Evaluation of antioxidant capacity of ulvan-like polymer obtained by regioselective oxidation of gellan exopolysaccharide

Gellan is an exopolysaccharide produced in high yield by the non-pathogenic bacterium Sphingomonas elodea ATCC 31461. In this study, four carboxylated derivatives of gellan (OG-1, OG-2, OG-3 and OG-4) with different uronics acid content were prepared using the TEMPO (nitroxyl radical 2,2,6,6-tetramethylpiperidine-1-oxyl radical) mediated oxidation and their antioxidant activities were investigated including scavenging activity of hydroxyl, superoxide anion and 1,1-diphenyl-2-picryl-hydrazyl radicals. The results of chemical analysis and 13C NMR spectrums indicated that the modification was successful. In addition, certain derivative exhibited stronger antioxidant activity compared to that of native ones. The high uronic acids derivative (OG-4) showed the most excellent antioxidant activity in three assays. These results suggested the potential of TEMPO-mediated oxidation in developing water-soluble antioxidative polysaccharides from gellan still taking advantage of its low-cost production. The original carbohydrate structure of OG-4 derivative might find use as surrogates of ulvan, a cell-wall polysaccharides extracted from green seaweeds Ulva sp.