Characterisation and phenolic profiles of two rare olive oils from southern Tunisia: Dhokar and Gemri-Dhokar cultivars.

The aim of this work was to study the chemical characteristics of two Tunisian cultivars, namely Dhokar and Gemri-Dhokar, to analyse the fatty acids, sterols, triacylglycerols, triterpenic alcohols, and to determine the phenolic composition and oxidative stability. Among the rare varieties, Gemri-Dhokar olive oil had the highest value of oleic acid (69.39%) whereas Dhokar oil was noteworthy for its lower content of phenolic compounds (94.56 mg kg(-1) gallic acid equivalents of oil) and presented the highest level of palmitic acid (19.37%). The main sterols found in all olive oil samples were β-sitosterol and Δ5-avenasterol, whereas cholesterol and 24-methylenecholesterol were also found in all samples but in lower amounts. Two triterpenic dialcohols (erythrodiol and uvaol) were also detected and their content ranged from 1.45 to 2.30%, in Gemri-Dhokar and Dhokar olive oil, respectively. Ten phenolic compounds were identified. In all samples, the main phenols found were oleuropein aglycon and pinoresinol. These phenolic compounds showed significant correlations with oxidative stability. The analytical parameters of two oils that were determined in this study were greatly influenced by genetic factors (cultivar).