Phenolic profile and biological activities of Micromeria graeca (L.) Benth. ex Rchb.

Abstract

The medicinal potential of the ethanol extract of Micromeria graeca (L.) Benth. ex Rchb., harvested in Algeria (MG extract), was evaluated by assessing in vitro its antioxidant, antibacterial, and antityrosinase properties. The total phenolic (= 430 ± 30 mg gallic acid equivalent/100 g of dry weight) and flavonoid (= 190 ± 10 mg quercetin equivalent/100 g of dry weight) contents were evaluated by the Folin–Ciocalteu and the aluminium chloride methods, respectively. Silica gel thin-layer chromatography revealed the presence of chlorogenic, caffeic, and rosmarinic acids and diosmin; the presence of these compounds was confirmed by reverse phase high-performance liquid chromatography. The IC50 values indicate that the ethanol extract of M. graeca is highly potent in neutralizing the 2,2ʹ-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) cation radicals (ABTS•+; IC50 = 30.5 ± 0.9 µg/mL) and the 2,2ʹ-diphenyl-1-picrylhydrazyl radicals (DPPH•; IC50 = 65.8 ± 2.4 µg/mL). The MG extract was also very active on a lipid peroxidation model (IC50 = 23.4 ± 1.9 µg/mL). The superoxide quenching index values (electrochemically measured) were 332 ± 37 (AI30) and 638 ± 53 µg/mL (AI50). The studied extract showed a moderate tyrosinase inhibitory activity (IC50 =302 ± 62 µg/mL) and a low antibacterial effect while the combination of this extract with antibiotics restored the activities of cefotaxime and streptomycin on resistant Staphylococcus aureus and Pseudomonas aeruginosa.