Quantification of trans fatty acid content in French fries of local food service retailers using attenuated total reflection – Fourier transform infrared spectroscopy

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 cm−1 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).