Vacuum frying as an alternative technique to increase the oxidative stability of sunflower oil. A comprehensive 1H NMR and SPME-GC/MS study focused on oxygenated compounds

The present study compares the oxidative stability of sunflower oil during vacuum frying (120 °C, low pressure) and conventional frying (170 °C, atmospheric pressure), focusing on the formation of oxygenated oxidation products. To discern between the effects of temperature and reduced concentration of oxygen during vacuum frying, the stability of sunflower oil under atmospheric frying conditions at 120 °C was also evaluated. Oil samples were analysed using Proton Nuclear Magnetic Resonance (¹H NMR) and Solid Phase Microextraction (SPME) followed by Gas Chromatography/Mass Spectrometry (GC/MS). Additionally, the percentage of Total Polar Compounds (TPC) and the viscosity were determined. Under vacuum frying conditions, the degradation rate of linoleate was slower than under atmospheric frying conditions. Likewise, the formation of different oxygenated oxidation compounds, including monohydroperoxy- monohydroxy- and monoketo-conjugated-octadecadienoates, Z-monoepoxy-Z-octadecenoates and aldehydes, some of which are potentially harmful, was also delayed. Similarly, the evolution of the TPC percentage and viscosity changes showed a slower rate. These results provide, for the first time, a comprehensive understanding of the effect of vacuum frying on the stability of sunflower oil, highlighting its potential as a promising alternative to conventional frying methods.