The determination of frying oil quality using Fourier transform infrared attenuated total reflectance

The possibility of using the whole spectra (wave numbers between 4000 and 850 cm(-1)) from Fourier transform infrared attenuated total reflectance spectroscopy (FTIR-ATR) to differentiate between good, marginal and unacceptable oils with regard to various intensities of oil rancidity was investigated. Fresh, used, and discarded oils were collected from several fast food restaurants from each frying cycle for 4 weeks. Dielectric constant, peroxide value, free fatty acid content, and density of oil samples significantly (P<0.01) increased with frying time. The correlation (r) between FTIR absorbance at 3300 cm(-1) and free fatty acid content was from 0.84 to 0.94 for oils from the three restaurants. Similarly, the correlation between FTIR absorbance at 3471 cm(-1) and peroxide value was from 0.90 to 0.97. The results of principal component analysis using the whole spectra (4000-850 cm(-1)) showed good discrimination and stability for identification between acceptable, marginal and unacceptable frying oils. (C) 2003 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved.