Effect of Time of Harvest on the Chemical Composition and Antioxidant Potential of Leaf Essential Oil of Syzygium guineense Growing in North Central Nigeria (Willd.) Dc. Var.

Abstract

Abstract. The use of synthetic antioxidants to ameliorate oxidative stress goes with side effects. Some plants are known to be sources of natural antioxidants and, hence, could be used as alternatives to synthetic antioxidants without side effects. Meanwhile, the presence of the phytochemicals that exhibit antioxidant activity in plants depends on environmental conditions that vary with the time of harvest of plant materials. This study, therefore, investigated the effect of time of harvest on the chemical composition and antioxidant potential of leaf essential oil of Syzygium guineense native to North central Nigeria. To accomplish these, pulverized (500 g) leaves of S. guineense harvested in the morning and afternoon were separately hydrodistilled and yielded 0.25 ± 0.002 % (w/w) and 0.27 ± 0.003 % (w/w) of essential oils. Characterization of the oils using GC-MS revealed the presence of twenty-two and twenty-three compounds in the oils from morning and afternoon harvests. The most abundant compound in the oils was β-bergamotene (30.1 % and 27.3 %). D-limonene (2.9 % and 5.6 %), β-ocimene (4.2 % and 10.2 %), α-santalene (7.4 % and 7.7 %), α-cedrene (8.6 % and 9.0 %), β-farnesene (9.1 % and 10.2 %) and calamenene (7.1 % and 5.2 %) were detected in significant quantities in the oils. DPPH radial scavenging assay was used to evaluate the antioxidant activity of the oils with butylated hydroxyl toluene (BHT) as standard. The oils exhibited antioxidant activity with IC50 of 41.92 μg/mL and 33.12 μg/mL for the oils from morning and afternoon harvests. Although the oils exhibited lower antioxidant activity than the standard (IC50 of 28.63 μg/mL), but the oils could be used to ameliorate oxidative stress after clinical trials.