Effects of deproteinization methods on primary structure and antioxidant activity of Ganoderma lucidum polysaccharides

Ganoderma lucidum polysaccharides (GLP) as one of water-soluble polysaccharides has attracted much attention because of its bioactivities, especially antioxidant activity. Deproteinization is an essential step in the purification process of polysaccharides. In this study, three classic deproteinization methods, including neutral protease method, TCA precipitation and CaCl2 salting out, were evaluated for crude GLP processing. The methods had ability to remove proteins (71.50-87.36%), and meanwhile polysaccharide loss (8.35-11.39%) was observed. Structure analysis indicated that these deproteinization methods had no significant effect (p > 0.05) on molecular weight of polysaccharides, but led to varying degrees of glycoside bond losses (1.14-64.05%). Moreover, the antioxidant activities of deproteinized polysaccharides were measured in vitro by hydroxyl radical, reducing power, 2, 2-diphenyl-1-picryl-hydrazyl (DPPH) free radical and ferric-reducing antioxidant power tests. Purified GLP by enzymolysis maintained the strongest antioxidants activities with the retention rate of over 47.40%, and its deproteinization efficiency and polysaccharide loss ratio were 74.03% and 11.39% respectively. In view of relatively high purity and antioxidant activity, enzymolysis was a suitable deproteinization method for GLP production.