Effect of Seasonal Variation on Chemical Composition, Antidiabetic and Antioxidant Potentials of Leaf Essential Oil of Eucalyptus globulus L.

Abstract

This study investigated the effect of seasonal variation on the chemical composition, antioxidant and antidiabetic activities of essential oil from leaves of Eucalyptus globulus. Pulverized leaves (500 g) of E. globulus from dry and rainy season harvests afforded 0.54 and 0.43 % (w/w) of essential oils respectively when subjected to hydrodistillation. GC and GC/MS analyses revealed the presence of forty-five and thirty-three compounds that represented 95.4 and 98.4 % of the oils obtained from leaves harvested during the dry and rainy seasons. The principal constituents of the essential oils were; D-limonene, m-cymene, o-cymene, 6-camphenol, terpinen-4-ol, globulol, diosphenol and spathulenol. The oils showed scavenging activity for DPPH radical with IC₅₀ of 20.15 (dry) and 11.23 μL/mL (rainy). The essential oils showed significant reducing powers of 356.46±0.88 (dry) and 394.34±0.95 (rainy) FRAP equivalent. The oils inhibited the activity of α-amylase with IC₅₀ of 8.37 (dry) and 6.78 (rainy) μg/mL. The IC₅₀ for the α-glucosidase inhibition of the oils were 6.19 (dry) and 7.20 (rainy) μg/mL. The antioxidant and antidiabetic activities of the oils compared favourably with the standards used for the study. Hence, the essential oils can serve as an alternative to synthetic drugs to ameliorate oxidative stress and management of type 2 diabetes.

Key words:

• Antioxidant
• antidiabetic
• D-limonene
• Eucalyptus globulus