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The antioxidant activity of a commercial rectified clove leaf essential oil (Eugenia caryophyllus) and its main constituent eugenol was tested. This essential oil comprises in total 23 identified constituents, among them eugenol (76.8%), followed by beta-caryophyllene (17.4%), alpha-humulene (2.1%), and eugenyl acetate (1.2%) as the main components. The essential oil from clove demonstrated scavenging activity against the 2,2-diphenyl-1-picryl hydracyl (DPPH) radical at concentrations lower than the concentrations of eugenol, butylated hydroxytoluene (BHT), and butylated hydroxyanisole (BHA). This essential oil also showed a significant inhibitory effect against hydroxyl radicals and acted as an iron chelator. With respect to the lipid peroxidation, the inhibitory activity of clove oil determined using a linoleic acid emulsion system indicated a higher antioxidant activity than the standard BHT.

The essential oil of juniper berries (Juniperus communis L., Cupressaceae) is traditionally used for medicinal and flavoring purposes. As elucidated by gas chromatography/flame ionization detector (GC/FID) and gas chromatography/mass spectrometry (GC/MS methods), the juniper berry oil from Bulgaria is largely comprised of monoterpene hydrocarbons such as α-pinene (51.4%), myrcene (8.3%), sabinene (5.8%), limonene (5.1%) and β-pinene (5.0%). The antioxidant capacity of the essential oil was evaluated in vitro by 2,2-Diphenyl-1-picrylhydrazyl (DPPH) scavenging, 2,2-azino-bis-3-ethylbenzothiazoline-6 sulfonic acid (ABTS) radical cation scavenging, hydroxyl radical (ОН•) scavenging and chelating capacity, superoxide radical (•O2−) scavenging and xanthine oxidase inhibitory effects, hydrogen peroxide scavenging. The antioxidant activity of the oil attributable to electron transfer made juniper berry essential oil a strong antioxidant, whereas the antioxidant activity attributable to hydrogen atom transfer was lower. Lipid peroxidation inhibition by the essential oil in both stages, i.e., hydroperoxide formation and malondialdehyde formation, was less efficient than the inhibition by butylated hydroxytoluene (BHT). In vivo studies confirmed these effects of the oil which created the possibility of blocking the oxidation processes in yeast cells by increasing activity of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx).

The chemical composition of the essential oil from peppermint (Mentha x piperita L.) was analyzed by GC/FID and GC-MS. The main constituents were menthol (40.7%) and menthone (23.4%). Further components were (+/-)-menthyl acetate, 1,8-cineole, limonene, β-pinene and β-caryophyllene. Peppermint oil possessed antiradical activity with respect to DPPH (diphenyl picryl hydrazyl) and hydroxyl (OH•) radicals, exercising stronger antioxidant impact on the OH• radical. The concentrations required for 50% inhibition of the respective radical (IC 50 ) were 860 µg/mL for DPPH and 0.26 µg/mL for OH•. Peppermint essential oil demonstrated antioxidant activity in a model linoleic acid emulsion system in terms of inhibiting conjugated dienes formation by 52.4% and linoleic acid secondary oxidized products generation by 76.9% (at 0.1% concentration).

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