Seasonal Variation in Essential Oils Composition and the Biological and Pharmaceutical Protective Effects of Mentha longifolia Leaves Grown in Tunisia

This research assessed the seasonal variation of the chemical composition and antibacterial and anticholinesterase activities of essential oils extracted from M. longifolia leaves. The leaves organic fractions were also investigated for their biological activities and pharmacological functions. The essential oil highest yield was recorded in the spring season. Pulegone (26.92%), 1.8 cineole (21.3 %), and L-menthone (10.66 %) were determined as its major compounds in the winter season. In the spring oil, the main components were pulegone (38.2 %) and oleic and palmitic acids (23.79 % and 15. 26 %, respectively). Oxygenated monoterpenes were predominant in the two analyzed samples. The tested oils and organic extracts exhibited promising antibacterial effects against all of the tested bacterial strains. Thanks to its richness in phenolic and flavonoid compounds, the ethyl acetate fraction (Ml EtOAcF) displayed the most active DPPH scavenging ability (IC(50) =12.64 μg/ml) and an interesting β-carotene bleaching inhibition (IC(50) =34.75 μg/ml) making it a potential candidate for anti-inflammatory evaluation on rats. This evaluation evidenced that M. longifolia pretreated rats showed a marked decrease in paw oedema and inflammatory cells. Additionally, a remarkable acetylcholinesterase inhibitory activity of the Ml EtOAcF (IC(50) = 12.3μg/ml) and essential oils were also observed suggesting their neuroprotective property against Alzheimer's disease. Moreover, it was found that its activity level was season dependent. Our investigation, therefore, clearly revealed the medicinal characteristics of M. longifolia leave indicating their potential uses for natural remedies.