A product of Olea europaea and its cultivars and a major source of fat in Mediterranean-style diets, olive oil, naturally rich in oleic acid (18:1, n-9), a monounsaturated fatty acid (MUFA), has been associated with a decreased risk of cardiovascular disease (CVD) and cognitive decline (Perez-Jimenez et al., 2005). The potential healthful benefits associated with olive oil fatty acid composition, antioxidant activity, and phenolic profile depend on harvesting technologies, cooking applications, and storage environments, as well as the cultivar (Cicerale et al., 2009a, b; Baiano et al., 2009; Trichopoulou and Dillis, 2007).
The foundational “seven countries” study by Keys et al. (1986) suggested that oleic acid, the primary fatty acid in olive oil, significantly contributed to the lower risk of CVD. Central to the Mediterranean diet and its purported health benefits is increased consumption of olive oil and possibly other MUFA-rich oils. A meta-analysis of earlier studies suggests these kinds of diets may contribute to decreased plasma LDL, increased HDL, and reduction in total cholesterol (Gardner and Kraemer, 1995; Howard et al., 1995). However, the magnitude and consistency of these CVD-risk outcomes remain controversial since the effects may reflect meal composition and individual genetic variations (Rivellese et al., 2006; Konstantinidou et al., 2010).
With so many health benefits attributed to olive oil and MUFAs, consumers wonder if all food grade olive oils are the same. In fact, while traditional virgin olive oils are obtained mechanically, there are subtle differences in the fundamental chemistry of these food products that reflect the categorization of extra virgin olive oil (EVOO), virgin olive oil (VO), and ordinary olive oil. The fundamental difference is the free acidity content, with EVOO having not more than 0.8% (w/w) expressed as oleic acid, whereas VO has a free acidity of < 2% (w/w).
Available throughout the world, each olive oil differs in composition, such as phenolic content and potential antioxidant activity, and in flavor profile. Consumers as well as food scientists raise questions as to the stability of the phenolics, such as oleuropein, pinoresinol, and oleocanthal, which are are responsible for the unique pungent taste. Recent data suggest that regardless of the Italian cultivar, total phenolics in olive oil are subject to continuous degradation, at least for 12 months when stored at room temperature and under short-term accelerated storage conditions (Baiano et al., 2009; Lerma-Garcia et al., 2010). Similarly, based on the β-carotene antioxidant activity method, there is a gradual decline in the percent antioxidant activity from time of production through a 12-month storage period. These phenols are subject to destruction at various temperatures and subsequent diminution of potential biological activity, some of which are close to typical thermal processing conditions (Cicerale et al., 2009).
Oleocanthal, one of several apparently anti-inflammatory phenolics that is a normal constituent of EVOO, is of pharmacological interest. In vitro studies suggest that it exhibits ibuprofen-like properties, possibly through the down regulation of eicosanoid inflammatory mediators (Beauchamp et al., 2005). However, the bioavailability of this phenolic and similar compounds is uncertain. In general, phenolics such as those found in olive oil may be modified in the hostile environment of gastric acidity, leading to the production of aglycones (sugars released by hydrolysis of glycosides). The small intestine is the primary site of absorption of these olive oil–derived phenols. These absorbed compounds may be transformed within the liver’s cytochrome P450 system or selected methyl-transferases. Within the distal bowel and in the increased presence of microflora, phenolics can be further transformed to compounds, such as hydroxytyrosol, tyrosol, and secoiridoids that may reduce the risk of some cancers (Corona et al., 2009; Hashim et al., 2005).
With the continued interest in decreasing CVD risk by reducing dietary saturated fatty acids, there is a movement to introduce alternative sources of MUFAs other than olive oil. Novel technologies, including interesterification and fractionation, will yield high oleic acid oils with improved processing and storage stability and potential health benefits through the reduction of saturated fatty acids and industrial trans fatty acids, and the decrease of some n-6 fatty acids. However, none of these technologies has produced an olive oil–like product with its rich history, polyphenolic content, or Mediterranean characteristics of flavor and health.
References for the studies cited in this article are available from the authors.
by Roger Clemens, Dr.P.H.,
ETHorn, La Mirada, Calif.
by Wayne Bidlack, Ph.D.,
Professor, California State Polytechnic University, Pomona