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Influence of thermal treatment on phenolic compounds and antioxidant capacity of Istarska bjelica cv. extra virgin olive oil

Traditional preparation of meals in Mediterranean countries, as well as in Croatia, includes oven roasting of meat, fish and vegetables with extra virgin olive oil (EVOO). Considering that, the main aim of this study was to determine changes in phenolic composition and antioxidant capacity in Istarska bjelica cv. EVOO after thermal treatment at different temperatures. Istarska bjelica was chosen for this purpose, as the most commonly used autochthonous cultivar whose oil is characterized by a high phenolic content. Istarska bjelica oil samples were heated at 180 °C and 220 °C in an oven for one hour, fresh oil was used as a control. Quality parameters, peroxide value (PV) and spectrophotometric indices (K232, K270 and ΔK), were determined according to the analytical methods described in the European Commission Regulation (EEC, 1991). The HPLC-DAD system was used for phenol content analysis. Antioxidant capacity was determined spectrophotometrically by evaluating the free radical-scavenging effect of DPPH radical. PV reduced at 180 °C, but maintained unchanged at 220 °C. Differently, a higher increase in K value parameters was observed with temperature alteration. This might have occurred as a result of highly unstable primary oxidation products who, due to enhanced oxidation, converted into secondary products. Total phenol and secoiridoid content decreased significantly only at 220 °C. Regarding individual phenols, most of them decreased at 220 °C, except in the cases of p-HPEA-EDA and hydroxytyrosol acetate whose concentration increased. Antioxidant capacity correlated with total phenol content showing a major decrease at 220 °C. Obtained results demonstrated that lower cooking temperatures (about 180 °C) have no significant negative effect on Istarska bjelica cv. EVOO total phenolic composition, as well as on its antioxidant capacity. Acknowledgement: This work has been supported in part by Croatian Science Foundation under the project “Young researchers' career development project – training of new doctoral students”, DOK-2018-09-2293.

thermal treatment, phenolic compounds, antioxidant capacity, extra virgin olive oi

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