Heterocyclic amine content in beef cooked by different methods to varying degrees of doneness and gravy made from meat drippings

Abstract

Meats cooked at high temperatures sometimes contain heterocyclic amines (HCAs) that are known mutagens and animal carcinogens, but their carcinogenic potential in humans has not been established. To investigate the association between HCAs and cancer, sources of exposure to these compounds need to be determined. Beef is the most frequently consumed meat in the United States and for this study we determined HCA values in beef samples cooked in ways to represent US cooking practices, the results of which can be used in epidemiological studies to estimate HCA exposure from dietary questionnaires. We measured five HCAs [2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)] in different types of cooked beef using solid-phase extraction and HPLC. Steak and hamburger patties were pan-fried, oven-broiled, and grilled/barbecued to four levels of doneness (rare, medium, well done or very well done), while beef roasts were oven cooked to three levels of doneness (rare, medium or well done). The measured values of the specific HCAs varied with the cut of beef, cooking method, and doneness level. In general, MeIQ× content increased with doneness under each cooking condition for steak and hamburger patties, up to 8.2 ng/g. PhIP was the predominant HCA produced in steak (1.9 to 30 ng/g), but was formed only in very well done fried or grilled hamburger. DiMeIQx was found in trace levels in pan-fried steaks only, while IQ and MeIQ were not detectable in any of the samples. Roast beef did not contain any of the HCAs, but the gravy made from the drippings from well done roasts had 2 ng/g of PhIP and 7 ng/g of MeIQx. Epidemiological studies need to consider the type of meat, cooking method and degree of doneness/surface browning in survey questions to adequately assess an individual's exposure to HCAs.

Introduction

Heterocyclic amines (HCAs) are sometimes formed in meats cooked at high temperature (Adamson, 1990; Felton and Knize, 1990; Skog, 1993). HCAs are known to be potent mutagens and animal carcinogens (Ghoshal et al., 1994; Ito et al., 1991; Ohgaki et al., 1986; Weisburger et al., 1994); however, the carcinogenic potential in humans has not been established (Steineck et al., 1993). Epidemiological studies of colon and breast cancer using crude surrogates for HCA exposure from meat (e.g. doneness, surface browning, frying, intake of gravy) have produced suggestive but somewhat inconsistent results (Gerhardsson et al., 1991; Knekt et al., 1994; Muscat and Wynder, 1994; Ronco et al., 1996; Schiffman et al., 1990; Schiffman and Felton, 1990; Steineck et al., 1993). Currently used surrogates such as doneness of ‘red meat’ may be inadequate to assess an individual's exposure to HCAs since substantial heterogeneity of HCA levels is present in a variety of meats all considered as ‘well done’ (Sinha and Rothman, 1997). The resultant misclassification may result in decreased ability to observe a true association. Thus, to decrease misclassification and better assess true risk of HCAs in cancer aetiology there is a need to improve exposure assessment of HCAs. To this end we are developing a database of HCA concentrations in commonly consumed meat items cooked by various techniques and to various degrees of doneness.

There is an extensive literature on the presence of HCAs in meats cooked at high temperature, but in many of the reported studies the cooking was not well described, analysis methods varied and might not be comparable, or samples were cooked to maximize the production of HCAs, and not to be representative of the way meats are usually cooked by the general population in the US (Aeschbacher, 1991; Gross et al., 1993; Johansson and Jagerstad, 1994; Layton et al., 1995; Skog, 1993; Sugimura et al., 1988). Thus, systematic measurement of HCA values in most commonly consumed meat types cooked by representative practices are needed to accurately assess HCA exposure in epidemiological studies in the US.

Beef is the most frequently consumed meat in the US (National Live Stock and Meat Board, 1994), and is likely to be one of the main contributors to HCA exposure. Exposure to HCAs varies depending on the cooking technique and the degree of doneness. In this study we report the HCA content of some of the most commonly consumed cuts of beef: hamburger patties, steak, roast beef, and gravy made from roast drippings cooked by different methods to varying degrees of doneness.