Antioxidant profile of Lamiaceae plant extracts: Impact of rosmarinic acid content

Introduction. There is a great demand in the food industry for compounds that effectively inhibit the oxidation of lipids, which is the major cause of food deterioration. This auto-oxidation process may be avoided or delayed by antioxidants. The possible toxicity of the conventional synthetic antioxidants, together with consumers' preference for natural products have intensified research of different plant extracts which are known to possess the antioxidant activity. Among the plants reported to have antioxidant activity, Lamiaceae plants (mint family) are the most widely used and commercialized. The aim of this study was to compare the antioxidant properties of five different Lamiaceae extracts using spectra of different methods and to investigate the influence of the rosmarinic acid content on the antioxidant properties of investigated plant extracts. Methods and materials. The research includes five plant extracts: Melissa officinalis, Mentha piperita, Origanum vulgare, Salvia officinalis and Thymus serpyllum. The antioxidant properties of plant extracts were evaluated using eight different antioxidant assays: Folin-Ciocalteu method, Ferric Reducing/Antioxidant Power (FRAP), free radical scavenging activity using two stabile synthetic radicals (DPPH and ABTS) and against superoxide anion radical, Fe2+ chelating activity, inhibition of the Briggs-Rauscher reaction and efficiency in preventing the oxidation of emulsified linoleic acid using β-carotene bleaching method. The content of the rosmarinic acid in plant extracts was determined using HPLC-RP-DAD. Results and conclusions. All extracts were extremely rich in phenolic compounds and contained extremely high concentrations of the rosmarinic acid. The highest rosmarinic acids content as well as the best results for antioxidant properties using most of the methods were obtained for Melissa officinalis extract. The significance and role of the rosmarinic acid in the antioxidant properties of Lamiaceae plant extracts was confirmed and undoubted, but the contribution of other compounds and their possible cumulative or synergistic action should not be neglected.