Chemical Composition and Antioxidant Activity of the Essential Oil of Oregano (Origanum vulgare L.) Grown Wild in Croatia

The application of synthetic antioxidants as inhibitors of lipid oxidation is well known in food industry. Widely used artificial antioxidants, such as butylated hydroxytoluene BHT and butylated hydroxyanisole BHA1, 2, are very effective in their role. However, their use in food products have been failing off due to their instability as well as due to suspected action as promoters of carcinogenesis.3, 4 Among the herbs and spices extensively studied, those obtained from the plants of the Lamiaceae (Labiatae) family have been found to possess a significant antioxidant activity. A number of studies on the antioxidant activities of their dried ground leaves, flowers and various extracts were reported in the past. It is now well known that the antioxidative activity of this spices is due to phenolic compounds.5 The antioxidative effect is correlated to their hydroxy groups.6 Regarding the nonvolatile components, oregano7 (Origanum vulgare L.) is one of the most effective aromatic herb. Herrmann et al.8, 9 examined the activity of rosmarinic and caffeic acid, both of which had been isolated from rosemary, but also from oregano and other species such as sage, mint, thyme, marjoram and balm. The study of Banias et al.10 showed that oregano and thyme extracts have strong antioxidant effects in stabilizing lard. Recently, Abdalla and Roozen11 studied effect of different plant extracts on the formation of conjugated diene hydroperoxides in sunflower oil. Very little is known about the extent to which the volatile compounds from aromatic herbs may contribute to the total antioxidant activity.12 In the essential oil of aromatic herbs, eugenol, isoeugenol, thymol, carvacrol and other phenolic volatile components exhibited appreciable antioxidant effect, but they have too strong characteristic odors to use as food additives. However, small amounts of essential oils do not always affect the odor note of food products and contrary may have a favorable effect. Oregano is widely distributed in Mediterranean basin, as well as in Croatia, and is of great economic importance for the spice market. Lagouri et al.13 investigated the chemical composition and antioxidant activity of essential oils from Oregano plants grown wild in Greece by measuring peroxide values of lard stored at 35 oC. In recent studies, Yanishlieva et al.14, 15 examined antioxidant activity of hexane extract from oregano grown in Bulgaria and mechanism of action of pure thymol and carvacrol. Baratta et al.16 investigated chemical composition and antioxidative activity of laurel, sage, rosemary, coriander and oregano essential oil. The potential antioxidant capacity of the oils was examined by modified thiobarbituric acid reactive species using egg yolk and rat liver homogenates as lipid rich media. In the present study, the essential oil of oregano, with thymol and carvacrol as major components, was examined for antioxidant activity on process of autoxidation of lard and sunflower oil. In order to correlate properly the antioxidant activity to the chemical composition, the essential oil was fractionated according to acidity and polarity. Antioxidant effect was examined by peroxide value measurements on lard and sunflower oil samples stored at 60 oC with and without 0.02 or 0.1 % of thymol, complete essential oil or each separated fraction.