Chemical Composition and Antioxidant Potential of Leaf Essential Oils of Ocimum Canum Sims Harvested at Various Times Daily

Abstract

Fresh Ocimum canum leaves were harvested five times at interval of three hours in a twelve hour-cycle daily (7:00, 10:00, 13:00, 16:00, and 19:00 hours). The leaves from each harvest were separately subjected to hydrodistillation for three hours in a Clevenger-type apparatus. The oils obtained were analyzed by Gas Chromatography (GC) and Gas Chromatography-Mass Spectrometry (GC-MS). Cluster analysis was used (based on the data, select variables > 0.2% of 43 oil components from five harvest times) to classify the oils. Antioxidant potential of the oils were determined using 2, 2-diphenyl-1-picrylhydrazyl (DPPH) and Sodium Nitroprusside (SNP)-Induced Lipid Peroxidation assays. The oils afforded yield in the range of 0.15-0.23% (w/w), with the highest and lowest yields observed at 7:00 and 13:00 hours respectively. A total of 23-40 compounds, representing 99.4-99.8% of the total oils were identified from their mass spectra with predominance of oxygenated monoterpenoids (50-65.7%), hydrogenated monoterpenoids accounted for 5.4-19.1%, whereas hydrogenated sesquiterpenoids constituted between 10.1-21.4% of the total oils. The most abundant compound was linalool (46.7-52.4%), other major compounds identified were terpinen-4-ol (8.5-9.5%), eugenol (1.9-10%) and trans-α-bergamotene (5.5-10.2%). Cluster analysis revealed a significant variability within the oil samples obtained from various harvest times. The oils presented a considerable antioxidant activity (IC50 of 5.45-10.87µg/ml compared with 4.05-6.11µg/ml for BHT standard) for DPPH assay; and (3.86- 5.36 µg/ml compared with 2.12-4.33 µg/ml for BHA standard) for SNP-Induced lipid peroxidation assay. The oil obtained from 10:00 hours harvest had the best antioxidant activity at IC50 for both assays. Chemical composition and antioxidant activity of the oils varied significantly with harvest times. The oils exhibited antioxidant property comparable to those of standards, hence could serve as cheaper and safer alternative to synthetic drugs to ameliorate oxidative stress after clinical trials.