Study by 1H NMR spectroscopy of the evolution of extra virgin olive oil composition submitted to frying temperature in an industrial fryer for a prolonged period of time

► Extra virgin olive oil was heated at 190 °C in an industrial fryer for 40 h. ► The evolution of oil composition was monitored by 1H NMR. ► Equations that relate oil composition and heating time were obtained. ► Monounsaturated groups degraded at faster rate than polyunsaturated groups. ► 4-Hydroxy-2-alkenals were not found and 2,4-alkadienals were formed in small amount.