Wild Thymus zygis L. ssp. gracilis and Eucalyptus camaldulensis Dehnh.: Chemical composition, antioxidant and antibacterial activities of essential oils

Abstract

Natural substances extracted from plants have been increasingly studied and recognized, recently. Essential oils (EOs), for example, possess antioxidant and antibacterial properties, enabling their application across different sectors like agro-food, pharmaceuticals, and cosmetics. In Morocco, exceptional plant diversity, mirroring the diversity of ecosystems, has not yet revealed all its secrets. Therefore, the aim of this study is to determine the chemical composition and evaluate the antibacterial and antioxidant activities of EOs from Thymus zygis L. ssp. gracilis and Eucalyptus camaldulensis Dehnh. collected in the El Hoceima and Mamora regions, respectively. The EOs were extracted by hydrodistillation employing a Clevenger-type apparatus. Gas chromatography/mass spectrometry (GC/MS) analyses identified 54 constituents representing 92.65% of the total for T. zygis and 55 components representing 99.60% for E. camaldulensis. The primary components found in the EO of T. zygis are δ-terpineol (27.64%), followed by δ-3-carene (15.7%), thymol (14.17%), and dehydrolinalool (4.99%). The main compounds in E. camaldulensis EO are 1,8-cineole (43.61%), γ-terpinene (11.71%), α-terpineol (10.58%), and p-cymene (4.93%). The antioxidant properties of these oils were investigated by utilization of the 2,2-diphenyl-1-picrylhydrazyl method and the ferric reducing antioxidant power (FRAP) test. The antibacterial activity was assessed against two Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis) and two Gram-negative bacteria (Micrococcus luteus and Escherichia coli). Both EOs showed significant antioxidant activity but were less effective than reference antioxidants quercetin and catechin. Antibacterial studies demonstrated strong activity of T. zygis and E. camaldulensis EOs against the studied bacteria, as well as good inhibitory properties (minimum inhibitory concentration).