The contents of trans fatty acids in French fries served at the local food service retailers in Honolulu were
determined by simple Fourier transform infrared (FTIR) spectroscopic technique without the pretreatment
of fatty acid extraction. A horizontal attenuated total reflection (ATR) crystal made of zinc selenide
(ZnSe) was used to obtain FTIR spectra of French fries with and without fatty acid extraction. Residual oil
films obtained by pressing French fries directly on the ATR crystal surface without removal of any solid
particles or air bubbles were scanned for the spectral measurement. The calibration set consisted of triolein
(C18:1, 9-cis) and trielaidin (C18:1, 9-trans) mixed in varying ratios. All spectral data were averaged
and converted into GRAMS format. The peak heights of each spectrum at 966 cm1 were found to be linearly
correlated with the contents of trans fatty acids in the validation set (n = 8, R2 = 0.9835). The developed
calibration model was validated by comparing the results obtained from the ATR-FTIR with
Mojonnier extraction and gas chromatography–mass spectrometry (GC–MS).