Three series of fourteen deep-frying experiments on three foods of very different compositions were carried out using extra virgin olive oil as the original frying medium. The aim of the study was to establish how the nature of the food being fried influences the composition of the frying medium. The changes in the composition of the frying media referred to the evolution of molar percentage of the different kinds of acyl groups, as well as to the evolution of the concentration of newly formed compounds such as aldehydes, epoxystearyl groups, primary and secondary alcohols were monitored in a simultaneous way by (1)H NMR spectroscopy. Changes due to hydrolytic processes were also considered. In addition, the evolution of the Iodine Value and percentage in weight of polar compounds was also analysed. The influence of food lipids migration to the frying medium on the composition of this latter was evidenced.
Keywords: Acyl groups; Alcohols; Aldehydes; Deep-frying; Degradation; Epoxides; Extra virgin olive oil; Food lipids migration; Frying media composition; Hydrolysis; Iodine Value; Percentage in weight of polar compounds.
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