Influence of heating on antioxidant activity and the chemical composition of some spice essential oils

Oxidation of lipids is one of the basic processes causing rancidity in food products. Since application of natural antioxidants may be one of the technically simplest ways of reducing fat oxidation, we studied the effect of heating on antioxidant effectiveness and the chemical composition of basil, cinnamon, clove, nutmeg, oregano and thyme essential oils. When maintained at room temperature, all the oils tested appeared endowed with good radical-scavenger properties in the DPPH assay (effectiveness order: clove ≫ cinnamon > nutmeg > basil ⩾ oregano ≫ thyme). When heated up to 180 °C, nutmeg oil (but not the other essential oils under study) showed a significantly higher free radical-scavenger activity and evident changes in its chemical composition. Furthermore, the ability of these essential oils to protect α-tocopherol, contained in virgin olive oil, against thermal oxidative degradation was investigated. All the essential oils tested appeared able to prevent α-tocopherol loss following oil heating at 180 °C for 10 min (efficiency order: clove > thyme ⩾ cinnamon > basil ≫ oregano > nutmeg). In conclusion, the essential oils under study exhibited good antioxidant properties and might be efficiently used to control lipid oxidation during food processing.