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

Abstract

The degradation process of edible oils of very different nature, submitted to 190 7C with aeration, is studied by means of 1 H nuclear magnetic resonance (NMR). In this study, no primary oxidation products, such as hydroperoxides, are detected, the signals of aldehydes being the first to be observed in the 1 H NMR spectra. Differences between this degradation process and those occurring at 70 7C with aeration or under microwave action are discussed, not only in relation to the degradation rate of the different acyl groups, but also in relation to the nature and proportions of some of the degradation products generated. Oils rich in oleic acyl groups are not only more resistant to degradation than oils rich in linoleic and linolenic acyl groups, but also produce lower proportions of toxic aldehydes.

Monitoring by 1H nuclear magnetic resonance of the changes in the composition of virgin linseed oil heated at frying temperature. Comparison with the evolution of other edible oils

“…This fact indicates that if these functional groups (hydroperoxides and conjugated dienic associated systems) are formed when heating the oils at frying temperature, they degrade very fast, and are not present in enough concentration to be detected by this technique. This is also in agreement with previous studies on oils of different natures submitted to high temperature (Guillén & Ruiz, 2006, 2008 and with the absence of significant changes in the Peroxide Value of some edible oils submitted to frying temperature for a prolonged period of time (Dobarganes & Pérez Camino, 1988).…”

Simultaneous control of the evolution of the percentage in weight of polar compounds, iodine value, acyl groups proportions and aldehydes concentrations in sunflower oil submitted to frying temperature in an industrial fryer

“…As the temperature increases (70 C, 100 C), the ratio of cis,trans/trans,-trans hydroperoxy dienic conjugated systems becomes smaller. However, at high temperature (190 C) the formation of intermediate compounds is not observed by 1 H nuclear magnetic resonance (Guillén & Ruiz, 2008), which is in accordance with the absence of significant changes in the classical Peroxide Value of the oil observed by other authors (Dobarganes & Perez-Camino, 1988). Final compounds of oil degradation are also, like intermediate ones, dependent on both the original oil composition and processing conditions.…”

Formation of toxic alkylbenzenes in edible oils submitted to frying temperature

“…Among these can be cited the breakdown of carbon-carbon double bonds of the acyl group chains, producing small volatile molecules and truncated acyl group chains linked to the triglyceride structure, as commented on by different authors (Choe & Min, 2007;Guillén and Ruiz, 2008). In this way, very different kinds of volatile compounds are generated, among which aldehydes are cited as being the main ones (Velasco, Marmesat, Marquez-Ruiz & Dobarganes, 2004;Guillén & Uriarte, 2009).…”