Antioxidant properties of cell wall polysaccharides of Stevia rebaudiana leaves

Objective:To examine the total phenolic and protein contents,and the antioxidant activities of cell wall polysaccharide fractions of Stevia rebaudiana leaves.Methods:Three different polysaccharide-enriched fractions,namely FPE(extract with 50 mmol/L ethylene diamine tetra acetic acid),FPK(extract with 0.05 mol/L KOH)and FH(extract with 4 mol/L KOH)were extracted from Stevia rebaudiana leaves.The antioxidant activity of these fractions was evaluated based on their ability to scavenge DPPH(1,1-diphenyl-2-picryl hydrazyl)free radical,to reduce ferric power,to chelate ferrous ion and to protect human DNA.Results:The results indicated that protein content was found to be higher in FPK polysaccharide enriched fraction(47.48μg per mg of FPK).Furthermore,the phenolic compound analysis according to the Folin-Ciocalteu method was higher in FPK(17.71μg ferulic acid).The DPPH maximal inhibition percentage of the three polysaccharide-enriched fractions at 400μg/mL was 27.66%,59.90%and 23.21%respectively for FPE,FPK and FH.All the polysaccharide fractions exhibited a ferric reducing power except the FH one.The three fractions also exhibited lipid peroxidation inhibition,and they completely reverted the DNA damage induced by H_(2)O_(2)/FeCl_(2).FPK showed the strongest scavenging activity against the DPPH radical,the best chelating ability and lipid peroxidation inhibition.Conclusions:Stevia cell wall polysaccharide fractions are potent protective agents against oxidative stress.The analysis revealed major differences in the antioxidant activity in the three polysaccharides fractions.However,the 0.05 mol/L KOH pectin fraction(FPK)showed better antioxidant activity.