Structure characterization and antioxidant activity of carboxymethylated polysaccharide from Pholiota nameko

The objective of this paper was to prepare the carboxymethyl polysaccharide of Pholiota nameko (CPPN) and further evaluate its structural characteristics, water solubility, and antioxidant activities. The optimal carboxymethylation conditions were as follows: 20% NaOH concentration, 1.5 hr alkalization, 4 hr etherification time, and 60°C with 2 g chloroacetic acid. Under these conditions, a substitution degree of 0.72 and a yield of 88.3% were achieved. The results of NMR and FT-IR spectra showed that carboxymethylation modification was successful. The protein, total sugar, and total phenol content decreased, while the molecular weight increased, and the monosaccharide composition content and surface structure changed upon carboxymethylation. Compared with unmodified polysaccharides, CPPN had significant antioxidant activity and water solubility. Thus, this study could provide a potential antioxidant for functional foods and pharmaceuticals. Practical applications Pholiota nameko is an edible and medicinal mushroom, rich in carbohydrates, cellulose, and minerals. Pharmacological studies have shown that P. nameko polysaccharides have many medicinal effects on the human body. In this study, CPPN was synthesized by carboxymethylation of P. nameko polysaccharides. Through structural characterization, antioxidant activity, and solubility studies, carboxymethylated polysaccharides shown significant antioxidant properties and increased solubility. Therefore, this research lays the foundation for the high-value application of P. nameko polysaccharides in functional food and pharmaceutical industry.