Determination of Fatty Acids in the Subcutaneous Fat of Iberian Breed Swine by near Infrared Spectroscopy. A Comparative Study of the Methods for Obtaining Total Lipids: Solvents and Melting with Microwaves

Near infrared (NIR) spectroscopy has been used to predict the composition of the fatty acids of samples of subcutateous fat from Iberian breed swine, comparing the two methods employed for collecting total lipids—extraction with solvents and microwave melting—using gas chromatography as a reference method. The regression method used was modified partial least squares. The calibration results for 115 samples of subcutaneous fat extracted with solvents and the calibration measured with NIR permitted the determination of 12 fatty acids: C12:0, C14:0, C16:0, C16:1, C17:0, C17:1, C18:0, C18:1, C18:2, C18:3, C20;0 and C20:1, total polyunsaturated, total monosaturated and total saturated acid with squared multiple correlation coefficients of 0.84, 0.70, 0.89, 0.75, 0.62, 0.66, 0.85, 0.91, 0.88, 0.77, 0.85, 0.66, 0.90, 0.89 and 0.92, respectively, and a standard error of calibration (SEC) for these acids (%) of 0.007, 0.091, 0.48, 0.14, 0.03, 0.03, 0.42, 0.72. 0.31, 0.09, 0.02, 0.15, 0.31, 0.70 and 0.68, respectively. Extraction of total lipids by microwave melting for the same samples and using NIR calibration allowed the determination of six fatty acids: C16:0, C16:1, C18:0, C18:1, C18:2, C18:3, total polyunsaturated, total monounsaturated and total saturated acid, with a squared multiple correlation coefficients (RSQ) of 0.93, 0.70, 0.88, 0.90, 0.83, 0.63, 0.82, 0.92 and 0.95, respectively, and an SEC for these acids (%) of 0.36, 0.14, 0.44, 0.77, 0.33, 0.08, 0.39, 0.69 and 0.56, respectively. The robustness of the two extraction methods and of the determination was checked by applying them to 20 samples for external validation.