Chemistry, formation and occurrence of genotoxic heterocyclic amines identified in model systems and cooked foods

Some 20 years ago, Japanese scientists discovered a new group of highly mutagenic compounds, classified as heterocyclic aromatic amines, from broiled and grilled meat and fish dishes. Many of these extremely mutagenic heterocyclic amines have been shown to be multi-site tumour inducers in long-term animal studies on rodents and monkeys. Studies on human cells in vitro have demonstrated that they are metabolised into bio-active compounds and form DNA adducts. Up until now, around 20 different mutagenic and/or carcinogenic heterocyclic amines have been identified. The present knowledge concerning the chemistry, formation and occurrence of these compounds in foods is briefly summarised. They are generally formed at ppb levels, and their formation is affected by temperature, time, water activity, pH, and the amounts and proportions of precursors. Some precursors are amine compounds, especially creatine and amino acids, peptides, and proteins. The Maillard reaction, involving reducing sugars and amino acids, is important for the formation of certain heterocyclic amines in liquid systems, e.g. the amino-imidazo-azaarenes. Dry heating, on the other hand, also produces the amino-carbolines, the formation of which seems to be favoured by free radical reactions/fragmentations and a low water activity.