Stability of virgin olive oil. 2. Photo-oxidation studies.
Virgin olive oil samples with similar oxidative stabilities and fatty acid compositions were exposed to 12100 lx (25 +/- 1 degrees C) in closed bottles until bleached. The observed low changes in the substrate and polar phenols were related to oxygen availability. HPLC monitoring showed that pheophytin agradual degradation (> 90%) was accompanied by a considerable alpha-tocopherol loss (22-35%) due to the reaction of the latter with singlet oxygen. No changes were recorded for carotenoids, which acted as physical quenchers and light filters. Squalene loss was confined (4-12%). Complementary experiments on the activity of pheophytin a, using olive oil models, indicated a concentration dependence, enhanced by oxygen availability. In closed bottles, the degradation rate constant was higher at low amounts of pheophytin a. Squalene was preferentially consumed to protect alpha-tocopherol. An urgent change in the practice of packaging is needed to preserve the precious characteristics of the product during commercialization.
Psomiadou
Eleni
E
Laboratory of Food Chemistry and Technology, School of Chemistry, Aristotle University of Thessaloniki, 54006 Thessaloniki, Greece.
Tsimidou
Maria
M
D002734:Chlorophyll / Q000032:analysis; D002851:Chromatography, High Pressure Liquid; D004355:Drug Stability; D008055:Lipids / Q000032:analysis; D000069463:Olive Oil; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D010636:Phenols / Q000032:analysis; D010674:Pheophytins / Q000032:analysis / Q000737:chemistry; D010777:Photochemistry; D010938:Plant Oils / Q000737:chemistry*; D026082:Singlet Oxygen / Q000737:chemistry; D013185:Squalene / Q000737:chemistry; D024502:alpha-Tocopherol / Q000032:analysis / Q000737:chemistry
D008055:Lipids; D000069463:Olive Oil; D010636:Phenols; D010674:Pheophytins; D010938:Plant Oils; D002734:Chlorophyll; D026082:Singlet Oxygen; D013185:Squalene; D024502:alpha-Tocopherol; D010100:Oxygen