Formation of protein adducts of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine in cooked foods.

Heterocyclic amines (HCAs) are mutagenic and carcinogenic compounds found in cooked meat and fish. Although HCAs are known to form adducts with protein after metabolic activation, adduct formation during cooking has not been elucidated. In this study, we showed that 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is released from high molecular weight compounds by acid or enzymatic hydrolysis of cooked foods. Formation of free and protein adduct forms of PhIP was dependent on cooking temperature and time, and PhIP-protein adducts were estimated to form after formation of free PhIP. We also demonstrated that PhIP-protein adduct is formed by heating of PhIP and albumin as a model protein. A new adduct peak including [M+H](+) (m/z=225) of PhIP as a fragment ion was detected in the high molecular weight fraction of heat-treated protein by LC-MS analysis. From model experiments by heating of PhIP and amino acids, the adduct was estimated to be produced by condensation of the amino group of PhIP and the carboxyl group of protein. PhIP-protein adducts were detected in several cooked meat and fish at ng/g food level as PhIP content. These results suggest that food-borne protein adducts of HCAs may influence human HCA exposure and carcinogenic risk.