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 mad e it possible to extract relevant information from MIR spectra of lipi d rich food products. Wavenumber assignments for typical functional gr oups in fatty acids were made for standard fatty acids: Absorp tion ba nds 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, re spectively. In lipid-rich food products, some bands are modified. Wate r 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 th e foods as function of their water content. Principal component analys is was used to emphasize the differences between spectra and to rapidl y classify 27 commercial samples of oils, butters and margarines. As t he MIR spectra contain information about carbonyl groups and double bo nds, the foods were classified with ATR-MIR, in agreement with their d egree 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 cha inlength.