Use of ATR-FTIR spectroscopy to detect the changes in extra virgin olive oil by adulteration with soybean oil and high temperature heat treatment

The structural changes induced in extra virgin olive oil (EVOO) by adulteration with soybean oil (SBO) and heat treatment at 185 degrees C for 4 and 8 h were investigated using Attenuated Total Reflectance - Fourier Transform Infrared (ATR-FTIR) spectroscopy. Our results revealed that the band around 3006 cm(-1) recorded shifts versus the percentage of adulterant. The changes in the absorbance at 3006 cm(-1) (A3006) and in the ratio of the maximum heights of the bands at 3006 and 2925 cm(-1) (A3006/A2925) were used to evaluate the EVOO adulteration. The regression analysis of A3006 and A3006/A2925 versus the percentage of adulterant was used to calculate the detection limits of adulteration. The time course of spectral changes showed that the oil heating caused notable modifications in the intensity of the absorption bands and induced no shifts in their exact position. The most relevant changes were reflected by conjugation and cis-trans isomerisation of double bonds, the formation of epoxides and widening of the band in the C=O region due to formation of secondary oxidation products. This study highlights that ATR-FTIR spectroscopy may be a promising means to differentiate among pure and adulterated oils and to study the thermo-oxidative processes in oils undergoing thermal stress.