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The health benefits of the Mediterranean diet have been associated with the consumption of extra virgin olive oil (EVOO) as the main source of fats. Nowadays, the usage of EVOO as cooking oil to prepare meals is highly recommended. During heating, the oil undergoes several chemical reactions that influence its chemical composition and quality. Therefore, this study aimed to investigate the influence of heating on quality parameters, phenolic and volatile compounds in Leccino, Istarska bjelica, and Buža monovarietal EVOO. The oil samples were submitted to heating in an air oven at two different temperatures (180 °C and 220 °C), simulating usual roasting conditions typical for Mediterranean cuisine. Fresh, unheated oil was used as a control. Quality parameters related to oxidation status of oil, peroxide value, and spectrophotometric indices (K232, K268, and ΔK) were determined according to the analytical methods described in the European Commission Regulation from 1991, amendments included. The composition of phenolic compounds was determined by HPLCDAD, and volatiles’ profiles using SPME and GC-FID techniques. Significant losses in oxidative stability and decrease in phenolic and volatile compounds were more pronounced at higher heating temperatures, which underlined the temperature dependency of oxidative degradation during cooking conditions. However, there was still a considerable amount of phenolic compounds preserved after heating. In addition to quality parameters that served as oxidation indicators, hydroxytyrosol acetate among phenolic compounds and octanal, (E)- 2-octenal, hexanal, 3-pentanone, and 1-penten-3- one among volatiles, were underlined as possible thermal oxidation markers. Aside from being influenced by the heating temperature, the changes in the phenolic composition were cultivar dependent, while the changes in the composition of volatile compounds were found to be caused primarily by the heating temperature with no significant influence of the cultivar as an investigated factor. The obtained results contribute to the understanding of changes in quality and composition of Croatian monovarietal EVOO after heating, as well as provide new insights on the preservation of bioactive compounds in the course of the cooking process. Acknowledgement: This work has been supported by the Croatian Science Foundation under the project “Young researchers' career development project – training of new doctoral students”, DOK-2018-09-2293. |
