These results further suggested that the highest EPS production and activity from corn straw-containing medium lacking thiourea was attributed to hydroxyl radical generation due to lignocellulose decomposition. The main monosaccharides components of EPS obtained from corn straw-containing medium are rhamnose, arabinose, xylose, mannose, glucose, and galactose with molar proportion at 2.98%, 2.97%, 0.91%, 46.65%, 11.39%, 35.10%, which are different from those of EPS from the basal medium and corn straw-containing medium with the addition of thiourea.