Towards a wicking rapid test for rejection assessment of reused fried oils: Results and analysis for extra virgin olive oil

This work investigates the potential of developing a rapid test based on wicking of oil into paper for determining whether a reused frying oil is to be rejected. To achieve this goal, wicking patterns (oil penetration rate and oil front shape versus time) of both fresh and prolonged fried extra virgin olive oil are optically registered at six different paper stripes. Four of them are double-ply towel papers whereas the other two are single-ply chromatographic papers. Wicking tests are performed at 20 °C and 30 °C. It is shown that the type of paper affects seriously the wicking patterns. Double-ply papers present high oil penetration rates but very irregular oil front shapes whereas single-ply papers yield lower oil penetration rates but pretty flat oil fronts. Furthermore, it is found that only under certain conditions the penetration rates obey the well known Lucas-Washburn equation. A discussion is made on the phenomena that take place during wicking of oil into paper which may cause deviations from the Lucas-Washburn equation. A semi-empirical model is proposed to describe the above deviations by incorporating the effect of time evolving pore sizes.