Formation of Carcinogenic 4(5)-Methylimidazole in Maillard Reaction Systems

4(5)-Methylimidazole has received the attention of federal and state regulatory agencies because of its carcinogenicity and common presence in foods and beverages. In the present study, the formation of 4(5)-methylimidazole in Maillard reaction model systems consisting of D-glucose/NH3, L-rhamnose/NH3, methylglyoxal/NH3, and methylglyoxal/formaldehyde/NH3 was investigated. 4(5)Methylimidazole was formed at levels ranging from 0.49 to 0.71 mg/mL in the D-glucose/NH3 model system. The formation of 4(5)-methylimidazole was slightly higher in the L-rhamnose/NH3 system (0.91 mg/mL) than in the D-glucose/NH3 system (0.71 mg/mL) under the conditions used in the present study. A methylglyoxal/NH3 system produced significantly higher levels of 4(5)-methylimidazole (5.70 mg/mL), suggesting that methylglyoxal is an important precursor of 4(5)-methylimidazole. Ammonolysis of methylglyoxal, which is one of the glucose degradation products, was proposed to form formamide, which subsequently reacted with 2-aminopropanal (alpha-aminocarbonyl intermediate) formed from methylglyoxal to give 4- or 5-methylimidazole. The levels of 4(5)-methylimidazole found in commercial cola soft drinks range from 0.30 mu g/mL (brand 3) to 0.36 mu g/mL (brands 1 and 5).