Abstract:In this study, crude polysaccharide isolated from Chinese yam by enzymatic hydrolysis and ultrasoundassisted extraction, was separated and purified using a gel column, and then subjected to structural analyses by high performance liquid chromatography, ultra-high performance polymer chromatography, Fourier transform infrared spectroscopy, and scanning electron microscopy. Moreover, its ferric ion reducing antioxidant power (FRAP) and oxygen radical absorbance capacity (ORAC) were examined. The results revealed that the crude polysaccharide after purification yielded three polysaccharide fractions. The yield of the third fraction, CYP-III, was the highest (65.2%), followed by CYP-II (4.2%) and CYP-I (2.5%). Fourier transform infrared spectroscopy revealed that all three polysaccharide fractions contained pyranose and α-glycoside bonds, but CYP-I contained a higher amount of carboxyl groups. CYP-I was identified as a heteropolysaccharide composed of mannose (38.29%), galactose (30.61%), and glucose (21.41%), and had the highest molecular weight (5.1 ku) and the strongest antioxidant activity. CYP-II was found to be composed mainly of glucose (87.92%) and had a molecular weight of 4.0 ku. CYP-III was identified as a glucan (glucose 99.09%) with a molecular weight of 2.5 ku and the weakest antioxidant activity. The scanning electron microscopy examination revealed that CYP-I was disordered and appeared in clusters with numerous pores; CYP-II had a ompact but uneven surface, whilst CYP-III had smooth surfaces but distributed randomly. The results showed that the antioxidant activity of Chinese yam polysaccharide in this study was significantly positively correlated with the contents of acid sugars, mannose, galactose, rhamnose, and carboxyl groups. This study can provide a theoretical basis for the development and utilization of yam polysaccharides.
