Removal of pomace residues is critical in quantification of element concentrations in extra virgin olive oil

Analysis of elements in Extra Virgin Olive Oil (EVOO) is challenging due to the complex oil matrix as well as very low element concentrations in oil. We postulate that inadequate sample preparation (in particular, the presence of pomace residue in oil) may significantly contribute to variations in EVOO element concentrations. In order to confirm this hypothesis, EVOO and pomace samples were analysed for content of 29 elements by ultrasonic acid extraction and ICP-MS detection. Comparative analyses of non-centrifuged and centrifuged EVOO samples confirmed significant influence of pomace residues on element concentrations. Ranges of macronutrients (25-286 ng g(-1)), micronutrients (0.3-1.1 ng g(-1)) and trace elements (0.001-0.2 ng g(-1)) in centrifuged EVOO samples were up to 1000 times lower than in non-centrifuged oils. We have shown that pomace residue, even when present in very small quantity (1 g of pomace in 1 kg of oil), significantly altered concentrations and relative proportions of many elements in EVOO. Therefore, adequate sample pre-treatment (removal of pomace residue via centrifugation) is essential for determining real multi-element composition of olive oil. This is critical in application of EVOO multi-element composition in traceability studies and determination of geographic origin of olive oil.