A mutagen is defined as a chemical or physical agent that induces or increases a change in genetic material (DNA). (A common gene mutation test, the Ames test, is conducted in a strain of Salmonella bacteria.) Mutagens are not automatically considered to be carcinogens. Likewise, carcinogens, defined as agents that cause cancer, may not be mutagens.
This complex interaction of normal food components, including those found in meat, must be viewed in a realistic framework and kept in the proper perspective of the total diet. For example, natural mutagens are present in substantial quantities in fruits and vegetables, an essential part of any diet. However, other mutagens are formed in cooking as a result of reactions involving proteins, fats and heat. Dietary practices, therefore, may be an important determinant of current cancer risks.
To identify a substance, natural or man made, as a mutagen or carcinogen, is just a first step. It is also necessary to approximate the magnitude of the risk and to consider the risks for alternative courses of action. Mutagens and carcinogens may vary greatly in their potency in rodents, and extrapolation of risk from rodents to humans is difficult due to longevity difference, antioxidant factors and the multicausal nature of most human cancer (2).
Three Categories of Mutagens-Carcinogens
Mutagens and carcinogens in food can be divided into three groups. The first group is naturally occurring, including plant alkaloids and plant toxins (e.g.- aflatoxin B1). Compounds in this group are usually limited to particular food materials and are easily avoidable.(They will not be discussed in this review.)
The second group is composed of compounds formed by heating food. Compounds in this group are the most difficult to remove or avoid completely. The third group includes food additives and pesticide residue contaminants.
This group is fairly well regulated and monitored (3,4). (Approved additives for meat will be noted.) Formed by heating. In the 1930s, polycyclic aromatic hydrocarbons (PAHs) were identified as potential carcinogens (5). There are at least 100 distinct PAHs found in the environment and in foods. Chemically, PAHs are fused benzene (aromatic) ring structures and most are derivatives of benzo[a]pyrene or benzo- [a]anthracene [Fig.1].
How to Limit Exposure
HAs and PAHs are not direct-acting chemical carcinogens,but must first undergo metabolic activation.Thus, opportunities exist for inhibitors such as antioxidants to exert modifying effects.
There are several ways to modify the amount of PAHs and HAs produced. Formation can be influenced by how meat is prepared, such as the cooking method, temperature and the cooking time. PAHs are formed when fat is burned. HAs are formed when protein is burned. Thus, more intensive cooking methods such as frying, broiling, grilling and barbecuing can promote mutagen formation, whereas negligible amounts are created during more moderate heating methods such as microwaving, stewing, simmering, or poaching.
The use of medium to low heat, and placement of the meat further from the heat, can greatly reduce mutagen formation. Other recommendations, associated with grilling, include: choose lean cuts; trim visible fat before cooking; when possible choose thin cuts that will cook quickly; avoid charring the meat; precook meat in an oven or microwave to reduce time on the grill; use a drip pan over a uniform coal layer; and raise the grill so the meat is further from the heat.
As research continues to understand the formation of meat mutagens (specifically HAs), factors are identified which may help control the formation of these compounds. It is already known that carcinogenic potency of HAs can be readily modified by changing variables such as time, temperature, water and the presence or absence of certain amino acids and sugars (13).
The most realistic method for reducing the risk of HAs is to reduce the formation and intake of HAs in a practical way without affecting the food’s taste or a person’s normal daily life. Avoiding the formation of char on food and the overcooking of food, as well as minimizing the contact of protein foods with a flame, are desirable. Also, the removal of char on food can adequately eliminate a major source of HAs.
Microwaving is also recommended (9,12).
Under laboratory conditions, microwave pretreatment of beef patties has been shown to reduce the formation of two HAs (MeIQx and 4,8-DiMeIQx).