Abstract:A crude polysaccharide extract was obtained from Eurycoma longifolia via ultrasound-assisted water extraction, and the optimal extraction conditions were determined by the L9(34) orthogonal test. A novel polysaccharide component containing uronic acid, Ali-1, was obtained through purification by column chromatography. The basic structure of Ali-1 was determined through analyses of its molecular weight and monosaccharide composition. The antioxidant activity of Ali-1 was evaluated based on the oxygen radical absorption capacity (ORAC), as well as the changes in the levels of reactive oxygen species (ROS), malondialdehyde (MDA) and catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) of red blood cells in the human erythrocyte hemolysis model. The results showed that the optimal extraction conditions for the crude polysaccharide were: ratio of material to liquid 1:40, extraction temperature 95 oC, ultrasonic power 300 W, extraction time 2 h. The yield of the crude polysaccharide from Eurycoma longifolia was 10.09% under the optimum conditions. Ali-1 had an average molecular weight of 14.3 ku and was mainly composed of xylose, arabinose, glucuronic acid and galacturonic acid at a molar ratio of 4.43:1.10:1:1.14. The ORAC value of Ali-1 was 302.48±2.71 μmol Trolox equivalents/g. Pretreating with Ali-1 could effectively reduce the levels of MDA and ROS in the 2-2′-azo-bis- (2-amidinopropane) dihydrochloride (AAPH)-injured erythrocytes, restore the erythrocytes to the normal state, and protect the weak erythrocytes (even though their average SOD, GSH-Px and CAT activities decreased). In summary, the isolated and purified polysaccharide Ali-1 from Eurycoma longifolia can protect human red blood cells against AAPH-induced injury and exhibit good antioxidant activity.
