Formation of genotoxic dicarbonyl compounds in dietary oils upon oxidation

Dietary oils-tuna, salmon, cod liver, soybean, olive, and corn oils-were treated with accelerated storage conditions (60degreesC for 3 and 7 d) and a cooking condition (200degreesC for 1 h). Genotoxic malonaldehyde (MA), glyoxal, and methylglyoxal formed in the oils were analyzed by GC. Salmon oil produced the greatest amount of MA (1070 +/- 77.0 ppm of oil) when it was heated at 60degreesC for 7 d. The highest formation of glyoxal was obtained from salmon oil heated at 60degreesC for 3 d. More glyoxal was found from salmon and cod liver oils when they were heated for 3 d (12.8 +/- 1.10 and 7.07 +/- 0.19 ppm, respectively) than for 7 d (6.70 +/- 0.08 and 5.94 +/- 0.38 ppm, respectively), suggesting that glyoxal underwent secondary reactions during a prolonged time. The amount of methyglyoxal formed ranged from 2.03 +/- 0.13 (cod liver oil) to 2.89 +/- 0.11 ppm (tuna oil) in the fish oils heated at 60degreesC for 7 d. Among vegetable oils, only olive oil yielded methylglyoxal (0.61 +/- 0.03 ppm) under accelerated storage conditions. When oils were treated under cooking conditions, the aldehydes formed were comparable to those formed under accelerated storage conditions. Fish oils produced more MA, glyoxal, and methylglyoxal than did vegetable oils because the fish oils contained higher levels of long-chain PUFA, such as EPA and DHA, than did the vegetable oils. A statistically significant correlation (P < 0.05) between the alpha-tocopherol content and the oxidation parameters was obtained from only MA and fish oils heated at 60degreesC for 3 d.