Abstract
This research aimed to establish the influence of frying on the oxidation products in polar compounds extracted from three different vegetable oils. For this purpose, Fourier transform infrared spectroscopy (FTIR) and 1H nuclear magnetic resonance (NMR) were used. The FTIR spectral alterations demonstrated that the frying led to significant shifts in the intensity of the absorption bands at 3006 and 1746 cm−1 for samples. The changes in the various kinds of acyl groups, 1,2-diglycerides, and oxygenated compounds in polar compounds were determined by 1H NMR spectroscopy. The aldehyde and alcohol contents were much higher in soybean and rapeseed oils than in palm oil. Thus, from the perspective of toxic aldehyde (4-hydroxy-[E]-2-alkenals) content, the palm oil-frying media were much safer than others. Principle component analysis results also revealed that the levels of n-alkanals, 4-oxo-alkanals, and absorbance at 1746 cm−1 were strongly associated with the oxidation degree of polar compounds. Novelty impact statement The oxidation products in polar compounds of different vegetable oils during the 32 h repeated frying at 180°C were determined using HPSEC, FTIR, and 1H NMR. Given 10% is taken as the discard value for triglyceride oligopolymers, palm oil was the only oil that did not reach the threshold value. The results in FTIR spectra and 1H NMR are associated with increased formation of secondary oxidation products and decreased degree of unsaturation in polar compounds. Thus, a combination of these techniques could effectively reflect the oxidation degree of polar compounds during frying process.