Written by Tatjana Djakovic, Staff Writer. The study showed that the rate of vitamin E degradation was highest in half-filled clear bottle of olive oil (92.6%) and lowest in filled dark bottle (24.2%).
The health benefit of extra virgin olive oil (EVOO) is important for preventing heart disease and cancer, which are amongst the most prevalent diseases in the today’s society (1). The extra virgin olive oil contains a very high percentage (74%) of monounsaturated fatty acids (has one double bond) and a reduced level of poly-unsaturated fatty acid ( with two or more double bonds) in their chemical structures. The higher composition of mono-unsaturated fatty acid is believed to provide resistance to chemical and biological oxidation that occurs with the less stable fatty acids with multiple double bonds. (2,3)
The second factor contributing to the health benefits of extra virgin olive oil is the presence of antioxidants, which protect the pleasant flavor and taste. The antioxidants include vitamin E, which works to protect against lipoperoxidation, which is a process by which harmful free-radicalsn initiate a chain reaction with the fat molecules which leads to fatty acid oxidation and rancidity (4)
Since olive oil is prevalent oil used in cooking especially in Mediterranean diet, the researchers in the study investigated the change in olive oil quality during storage. The olive oil was filtered and stored in twenty 500 ml glass bottles. The researchers monitored the loss of vitamin E, antioxidants and polyunsaturated fatty acid in the oil stored at four different conditions for a period of 12 months. The four different conditions that were analyzed included filled dark glass bottle, filled clear glass bottle, half-empty dark glass, and half-empty clear glass bottle.
The concentration of polyunsaturated fatty acids remained almost constant during 8 months for all four different storage conditions. After 1 year of storage the percentage of polyunsaturated fatty acids in the olive oil decreased by 2.52% in the half-filled dark bottle and by 2.75% in the half-filled clear bottle and remained constant in the both of the filled bottles. The degradation of the poly-unsaturated fatty acids started when the level of antioxidant decreased. The levels of antioxidant (o-diphenol) decreased by 65.6% in the half-filled dark bottle, by 66.1% in the half-filled clear glass bottle in contrast to 19.2% in filled dark bottle, and 20.4% in the filled clear bottle after 1 year of storage.
The rate of vitamin E degradation was also most significant in the half-filled bottles as compared to empty-filled bottles. The level of vitamin E degraded by 91.4% in the half filled dark bottle, by 92.6% in the half-filled clear bottle, in contrast to 20.9% in the filled dark bottle and 24.2% in the clear bottle.
The authors suggest that the vitamin E, which is the most important antioxidant of olive oil was quickly oxidized or degraded. The vitamin E then began a chain reaction by oxidizing other molecules such as o-diphenols which proceeds with free radicals creating other f ree radicals after oxidation of a molecule. The decrease in the antioxidant concentrations and the presence of free radicals oxidizes the fatty acids in the oil ultimately causing their degradation.
The results of the experiment indicate the extra virgin olive oil is most stable and maintains most of its heart protective properties when it is placed in a filled dark bottle or containers with minimal oxygen available to degrade the fatty acids and antioxidants in the oil. (5). Many olive oil products are protected by removing oxygen from the head space, according to Jim Emme, Operations manager at Now Foods who says, “… most companies who package olive oil are flushing the head space in the bottles with either nitrogen or carbon dioxide. Some are using plastic bottles that have high oxygen permeability ratings, so the flushing is short-lived. There are some who don’t, usually suppliers to some of the big box mass chains who are trying to keep their costs down”. If olive oil is kept for over a month at room temperature in partly filled bottled, a significant amount of the antioxidants will be lost. It can be refrigerated to reduce this, but this causes part of the oil to settle out.
Source: Rastrelli, Luca, et al. “Rate of degradation of α-tocopherol, squalene, phenolics, and polyunsaturated fatty acids in olive oil during different storage conditions.” Journal of agricultural and food chemistry 50.20 (2002): 5566-5570.
© 2002 American Chemical Society
Posted February 19, 2013.
References:
- Fito, M., et al. “Antioxidant effect of virgin olive oil in patients with stable coronary heart disease: a randomized, crossover, controlled, clinical trial.” Atherosclerosis 181.1 (2005): 149-158.
- Eyre, Harmon, et al. “Preventing Cancer, Cardiovascular Disease, and Diabetes: A Common Agenda for the American Cancer Society, the American Diabetes Association, and the American Heart Association*†.” CA: a cancer journal for clinicians 54.4 (2008): 190-207.
- Maria-Isabel C. The Effect of Polyphenols in Olive Oil on Heart Disease Risk Factors: A Randomized Trial. Ann Int Med 2006; 145(5): 333-341.
- Boskou, D. Olive oil quality. In Olive oil: Chemistry and Technology; Boskou, D., Ed.; AOCS Press: Champaign, IL, 1996; Chapter 7, p 101.
- De Simone F. et al, Rateo f Degradation of r-Tocopherol, Squaliene, Phenolics, and Polyunsaturated Fatty Acids in Olive Oil Turing Different Storage Conditions. 2002. J. Agric. Food Chem. (50): 5566-5570.
