ABSTRACT: Different emulsifying techniques were used to study the influence of water on the oxidative degradation of extra virgin olive oil. The emulsions of water/extra virgin olive oil, oxidized with O 2 , UV radiation, and Air, were prepared by dispersing water under different conditions. Oil oxidation, mon- itored by measuring the PV and polyphenolic content, was greater for emulsions obtained with low dispersing power. A linear model was used to correlate the PV and the polyphenolic content with dispersing energy. An important result was that the dispersed water exerted a positive antioxidant effect on the oil. Paper no. J9935 in JAOCS 79, 577–582 (June 2002). KEY WORDS: Extra virgin olive oils, oxidation, phenolic antioxidants, water-in-oil emulsions. Olive oil has received a great deal of attention lately since in- dustrialized nations have realized that obesity, arteriosclero- sis, high blood pressure, and diabetes are correlated to poor eating habits (1). Olive oil not only is highly digestible but also possesses excellent nutritional values (2). Before becoming suitable for marketing, from a techno- logical viewpoint, it undergoes a decanting or centrifugal step, during which water and other material in suspension are separated from the oil in order to make it transparent (3). In recent years, some authors have shown that the water and the small particles dispersed in the oil act as antioxidants. In other words, the depletion of such substances, which occurs during the filtering process, may favor oil degradation (4). It must be stressed that in addition to the water, other fac- tors, e.g., phenolic compounds, prooxidants, and enzymes, contribute to the oxidative process (5). Further, olive oil is a natural product, and the chemical composition of its nonpolar part and of the liposoluble antioxidants may differ signifi- cantly from oil to oil. To emphasize the role of the dispersed water as a stabilizing agent against the oxidative deteriora- tion of the olive oil, we decided to check this effect by look- ing at the conditions under which the water can be dispersed into the apolar matrix. For this reason, we did not analyze the natural oil as a whole, but as samples treated by filtering the particulate solid and adding water under controlled conditions. An important result was that the antioxidizing function took place anyway. Such a system represents a multiphase (heterogeneous) sys- tem, in which one phase (water) exists in the form of small droplets (dispersed phase) and the rest constitutes the so- called continuous phase. In general, the area of the interface between the dispersed and continuous phases is rather large, and the more numerous the small-sized droplets, the larger the interfacial area. This is the reason the interfacial proper- ties are of crucial importance for the stability of emulsions. Moreover, the large interface is the boundary where physico- chemical processes of great interest occur (6,7). The way in which water can be dispersed in the oil matrix affects the interfacial properties of the emulsion itself. Thus, a correlation between the oxidation rate and the structure of the water/olive oil emulsion might be expected. In order to test this hypothesis, differently prepared emul- sions of water/olive oil were oxidized in different ways. The final mixtures were analyzed using both chemical and physi- cal methods. In the present paper we show the results of some chemical investigations that addressed the influence of dis- persed water in the oxidative process. EXPERIMENTAL PROCEDURE Chemicals. All the chemicals used were reagents of analyti- cal grade of 99.9% purity purchased from Carlo Erba Com- pany (Milan, Italy) and used without any further purification. Oil sampling. The oil was taken directly from the crusher and treated for 15 min with an N 2 current and stored at 4°C. Olives of mixed cultivars (Cima di Mola, Cima di Bitonto, and others) were picked during the first 10 d of the 1999–2000 November oil campaign and pressed a few days later. The oil, produced with a discontinuous process, was characterized using conventional analytical methods. Analytical methods. PV, total acidity, spectrophotometric indexes, and refractive index were determined by the official method recommended by the European Community (8). Analysis of polyphenols consisted of two steps: (i) The compounds were extracted by a methanol/water mixture, as described by Montedoro et al. (9), and then (ii) a spectropho- tometric assay was used to estimate their relative amounts. The Folin–Ciocalteu reagent and the Arnow mixture were uti- lized to discriminate between the total phenols and ortho- diphenols, respectively. The content of phenolics was ex- pressed as ppm of caffeic acid equivalents. A spectrophotometric assay, together with the Emmerie– Engel procedure, was used to determine the tocopherol con- Copyright © 2002 by AOCS Press 577 JAOCS, Vol. 79, no. 6 (2002) *To whom correspondence should be addressed at Consorzio per lo sviluppo dei Sistemi a Grande Interfase (C.S.G.I.), Department of Food Technology (DISTAAM), Università del Molise, via De Sanctis 86100 Campobasso, Italy. E-mail: ambroson@unimol.it The Role of Water in the Oxidation Process of Extra Virgin Olive Oils L. Ambrosone*, R. Angelico, G. Cinelli, V. Di Lorenzo, and A. Ceglie* Consorzio per lo sviluppo dei Sistemi a Grande Interfase (C.S.G.I.), Department of Food Technology (DISTAAM), Università del Molise, Campobasso, Italy