Composition and Concentrations of Phenolic Compounds in Various Extracts from Stevia (Stevia rebaudiana Bertoni)

Abstract

The composition and concentrations of phenolic compounds (PCs) in aqueous and water–ethanol extracts from the leaves of stevia (Stevia rebaudiana Bertoni) obtained by various extraction methods (maceration, microwave and ultrasound assisted and subcritical extraction, and refluxing) are discussed. The efficiency of PC extraction was assessed by the concentrations of individual compounds and their total yield. The chromatographic identification of PCs in the extracts was studied. Chromatographic determination of PCs in the extracts was carried out in the reversed phase mode on a column with silica gel modified with octadecyl groups. Neochlorogenic and chlorogenic acids, rutin, quercetin glycosides I and II containing various sugar residues, two dicaffeoylquinic acid isomers, and apigenin-7-glucoside were identified by comparing the chromatographic retention parameters of the components and the absorption spectra and mass spectra with similar characteristics of standard reference compounds and with published data. The concentrations of individual PCs extracted into water–ethanol extracts by different methods and from different geographical areas varied greatly. The antioxidant activity of water–ethanol and aqueous extracts from the samples of stevia leaves from different vendors was evaluated, and this evaluation showed different contributions of individual PCs to the value of antioxidant activity.