Abstract:

In this study, the synthesis of acetylated polysaccharides extracted from longan (Dimocarpus longan) pulp was
investigated using acetic anhydride. The influences of reaction time, reaction temperature and polysaccharides-to-acetic
anhydride ratio on the degree of substitution (DS) of the synthesized derivatives were examined to select and optimize
important reaction conditions by response surface methodology. The antioxidant activity of acetylated polysaccharides
in vitro was determined. The optimized conditions that provided the maximum DS of 0.443 were determined as follows:
reaction time, 30 min; polysaccharides-to-acetic anhydride ratio, 10.21:1; and reaction temperature, 42 ℃. The acetylated
derivatives could scavenge hydroxyl free radical, and inhibit lipid peroxidation and red cell hemolysis induced by H2O2, with
50% inhibition concentrations (IC50) of 702.41, 646.04 μg/mL and 380.11 μg/mL, respectively. The antioxidant ability of the
synthesized acetylated derivatives was improved as compared to the native polysaccharides.

Key words: longan pulp polysaccharides, acetylation, degree of substitution, response surface methodology (RSM), antioxidant ability