Effects of oxygenation and process conditions on thermo-oxidation of oil during deep-frying

Deep-frying exposes edible oils to high temperature and oxygen for long periods causing its rapid breakdown. This study elucidates why oxygen transport shortens more oil usage lifetime than the frying temperature itself. The role of oxygen transport on the propagation of auto-oxidation of lipids was investigated in a 3 L household deep-fryer modified into a bubbling reactor working under controlled oxygen partial pressures (from 2.5 kPa to 21 kPa), air flow rates (from 0 to 55 L/min) and temperatures (140-180 degrees C). The possible role of oil hydrolysis on oxidation kinetics was specifically investigated by comparing results with and without fried product. Primary and secondary oxidation products were measured for up to 8 h and included: peroxide value, conjugated dienes, p-anisidine value. Oxidation kinetics were shown not to depend anymore on oxygen transport for specific air injection flow rates above 6 L min(-1) kg(-1) oil. Beyond this value, only temperature and partial pressure of oxygen were able to affect oxidation kinetics. A comprehensive mechanistic model is proposed and validated to reconcile data obtained under various oxygenation, bath geometry and temperature conditions. (C) 2016 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.