Phenolic Compounds, Antioxidant and Antibacterial Activities of Extracts from Aerial Parts of Thymus zygis subsp. gracilis, Mentha suaveolens and Sideritis incana from Morocco

Thymus zygis subsp. gracilis, Mentha suaveolens and Sideritis incana (Lamiaceae family) are well recognized for their medicinal, pharmaceutical and aromatic properties. The present study aimed to investigate for the first time the phenolic composition, the antioxidant and antibacterial properties of the extracts obtained from the aerial parts of these species collected from the Ifrane region of Morocco. The phenolic compounds were determined using high-performance liquid chromatography coupled to photodiode array and electrospray ionization mass spectrometry (HPLC-PDA-ESI/MS). The antioxidant activity was investigated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging, reducing power and ferrous ion chelating assays. The antibacterial activity was evaluated against three Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa and Salmonella typhimurium) and three Gram-positive bacteria (Staphylococcus aureus, Enterococcus faecalis and Listeria monocytogenes). A total of thirty-three, sixteen and thirteen phenolic compounds were positively identified and characterized in T. zygis subsp. gracilis, M. suaveolens and S. incana extracts, respectively. Among the extracts, M. suaveolens exhibited the highest antioxidant activity, followed by S. incana and T. zygis subsp. gracilis in both DPPH and reducing power assays; all extracts showed the lowest activity in the chelating assay. In addition, all extracts demonstrated a bactericidal effect against Gram-positive bacteria and bacteriostatic effect against Gram-negative bacteria. Therefore, the aerial parts of Moroccan T. zygis subsp. gracilis, M. suaveolens and S. incana might be considered as a valuable source of natural antioxidant and antibacterial agents with potential application in food and pharmaceutical industries.