Oxidative stability and antioxidant activity of essential oils

The use of essential oils in food technology, in aerobic conditions and prolonged storage, requires a deep knowledge of their oxidative chemistry. Essential oils are rich in unsaturated components (i.e. linalool, -pinene, -caryophyllene) and thus are subjected to air oxidation during storage. These reactions alter their compositions and organoleptic properties. Various oxidized compounds are formed some of which have been demonstrated to be contact allergens. A vast amount of experimental data show that essential oils containing significant amounts of phenolic components (i.e. thymol, carvacrol, eugenol) or special monoterpenes like -terpinene are able to retard the oxidation of unsaturated lipids. In this chapter, the free-radical chemistry underlying these properties is outlined, and the main mechanisms that are responsible for the possible antioxidant activity of essential oils are described. The behaviour of essential oils under oxidative conditions ultimately depends on the reactivity of their components with peroxyl radicals which are responsible for hydrocarbon autoxidation.