Heterocyclic amine content of pork products cooked by different methods and to varying degrees of doneness

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Abstract

Heterocyclic amines (HCAs) are known mutagens and animal carcinogens produced in meats cooked at high temperature. As pork is the second most frequently consumed meat in the United States, five predominant 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)] were measured in various pork products, cooked by different techniques and to varying doneness levels. Pork chops and ham slices were pan-fried and oven-broiled; bacon was pan-fried, oven-broiled or microwaved; hot dogs were pan-fried, oven-broiled, grilled/barbecued or boiled; sausage links and patties were pan-fried. All the products were cooked to three levels of doneness: just until done, well done or very well done. HCA type and level varied substantially by pork product, cooking method and doneness level. The highest PhIP levels were found in well done and very well done oven-broiled bacon; for very well done 30.3 and 4.0 ng per gram of meat of PhIP and MeIQx, respectively. Pan-fried very well done sausage patties contained 5.4 ng of MeIQx per gram of meat, while sausage links contained 1.3 ng per gram of meat. MeIQx was formed in well done and very well done pan-fried but not broiled pork chops. Hot dogs or ham slices had low or undetectable levels of HCAs. These results demonstrate that epidemiological studies investigating the relationship between HCA intake and cancer risk need to incorporate type of meat, cooking method and degree of doneness/surface browning into questions to assess adequately an individual's HCA exposure.

Introduction

Heterocyclic amines (HCAs) are formed in meats cooked at high temperatures. HCAs are potent mutagens and animal carcinogens (Adamson, 1990; Felton and Knize, 1990; Ghoshal et al., 1994; Ito et al., 1991; Ohgaki et al., 1986; Skog, 1993; Weisburger et al., 1994). However, the carcinogenic potential in humans is yet to be established (Steineck et al., 1993). Epidemiological studies of colon and breast cancer using crude surrogates for HCA exposure (e.g. doneness, surface browning, frying, intake of gravy) have produced suggestive but somewhat inconsistent results (Gerhardsson De Verdier et al., 1991; Knekt et al., 1994; Muscat and Wynder, 1994; Ronco et al., 1996; Schiffman et al., 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 exists in a variety of meats all considered as ‘well done’ (Sinha and Rothman, 1996). The misclassification may result in decreased ability to observe a true association of HCA and cancer risk. Thus, to decrease misclassification and better assess the contribution 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 to various degrees of doneness (Knize et al., 1995, Knize et al., 1996; Sinha et al., 1995, Sinha et al., 1998).

Pork is the second most frequently consumed meat in the US (National Live Stock and Meat Board, 1994), and could contribute to HCA exposure in the general population. Cooking techniques and the degree of doneness (Berg et al., 1990; Gross et al., 1993; Johansson and Jagerstad, 1994) influences HCA content in pork products. Here we report the HCA content of some of the most commonly consumed pork products: bacon, pork chops, ham slices, sausage links and patties, hot dogs and bacon drippings cooked by different methods to varying degrees of doneness. These measurements will provide data to accurately assess HCA exposure in epidemiological studies.

Section snippets

Materials and methods

Five pork products were purchased from a local supermarket: bacon (regular sliced); sausages (patties, regular links and fully cooked and pre-browned links or ‘brown-n-serve’); hot dogs; pork chops; and ham slices. The pork products were cooked by commonly used techniques for that particular meat. Bacon was pan-fried, oven-broiled or microwaved; hot dogs were pan-fried, oven-broiled, grilled/barbecued or boiled; sausage was pan-fried; pork chops and ham slices were pan-fried or oven-broiled.

Results

Figs. 1–4 show pork products cooked to three levels of doneness. Fig. 1 presents the concentrations of MeIQx and PhIP in bacon samples cooked by different methods to varying degrees of doneness. In general, both MeIQx and PhIP levels were higher in very well done and well done bacon than in samples cooked just until done. Oven-broiled bacon contained high levels of PhIP compared with bacon cooked by other methods. Even bacon cooked to a very well done level in the microwave oven contained both

Discussion

HCA values for various pork products cooked by different methods and to different level of doneness are presented so that they can be used in calculating exposure to these compounds in epidemiological studies. Bacon contained the highest levels of PhIP while the other pork products had undetectable or low levels of HCAs. Bacon is different from other meats in that oven broiling produced relatively high levels of PhIP compared with that produced by other cooking methods. In contrast,

Acknowledgements

This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under contract no. W-7405-Eng-48, and supported by the NCI IAG agreement No.YO1CP2-0523-01 and grant CA55861 from the National Cancer Institute.

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