Volatile compounds in intermittent frying by gas chromatography and nuclear magnetic resonance

Identification of volatile compounds formed when frying food represents an important tool to identify markers of oil thermal degradation, and can help to elucidate the chemical reactions occurring during deep frying. In particular, in this study the heat-induced degradation of edible oil has been evaluated by analyzing the composition of volatile organic compounds (VOCs) and fatty acids formed during intermittent frying with the aim of finding new possible markers to correlate with the total polar compounds (TPC) fraction. The frying was realized using a thermostatically temperature-controlled fryer at a temperature of 180 58C. A mixed oil constituted by palm, sunflower, and soybean frying oil and commercially available frozen potatoes have been used. The intermittent frying (4 h per day) with the same oil was repeated at 24 h intervals for a total of 40 h. VOCs were identification has been obtained by dynamic head space analysis combined with high resolution GC???MS. Among the VOCs, two compounds, namely (E,E)-2,4-decadienal, and (E)-2-undecenal, showed good correlations with the TPC values. NMR spectra (1H NMR) confirmed that 2-alkenals and alka-2,4-dienals are the major compounds formed during the deep frying.