Chemical and thermal evaluation of olive oil refining at different oxidative levels

In this work, differential scanning calorimetry (DSC) was for the first time applied to evaluate cooling and heating curves and related thermal properties of olive oil during refining process steps starting from two series of samples at different initial peroxide values (low, 15 meq O2/kg and high, 30 meq O2/kg). Thermal properties were statistically correlated by means of principal component analysis (PCA) to those substance classes (products deriving from oxidation, polymerization and hydrolysis of triacylglycerols (TAG)) that could exert adverse effects on consumer health and a negative contribution to the shelf-life of the refined oil. A concomitant significant increase of K270 and polymerized TAG, as a general decrease of oxidation level was exhibited by oils during bleaching. Crystallization significantly shifted towards lower temperatures as well as onset temperature of heating, enlarging transition range, starting from bleaching and at both oxidation levels. PCA was performed to tentatively discriminate among samples according to different refining steps and/or initial level of oxidation correlating thermal properties and chemical results. The first principal component clearly clustered samples according to different refining steps and this differentiation was possible on the basis of the relation of thermal parameters with polymerized TAG conjugated dienes and trienes (K232 and K270, respectively). This preliminary goal should lead to deepen the study of DSC application in the evaluation of the quality of olive and other vegetable oils during refining. Practical applications: DSC is a thermal technique that nowadays covers a large set of applications in lipid technology due to its indisputable advantages as it does not require sample preparation and use of solvents, resulting in a reduced environmental impact. The preliminary findings of this study promote the application of the technique in the evaluation of olive oil quality during refining steps in relation with molecular species formed as polymerized TAG and conjugated trienes discriminating crude and neutralized samples to bleached and deodorized oils. DSC could be also applied on other vegetable oils where refining process is more frequently applied