Determination of unsaturation grade and trans isomers generated during thermal oxidation of edible oils and fats by FTIR

The oxidative deterioration of culinary oils and fats during episodes of he ating associated with normal usage (80 degrees C-300 degrees C, 20-40 min) was monitored by FTIR spectroscopy. The thermal oxidation of polyunsaturate d fatty acids during heating was studied by the determination of unsaturati on percentage and trans isomers at various temperatures and heating times. Oils frequently used in food frying such as olive oil, sunflower oil, corn oil and seeds oil (sunflower, safflower and canola seed), and lard were stu died. The Absorbance Correction Method is proposed to correct the spectral interference and allows the analytic use of signal which would not be initi ally valid for quantitative analysis. The results show that there is a decr ease in unsaturation and an increase in trans isomers starting at 150 degre es C and becomes more pronounced at temperatures around 250 degrees C. This variation in unsaturation grade and conformation provides evidence of the transformation of essential polyunsaturated fatty acids and subsequent decr ease in the oils' nutritional value. (C) 1999 Elsevier Science B.V. All rig hts reserved.