September 06, 2005
Hydroxytyrosol and tyrosol are some of the many phenol compounds in olive oil that contribute to bitter taste, astringency, and resistance to oxidation. They are now being played up in the press as a desirable health component of olive oil. The flavenoid polyphenols in olive oil are natural anti-oxidants which have been shown to have a host of beneficial effects from healing sunburn to lowering cholesterol, blood pressure, and risk of coronary disease. There are as many as 5 mg of antioxidant polyphenols in every 10 grams of olive oil. Many other nut and seed oils have no polyphenols. Phenol content is determined by olive variety, time of picking, oil processing method, whether the oil is refined and the length of time the oil has been stored.
Variety - Specific types of olives, such as the Tuscan varieties, will have higher polyphenol values. These oils are valuable in that when blended with a low polyphenol oil they will extend the shelf life by preventing rancidity.
Time of picking - Most olives picked earlier in the year will have more polyphenols. Olives picked later in the winter have fewer polyphenols and a more mellow taste. Polyphenol concentrations increase with fruit growth until the olives begin to turn purple then begins to decrease. Years ago farmers valued the more mellow taste and tried to wait to pick their olives but risked freezing or loss to the elements. Now the strong earlier harvest taste has become popular.
Processing method - Much is made of how the type of olive oil machinery will affect the flavor of extra virgin oil but in reality if used properly it has only a small influence. Extra virgin olive oil is made the same way with the same machinery in the US as in Italy. Only a tiny percent of the oil sold in the US is made in the US and is mostly artisanal extra virgin oil which is high in phenols.
Most of the olive oil consumed in the US comes from Spain and Italy, and is usually refined. These mass market oils are generally refined and low in phenols.
Refining takes olive oil which has already been made but which is old, rancid, was made from diseased olives or has some other sort of defect and makes it palatable. This is done by filtering, charcoal treatment, heating, and chemical treatment to adjust acidity. Refined oils are lower in tyrosol and other phenols. According to Wayne Emmons at Intertech, Extra Virgin Olive oil typically has 50-80 ppm polyphenols while refined oil has only 5 ppm.
Storage - As oil sits in storage tanks or the bottle, the polyphenols will slowly be oxidized and used up. If you want an oil with more polyphenols, buy one that displays a date guaranteeing that it is fresh and that has been stored properly.
Hydroxytyrosol and other phenols are not used in any legal definition so you can only make generalizations to how many there are in various types of oil. Oils labeled as "lite" or "light" refer to flavor, not caloric content, as all vegetable oils have the same amount of calories. Theoretically "light" could refer to an excellent extra virgin oil made from olives picked late in the year but usually it signifies a flavorless low quality (refined) oil from Italy or Spain.
If you want an oil high in polyphenols, pick one that is guaranteed to be extra virgin (has the COOC seal if produced in the US), is from the current harvest season and that has been properly stored. Some varieties have high polyphenols; Frantoio, Lucca, etc. Look for US oils made from these varieties (go to custom search and search by olive oil variety) or look in a quality store or deli for a high quality extra virgin oil made with care and well labeled.
There are as many as 5 mg of antioxidant polyphenols in every 10 grams of olive oil. Many other nut and seed oils have no polyphenols.
The Antioxidant Activity of Polyphenols in Olive Oil Has Shown Promising Results with Respect to:
ATHEROSCLEROSIS. Oxidized low-density lipoproteins (LDL) contribute to the progression of human atherosclerosis. Antioxidants have been shown to prevent LDL modification. The beneficial effects of a Mediterranean diet may be defined by the unique antioxidant properties of its phenolic compounds.
ANTIMICROBIAL ACTIVITY. Olive polyphenols have been demonstrated to inhibit or delay the rate of growth bacteria such as Salmonella, Cholera, Staphylococcus, Pseudomonas, and Influenza in vitro. These data suggest a potential role of olive water polyphenol antioxidants in promoting intestinal and respiratory human and animal wellness, and as an antimicrobial food additive in pest management programs.
CANCER. There is a growing body of evidence that reactive oxygen species are involved in the etiology of fat-related neoplasm, especially in patients suffering from predisposing inflammatory conditions where high quantities of reactive oxygen are produced. Recent studies have shown that the abundant phenolic antioxidant fractions of olive oil have a potent inhibitory ability on reactive oxygen species associated with colon and breast pathologies.
OXIDATIVE STRESS FROM PASSIVE SMOKING Recent studies which involve administration of the phenolic fraction from olive water in rats exposed to oxidative stress from secondary smoke, show a dramatic reduction of stress and protective activity by polyphenols in the diet.
SKIN DAMAGE AND PHOTOPROTECTION. The skin damage produced by overexposure to sun rays and environmental stress is related to the destructive activity of free oxygen related radicals produced by skin cells. Polyphenolic components of olive oil have been compared to traditional antioxidants, such as tocopherols, used by the cosmetic and pharmaceutical industry to prevent skin damage. Results show polyphenols as having the highest activity as radical scavengers.