Furan in heat‐treated foods: Formation,exposure, toxicity,and aspects of risk assessment

Furan is formed in a variety of heat‐treated foods through thermal degradation of natural food constituents. Relatively high levels of furan contamination are found in ground roasted coffee, instant coffee, and processed baby foods. European exposure estimates suggest that mean dietary exposure to furan may be as high as 1.23 and 1.01 μg/kg bw/day for adults and 3‐ to 12‐month‐old infants, respectively. Furan is a potent hepatotoxin and hepatocarcinogen in rodents, causing hepatocellular adenomas and carcinomas in rats and mice, and high incidences of cholangiocarcinomas in rats at doses ≥2 mg/kg bw. There is therefore a relatively low margin of exposure between estimated human exposure and doses that cause a high tumor incidence in rodents. Since a genotoxic mode of action cannot be excluded for furan‐induced tumor formation, the present exposures may indicate a risk to human health and need for mitigation. This review summarizes the current knowledge on mechanisms of furan formation in food, human dietary exposure to furan, and furan toxicity, and highlights the need to establish the risk resulting from the genotoxic and carcinogenic properties of furan at doses lower than 2 mg/kg bw.     

Functional and proliferative effects of repeated low‐dose oral administration of furan in rat liver

Scope: Furan, a food contaminant formed during heat processing, induces hepatocellular tumors in rodents and high incidences of cholangiocarcinomas in rats even at the lowest dose (2 mg/kg b.w.) administered. Initial estimates suggested that human intake of furan may be as high as 3.5 μg/kg b.w./day, indicating a relatively narrow margin of exposure. The aim of this study was to establish dose–response data for cytotoxicity, regenerative cell proliferation and secondary oxidative DNA damage in livers of male F344 rats treated with furan at doses ≤2 mg/kg b.w. for 28 days. Methods and results: No significant signs of hepatotoxicity other than a mild, dose‐dependent increase in serum cholesterol and unconjugated bile acids, and no evidence of oxidative DNA damage were seen. Histopathological alterations and proliferative changes were restricted to subcapsular areas of the left and caudate liver lobes. Conclusion: Although statistically significant effects were only seen at the 2 mg/kg b.w. dose during the course of our study, a ～two and ～threefold increase in 5‐bromo‐2′‐deoxyuridine labeling index was observed at 0.1 and 0.5 mg/kg b.w., respectively, suggesting that chronic exposure to doses even below 2 mg/kg b.w. may cause proliferative changes in rat liver and highlighting the need to assess furan carcinogenicity at lower doses.     

Effect of consumer cooking on furan in convenience foods

The effect of domestic preparation regimes on the level of the heat-formed toxicant furan was studied to provide useful information for exposure assessment and advice for manufacturers and consumers. Foods were cooked in a saucepan on a gas hob or microwaved and furan was determined by headspace sampling with gas chromatography-mass spectrometry. In general, furan levels did not decrease as much when foods were cooked in a microwave oven when compared with the same foods cooked in a saucepan. Furan levels decreased in most canned and jarred foods after heating in a saucepan. Low levels of furan in soups in cartons were not changed by any procedure. Furan decreased slightly in foods on standing before consumption, but did so more rapidly on stirring. The levels also decreased slightly when foods were left to stand on plates; this observation is attributed to the volatility of furan.     

Effect of consumer cooking on furan in convenience foods

The effect of domestic preparation regimes on the level of the heat-formed toxicant furan was studied to provide useful information for exposure assessment and advice for manufacturers and consumers. Foods were cooked in a saucepan on a gas hob or microwaved and furan was determined by headspace sampling with gas chromatography-mass spectrometry. In general, furan levels did not decrease as much when foods were cooked in a microwave oven when compared with the same foods cooked in a saucepan. Furan levels decreased in most canned and jarred foods after heating in a saucepan. Low levels of furan in soups in cartons were not changed by any procedure. Furan decreased slightly in foods on standing before consumption, but did so more rapidly on stirring. The levels also decreased slightly when foods were left to stand on plates; this observation is attributed to the volatility of furan.     

Toxicology and risk assessment of 5-Hydroxymethylfurfural in food

5-Hydroxymethylfurfural (5-HMF) as a product of the Maillard reaction is found in many foods. Estimated intakes range between 4 and 30 mg per person and day, while an intake of up to 350 mg can result from, e.g., beverages made from dried plums. In vitro genotoxicity was positive when the metabolic preconditions for the formation of the reactive metabolite 5-sulphoxymethylfurfural were met. However, so far in vivo genotoxicity was negative. Results obtained in short-term model studies for 5-HMF on the induction of neoplastic changes in the intestinal tract were negative or cannot be reliably interpreted as "carcinogenic". In the only long-term carcinogenicity study in rats and mice no tumours or their precursory stages were induced by 5-HMF aside from liver adenomas in female mice, the relevance of which must be viewed as doubtful. Hence, no relevance for humans concerning carcinogenic and genotoxic effects can be derived. The remaining toxic potential is rather low. Various animal experiments reveal that no adverse effect levels are in the range of 80-100 mg/kg body weight and day. Safety margins are generally sufficient. However, 5-HMF exposure resulting from caramel colours used as food additives should be further evaluated.     

Some factors affecting the formation of furan in heated foods

Levels of furan in various foods were measured before and after heating under heating and laboratory conditions. The effect of contact with can coatings, sealing gaskets and the epoxidized oils used in gasket manufacture on furan formation was studied. The objective was to identify factors affecting furan formation. Furan present in heat-processed food samples persisted during cooking. Furan was shown to form in foods on heating, although it did not accumulate to a significant degree on heating in an open vessel. There were no interactions between foods and cans, can coatings or gaskets that had a significant influence on furan formation. Furan accumulated particularly in heat-processed canned and jarred foods because they are sealed containers that receive a considerable thermal load. Heating epoxidized oils used in sealing gaskets formed furan. At the levels used in gaskets, however, epoxidized oils should not affect the formation of furan in foods.     

Occurrence of furan in coffee from Spanish market: Contribution of brewing and roasting

In this work, we evaluated the occurrence of furan in brews obtained from regular, decaffeinated, and instant coffee and commercial packed capsules. For this purpose, a previously developed automated headspace solid-phase microextraction method coupled to gas chromatography–mass spectrometry (HS-SPME-GC–MS) was used. Initially, the influence of HS-SPME conditions on furan formation was evaluated. In addition, the effect of roasting conditions (temperature and time) used for coffee beans on furan formation was also studied. We found that low temperature and long roasting time (140 °C and 20 min) decreases the final furan content. Furan concentrations in regular ground coffee brews from an espresso coffee machine were higher (43–146 ng/ml) than those obtained from a home drip coffee maker (20 and 78 ng/ml), while decaffeinated coffee brews from a home drip coffee maker (14–65 ng/ml) showed a furan concentration similar to that obtained from regular coffee. Relatively low concentrations of this compound (12–35 ng/ml) were found in instant coffee brews, while commercial packed coffee capsules showed the highest concentrations (117–244 ng/ml). Finally, the daily intake of furan through coffee consumption in Barcelona (Spain) (0.03–0.38 μg/kg of body weight) was estimated.     

Analysis of furan in foods. Is headspace sampling a fit-for-purpose technique?

Headspace GC-MS has been opitimized for the determination of furan in foods. The conditions of sample preparation, headspace sampling and GC separation were optimized to enhance sensitivity during GC-MS analysis. Green coffee was used to prepare a matrix matched calibration curve for furan. However, it was unexpectedly found that a green coffee sample was not blank. GC-MS analysis performed after equilibration for 30 min at 40°C showed the presence of 4.2 ng/g furan in green coffee. In order to understand whether furan was naturally present or formed during headspace sampling, green coffee was investigated in time-dependent manner at headspace equilibration temperatures of 40 and 70°C. It was observed that furan response continued to increase in a way similar to first order formation kinetics. The same behavior was found for freshly squeezed tomato and orange juices leading to the suspicion of furan formation during headspace equilibration. It is concluded that a matrix matched calibration for each particular food matrix is necessary to compensate for furan formation during headspace sampling, and thus, to quantify furan more accurately.     

Relative importance and interactions of furan precursors in sterilised,vegetable-based food systems

Mitigation strategies aimed at an intervention in the reaction pathways for furan formation (e.g., by adjusting precursor concentrations) might offer an additional route for furan reduction in sterilised, vegetable-based foods, without adverse effects on other food safety or quality attributes. As a first step towards product reformulation, the aim of the present study was to determine the relative importance and interactions of possible furan precursors in these types of foods. Based on an I-optimal experimental design, potato purée (naturally low in furan precursors) was spiked with known amounts of sugars, ascorbic acid, olive oil and β-carotene, and subjected to a thermal sterilisation. Significant correlations were observed between furan concentrations after thermal treatment and starting concentrations of ascorbic acid and monosaccharides (i.e., fructose and glucose). Ascorbic acid had a clear furan-reducing effect as an antioxidant by protecting (polyunsaturated) fatty acids against oxidative degradation. Fructose and glucose were the main precursors, which can most probably be attributed to their high, but realistic, concentrations in the product. The contributions of fatty acids and β-carotene were strongly dependent on redox interactions with other food constituents. In the same potato purées, only low concentrations (0–2 ng g^–1 purée) of 2-methylfuran were detected, indicating that the direct importance of the spiked food constituents as a precursor for methylfuran formation was rather small. Based on the results of this study, reducing the amount of monosaccharides or adjusting the redox conditions of the matrix are suggested as two possible approaches for furan mitigation on the product side.     

Characterisation of furan fatty acids in Adriatic fish

Furan fatty acids (F-acids) were characterised in the fillet of European hake (Merluccius merluccius), horse mackerel (Trachurus trachurus), common sole (Solea solea), European anchovy (Engralius encrasicolus), Atlantic mackerel (Scomber scombrus), European pilchard (Sardina pilchardus) was harvested in Adriatic Sea during the spring and the summer. The main F-acids were of the saturated series: 12,15-epoxy-13-methyleicosa-12,14-dienoic acid [MonoMe(11,5)] in European hake and 12,15-epoxy-13,14-dimethyleicosa-12,14-dienoic acid [DiMe(11,5)] in all the other fish species; 12,15-epoxy-13,14-dimethyloctadeca-12,14-dienoic acid, 10,13-epoxy-11-methyloctadeca-10,12-dienoic acid and 14,17-epoxy-15,16-dimethyldocosa-14,16-dienoic acid were present in all fish species in trace amounts. Other identified F-acids were the olefinic congeners 12,15-epoxy-13,14-dimethyleicosa-12,15,16-trienoic acid and 12,15-epoxy-13,14-dimethyleicosa-10,12,14-trienoic acid. European pilchard had the highest F-acids content (30 mg/100 g fillet), whereas horse mackerel showed the lowest content (less than 0.1 mg/100 g fillet). Eicosapentaenoic acid (EPA) was positively correlated with MonoMe(11,5) and DiMe(11,5), showing that the biosynthesis of docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA) is presumably competitive with that of F-acids.     

Furan in commercial baby foods from the Spanish market: estimation of daily intake and risk assessment

ABSTRACT

The occurrence of furan in commercial baby food samples from the Spanish market was evaluated using an automated headspace solid-phase microextraction method coupled to gas chromatography-mass spectrometry (HS-SPME-GC-MS). A total of 76 baby food samples including infant formula, baby cereals, fruit in cans and/or jars, vegetables, meat, and fish, were surveyed for furan content. The lowest concentration of this compound was found in infant formula (<0.02–0.33 ng ml^?1), and cereal-based food (0.15–2.1 ng g^?1) while baby food containing fish showed the highest concentrations (19–84 ng g^?1). Following recommendation of the European Food Safety Authority (EFSA), the effect on furan content was evaluated of consumer home preparation of foods, heating and handling. Furan concentrations were reduced by up to 35% when samples were heated in a dish using microwave oven and by up to 53% when a hot water bath was used. Finally, we estimated the furan intake from baby food consumption (0.002–1.18 µg kg^?1 body weight day^?1) and we calculated the margin of exposure (MOE) from samples as purchased and also after home preparation of the food. For infant formula and cereal baby foods, the MOEs (26,278–412,776) indicated no infant health concern or priority, while for meat and fish-based baby foods the values pointed to a potential public health risk, even considering the furan losses during preparation at home.     

Survey of furan in heat processed foods by headspace gas chromatography/mass spectrometry and estimated adult exposure

Furan is a suspected human carcinogen that is formed in some processed foods at low ng per g levels. Recent improvements in analytical methodology and scientific instrumentation have made it possible to accurately measure the amount of furan in a wide variety of foods. Results from analysis of more than 300 processed foods are presented. Furan was found at levels ranging from non-detectable (LOD, 0.2–0.9 ng g^?1) to over 100 ng g^?1. Exposure estimates for several adult food types were calculated, with brewed coffee being the major source of furan in the adult diet (0.15 µg kg^?1 body weight day^?1). Estimates of mean exposure to furan for different subpopulations were calculated. For consumers 2 years and older, the intake is estimated to be about 0.2 µg kg^?1 body weight day^?1.     

Survey of furan in heat processed foods by headspace gas chromatography/mass spectrometry and estimated adult exposure

Furan is a suspected human carcinogen that is formed in some processed foods at low ng per g levels. Recent improvements in analytical methodology and scientific instrumentation have made it possible to accurately measure the amount of furan in a wide variety of foods. Results from analysis of more than 300 processed foods are presented. Furan was found at levels ranging from non-detectable (LOD, 0.2-0.9 ng g^-1) to over 100 ng g^-1. Exposure estimates for several adult food types were calculated, with brewed coffee being the major source of furan in the adult diet (0.15 µg kg^-1 body weight day^-1). Estimates of mean exposure to furan for different subpopulations were calculated. For consumers 2 years and older, the intake is estimated to be about 0.2 µg kg^-1 body weight day^-1.     

体内碱性彗星试验法检测纳米氧化锌遗传毒性

目的利用体内碱性彗星试验方法,检测长期给予纳米氧化锌颗粒(ZnO NPs)对大鼠的遗传毒性作用。方法结合扩展一代生殖毒性试验,使用13周龄的亲代SD大鼠,经口每天灌胃给予ZnO NPs 0、7、50、350 mg/kg(纳米尺度分散状态最大浓度),记录体质量变化并观察。70 d后每个剂量组取亲代大鼠雌雄各10只处死后取乙二胺四乙酸抗凝全血,采用彗星试验试剂盒进行制片,用定量分析专业软件(Casp)进行彗星结果分析。结果与溶剂对照组比较,雄性大鼠高剂量组外周血DNA损伤细胞率和尾部DNA含量百分比明显上升,分别为28.60%和(36.38±5.84)%,差异有统计学意义(P0.05);雌性大鼠高剂量组外周血DNA损伤细胞率和尾部DNA含量百分比明显上升,分别为27.31%和(18.80±2.96)%,差异有统计学意义(P0.05)。结论在350 mg/kg剂量下ZnO NPs体内碱性彗星试验结果阳性。     

Aromatic DNA adducts in relation to dietary and other lifestyle factors in Spanish adults

The aim of this study was to assess the relationship between bulky DNA adducts in white blood cells (WBC) and lifestyle factors in a sample from the Spanish cohort of the European Prospective Investigation into Cancer and Nutrition (EPIC). 296 subjects aged between 35 and 64 years, from five regions, were included. Food intake was estimated with a computerized version of dietary history questionnaire. Daily intake of polycyclic aromatic hydrocarbons (PAH) was estimated using a database with information on food content of potential carcinogens. Data on lifestyle and health factors were collected and DNA adducts measured using the nuclease P1 ³²P-postlabelling technique. Geometric means of adducts were similar for men and women (4.11/10⁹ and 3.94/10⁹ nucleotides, respectively). Highest levels of adduct were observed in non-smokers and non-occupationally exposed. Meat intake, oils and fats were associated with higher levels of adducts, but all non-statistically significant. Higher intakes of calcium, sodium and phosphorus were associated with lower adducts levels. Summarising, our study shows that bulky adducts measured by ³²P-postlabelling in DNA from WBC do not correlate with the usual diet of healthy Spanish adults. Although it has been proposed that diet be the main source of PAH in nonsmokers without occupational exposure, DNA adducts do not seem to be suitable biomarkers of dietary PAH in general population.     

Effect of oxygen availability and pH on the furan concentration formed during thermal preservation of plant-based foods

Thermally treated fruit- and vegetable-based foods are important contributors to the furan exposure of children and adults. Furan reduction by adding or removing precursors from the product has proven to be challenging because of major food constituents and interactions involved in the reaction pathways leading to furan formation. Instead of intervening at the precursor level, it might be more feasible to influence these formation pathways by adjusting the matrix properties of the product. As opposed to many previous literature sources, the present study investigated the effects of oxygen availability (normal versus reduced) and pH (acid versus low acid) on the furan formation in a real food system. Different combinations of both matrix properties were prepared in a reconstituted potato purée and subjected to a thermal treatment with a pasteurisation or sterilisation intensity. Irrespective of the addition of the furan precursors ascorbic acid, fructose and fatty acids, a considerable furan reduction was observed for the sterilised purées (F₁₂₁¹⁰ = 15 min) with either a reduced oxygen availability (0.1–1.8 mg l^–1) or at pH 3. The effects of both matrix properties were less pronounced in the pasteurised purées (P₉₀¹⁰ = 10 min), because of the lower furan concentrations. Even though the mechanisms of furan reduction for both types of matrix properties could not be fully elucidated, the results showed that lowering the oxygen concentration or pH prior to thermal processing offers a powerful, additional strategy for furan mitigation in thermally treated plant-based foods.     

Two food-borne heterocyclic amines: metabolism and DNA adduct formation of amino-alpha-carbolines

The amino-alpha-carbolines 2-amino-9H-pyrido[2,3-b]indole (AalphaC) and 2-amino-3-methyl-9H-pyrido-[2,3-b]indole (MeAalphaC) are two mutagenic and carcinogenic heterocyclic amines formed during ordinary cooking. Amino-alpha-carbolines can be formed in model systems by pyrolyzing tryptophan or proteins of animal or vegetable origin, furthermore they are found in many cooked foods, such as fish, meat, and chicken. The specific mutagenicity of the amino-alpha-carbolines are lower in the Ames Salmonella assay than other heterocyclic amines, but in rodent studies the carcinogenicity of the amino-alpha-carbolines are comparable to other heterocyclic amines. The metabolic pathways of the amino-alpha-carbolines have been studied in vitro and in vivo, and the detoxified phase I and phase II metabolites characterized and quantified. The metabolic activation of the amino-alpha-carbolines and the formation of DNA-adducts have also been studied. Characteristic for the amino-alpha-carbolines are that relatively large amounts of these compounds in rat and human hepatic microsomes are activated to potent carcinogenic compounds compared with other heterocyclic amines, but further in vivo studies of the amino-alpha-carbolines are needed to highlight these indications. In this review, the main characteristics with focus on the metabolism and the DNA-adduct formation of the amino-alpha-carbolines are described and compared with other heterocyclic amines.     

Identification of glucosinolate congeners able to form DNA adducts and to induce mutations upon activation by myrosinase

Scope: Juices from Brassicales are mutagenic in Salmonella typhimurium and characteristic adducts are formed with the endogenous DNA in Brassicales homogenates. These effects require myrosinase activity, suggesting an involvement of breakdown products of glucosinolates (GLs). We aimed to identify GLs congeners producing these effects. Methods and results: We investigated twelve individual GLs for mutagenicity in S. typhimurium TA104 and TA100 and for adduct formation with herring sperm DNA using the 32P‐postlabelling/thin‐layer chromatography method. All bacteriotoxic and mutagenic effects observed required the presence of myrosinase. Neoglucobrassicin, 4‐methoxyglucobrassicin and sinalbin showed mutagenicity over wide concentration ranges, with neoglucobrassicin being the most potent congener. Six other GLs led to modest increases in the number of revertants in a small concentration range, before toxicity overshadowed this effect. The remaining three GLs showed some toxicity, but no mutagenicity. However, all twelve GLs formed DNA adducts. Clearly the highest adduct levels were detected with the indole GLs tested. They matched the major adduct spots formed in Brassicales homogenates. Conclusion: The observation that GLs are genotoxic demands follow‐up studies on possible genotoxic and carcinogenic effects of these common food compounds in animal models and humans. Our study may be used to prioritize the congeners in further studies.     

Absence of 2'-deoxyguanosine-carbon 8-bound ochratoxin A adduct in rat kidney DNA monitored by isotope dilution LC-MS/MS

The contribution of DNA adduct formation in the carcinogenic action of the mycotoxin ochratoxin A (OTA) has been subject to much debate. Recently, a carbon-bonded ochratoxin A-2'-deoxyguanosine adduct (dGuoOTA) formed by photochemical reaction in vitro has been shown by 32P-postlabeling/TLC to comigrate with a spot detected in DNA isolated from rat and pig kidney following exposure to OTA. Considering the large body of evidence arguing against covalent DNA binding of OTA and the poor resolution and specificity of postlabeling analysis, we developed a stable isotope dilution LC-MS/MS method to analyze dGuoOTA in kidney DNA isolated from rats treated with OTA. dGuoOTA and nitrogen-15-labeled dGuoOTA (15N(5)-dGuoOTA) were prepared by photoirradiation of OTA in the presence of dGuo or nitrogen-15-labeled dGuo. Conditions for DNA hydrolysis were optimized using a synthetic oligonucleotide containing dGuoOTA to ensure complete release of dGuoOTA. The LOD of the method (S/N > 3) was 10 fmol dGuoOTA on-column. However, dGuoOTA was not detected in DNA samples isolated from male F344 rats treated with OTA for up to 90 days at doses known to cause renal tumor formation. Detection limits, calculated for each individual sample based on the absolute LOD and the amount of DNA injected, were as low as 3.5 dGuoOTA/10(9) nucleotides. These data are consistent with previous results showing lack of DNA adduct formation by OTA and demonstrate that dGuoOTA is not formed in biologically relevant amounts under physiological conditions in vivo.     

Determination of furan in food samples using two solid phase microextraction fibers based on sol-gel technique with gas chromatography-flame ionisation detector

The headspace solid-phase microextraction (HS-SPME) method with two different coatings synthesized by sol-gel technology [such as poly(ethylene glycol) (PEG) and PEG reinforced with multi-walled carbon nanotubes (PEG/CNTs)] coupled with gas chromatography-flame ionization detector (GC-FID) was proposed for the determination of furan at trace levels in food samples. Under optimized conditions, the linear range for furan with PEG and PEG/CNTs fibers was 0.005-10 and 0.0005-10 ng/mL, the limit of detection (S/N = 3) was 0.001 and 0.00025 ng/mL and the limit of quantification (LOQ) was 0.005 and 0.0005 ng/mL, respectively. For PEG and PEG/CNTs fibers, repeatability (n = 5) was 6.2% and 4.9% and reproducibility (n = 3) was 6.6% and 5.3%, respectively. Relative recoveries for the spiked samples with 0.1 ng/mL of furan were ranged from 92% to 103%. The proposed HS-SPME-GC-FID method was successfully applied for the extraction of furan in two environmental food samples (baby food and fruit juice).