Study On Preparation And Antioxidant Activity Of Momordica Charantia Polysaccharide And Its Derivatives

Momordica charantia belongs to balsam pear of cucurbitaceae.Polysaccharide is one of the most important active substances in balsam pear.Molecular modification of Momordica charantia polysaccharide（MCP）is helpful to improve its biological activity and accumulate basic data for further exploring the structure-activity relationship of balsam pear polysaccharide.Therefore,in this paper,Momordica charantia polysaccharide was extracted from balsam pear.The extraction and deproteinization of Momordica charantia polysaccharide were studied.The sulfated Momordica charantia polysaccharide（S-MCP）,phosphorylated Momordica charantia polysaccharide（P-MCP）,carboxymethylated Momordica charantia polysaccharide（CM-MCP）and acetylated Momordica charantia polysaccharide（Ac-MCP）were obtained by chemical modification.The structure analysis and antioxidation of the modified polysaccharide were carried out.The main contents are as follows:1.Momordica charantia polysaccharides was extracted by water and precipitated by ethanol.After trying a lot of experiments and referring to many references,the extraction conditions were determined as:the ratio of dry powder and extractant was1:20（g/m L）,the extraction temperature was 90℃,the extraction time was 2 h,respectively.The yield of polysaccharide was 3.1%.The number of deproteinization was determined to be twice by single factor experiment.2.The S-MCP was prepared by chlorosulfonic acid pyridine method,the P-MCP was prepared by POCl₃method,the CM-MCP was prepared by chloroacetic acid method,and the Ac-MCP was prepared by acetic anhydride method.Phenol sulfuric acid method was used to determine the sugar content of several derived polysaccharides,59.8%,68.1%,43.5%and 62.3%respectively.The sugar content was lower than that of the original polysaccharide by 74%.However,it was found that there was a certain relationship between the content of sugar and the degree of substitution after the modification.The degree of substitution of several derived polysaccharides was 0.45,0.12,0.89 and 0.27,respectively.The higher degree of substitution,the lower the content of sugar.This relationship also provided a clue for the later test of reducing ability in antioxidant activity.The results of IR and NMR analysis of several polysaccharides,combined with literature and analysis,showed that these chemical modifications were successful.3.The antioxidant activity of Momordica charantia polysaccharide before and after chemical modification was studied.The results showed that the scavenging ability of P-MCP was the strongest,and the scavenging ability of modified S-MCP and Ac-MCP was weaker than that of original polysaccharide.The scavenging ability of modified Momordica charantia polysaccharide to O₂^-?was significantly stronger than that of unmodified polysaccharide,but the scavenging rate of MCP was stronger than that of CM-MCP at high concentration.Compared with V_C,the reducing ability of several kinds of Momordica charantia polysaccharides is very low,and it can be found that after chemical modification,the reducing ability of MCP is decreased.The reduction ability of MCP is stronger than that of modified polysaccharide,and the lower the sugar content,the weaker the reduction ability of derivative balsam pear polysaccharide.In DPPH free radical scavenging experiment,P-MCP is a kind of scavenging rate of DPPH free radical which is greatly enhanced.The scavenging ability of S-MCP and Ac-MCP is not significantly different,both of them are higher than the original polysaccharide,while CM-MCP showed lower activity than the original polysaccharide.Several kinds of Momordica charantia polysaccharides showed inhibitory effect on lipid peroxidation,but the inhibitory effect of modified Momordica charantia polysaccharides was enhanced.The overall order of its strength was:P-MCP>S-MCP>CM-MCP>Ac-MCP>MCP.The above conclusion shows that phosphorylation of Momordica charantia polysaccharide can significantly improve its antioxidant activity.