Quantitative evaluation of the aldehydes formed in heated vegetable oils using high resolution proton-NMR spectroscopy

摘要

High-resolution proton nuclear magnetic resonance (~1H-NMR) spectroscopy (400-600 MHz) was applied to the quantitative analysis of hydroperoxide decomposition products in thermally oxidized oils.Different oils (olive,sunflower and soybean) were heated in a thermostatic bath (180 deg C for 360 min).Proton NMR quantitative aldehyde analysis (n-alkanals,trans-2-alkenals,4-hydroxy-trans-2-alkenals,alka-2,4-dienals) of fifteen oil samples (0,60,120,240 and 360 minute heating) was compared with that of total polar compounds through silica column chromatography and of short-chain fatty acids.A good linear relationship (R~2=0.94) was found between the unsaturated aldehyde level and the amount of methyl-octanoate as well as between total aldehyde determined by ~1H-NMR and total polar compounds (R~2=0.92).The same NMR sensitivity obtained at 400 MHz through 3000 scans was reached with only 64 scans for a total acquisition time of 2 min at 600 MHz.The potential use of ~1H-NMR as a direct tool to monitor the quality and oxidative degradation in heated and fried oils is discussed.