Determination of Palmitic Acid, Oleic Acid and Linoleic Acid by Near-Infrared Transflectance Spectroscopy in Edible Oils

Abstract

Near-infrared (NIR) transflectance spectroscopy scanning from 1100 nm to 2500 nm was applied for the determination of palmitic acid (C_16:0), oleic acid (C_18:1) and linoleic acid (C_18:2), the major fatty acids in edible oils. Edible oil samples were divided into two sets: 95 and 46 samples as a calibration and a prediction set, respectively. The multiple regression equations (MREs) established for the calibration set between the reference data analyzed by gas chromatography (GC) and the NIR raw spectral data gave the multiple correlation coefficients of 0.996, 0.989 and 0.993 for C_16:0, C_18:1 and C_18:2, respectively. The best MREs were established with the NIR raw spectral data recorded at 1724, 1756, 2140 and 2180 nm. The Fourier transform mid-infrared spectra of the standard C_16:0, C_18:1 and C_18:2 supported the belief that the absorptions at these wavelengths were attributed to the CH₂ of the straight carbon chain and the C=C of the unsaturated fatty acid. Standard errors of predictions between the data calculated from the best MREs and the reference data analyzed by GC for the prediction samples were 0.925%, 2.186% and 2.011%, and the correlation coefficients between those were larger than 0.99 for C_16:0, C_18:1 and C_18:2, respectively. The obtained results indicate that the NIR procedure can potentially be used as a nondestructive analysis method for the purpose of rapid and simple determination of C_16:0, C_18:1 and C_18:2 in edible oils.