Structural characterization and DPPH· radical scavenging activity of a polysaccharide from Guara fruits

The crude polysaccharides were extracted from fruits of Psidium guajava Linn. by hot water. After removal of proteins, isolation and purification by DEAE-52 Cellulose chromatography and Sephadex G-75 gel filtration, a polysaccharide (GP70-2) was obtained and structurally characterized. GP70-2 has a relative molecular weight of 74 kDa and was composed of d-galactose and l-arabinose in the ratio of 1:1, with a specific optical rotation of [ a ] D 25 = + 1 0 1 ° . Structural characterization of this novel polysaccharide was carried out using infrared spectroscopy, methylation analyses, and NMR studies (1H, 13C, 1H-1H-COSY, HMQC, and HMBC). Based on the above data, the following structure was assigned to the repeated core unit of GP70-2: olysaccharide showed a concentration dependent DPPH· radical scavenging activity.