Determination of solid fat index by Fourier transform infrared spectroscopy

A unique and rapid Fourier transform infrared (FTIR) spectroscopic method for the determination of solid fat index (SFI) of fats and oils was developed, which is capable of predicting the SFI profile of a sample in approximately two minutes, without the need for tempering. Hydrogenated soybean oil samples (n = 72), pre-analyzed for SFI by dilatometry, were melted and their FTIR spectra acquired using a 25 micrometer NaCl transmission flow cell maintained at 80 degrees C. Approximately half the samples were used for calibration, with the balance used as validation samples. Partial least squares (PLS) calibrations were developed from selected spectral regions that are associated with the cis, trans, ester linkage and fingerprint regions of the spectrum and related to the dilatometric SFI values obtained at 50, 70, 80, and 92 degrees F. The calibrations were initially optimized and cross-validated by using the "leave one out" approach, with the accuracy and reproducibility of the calibration models assessed by predicting the validation samples. The overall cross validation accuracy of the PLS calibration models was in the order of +/- 0.71 SFI units over the four temperatures. Week-to-week validation accuracy and reproducibility was determined to be +/- 0.60 and +/- 0.38 SFI units, respectively, the reproducibility being within the specifications associated with the dilatometric reference method. To facilitate routine "on-line" FTIR analyses, a Visual Basic program was written to drive the spectrometer, prompt the user to load the sample, calculate, and print the SFI values determined from the PLS calibrations. As structured, the FTIR method has the potential to serve as a viable substitute for the traditional dilatometric SFI method, with the elimination of the tempering step reducing analysis time from hours to minutes. The FTIR approach should also be applicable to the determination of solid fat content if calibrated against solids data