Bioaccessibility and Antioxidant Activity Stability of Phenolic Compounds from Extra-Virgin Olive Oils during in Vitro Digestion CATERINA DINNELLA,* PATRIZIA MINICHINO,ANNA MARIA D’ANDREA, AND ERMINIO MONTELEONE Dept. Biotecnologie Agrarie, Università degli Studi di Firenze, via Donizetti, 6 50144 Firenze, Italy The impact of an in vitro procedure that mimics the physiochemical changes occurring in gastric and small intestinal digestion on the bioaccessibility and antioxidant activity of phenols from 10 extra- virgin olive oil samples was assessed. Extra-virgin olive oil phenols were totally extracted in the aqueous phase, which reproduces gastric fluids during the digestion procedure. A linear bioaccessibility model, based on tyrosol behavior in model oil samples, was used to estimate the bioaccessibility index (BI%) of extra-virgin olive oil phenols. The BI% varied amongst samples from a maximum of 90% to a minimum of 37%, thus indicating that only a fraction of phenols can be considered bioaccessible. The specific antioxidant activity of olive oil phenols proved to be negatively affected by the digestion procedure. By computing a principal component analysis, it was possible to show that differences in the potential bioactive effect of extra-virgin olive oil samples were related to different phenolic profiles. KEYWORDS: Health properties; phenolic profile; gastrointestinal digestion; bioaccessibility model INTRODUCTION Phenolic compounds in plant-derived foods and beverages have been shown to have important physiological properties and may be responsible for both detrimental and beneficial effects on human health (1, 2). Peroxidative chain reactions have been positively linked to the pathogenesis of coronary heart diseases and various forms of cancer (3). The strong radical scavenging activity of phenolic compounds probably accounts for their role in preventing diseases related to oxidative stress. It is well known that the beneficial effects of a Mediterranean diet on human health are mainly attributable to the presence of antioxidant-rich foods. Virgin olive oil is a source of at least 30 phenolic compounds, and it represents the principal fat component of the Mediterranean diet. Oleuropein–aglycone and ligstroside–aglycone are the esters of elenolic acid with 3,4′- dihydroxyphenylethanol (hydroxytyrosol) and 4-hydroxyphen- ylethanol (tyrosol), respectively. These aglycones and their derivatives, such as hydroxytyrosol and tyrosol (end products of oleuropein– and ligstroside–aglycones hydrolysis), are the most abundant phenols in olive oils (4, 5). The antioxidant activity of olive oil phenols is related to their chemical structure (6). Oleuropein-aglycone derivatives with an ortho-diphenolic structure are considered the main source of the overall antioxidant activity of extra-virgin olive oils (EVOOs). On the other hand, little or no antioxidant activity has been found for mono-phenols such as ligstroside–aglycone and tyrosol. The importance of the intake of phenolic compounds through the consumption of olive oil and the possible role of phenols in human health have been extensively investigated and critically reviewed (1, 4, 5, 7). A number of studies have shown that these phenols are inhibitors of low-density lipoprotein (LDL) oxidation in Vitro; thus, their role in in ViVo protection from the formation of atherosclerotic plaques has been postulated (8). On the other hand, it has been suggested that the amount of olive oil phenols in the diet is too low to protect in ViVo LDLs against oxidative modification to any important extent (7). The in ViVo adsorption of tyrosol and hydroxytyrosol from realistic doses of virgin olive oil has been demonstrated, and it has been suggested that they could exert beneficial effects on human health (9). Investigations on intestinal adsorption in perfused rats indicated that oleuropein is capable of permeating the intestine even if the amount that reaches the systemic circulation unchanged is quite small (10). Positive health benefits have been postulated due to oleuropein metabolites. Furthermore, oleu- ropein may act locally to protect other dietary antioxidants from degradation at the intestinal level and thus increase the total antioxidant status of the body. It is generally accepted that there are two major requirements of a dietary compound for it to be a potential in ViVo antioxidant. The first requirement is to be bioaccessible, which refers to the compound’s tendency to be extracted from the food matrix and then absorbed by intestinal cells. The second requirement is the * Author to whom correspondence should be addressed. Tel.: 055 3220326; fax 055 355995; e-mail dinnella@unifi.it. J. Agric. Food Chem. 2007, 55, 8423–8429 8423 10.1021/jf072244+ CCC: $37.00  2007 American Chemical Society Published on Web 09/20/2007