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) = +101 degrees. Structural characterization of this novel polysaccharide was carried out using infrared spectroscopy, methylation analyses, and NMR studies (H-1, C-13, H-1-H-1-COSY, HMQC, and HMBC). Based on the above data, the following structure was assigned to the repeated core unit of GP70-2: -> 3)-alpha-L- Araf-(1 -> 3)-beta-D-Galn-(1 -> 3)-alpha-L- Araf-(1 -> 3) - alpha-L- Araf-(1 ->(6 <- 1)- beta-D-Galp-(6 -> 1) -beta-d-Galp This polysaccharide showed a concentration dependent DPPH center dot radical scavenging activity. (C) 2013 Elsevier Ltd. All rights reserved.