Phytochemistry and Antioxydante Activity ofStevia rebaudiana

Abstract

Stevia rebaudianais a perennial shrub belonging to the Asteraceae family. Recently, it has been introduced to Morocco from its native Paraguay; its molecules have a sweetening power that is about 300 times sweeter than sucrose. This characteristic makes of this plant a considerable natural noncalorific sweetener in case of hypoglycemic or low carbohydrate diet. This important interest has prompted us to make further studies on this plant. The objective of this work is to show the value ofStevia rebaudianagrown in the Larache region of Morocco by the chemical characterization and evaluation of the antioxidant activity of its extracts. A phytochemical screening was carried out to highlight the qualitative composition of secondary metabolites. This analysis showed the presence of flavonoids, tannins, oses and holosides, sterols, triterpenes, and free anthraquinones. However, the absence of alkaloids and reducing compounds has been observed. In addition, extraction of the total polyphenols was carried out by maceration using a 70% methanol–water mixture. The yield is of the order of 28.6%. Subsequently, fractionation of the crude extract was carried out by successively using three organic solvents of different polarities: chloroform, ethyl acetate, andn-butanol. Polyphenol dosage with Folin-Ciocalteu’s reagent showed that ethyl acetate fraction is richer in phenolic compounds (26.4%) than the other fractions. Flavonoids dosage with aluminum trichloride showed the richness of this plant in these compounds. The antioxidant activity of different fractions was evaluated by 2,2-diphenyl-1-picrylhydrazyl-free radical scavenging method and ferric reducing/antioxidant power method; the values of the 50% inhibitory concentrations (IC50) were determined graphically. It is equal to 0.32 mg/ml for the ethyl acetate fraction, compared to 0.08 mg/ml for the ascorbic acid used as a reference. In this study, we have shown thatStevia rebaudianais very rich in phenolic compounds and possesses a very important antioxidant power.