Chemical changes in extra virgin olive oils from Slovenian Istra after thermal treatment

Changes in the physico-chemical parameters of extra virgin olive oils after heating for 142 h at 100 °C with an air flow 10 L/h were investigated. The experimental study was carried out on the two predominant olive cultivars in Slovenian Istra – cv. Istrska belica and cv. Leccino. The data obtained showed that oils from Istrska belica were more stable than those from Leccino. Peroxide values and spectrophotometric data showed higher amounts of oxidation products in oils from Leccino than in those from Istrska belica. After thermal treatment fatty acid composition was changed more in Leccino oils; particularly the amounts of polyunsaturated fatty acids dropped significantly, while α-tocopherol was completely depleted in all samples. The content of total biophenols decreased from 598 mg/kg to 241 mg/kg in Istrska belica oils and from 391 mg/kg to 176 mg/kg in Leccino oils. HPLC data showed that transformation of secoiridoid biophenols to the simple biophenols, tyrosol and hydroxytyrosol took place.