Antioxidant activity of selected essential oil components in two lipid model systems

About 100 pure components of essential oils have been tested for their antioxidant effectiveness. The main classes of compounds, namely monoterpene hydrocarbons, oxygenated monoterpenes, sesquiterpene hydrocarbons, oxygenated sesquiterpenes, benzene derivatives, and non isoprenoid components comprising alcohols, aldehydes, ketones, which are the most common constituents of essential oils, have been analysed. Two model systems for the antioxidant efficacy have been used; the first exploiting the thiobarbituric acid reactive species (TBARS) method using egg yolk as oxydable substrate, the second measuring the formation of hydroperoxydienes from linoleic acid in a micellar system, using in both cases 2,2′-azobis (2-amidinopropane) dihydrochloride (ABAP) as a radical initiator, and α-tocopherol as a reference compound. From a general point of view phenols were confirmed to possess the highest antioxidant activity. In particular some monoterpene hydrocarbons, namely, terpinolene, α- and γ-terpinene showed a significant protective action, whereas among the oxygenated components, beside the aforesaid phenols, allylic alcohols manifested an appreciable activity. Sesquiterpene hydrocarbons and non isoprenoid components subjected to this study showed a low, if any, antioxidant effect. The role of the different model systems and the relationship between structure and antioxidant effectiveness are discussed.