Investigation of Toxic ?- Dicarbonyl Compounds Formed in the Headspace of Various Heated Cooking Oils

Glyoxal, methylglyoxal, and diacetyl formed in the headspace of heated oil samples were analyzed as corresponding quinoxaline derivatives. Formation of these compounds increased in the gutter oil as the number of heating repetitions increased. In particular, methylglyoxal increased from 198.43 ± 92.9 µg to 432.16 ± 161.86 µg. The total phenolic compounds in four extra virgin olive oils ranged from 231.01 ± 16.75 µg/g to 492.78 ± 39.34 µg/g (Olio Nuovo olive oil). The carbonyl compounds formed from the Olio Nuovo oil ranged from 52.76 ± 11.26 µg (glyoxal) at 150°C for 0.5 h to 801.22 ± 147.88 µg (diacetyl) at 300°C for 1 h Addition of cysteine reduced the formation of all three α-dicarbonyl compounds significantly, suggesting that cysteine forms adducts with carbonyl compounds. Standard antioxidant BHT reduced formation of all three compounds at lower heating temperatures, whereas standard antioxidant vitamin E increased them considerably at higher temperatures, suggesting that vitamin E degrades into carbonyl compounds.