Measuring Oxidative Resistance of Olive Oil Using Benchtop EPR

The oxidative rancidity of vegetable oil is a major problem in food related industries. It occurs during storage and is due to the oxidation of unsaturated fatty acids and the subsequent formation of foul odor and taste. Extra virgin oil (EVOO) oxidation is of particular interest due to the complexity of its distribution channels around the world and the fact that it is an individually packaged product (its final quality reflects either positively or negatively on the producer). Oxidative stability is affected by a number of factors, such as oxygen, temperature, presence of metals and light. The resistance of EVOO to oxidation is related to the high levels of monounsaturated triacylglycerols and the presence of natural phenolic antioxidants. Electron paramagnetic resonance (EPR) is a useful tool to detect free radicals and to determine the level of free radical formation in olive oil during forced oxidation at different temperatures.

Various methods exist to measure the end products of rancidity. However, many of these methods require cumbersome HPLC separations and can be very non-specific. Fatty acid hydroperoxides (intermediates in the rancidity process) can be measured using iodometric titration. However, this method is time consuming, lacks sensitivity and because these hydroperoxides are unstable, can underestimate the true extent of rancidity.

There has also been some previous work using EPR to measure oxidation in vegetable oil. Here, we describe a simple “forced oxidation” assay that uses EPR spin trapping to measure the fatty acid free radicals.