CHARACTERIZATION OF EDIBLE OILS, BUTTERS AND MARGARINES BY FOURIER-TRANSFORM INFRARED-SPECTROSCOPY WITH ATTENUATED TOTAL REFLECTANCE

The combination of attenuated total reflectance (ATR) and mid infrared spectroscopy (MIRS) with statistical multi dimensional techniques made it possible to extract relevant information from MIR spectra of lipid rich food products. Wavenumber assignments for typical functional groups in fatty acids were made for standard fatty acids: Absorp tion bands around 1745 cm(-1), 2853 cm(-1), 2954 cm(-1), 3005 cm(-1), 966 cm(-1), 3450 cm(-1) and 1640 cm(-1) are due to absorption of the carbonyl group, C-H stretch, = CH double bonds of lipids and O-H of lipids, respectively. In lipid-rich food products, some bands are modified. Water strongly absorbs in the region of 3600-3000 cm(-1) and at 1650 cm(-1) in butters and margarines, allowing one to rapidly differen tiate the foods as function of their water content. Principal component analysis was used to emphasize the differences between spectra and to rapidly classify 27 commercial samples of oils, butters and margarines. As the MIR spectra contain information about carbonyl groups and double bonds, the foods were classified with ATR-MIR, in agreement with their degree of esterification and their degree of unsaturation as determined from gas-liquid chromatography analysis. However, it was difficult to differentiate the studied food products in terms of their average chainlength.