The Role of Extra Virgin Olive Oil Phenolic Fraction in Autoxidation Process Catalyzed by Copper Ion

During storage, fatty acids contained in extra virgin olive oil undergo oxidative degradation with a progressive accumulation of odorless molecules, such as hydroxyperoxides and secondary products. Lipid oxidation occurs by the interaction of lipids with molecular oxygen by a self-catalyzed mechanism. However, since the activation energy of the reaction is high, the initiation of lipid oxidation is due mostly to the decomposition of hydroperoxides using metal catalysts such as copper and iron, or by exposure to light. The high oxidative stability of extra virgin olive oil is mainly due to its fatty acid composition, and in particular to the monounsaturated to polyunsaturated ratio, and to the presence of minor compounds that also have a major role in preventing oxidation. This means that extra virgin olive oil has a longer shelf-life compared to other edible vegetable oils, with long-term preservation of its intrinsic nutritive and hedonistic properties. Several classes of phenolic compounds have been identified in extra virgin olive oil: phenolic acids, phenylethyl alcohols, flavonoids, lignans and secoiridoids [1]. Phenolic compounds can inhibit oxidation by a variety of mechanisms based on radical scavenging, hydrogen atom transfer, and metal chelating attributes. During storage, fatty acids contained in extra virgin olive oil undergo oxidative degradation with a progressive accumulation of odorless molecules, such as hydroxyperoxides and secondary products. Lipid oxidation occurs by the interaction of lipids with molecular oxygen by a self-catalyzed mechanism. However, since the activation energy of the reaction is high, the initiation of lipid oxidation is due mostly to the decomposition of hydroperoxides using metal catalysts such as copper and iron, or by exposure to light. The high oxidative stability of extra virgin olive oil. The presence of metals in extra virgin olive oil is due to endogenous factors linked to plant metabolism, exogenous factors such as olive contamination by agricultural practices, or during oil extraction, or oil storage [2]. Endogenous and exogenous metals can be dissolved in oils as fatty acid salts ( 13). Phenolic compounds in extra virgin olive oil normally act as antioxidants but, in particular conditions become pro-oxidant agents and increase the oxidative reaction rate. In fact, their metal reducing properties take metal ions to their lowest oxidation state (for example Fe3+ → Fe2+ or Cu2+ → Cu+) where they are more active to catalyze hydroperoxide decomposition. The aim of the present study was to investigate the protective effects on the oxidative stability of virgin olive oil samples of the phenolic fraction in the presence and absence of copper ions. For this purpose, we have determined how copper ions or heat affect olive oil composition, including changes in the content of phenolic compounds, tocopherols, FAMEs analysis, primary and secondary auto-oxidation products, oxidative stability, bitterness index, and antioxidant activity. The depletion in polar phenolic compounds in extra virgin olive oil has the major goal of studying their protective effects on oxidative stability in presence of copper, which has not been previously investigated.