Fractionation,characterization and antioxidant activity of exopolysaccharides from fermentation broth of a Cordyceps sinensis fungus |
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Authors: | Qi-Lin Huang Ka-Chai Siu Wen-Qiang Wang Yi-Ching Cheung Jian-Yong Wu |
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Affiliation: | 1. Department of Applied Biology & Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong;2. College of Food Sciences and Technology, Huazhong Agricultural University, Wuhan 430070, China |
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Abstract: | Exopolysaccharide (EPS) fractions P1/5, P2/5, P1, P2 and P5 were isolated from the fermentation medium of a medicinal fungus Cordyceps sinensis by gradient precipitation with ethanol at 1/5, 2/5, 1, 2, and 5 volume ratios to the liquid medium. P1/5 and P2/5 were mainly composed of polysaccharides with negligible protein content and a large molecular or particle size (intrinsic viscosity [η] 2025 mL/g; hydrodynamic radius Rh 905 nm). The fraction attained at a higher ethanol volume ratio had a much higher protein and lower carbohydrate content, and a smaller molecular size. In particular, P5 was composed of mainly protein with an average molecular weight 16 kDa, [η] 4.3 mL/g and Rh 23.5 nm. The antioxidant activities of EPS fractions showed a significant dependence on the protein content, being negligible of P1/5 and P2/5, low to moderate of P1 and P2, and very strong of P5. Gradient ethanol precipitation was proven a simple and workable method for initial fractionation of polysaccharides, proteins and their complexes with different molecular sizes and for further identification of the bioactive components. |
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