Contribution to Further Understanding of the Evolution of Sunflower Oil Submitted to Frying Temperature in a Domestic Fryer: Study by 1H Nuclear Magnetic Resonance

A study is made of the evolution of the composition of sunflower oil kept over prolonged periods of time at high temperature (190 degrees C) in a domestic fryer. The technique used is H-1 NMR spectroscopy. The degradation rate of linoleic acyl groups is determined in this process, as well as the proportions of monounsaturated, of saturated plus modified acyl groups and the iodine values. Intermediate oxidation compounds having hydroperoxide groups and conjugated dienic systems were not detected; however, some secondary oxidation compounds such as aldehydes are generated very early, among them, the genotoxic and cytotoxic 4-hydroxy-trans-2-alkenals. Both concentrations of each kind of aldehyde at different heating times and changes in their concentration were also determined. Simultaneously, the level of oil degradation corresponding to a content of 25% of polar compounds measured by Viscofrit test was analyzed in function of the H-1 NMR spectra derived data.