Evaluation of the oxidative status of virgin olive oils with different phenolic content by direct infusion atmospheric pressure chemical ionization mass spectrometry

Atmospheric pressure chemical ionization (APCI) mass spectrometry was used to predict the oxidative status of virgin olive oils (VOO) during storage. VOO samples, with and without phenolic compounds, were stored at 60 ºC for 7 weeks, to create references of different oxidation levels. For this purpose, VOO samples were 1:4 diluted in an alkaline 85:15 (v/v) propanol/methanol mixture and directly infused into the APCI source of an ion trap mass spectrometer. The abundances of the [M-H]- peaks of free fatty acids, oxidized fatty acids, tocopherols and phenolic compounds, jointly with their oxidized forms, were measured. Linear discriminant analysis models, using ratios of pairs of peak abundances as predictors, were constructed in order to classify samples according to their oxidative levels. Based on these models, VOO samples with and without phenolic compounds at different storage times, divided in 8 categories, were correctly classified with an excellent resolution among all the category pairs. This method is a very fast tool for on-line monitoring of VOO oxidation status.