Antioxidant activity of benzoic and cinnamic acid derivatives

Abstract

Background: Cinnamic and benzoic acid derivatives, belonging to the class of phenolic acids, are one of the most potent antioxidants [Error! Reference source not found., 1]. Number and position of hydroxyl groups, other features in the chemical structure create significant variety of the phenolic acids [1]. The aim of this research was to analyse antioxidant activity of the benzoic and cinnamic acid derivatives. Materials and methods: The stock solutions of benzoic acid and its derivatives (salicylic, vanillic, protocatechuic, syringic, gallic acids), cinnamic acid and its derivatives (p-coumaric, sinapic, caffeic, rosmarinic, chlorogenic, 4-O-caffeoylquinic, 3,5-di-O-caffeoylquinic, 3,4-di-O-caffeoylquinic, 4,5- di-O-caffeoylquinic acids) were diluted to five concentrations. All samples were analyzed by spectrophotometric ABTS and FRAP assays. The obtained data were used to construct calibration curves. According to the ratio of the sample and trolox slopes, relative trolox equivalent antioxidant capacity (TEAC) values were calculated. Results: Benzoic and cinnamic acids, without hydroxyl groups, had almost no activity. The hydroxybenzoic acids had lower TEAC values than hydroxycinnamic acids, except gallic acid. The highest TEAC values were determined for cinnamic acid derivatives – 3,4-di-O-caffeoylquinic acid (2,43±0,05) by ABTS assay, and for 4,5-di-O-caffeoylquinic acid (2,12±0,03) by FRAP assay. Conclusion: This study reveals that antioxidant activity of phenolic acids is enhanced by the introduction of hydroxy and methoxy groups on the aromatic ring and additional conjugated double bond in the side chain. It is also suggested that dicaffeoylquinic acids can be potential chemical markers of the antioxidant properties.