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

A simple and rapid method for the quantitative determination of free fatty acid (FFA) contents in palm olein by Fourier transform infrared (FTIR) tran smission 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 predict ion 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 err or were 0.997 and 0.017% of a FFA unit. Accuracy of the method was determin ed by comparing the FFA of a series of oleic acid-spiked palm oleins predic ted by a PLS model to values obtained by the AOCS titration method. For acc uracy, the difference between the mean FFA determined by the chemical metho d and the mean FFA determined by the FTIR method (MDa) gave FFA contents of a value of 0.00016, with the FTIR method giving a higher prediction of pal m olein than the AOCS method. For reproducibility, the mean differences bet ween duplicates (MDr) 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 so lvents required by the chemical method, and drastically reduce analysis tim e to less than 2 min/sample. (C) 1999 Elsevier Science Ltd. All rights rese rved.