Scientists at the University of Basque Country claim to have shown, for the first time, that the breakdown of lipids in foods can produce toxic oxygenated aldehydes.
These compounds, known in medical studies for their geno- and cytotoxic (poisonous to cells) activity, had not previously been detected in foodstuffs, say the scientists.
"The oxidation or thermal degradation of food lipids causes deterioration in foodstuffs and the generation of toxic substances," they add.
Investigating a range of oils, the scientists found that some oils produce these toxic substances in greater quantities and at a greater rate.
For the study researchers investigated processes of oxidative degradation - firstly that caused at 70ºC with ventilation of a broad group of oils with wide-ranging compositions.
And the second degradation process investigated microwave action that does not heat greater than a temperature of 190 ºC.
In both processes deterioration of the oils takes place. In the first type of process (70 ºC with ventilation) hydroperoxides are produced first, and then subsequently aldehydes. In the second process (microwave), aldehydes are essentially produced.
"Both the oxidative conditions and the composition of the oil determined the velocity of the degradation and both the nature and concentration of the compounds produced," underlined the researchers.
And among all the oils tested, virgin olive oil appeared to be the most 'healthy', taking longer to produce the toxic compounds, and producing lower concentrations.
The Spanish researchers studied the liquid phase of the oil by means of Proton Nuclear Magnetic Resonance and Fourier Transform Infrarred Spectroscopy. The gaseous phase of the oil was examined using Solid Phase Microextraccion techniques followed by Gas Chromatography-Mass Spectrometry.
"Confirmation of the identity of the aldehydes detected was carried out with pattern substances and with proton nuclear magnetic resonance spectra for a number of toxic aldehydes," add the scientists.