Application of Fourier transform infrared spectroscopy to determine free fatty acid contents in palm olein

Abstract

A simple and rapid method for the quantitative determination of free fatty acid (FFA) contents in palm olein by Fourier transform infrared (FTIR) transmission spectroscope is described. A set of palm olein samples is used as the calibration set. This set was prepared by spiking increasing amounts of oleic acid into a series of palm oleins that covers a wide range of FFA (0.08–1.04%). A partial least squares (PLS) calibration model for the prediction of FFA contents was developed, based on the spectral range 1728–1662 cm −1. This model was tested by cross-validation steps to minimize standard error of the model. The coefficient of determination ( R 2) and standard error were 0.997 and 0.017% of a FFA unit. Accuracy of the method was determined by comparing the FFA of a series of oleic acid-spiked palm oleins predicted by a PLS model to values obtained by the AOCS titration method. For accuracy, the difference between the mean FFA determined by the chemical method and the mean FFA determined by the FTIR method (MD a) gave FFA contents of a value of 0.00016, with the FTIR method giving a higher prediction of palm olein than the AOCS method. For reproducibility, the mean differences between duplicates (MD r) of the chemical and FTIR methods were close to zero (−0.0064 and −0.0046, respectively). The implementation of such a method as a quality control tool would eliminate the use and disposal of hazardous solvents required by the chemical method, and drastically reduce analysis time to less than 2 min/sample.