Antioxidant activities and polyphenolic contents of three selected Micromeria species growing in Croatia

Abstract

The genus Micromeria (Lamiaceae) is represented by nine species in Croatia, three of which (M. croatica (Pers.) Schott, M. dalmatica Benth. and M. pseudocroaticaŠilic) are endemic [1]. Micromeria species are perennial herbs or dwarf shrubs growing mostly in the Mediterranean region. Some of them are traditionally used against heart disorders, headache, colds, wounds and skin infections, as well as condiments [2]. In the present paper, antioxidant activities of M. croatica, M. juliana and M. thymifolia were evaluated using five in vitro antioxidant assays, in comparison with plant polyphenolic constituents and reference antioxidants. All studied plant extracts exhibited considerable DPPH and hydroxyl free radical scavenging activity, reducing power, iron-chelating ability and total antioxidant capacity in the order: M. croatica >M. juliana>M. thymifolia. Among the tested plants, the ethanolic extract of M. croatica was found to be the most effective DPPH radical scavenger (IC50 4.7µg/ml), even stronger than BHT (IC50 6.5µg/ml). The highest activity toward hydroxyl free radicals was recorded for the same extract (IC50 249.65µg/ml). Additionally, it also showed the strongest reducing power (IC50 9.64µg/ml) and iron-chelating ability (IC50 227.47µg/ml). In phosphomolybdenum assay, M. croatica displayed twofold lower total antioxidant capacity than ascorbic acid. Total polyphenol (9.69–13.66%), phenolic acid (5.26–6.84%), flavonoid (0.01–0.09%) and tannin contents (3.07–6.48%) in dried plant samples were determined spectrophotometrically. A good correlation between antioxidant activities and contents of phenolic acids and tannins was established, indicating their responsibility for antioxidant capabilities of Micromeria species.