Quantification of glycerol-bound ω-oxo fatty acids in deep-frying oils from restaurants

Abstract ω-oxo fatty acids (ω-oxo FA) are abundant and relevant lipid oxidation products in thermally stressed edible oils. Although limited data on the occurrence of these compounds in frying oils are available, the GC–MS-based analysis of ω-oxo FA remains challenging, partly due to the lack of structurally analogous internal standards and the volatility of the analytes. Using GC–MS, ω-oxo FA were quantified, following derivatization to acetals, in 22 used frying fat samples from restaurants, fast-food restaurants, and one canteen. Total ω-oxo FA contents ranged from 53.0 to 889 ng/mg. Model oxidation experiments confirmed that the relative distribution of ω-oxo FA strongly depended on the fatty acid composition of the oil at lower temperatures, while selectivity was diminished under harsher oxidation conditions. Furthermore, 1 H NMR spectroscopy proved suitable for estimating total ω-oxo FA contents in medium to high oxidized samples when detailed specification for the individual compounds is not required.