HCAs are produced by food pyrolysis products derived from tryptophan, glutamic acid, phenylalanine, and lysine. Mutagenic activity has been found in cooked beef, pork,ham, bacon, lamb, chicken, fish, and eggs following broiling, frying, and barbecuing.
Such substances are formed as a result of reactions involving proteins, amino acids, or other nitrogen-containing food constituents or proteinaceous foods. Pan frying or broiling enhances formation of HCAs, compared with the much lower levels produced by deep frying or stewing. Cooking temperatures below 150 ? C (rare to medium rare) result in much lower amounts of amino acid pyrolysis. All amino acid breakdown products can be detected in broiled beef, fish (in ppb), bread crust, toast, fried potatoes, and coffee.
Dietary fiber, particularly wheat bran, appears to absorb HCAs and make such compound less available for absorption. Thus, four factors influence HCA formation: type of food, cooking method, temperature, and time. HCAs are found in cooked muscle meats; other sources of protein (milk, eggs, tofu, and organ meats such as liver) have very little or no HCA content naturally or when cooked. Temperature is the most important factor in the formation of HCAs. Frying, broiling, and barbecuing produce the largest amounts of HCAs, because the meats are cooked at very high temperatures. It is worthwhile noting that meats that are partially cooked in the microwave oven before cooking by other methods also have lower levels of HCAs.