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°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 (R2=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 (R2=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.
La spettroscopia 1H NMR ad alta risoluzione (400-600 MHz) è stata applicata per l'analisi quantitativa dei prodotti di decomposizione degli idroperossidi in oli termossidati. Tre differenti oli (oliva, girasole e soia) sono stati riscaldati in un bagno termostatato (180°C for 360 min). L'analisi 1H NMR delle aldeidi (n-alkanali, trans-2-alkenali, 4-idrossi-trans-2-alkenali, alca-2,4-dienali) dei quindici campioni di olio prelevati a diversi intervalli di tempo (0, 60, 120, 240 e 360 minuti di riscaldamento) è stata comparata con l'analisi dei composti polari totali, valutati mediante cromatografia su colonna di silice, e l'analisi degli acidi grassi a corta catena. È stata trovata una buona relazione lineare (R2=0,94) tra il totale delle aldeidi insature e del metil ottanoato così come tra le aldeidi totali ed i composti polari totali (R2=0,92). La sensibilità dell'analisi NMR ottenuta su uno spettrometro a 400 MHz con 3000 scansioni è stata ottenuta con solo 64 scansioni, per un tempo totale di 2 minuti, utilizzando uno spettrometro a 600 MHz. Nel lavoro viene discussa la possibilità di poter utilizzare la spettroscopia 1HNMR come un mezzo diretto per valutare la qualità e la degradazione ossidativa di oli sottoposti a riscaldamento e oli utilizzati per la frittura.
Quantitative evaluation of the aldehydes formed in heated vegetable oils using high resolution proton-NMR spectroscopy
De Giulio B;
2006
Abstract
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°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 (R2=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 (R2=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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
