Effect of cooking time and temperature on the heterocyclic amine content of fried beef patties

Methods for the determination of mutagenic heterocyclic amines and their applications in environmental analysis

The environmental analysis of heterocyclic amines is important to preserve human health, because all these compounds are potent mutagens and many are carcinogens in experimental animals. This review summarizes the analytical methods for the determination of mutagenic heterocyclic amines and their applications to various environmental samples. High-performance liquid chromatographic methods with ultraviolet, electrochemical and fluorescence detections are commonly used for the quantification of heterocyclic amines. Moreover, liquid chromatography-mass spectrometry, gas chromatography, gas chromatography-mass spectrometry, capillary zone electrophoresis and enzyme-linked immunosorbent assay are also developed. Heterocyclic amines in complex environmental matrices are present at low parts per billion or less, so that the sample preparation influences the reliable and accurate analysis of these compounds. Mutagenic heterocyclic amines are widely distributed in a number of ambient environmental components such as airbone particles, diesel-exhaust particles, cigarette smoke, cooking fumes, rain water, sewage water, incineration-ash and soil. These facts suggest that mutagenic heterocyclic amines are likely to be ubiquitous environmental pollutants and humans are continually exposed to these compounds in normal daily life.

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.

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.

Mutagenic heterocyclic aromatic amines (HAAs) in 'processed food flavour' samples

Eight samples of 'processed food flavours' (PFFs), chosen from five different categories, were analysed for their mutagenic activity using the Ames Salmonella assay, and also for the presence of eight heterocyclic aromatic amines (HAAs), namely 2-amino-3-(trideuteromethyl)imidazo[4,5-f]quinoline (IQ), 2-amino-3,8-dimethyl-imidazo[4,5-f]quinoline (MeIQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-3,7,8-trimethylimidazo[4,5-f]quinoxaline (7,8-DiMeIQx), 2-amino-3,7,8-trimethylimidazo[4,5-f]quinoxaline (4,7,8-TriMeIQx), 2-amino-I-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) using liquid chromatography and mass spectrometry (LC/MS). The isolation of HAAs was based on sequential liquid-liquid extraction procedures of samples at both acidic and basic pH values. The recoveries and the clean-up were monitored by introduction of quality control samples and by spiking with three tri-deuterated standards of HAAs. Although the results for the mutagenicity assay were comparable by testing less-purified and highly-purified extracts, the analysis for identification and quantification of HAAs by LC/MS required highly purified concentrates. Four samples had little or no mutagenic activity and these results were in agreement with their LC/MS results: they had no detectable levels (detection limits 1-3 ppb) of any of the HAAs monitored. The mutagenic activity of one sample was in complete agreement with the quantification of HAAs by LC/MS. Two samples produced strong mutagenic responses (3115 and 2664 revertants/g). In one sample, LC/MS analysis revealed the presence of 9.6 ppb IQ, whereas LC/MS of the other could not confirm the presence of any of the eight HAAs monitored. Two samples produced mild mutagenic activity (204 and 160 revertants/g), but relatively elevated concentrations of IQ (6.7 and 6.8 ng/g) by LC/MS. The extracts from all samples were tested for their modifying effects on mutagenicity of four HAAs. The discrepancy between the Ames test and the LC/MS analysis of some samples indicates several possibilities, such as the presence of some other HAAs, of their isomers or of other mutagens. In addition, the presence of mutagen modifiers (inhibitors or synergists) was observed in most samples. The results indicate that although chemical tests (e.g. LC/MS) can provide quantitative data for the HAAs monitored, the Ames mutagenicity test should also be conducted to determine the mutagenic activities of PFFs, in order to assess their health risk potential.

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.

Cytogenetic results from a chronic feeding study of MeIQx in mice

The primary food mutagens found in cooked meat are the heterocyclic aromatic amines, including 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx). High dose, acute exposures of MeIQx produce hepatic tumours in some mouse and rat strains. By assaying chromosome damage it may be possible to correlate aberrations with exposure to a mutagen. Whole chromosome painting by fluorescence in situ hybridization allows the rapid screening of metaphase chromosomes for rearrangements. This technique was applied to female mice (C57BL/6) chronically fed 100-400 ppms MeIQx for up to 6 months. Two tissues, blood and bone marrow, were screened with multicolour whole chromosome painting probes (1,2,3 and 8). The mice showed no outward signs of toxicity at any dose and very few chromosome aberrations were observed. A slight but significant increase in sister chromatid exchanges (SCE) was seen at 400 ppm in blood at 6 months. When MeIQx was removed from the diet for 1 month there was an apparent decline in SCEs only for animals previously given the 400 ppm diet.

Influence of frying fat on the formation of heterocyclic amines in fried beefburgers and pan residues

The influence of six frying fats (butter, margarine, margarine fat phase, liquid margarine, rapeseed oil and sunflower seed oil) on the formation of mutagenic/carcinogenic heterocyclic amines (HAs) during the frying of beefburgers was investigated. Frying was performed at 165 and 200 degrees C (i.e. under conditions that represented normal household cooking practices). The fried beefburgers and their corresponding pan residues were purified using solid-phase extraction and analysed for HAs using HPLC with photodiode array UV and fluorescence detection. The HAs 2-amino-3,8-dimethylimidazo[4,5-f]-quinoxaline (MeIQx), 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 9H-pyrido[3,4-b]indole (norharman) and 1-methyl-9H-pyridol[3,4-b]indole (harman) were recovered. The amount increased with the temperature, and the content of HAs in the pan residue was much higher than in the corresponding beefburger. The amounts of MeIQx ranged from 0.2 to 1.6 ng/g in the beefburgers and from 0.8 to 4.3 ng/g in the pan residues. DiMeIQx ranged from undetectable to 0.4 ng/g in the beefburgers and from 0.4 to 1.3 ng/g in the residues. PhIP ranged from 0.08 to 1.5 ng/g in the meat and from 0.4 to 13.3 ng/g in the residues. The total amount of HAs in meat and pan residue combined was significantly lower after frying in sunflower seed oil or margarine than after frying with the other fats. The observed differences in MeIQx and DiMeIQx formation could be explained in terms of oxidation status (peroxide and anisidine value) and antioxidant content (vitamin A, vitamin E and tocopherols/tocotrienols) using partial least squares analysis.

Airborne mutagens produced by frying beef, pork and a soy-based food

Airborne cooking by-products from frying beef (hamburgers), pork (bacon strips) and soybean-based food (tempeh burgers) were collected, extracted, tested for mutagenicity and chemically analysed. The fumes generated by frying pork and beef were mutagenic, with 4900 and 1300 revertants/g of food cooked, respectively. No mutagenicity was detected in fumes from frying tempeh burgers. Bacon fried to a well-done but non-charred state was eight times more mutagenic in a microsuspension Ames/Salmonella test (TA98 with S-9) than hamburgers and about 350 times more mutagenic than tempeh burgers. Among food samples cooked to a well-done, non-charred state, bacon strips had almost 15-fold more mass (109.5 ng/g) than that of the beef, whereas no heterocyclic amine (HCA) was detected in the fried tempeh burgers. 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) was the most abundant HCA, followed by 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx). No 2-amino-9H-pyrido[2,3-b]indole (A alpha C) was detected in the food samples fried at about 200 degrees C, although it was present in the collected airborne products. The total amounts of HCAs in the smoke condensates were 3 ng/g from fried bacon, 0.37 ng/g from fried beef and 0.177 ng/g from fried soy-based food. This study indicates that cooks are potentially exposed to relatively high levels of airborne mutagens and carcinogens and that long-term sampling inside restaurants and kitchens may be warranted in order to assess the potential risk of prolonged exposure.

Evaluation of hamburgers and hot dogs for the presence of mutagens

Food products derived from heat-treated (fried, broiled, baked) meat may contain traces of mutagenic heterocyclic amine contaminants, some of which are proven carcinogens in rodents. To confirm their presence and range in Canadian foods, and estimate the average human intake of these types of mutagens from frequently consumed heat-processed foods, several commercially prepared fried-beef patties (hamburgers) and hot dogs (weiners) were analysed for their mutagenic capacity. The mutagenicity of the extracts was tested in the Salmonella/microsome assay using strain TA98 with metabolic activation. 16 samples of hamburgers and 14 samples of hot dogs, randomly obtained from 'fast food' commercial establishments or street vendors, were used in this survey. The mutagenic activity of these samples ranged from very low to 1042 revertants/g equivalent for the hamburgers and from non-detectable to 4875 revertants/g equivalent for the hot dogs. The average values were 199 and 424 revertants/g for the hamburgers and hot dogs, respectively. The wide range in mutagenicity was found even for the same type of product obtained from the same outlet at different times. This indicates possible inconsistency in cooking procedures during the preparation of these products. It also shows the difficulty in accurately assessing the intake of mutagenic heterocyclic amines from hamburgers and hot dogs prepared in 'fast food' outlets.

Heterocyclic amine content in fast-food meat products

Heterocyclic aromatic amines are sometimes formed during the cooking of muscle meats, and their mutagenic and carcinogenic effects are of potential concern in the aetiology of human cancer. In a large survey of the heterocyclic amine content of foods, fried or charbroiled hamburgers, fried chicken, chicken breast sandwiches, fish sandwiches and breakfast sausages were purchased from fast-food restaurants. At least three different chains were visited per product and samples from five stores from each chain were pooled. The solid-phase extraction and HPLC method was used to analyse pooled samples for heterocyclic amine content and mutagenic activity with the Ames/Salmonella assay. Samples were analysed in a blind study which also contained quality control samples of two types, one high and one low in heterocyclic amine content and mutagenic activity. Results from the fast-food products showed undetectable levels of heterocyclic amines in 10 of 17 samples and only low levels [< or = 1 ng/g total of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx)] in the remaining samples. Compared with literature values based primarily on laboratory and home cooking conditions, fast-food meat products appear to contribute only a small percentage of the estimated daily dietary intake of heterocyclic amines.

Effect of microwave pretreatment on heterocyclic aromatic amine mutagens/carcinogens in fried beef patties

To investigate a method to reduce the amount of mutagenic/carcinogenic heterocyclic aromatic amines formed during frying of ground beef, the mutagenic activity in Salmonella strain TA98 was assessed and the amount of known heterocyclic amines was determined by solid-phase extraction and HPLC. The beef patties received microwave treatment for various times before frying. Microwave pretreatment for 0, 1, 1.5, 2 or 3 min before frying at either 200 degrees C or 250 degrees C for 6 min per side reduced heterocyclic aromatic amine precursors (creatine, creatinine, amino acids, glucose), water, and fat up to 30%, in the patties and resulted in a decrease in mutagenic activity up to 95%. The sum of the four heterocyclic aromatic amines shown to be present--2-amino-3,8-dimethylimidazo[4,5-f]-quinoxaline (MeIQx), 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,4,8-trimethylimidazo-[4,5-f]quinoxaline (DiMeIQx) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)--decreased three- to nine-fold compared with control, non-microwaved beef patties fried under identical conditions.

Heterocyclic amines formed by cooking food: comparison of bioassay results with other chemicals in the Carcinogenic Potency Database

Results in the Carcinogenic Potency Database (CPDB) on 11 mutagenic heterocyclic amines (HA) tested for carcinogenicity in rats, mice and cynomolgus monkeys are compared to results for other chemicals. An analysis of strength of evidence of carcinogenicity for HA vs. other mutagenic carcinogens and vs. all rodent carcinogens, indicates strong carcinogenicity of HA in terms of positivity rates and multiplicity of target sites. The liver is the most frequent target site in each species. Despite several target sites in each species, concordance in target sites between rats and mice is restricted to the liver for each HA except one. In cynomolgus monkeys, liver tumors have been induced rapidly by 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). Human exposures to HA in cooked animal foods are small, in the low ppb range. A comparison of possible carcinogenic hazards from a variety of exposures to rodent carcinogens in the American diet is presented, using an index (Human Exposure/Rodent Potency, HERP) that relates human exposure to carcinogenic potency in rodents. Results indicate that there is a large background of exposures to naturally-occurring rodent carcinogens in typical portions of common foods, and that possible hazards from HA rank below those of most natural pesticides and products of cooking or food preparation; synthetic pesticide residues also rank low.

Cancer potencies of heterocyclic amines found in cooked foods

Quantitative estimates of potential cancer risk associated with eating heterocyclic amines (HAs) in cooked foods and food products, known to be highly mutagenic in the Ames/Salmonella assay and to cause cancer in laboratory animals, rely on estimates of carcinogenic potency from animal bioassay data. New estimates of potential human cancer potency are presented for 10 HAs associated with potential human dietary exposure from cooked-food sources. These estimates differ from previous similar estimates in that they properly reflect the fact that most of these HAs exhibit a pronounced ability to induce tumours at multiple histologically distinct sites within each sex/species tested, and so might be expected to be multipotent carcinogens in humans as well. Thus, in addition to 82 tumour-type-specific potencies estimated for these compounds, 24 additional estimates of aggregate potency (to induce one or more tumour types) were made, using different methods to scale estimated bioassay cancer potency to humans. The currently unknown potency of an additional cooked-food HA was estimated using linear regressions of log-carcinogenic on log-mutagenic potency for the other 10 HAs, some of which were highly significant (e.g. r = 0.85, P < 0.004). The potency estimates obtained are consistent with an upper-bound cancer risk between 10(-3) and 10(-4) for an average lifetime cooked-beef intake of 3.3 g/kg/day (or approx. 0.5 lb/day). Use of these potency estimates to obtain more realistic upper-bound estimates of dietary-HA risk will require detailed HA-exposure assessments.