Influence of metal ions and phospholipids on electrical properties: A case study on pumpkin seed oil

Dielectric spectroscopy at low frequencies was applied to analyze vegetable oils, in particular roasted pumpkin seed oils (RPO). Large differences were observed for electrical conductivity not previously applied as a tool in the analysis of crude vegetable oils. RPO have two orders of magnitude higher conductivity than refined sunflower oils and extra virgin olive oils. Differences in dielectric constant were small and influenced by fatty acid composition and presence of minor components. The conductivity of pumpkin seed oils is highly correlated to phospholipid and metal contents. Phospholipids, magnesium, potassium and sodium are present at mmol/kg concentrations as determined by ICP-MS. We have shown that measurement of electrical conductivity can be used as a cost efficient method to detect adulteration of RPO with refined oils, even for those with similar fatty acid composition. Low background conductivity of triacylglycerols allows that even trace amounts of metals and phospholipids are detected in vegetable oils.