Influence of triacylglycerol characteristics on the determination of free fatty acids in vegetable oils by Fourier transform infrared spectroscopy

A rapid and direct Fourier transform infrared (FTIR) spectroscopic method u sing a 25-mum NaCl transmission cell was developed for the determination of free fatty acids (FFA) in six important vegetable oils (corn, soybean, sun flower, palm, palm kernel, and coconut oils) that differ in fatty acid prof ile. The calibrations were established by adding either standard FFA (oleic , lauric acids) or a representative mixture of FFA obtained after saponific ation of the refined oils. For all oils, up to a FFA level of 6.5% for coco nut oil, the best correlation coefficient was obtained by linear regression of the free carboxyl absorption at 1711 cm(-1). All correlation coefficien ts were greater than 0.993, and no significant difference between the calib ration methods could be detected. Upon validation of the calibration, no si gnificant difference (alpha = 0.05) between the "actual" and the "FTIR pred icted" FFA values could be observed. The calibration models developed for t he six oils differed significantly and indicate the need to develop a calib ration that is specific for each oil. in terms of repeatability and accurac y, the FTIR method developed was excellent. Because of its simplicity, quic k analysis time of less than 2 min, and minimal use of solvents and labor, the introduction of FTIR spectroscopy into laboratory routine for FFA deter mination should be considered.