Evaluation of the state of oxidation of olive-pomace oils. Influence of the refining process

The aim of this investigation was to trace the fate of oxidation levels in crude olive-pomace oil during refining. Seven series of samples were examined. Each series comprised samples of the unprocessed crude oil and of the same oil collected after each step of the refining process. The analyses were performed by means of silica gel column chromatography and high-performance size-exclusion chromatography. The data obtained showed that triglyceride oligopolymers increased during refining, especially during bleaching and deodorization, and that the levels of these compounds were on average similar to 4-fold greater in the refined oils than in the crude oils. Conversely, oxidized triglycerides decreased by an average of 49% as the oil was processed into a refined oil. When the percent values of oxidized triglycerides were plotted against the percent values of oligopolymers, a linear trend of the experimental data was depicted for all the series examined. The regression lines computed revealed correlation between the two classes. This indicated that one of the reasons oxidized triglycerides decreased during olive-pomace oil refining was related to the occurrence of polymerization reactions. It was finally suggested that the content of oligopolymers triglycerides may be usefully employed as a reliable analytical index for estimating the level of oxidation of a freshly refined oil.