Detection of Aldehydes and Their Conjugated Hydroperox Ydiene Precursors in Thermally-Stressed Culinary Oils and Fats: Investigations Using High Resolution Proton Nmr Spectroscopy

Abstract

High field (400 and 600 MHz) proton NMR spectroscopy has been employed to investigate the thermally-induced autoxidation of glycerol-bound polyunsaturated fatty acids present in intact culinary frying oils and fats. Heating of these materials at 180 degrees C for periods of 30, 60 and 90 min. generated a variety of peroxidation products, notably aldehydes (alkanals, trans-2-alkenals and alka-2,4-dienals) and their conjugated hydroperoxydiene precursors. Since such aldehydes appear to be absorbed into the systemic circulation from the gut in vivo, the toxicological significance of their production during standard frying practices is discussed.

Monitoring of heat‐induced degradation of edible oils by proton NMR

“…5 that the aldehydes generated in the different oils submitted to this degradation process, also shown in Tab. 4, are: trans-2-alkenals (doublet (a) at 9.480 and 9.500 ppm) and trans,trans-2,4-alkadienals (doublet (b) at 9.507 and 9.527 ppm); 4,5-epoxy-trans-2-alkenals (doublet signal (c) at 9.535 and 9.555 ppm); 4-hydroxy-trans-2-alkenals (doublet signal (d) at 9.562 and 9.582 ppm); moreover, in oils with a significant level of polyunsaturated acyl groups (such as corn, sunflower, soybean and linseed oils), cis,trans-2,4-alkadienals (doublet signal (f) at 9.586 and 9.606 ppm) whose assignment was made using as standard a mixture of trans,trans-2,4-decadienal and cis,trans-2,4-decadienal, and in addition in agreement with data provided by other authors [17,18,37]; n-alkanals (with wellknown triplet signal (g) centered at 9.748 ppm); other unidentified aldehydes which could be either saturated aldehydes having a small number of carbon atoms or oxo-alkanals (triplet signal (h) at 9.778 ppm) in agreement with different data from the literature [38].…”

“…However, to the best of our knowledge, none of the above studies provide information on the nature and proportions of the different types of aldehydes, including oxygenated a,b-unsaturated aldehydes, generated in oil degradation, and only those 1 H NMR of thermodegraded oils 53 studies carried out by 1 H nuclear magnetic resonance (NMR) spectroscopy are able to give this kind of information simultaneously and directly from the sample without previous separation or chemical change [17][18][19][20][21][22][23]. This technique for monitoring the degradation of edible oils, occurring either at 70 7C with aeration or by microwave action at temperatures below 190 7C, has proved that the nature and proportions of the aldehydes formed depend on both the oil nature and the degradation conditions.…”

Multicomponent analysis of encapsulated marine oil supplements using high-resolution 1H and 13C NMR techniques

“…1), a consequence of their closer proximity to the nearest carbon-carbon double bond and, as noted previously by our laboratory (36) and others (24,25), the ratio of the intensities of these two clearly resolved signals (i.e., 0.940:0.846 ppm) yields the n-3:n-6 fatty acid ratio for fish oil supplements. Moreover, expression of the 0.940 ppm resonance intensity to that corresponding to the sum of both the terminal-CH 3 group signals provides a useful index regarding the ratio of total n-3 to non-n-3 fatty acids, and hence the molar percentage of the former present in the samples examined.…”

Identification of odour‐active compounds in dried and roasted nori (Porphyra yezoensis) using a simplified gas chromatography–SNIF technique

“…Short-chain fatty acids, such as 3-methylbutanoic acid (17), hexanoic acid (18), and 2-ethylhexanoic acid (20), had an important effect on the overall aromas of both dried and roasted nori. Other acids, such as acetic acid (14), isobutyric acid (15), butanoic acid (16), and (E)-2-ethylhexanoic acid (21), were detected as the odour-active compounds only in the fraction of roasted nori probably due to the second heating technology, but not in that of dried nori. As most of the acids exhibited acidic and rancid aromas, the overall aromas of the acid fractions of the dried and roasted nori were quite similar.…”