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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 degrees 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 degrees 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. Journal of Food and Nutrition Research

In this work the effect of standard phenolic compounds such as trolox, phenolic acids (ferulic, gallic, protocatechuic and caffeic acid) and secoiridoids, extracted from virgin olive oil (VOO), on acrylamide formation in an emulsion system was investigated. The emulsion system was heated in an oil bath at different temperatures and for different periods of time. At 105 and 115 degrees C the generated amounts of acrylamide were negligible during the monitoring time. At 125 degrees C addition of standard phenolic compounds reduced acrylamide formation which was more pronounced at initial time of heating (20 min) reaching up to 70%. Protocatechuic and gallic acid were more effective than trolox, caffeic and ferulic acid in acrylamide reduction at the final time intervals of heating (30-60 min). On the contrary, addition of VOO extract in the emulsion system resulted in a remarkable increase of acrylamide level, which was ascribed to secoiridoids' structure containing aldehydic groups. (C) 2010 Elsevier Ltd. All rights reserved. Food Chemistry