Quantitative determination of saturated and unsaturated fatty acids in edible oils by infrared spectroscopy and chemometrics

The fatty acids of eight edible oil samples with varying composition were saponified, esterified into methyl esters and analysed by gas chromatography. These composition values were used in calculating the composition of 25 syntheic edible oil mixtures containing a wide range of saturation and unsaturation. All these 33 oils were then analysed by infrared spectroscopy using single reflectance technique. The reflectance infrared profiles in I/R format were calibrated against their saturated, unsaturated, 18:1 and 18:2 fatty acids composition using regions and the whole spectral profiles. Second derivated spectral profiles were also used in the calibration. The results show that the cross-validated calibration model established with second derivated data of the infrared spectral profiles in the 4000-2700 cm(-1) region against the GC evaluated unsaturated fatty acid composition predicted 5 unknown oil samples within an error limit of 2.5%. The same was the case with the unsaturated fatty acid composition against second derivated infrared profiles in the region 4000-2700 cm(-1). Oleic acid and linoleic acid composition in the calibration oil samples were calibrated against the second derivated profiles of the infrared spectra in the region 4000-600 cm(-1). The prediction values of the cross-validated calibration model for the unknown oil samples give oleic acid and linoleic acid composition in the oils with an error margin +/- 3.1% and +/- 4.1%, respectively. The calibration and prediction error includes the error in the quantitative determination of the fatty acids by gas chromatography. (c) 2005 Elsevier B.V. All rights reserved.