Heterocyclic amine content in fast-food meat products

Analysis of nonpolar heterocyclic amines in cooked foods and meat extracts using gas chromatography-mass spectrometry

Heat processing of muscle foods gives rise to the formation of mutagenic and carcinogenic heterocyclic amines, often at ng/g levels. A gas chromatographic-mass spectrometric (GC-MS) technique was introduced for the analysis of nonpolar heterocyclic amines in common cooked meats, pan residues, and meat extracts after solid-phase extraction. The mutagenic heterocyclic amines 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1), 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), 2-amino-9H-pyrido[2,3-b]indole (A alpha C) and 2-amino-3-methyl-9H-pyrido[2,3-b]indole (MeA alpha C) were identified in several samples in amounts up to 8 ng/g. Also the comutagenic substances 1-methyl-9H-pyrido [3,4-b]indole (harman) and 9H-pyrido[3,4-b]indole (norharman) were detected in the samples in amounts up to almost 200 ng/g. The GC-MS method can be applied without derivatisation of the sample. The technique offers high chromatographic efficiency, yielding detection limits for pure references in the range 0.1-2 ng per injection.

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

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, MeIQx 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.

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

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.

Pilot study of free and conjugated urinary mutagenicity during consumption of pan-fried meats: possible modulation by cruciferous vegetables, glutathione S-transferase-M1, and N-acetyltransferase-2

Epidemiological and experimental evidence indicates that consumption of fried meats in conjunction with certain genotypes of phase I and II metabolism genes poses an elevated risk for colorectal cancer. Parallel to this, the consumption of cruciferous vegetables is associated with a reduced risk of colon cancer. Therefore, we designed a 6-week pilot feeding study to evaluate the effect of these variables on urinary mutagenicity, which is a biomarker associated with fried-meat consumption. Eight subjects were fed fried meats daily for six weeks; four ate cruciferous vegetables, and four ate non-cruciferous vegetables. Urinary mutagenicity was evaluated in the presence of S9 in strain YG1024 of Salmonella, which is a frameshift strain that overproduces acetyltransferase. C18/methanol extracts of 24-h urines collected once each week were tested unhydrolyzed (free mutagenicity) and hydrolyzed (total mutagenicity); the difference between the two was the conjugated mutagenicity. Although not significant, the levels of conjugated urinary mutagenicity doubled among crucifera consumers and decreased to 30% of the initial levels among non-crucifera consumers, suggesting the possibility that crucifera may enhance the level of conjugated urinary mutagenicity resulting from consumption of fried meats. Such an effect would be consistent with the documented ability of cruciferous vegetables to induce phase II enzymes. The NAT2 rapid phenotype was significantly associated with approximately 2-fold increases in conjugated (p = 0.05) and total (p = 0.004) urinary mutagenicity relative to NAT2 slow subjects, consistent with the elevated risk confirmed by the NAT2 rapid phenotype for colorectal cancer among meat consumers. An approximately 2-fold increase in urinary mutagenicity among the GSTM1- subjects relative to the GSTM1+ subjects approached significance for free (p = 0.18) and total (p = 0.13) urinary mutagenicity. This is the first report on (a) the mutagenicity of hydrolyzed urine, which was consistently more mutagenic than unhydrolyzed urine; (b) the potential enhancement of conjugated urinary mutagenicity by crucifera; and (c) the association of the rapid NAT2 and possibly the GSTM1- phenotype with elevated levels of fried meat-associated urinary mutagenicity.

Polar and non-polar heterocyclic amines in cooked fish and meat products and their corresponding pan residues

Fourteen cooked dishes with their corresponding pan residues were analysed for polar and non-polar heterocyclic amines using HPLC. The choice of foods, including beef, pork, poultry, game, fish, egg and sausages, was based on an investigation of an elderly population in Stockholm participating in an analytical epidemiological case-control study on cancer risks after intake of heterocyclic amines. The food items were prepared using normal household cooking practices, and to reflect the wide range of surface browning of the cooked dishes that would be encountered in this population, four cooking temperatures were used in the range 150-225 degrees C. For all food samples, the total amount of heterocyclic amines formed at 150 degrees C was less than 1 ng/g cooked product, and at 175 degrees C less than 2 ng/g. The highest concentrations of heterocyclic amines were detected in fillet of pork, reindeer meat and chicken breast fried at 200 and 225 degrees C and their corresponding pan residues. The total sum of 2-amino-3,8-dimethylimidazo-[4,5-f]quinoxaline, 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine was about 1 microgram per 100 g portion (including pan residues) for reindeer meat and chicken breast, and between 1.9 and 6.3 micrograms per 100-g portion for fillet of pork. PhIP was the most abundant heterocyclic amine, identified in 73 of 84 samples, and the highest concentration of PhIP, 32.0 ng/g, was found in the pan residue from fillet of pork cooked at 225 degrees C. The non-polar heterocyclic amines 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole and 3-amino-1-methyl-5H-pyrido[4,3-b]indole were detected in the range of 0.5-7.4 ng/g in most foods cooked at 225 degrees C, and also in meat sauce prepared at 200 and 175 degrees C. The other heterocyclic amines tested for: 2-amino-3-methylimidazo-[4,5-f]quinoline, 2-amino-3,4-dimethylimidazo[4,5-f]quinoline, 2-amino-6-methyl-pyrido-[1,2-a:3',2'-d]-imidazole and 2-aminodipyrido-[1,2-a:3',2'-d]imidazole, were present only at very low or non-detectable levels. The low recoveries of the amino-alpha-carbolines 2-amino-9H-pyrido[2,3-b]indole and 2-amino-3-methyl-9H-pyrido[2,3-b]indole made it impossible to quantify them. However, the co-mutagenic substances 1-methyl-9H-pyrido-[3,4-b]indole and 9H-pyrido[3,4-b]indole were detected at levels of about 1-30 ng/g in most of the dishes cooked at 200 and 225 degrees C.

Analysis of cooked muscle meats for heterocyclic aromatic amine carcinogens

A number of related heterocyclic amines that are mutagenic in bacterial test systems and carcinogenic in animals are formed during the cooking of food. The most commonly reported and abundant compounds are PhIP, MeIQx, DiMeIQx, IQ and A alpha C. Using analysis by solid-phase extraction and HPLC, amounts found in foods range from less than one ng/g for products from fast-food restaurants, up to 14 ng/g in commercially cooked products and over 300 ng/g for well done flame-grilled chicken breast meat. Interestingly, marinating meat for 4 h greatly reduces the amount of PhIP produced during cooking, but not MeIQx. Comparing mutagenic activity in meat samples to the mutagenic activity accounted for by the known heterocyclic amines shows that most samples have activity that cannot be accounted for by the aromatic amines we can currently identify. This suggests that additional compounds are present in these foods and need to be investigated, particularly those grilled over open flames.

Exposure assessment of heterocyclic amines (HCAs) in epidemiologic studies

The carcinogenic potential of heterocyclic amines (HCAs) in humans has yet to be established. Epidemiologic studies of colon cancer using crude surrogates for HCAs exposure (e.g., doneness of meat) have produced inconsistent results. To improve exposure assessment of HCAs, we have developed a database of HCA concentrations in commonly consumed meat items cooked by various techniques and degrees of doneness. HCA type and level are dependent on multiple factors, including type of meat (e.g., steak, chicken, bacon), cooking technique (with substantial variability present even within high temperature cooking methods), place of preparation (e.g., home, restaurant, or 'fast-food' restaurant), as well as the degree of doneness and surface browning/charring. We have developed a questionnaire with meat photographs linked to this database, which we are using in a variety of case-control and cohort studies of cancer etiology. In addition, we have carried out a metabolic study of HCA exposure among 66 subjects to identify biomarkers of HCA exposure which may be useful in epidemiologic studies. These studies should help clarify the role of HCAs in human carcinogenesis, and eventually allow an estimation of the cancer burden in the population attributable to these compounds.

Effects of marinating on heterocyclic amine carcinogen formation in grilled chicken

This study compared heterocyclic aromatic amines in marinated and unmarinated chicken breast meat flame-broiled on a propane grill. Chicken was marinated prior to grilling and the levels of several heterocyclic amines formed during cooking were determined by solid-phase extraction and HPLC. Compared with unmarinated controls, a 92-99% decrease in 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) was observed in whole chicken breast marinated with a mixture of brown sugar, olive oil, cider vinegar, garlic, mustard, lemon juice and salt, then grilled for 10, 20, 30 or 40 min. Conversely, 2-amino-3, 8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) increased over 10-fold with marinating, but only at the 30 and 40 min cooking times. Marinating reduced the total detectable heterocyclic amines from 56 to 1.7 ng/g, from 158 to 10 ng/g and from 330 to 44 ng/g for grilling times of 20, 30 and 40 min, respectively. The mutagenic activity of the sample extracts was also measured, using the Ames/Salmonella assay. Mutagenic activity was lower in marinated samples cooked for 10, 20 and 30 min, but higher in the marinated samples cooked for 40 min, compared with unmarinated controls. Although a change in free amino acids, which are heterocyclic amine precursors, might explain the decrease in PhIP and increase in MeIQx, no such change was detected. Marinating chicken in one ingredient at a time showed that sugar was involved in the increased MeIQx, but the reason for the decrease in PhIP was unclear. PhIP decreased in grilled chicken after marinating with several individual ingredients. This work shows that marinating is one method that can significantly reduce PhIP concentration in grilled chicken.

Analysis of foods for heterocyclic aromatic amine carcinogens by solid-phase extraction and high-performance liquid chromatography

Carcinogenic and mutagenic heterocyclic aromatic amines (HAA) are natural products often present at ng/g levels in muscle meats when they are cooked at temperatures over 150 degrees C. Using solid-phase extraction and high performance liquid chromatography (HPLC) with photodiode array UV detection, samples were analyzed for the following heterocyclic amines: DiMeIQx (2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline); IQ (2-amino-3-methylimidazo[4,5-f]quinoline); MelQx (2- amino-3,8-dimethylimidazo[4,5-f]quinoxaline); and PhIP (2-amino-1-methyl- 6-phenylimidazo[4,5-b]pyridine). Quality control samples, analyzed periodically over two years in a blind study, show relative standard deviations ranging from 22 to 38% for the compounds found, variations typical for analysis at ng/g levels. Amounts range from undetectable levels (less than 0.1 ng/g) to hundreds of ng/g of PhIP for frying or grilling at high meat surface temperatures. Beef, chicken, pork and lamb can all have greater than 10 ng/g of PhIP. Ground chicken breast meat has lower amounts of heterocyclic amines than intact muscle pieces of the same size cooked identically. Restaurant prepared samples that we analyzed contained undetectable levels up to 14 ng/g total heterocyclic amines for a beef steak sample. Not extracted with the above method are related mutagenic heterocyclic amines, which have been reported in cooked foods in our laboratory and others. Method development using ion exchange on an SCX solid-phase extraction cartridge shows promise in providing a method for the quantitation of these mutagenic dimethyl-, trimethyl- and furo-imidazopyridines where a practical analysis method is needed.

Heterocyclic aromatic amine content in pre-processed meat cuts produced in Canada

In an ongoing survey, the presence of heterocyclic aromatic amines (HAAs) was determined in processed, ready-to-eat meat products sold as 'meat cuts'. HAAs are a group of recently recognized mutagenic/carcinogenic contaminants in foods that are produced during the heat processing of meat. 16 samples of meat cuts (e.g. turkey breast, salami, chicken loaf, cooked ham, all beef meat, pepperoni, etc.), randomly purchased from supermarkets and specialty food stores in the Ottawa area, were analysed for the presence of eight HAAs. The isolation of HAAs was based on sequential liquid-liquid extraction procedures of the samples at both acidic and basic pH values. The mutagenic activity of these samples was determined using the Ames/Salmonella microsome assay with the strain TA98 plus rat liver S-9 metabolic activation. The mutagenicity of these samples ranged from undetectable to slightly active. The highest mutagenic activity, 141 induced revertants/g, was found in a smoked turkey breast sample. 11 samples were not mutagenic, including two that indicated a tendency for inhibition of the spontaneous revertants. The remaining four samples exhibited very low mutagenic activity. For chemical analysis, the extracts were purified with two solid phase extraction cartridges. Quantitative analysis was performed by using liquid chromatography for separation and mass spectrometry for detection. With the exception of trace amounts (0.4 ng/g) of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) in the sample with highest mutagenic activity, the chemical analysis did not detect the presence of any of the eight most frequently found HAAs in fried or broiled meat products. These data suggest that consumption of meat cuts does not present a serious health risk from HAA-type contaminants.

Effect of commercial marinades on the mutagenic activity, sensory quality and amount of heterocyclic amines in chicken grilled under different conditions

The effect of processing conditions on the mutagenic activity and sensory quality of everyday food was studied by investigating grilled chicken samples seasoned with four different marinades and grilled at temperatures of about 110, 170 and 220 degrees C. The amounts of the heterocyclic amines 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline and 2-amino-1-methyl-6-phenylimidazo[4,5,-b]pyridine were determined only in samples grilled at 220 degrees C, using a gas chromatography-mass spectrometry technique with negative-ion chemical ionization. Sensory quality was determined using the extended ranking test method and the mutagenic activity using the Ames Salmonella assay. At 220 degrees C one of the marinades decreased the mutagenic activity in the chicken samples compared with the unseasoned control or samples treated with the other marinades. Great variations, without any clear correlation with mutagenicity, were observed in the amounts of heterocyclic amines between chicken samples treated with the same or different marinades. At the grilling temperatures of 170 degrees C and 110 degrees C the mutagenic activities of the chicken samples were lower or they were non-mutagenic. There was no correlation between mutagenic activity and sensory quality of the products. The samples with high mutagenic activity were ranked to be as good as the samples with lower or no mutagenicity. The results show that it is possible to prepare grilled products with reduced mutagenicity without compromising their sensory quality. It was also evident that marinades can have a reducing effect on the mutagenicity of grilled chicken. Variation observed in the amounts of heterocyclic amines between equivalent products makes it difficult to estimate their concentration in everyday foods.