Research on structure and antioxidant activity of polysaccharides from Ginkgo biloba leaves

Ginkgo biloba extract is regarded as one of the most popular natural plant preparations, among which polysaccharide is considered to be an important functional factor. In the study, polysaccharide was extracted from Ginkgo biloba leaves powder by ultrasonic-enzyme assisted water-soluble alcohol precipitation. The content of crude polysaccharide was 82.4% by the phenol sulfuric acid method. Structure and chemical composition of Ginkgo biloba leaves polysaccharide were investigated by chromatographic and nuclear magnetic resonance spectoscocopy analyses. Results showed that the purified Ginkgo biloba leaves polysaccharide was an acidic polysaccharide with a molecular weight of 12.08 kDa, containing glycosidic linkages of β-D-Rhap-(1→, β-L-Xylp-(1→, →4)-β-D-Manp-(1→, →4)-β-D-Glcp-(1→, →6)-β-D-Manp-(1→, →3)-β-L-Araf-(1→, →4)-β-D-Galp-(1→, →3,4)-β-D-Glcp-(1→. The monosaccharides were composed of rhamnose, arabinose, xylose, mannose, glucose and galactose with a molar ratio of 5.56:3.84:2.34:7.54:8.34:1, respectively. Scanning electron microscopy analysis showed that the microscopic conformation of the purified Ginkgo biloba leaves polysaccharide was fluffy and irregular honeycomb with certain pores. Antioxidant activities in vitro, including scavenging 1,1-Diphenyl-2-picrylhydrazine, scavenging hydroxyl radical activity and scavenging superoxide anion were 78.8%, 79.2% and 43.7%, respectively, which suggested that the purified Ginkgo biloba leaves polysaccharide had strong antioxidant activities. These findings indicate that Ginkgo. biloba leaves polysaccharides have potential as natural antioxidants in food processing.