Relationships between the Composition of Edible Oils and Lard and the Ratio of the Absorbance of Specific Bands of Their Fourier Transform Infrared Spectra. Role of Some Bands of the Fingerprint Region

Sixteen samples of edible oils and lard have been studied by means of Fourier transform infrared spectroscopy. The spectra were recorded from a film of pure oil or lard between two disks of KBr. The height and the area of the bands were measured taking two baselines. Ratios between the absorbances of the bands and the correlation matrix of these data were calculated. Some ratios between absorbances contain similar information. The iodine value of the samples was also determined according to the classical iodometric method, and very close relationships were found between this parameter and the ratios of absorbance of some bands. The direct use of some of the absorbance ratios as characteristic parameters of edible oils and fats is proposed. In addition, ratios of absorbance of specific bands, some of them of the fingerprint region, have been found to be highly dependent on the sample composition. Equations obtained from ratios of absorbances and composition data are valuable in the prediction of the proportion of saturated, monounsaturated, and polyunsaturated acyl groups in oils and lard. The importance of the absorbance of some specific bands of the fingerprint region of the infrared spectra to characterize edible oils and fats has been shown for the first time. Keywords: Edible oils; lard; characterization; Fourier transform infrared spectroscopy; fingerprint region; absorbance; iodine value; monounsaturated; saturated; polyunsaturated; acyl groups