Carcinogens Produced by Food Processing

Despite the widespread occurrence of potentially carcinogenic chemicals in the plant kingdom, most foodstuffs contain only low levels of these chemicals. However, it has now been recognized that a number of processes used in food preparation/ processing can introduce significant amounts of carcinogens into the food or the local environment. The most widely studied of these processes are preservation of meats and fish by salting or smoking; grilling or broiling of meats, and cooking in vegetable oils.

Traditional methods for preserving meat and fish involve either salting or smoking. Epidemiolo-gical evidence has been found for an association between an increased incidence of cancer of the mouth and pharynx and intake of salted meat. It seems likely that a reaction between sodium nitrate and/or nitrite used for preserving the meat and alkylamides present in the meat results in the formation of N-nitrosamines and nitrosamides. These compounds have been shown to be potent carcinogens in animal experiments to the mouth, pharynx and other sites. Levels of nitrosamines in cured meats and fish can be as high as 100-200 ppb (parts per billion) for the simple alkylnitrosamines and between 10 and 100 ppb for volatile hetero-cyclic nitrosamines. Although dose levels required to induce tumor formation in animal studies are substantially higher than those likely to be ingested by man, there is a concern that the presence of nitrosamines in food presents a significant hazard to man.

Preservation of meats and fish by smoking has also been shown to introduce chemicals known to be carcinogenic to animals, particularly polycyclic aromatic hydrocarbons (PAHs), although direct evidence for an association between an increased incidence of human cancers and consumption of smoked meat and fish is lacking.

The frying or grilling of meats and fish has been found to generate significant quantities of heterocyclic nitrogenous compounds derived from amino acids present in foods. These so-called cooked food mutagens include 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (methyl-IQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1), and 2-aminodipyrido[1,2-a:3',2-d]imidazole (Glu-P-2). They are some of the most potent bacterial mutagens known and have been shown to induce a wide range of tumors in animals. Levels as high as 500 ppb have been found in grilled chicken and it has been suggested that they may be implicated in the induction of colon and breast cancer in humans. PAHs can also be generated by the grilling of meat and fish and both carcinogenic and noncarcinogenic compounds have been identified. Levels of one particular PAH in foods, the carcinogen benzo(a)pyrene, have been reported to vary from <1ppb in grain to more than 30ppb in singed meat.

Cooking foods in hot oils has also been found to generate a range of carcinogenic chemicals. Many of these are volatile and may therefore represent more of a hazard to the cook than to the food consumer. Thus, cooking with unrefined rapeseed or soya bean oil, which contain significant levels of the polyunsa-turated fatty acid linolenic acid, has been shown to result in the release of aldehydes including formaldehyde, acetaldehyde and acrolein, hydrocarbons including 1,3-butadiene and benzene, and other chemicals. Many of these compounds are mutagenic to bacteria and carcinogenic in animals, and in areas of the world where such cooking practices are common (e.g., China), the incidence of lung cancer in the exposed population is high.

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