Oil Quality Control of Culinary Oils Subjected to Deep-Fat Frying Based on NMR and EPR Spectroscopy

The culinary oils, sunflower and olive, and the oil from the cultivated cardoon (Cynara cardunculus L.) were submitted to deep-fat frying during 36 h. The heterospectroscopy analysis by nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) allowed to control oil quality through the monitor of (1) the percentage of fatty acid types (increase of saturated and decrease of polyunsaturated fatty acids), (2) the new compounds formed (aldehydes and peroxides), and (3) the oil oxidative stability during the deep-fat frying. The aldehyde content was much higher in sunflower and cynara oils than in olive; however, the epoxides increased more in this oil. Oxidative stability measured by EPR was correlated (p < 0.05) with the aldehyde formation measured by NMR. The multivariate analysis of the NMR data allowed classifying the oils depending on (a) the oxidation degree (PC1) and (b) the fatty acid composition (PC2). Moreover, the favorable behavior of cynara oil suggests the potential use as frying edible oil.