Changes in the composition of soybean oil during
deep-fat frying with wheat dough (WD) and chicken
breast meat (CBM) were comparatively investigated using
gas chromatography–mass spectrometry and Fourier transform
infrared spectroscopy (FTIR). The amounts of saturated
fatty acids (FAs) and short-chain FAs were increased.
The amount of unsaturated FAs was decreased as the processing
time increased. An increase in the amount of tetradecanoic
acid and 9-cis-hexadecanoic acid was observed
during the CBM frying only. The FTIR spectrum of frying
oil was analyzed by extracting the entire information as the
area ratios based on vibration absorptions of the specific
functional groups. Changes in content of functional groups,
namely cis C=C, trans C=C, C=O, C–O, O–H, and C–H,
were studied by the FTIR-based method. Based on the
changes in the content of FAs and functional groups, soybean
oil fried with CBM degraded more quickly than that
fried with WD. Moreover, good linear correlations between
the change in contents of functional groups and the mass
percentages of FAs were also observed. The FTIR-based
method could be used in real time to monitor the quality of
frying oil during the deep-fat frying.