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The present paper reports on the changes in the volatile composition of virgin olive oils (VOO) stored for 18 months. VOO samples of five Greek olive varieties were stored in dark glass bottles (headspace 0.5%) in a basement without central heating. Even after 18 months of storage, the basic quality characteristics of the samples, such as free acidity, K232, K270, and peroxide values, did not exceed the upper limits set by European Community Regulations for VOO. Regarding the lipoxygenase pathway products, responsible for the positive sensory notes, it was shown that their total amount remained stable during the storage period. Even though the physicochemical characteristics did not exceed the upper limits, high rates of formation of volatile oxidation products, which are responsible for the off-flavors, were observed. Among the volatile oxidation products, the highest rates of formation were monitored for heptanal, 2-heptenal, and pentanal followed by hexanal and nonanal. The formation rate of volatile oxidation products was higher in VOO from Lianolia and Asprolia compared to VOO from Koroneiki, Native from Zakynthos and Thiaki varieties. Finally, stepwise linear regression analysis (SLRA) selected linoleic acid and total phenol/ ortho-diphenols ratio as having the maximum correlation with the formation rate of 2-heptenal. Practical applications: This research reports on the changes in the quality characteristics of VOO, stored for 18 months, of the main olive varieties cultivated in the western Greece. Furthermore, it provides information on the changes in volatile composition, which is responsible for positive and negative flavor attributes. Results from this study may contribute to a better understanding of the relationships between minor and/or major components and the autoxidation process. Moreover, results could be useful to VOO packagers and marketers in order to estimate the shelf-life of individual varieties. VOO from Koroneiki, Native from Zakynthos and Thiaki varieties, which are characterized by low linoleic acid contents, can be preserved for a longer period compared to VOO from Lianolia and Asprolia varieties, which are characterized by high linoleic acid contents. During storage of virgin olive oil (VOO) for 18 months, lipoxygenase pathway products, responsible for the positive sensory notes, remained stable. Among the volatile oxidation products, the highest rates of formation were monitored for heptanal, 2-heptenal, and pentanal, followed by hexanal and nonanal. 2-heptenal was correlated with VOO unsaturation and has been suggested as oxidation marker during storage. [ABSTRACT FROM AUTHOR]

Virgin olive oil is oil with a high biological value, due to its polyphenol content. Virgin olive oils were subjected to heat treatment simulating common domestic processing, including boiling, frying and storage. These processes can affect the phenolic compounds content of oils to a certain degree, depending on each one treatment. Thermal oxidation of oils at 180 °C (frying) caused a significant decrease (p < 0.005) in hydroxytyrosol derivatives (60% reduction after 30 min and 90% reduction after 60 min) and, to a lower degree, in tyrosol derivatives. No changes were observed in the content of lignans (p > 0.005). On the other hand, thermal oxidation of oils at 100 °C (boiling) for 2 h caused a decrease by less than 20% in all classes of phenolic compounds. The reduction of phenolic compounds during storage under environmental conditions was correlated with the peroxide value. When the peroxide value did not exceed the level of 20 meq⋅kg-1, as was recorded for low linoleic acid oils and low oxygen availability at the bottles' headspace, a degree of reduction of approximately 30% in hydroxytyrosol derivatives and 10% in tyrosol derivatives was observed, while lignans remained unchanged. Finally, during both heating and storage under environmental conditions, the evolution of oxidized phenolic compounds was observed. The structures of these oxidized products were confirmed by HPLC-MS. [ABSTRACT FROM AUTHOR]