Heat-treated Foods Research Articles

Evaluation of Benzo[a]pyrene in Food from China by High-Performance Liquid Chromatography-Fluorescence Detection

The occurrence and levels of benzo[a]pyrene in various heat-treated foods from China were evaluated by high-performance liquid chromatography-fluorescence detection. In a total of 119 samples, 105 were found to contain benzo[a]pyrene at levels of 0.03 to 19.75 µg/kg. The benzo[a]pyrene contents in 12 animal source foods were higher than the Chinese maximum permissible level in food (5 µg/kg) and the highest level was 19.75 µg/kg, nearly four times the maximum permissible level. The results revealed a widespread carinogenic public health risk from benzo[a]pyrene in heat-treated foods. The highest benzo[a]pyrene levels were found in animal source samples such as charcoal-grilled and smoked meats, especially pork, beef and sausage, while trace levels of benzo[a]pyrene were present in grain food. Charcoal-grilled vegetables were found to also contain certain levels of benzo[a]pyrene. This study provided new information on benzo[a]pyrene content of a variety of heat-treated foods from China.

Evaluation of acrylamide in food from China by a LC/MS/MS method.

Acrylamide is potential carcinogenic compound that possesses neurotoxicity activity. In this study, the levels of acrylamide in 123 selected food samples from China was evaluated using a LC/MS/MS method. One hundred and fifteen (115) out of 123 samples showed positive levels of acrylamide in the range of 0.41 to 4,126.26 µg/kg. Generally, the highest acrylamide levels were found in fried products, such as potato, prawn strips and rice crust, with average values of 604.27, 341.40, and 201.51 µg/kg, respectively. Heated protein-rich food also showed some acrylamide content (ranging from 2.31 to 78.57 µg/kg). The results revealed that a potential acrylamide public health risk occurred in processed snacks, as well as the food consumed daily. This study supplied new information on acrylamide content of a variety of heat-treated foods from China.

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.

Produce consumption in the United States: an analysis of consumption frequencies, serving sizes, processing forms, and high-consuming population subgroups for microbial risk assessments.

A great variety of fruits and vegetables are available in the United States. These items are produced in various geographic regions by a diverse industry. Produce has been increasingly identified as a vehicle for disease outbreaks. Changes in consumption may explain this increase, but analyses of produce consumption are limited. Comprehensive assessments of the public health risks associated with produce depend on quantitative consumption data, including the population fractions and subgroups of consumers, the quantities consumed by these individuals, and the processing that occurs before consumption. Here, we provide an analysis of nationally representative consumption estimates by estimating consumption frequencies, serving sizes, and processing forms for a variety of produce commodities based on 1999 through 2006 data from "What We Eat in America," the dietary interview component of the National Health and Nutrition Examination Survey performed by the National Center for Health Statistics. Consumption patterns for fresh and heat-treated produce were assessed, compared with U.S. food availability estimates from the U.S. Department of Agriculture Economic Research Service (ERS), and combined with ERS data on temporal trends in food availability and nondomestic produce origins. To identify high-consuming population subgroups, we explored consumer habits and demographic predictors of fresh produce consumption (data available at www.foodrisk.org). Our analysis of common outbreak vehicles revealed limited temporal changes in food availability but frequent consumption as fresh commodities. In addition to providing quantitative consumption estimates for risk assessments, our data clearly show that produce consumption differs among fruits and vegetables, fresh and heat-treated foods, and demographic subgroups. These results are valuable for risk assessments and outbreak investigations and allow targeting of risk communication or interventions to those individuals at greatest risk.

Does furan affect the thymus in growing male rats?

Furan has been identified in foods such as heat-treated foods, including coffee, canned meat, hazelnuts, and infant foods and formulas. Children may be exposed to furan via either consumption of these foods or their derivatives. We evaluated the effects of furan on the thymus of weaning male rats in the present study. Five separate groups containing male rats were used: control, oil control, and three furan-treated groups. Furan was given orally to rats in the treatment groups at doses of 2, 4, and 8 mg/kg/day for 90 days. At the end of the experiment, thymus of the rats were examined morphologically, histopathologically, and immunohistochemically. We observed that absolute and relative weights of thymus were decreased significantly in rats treated with 4- and 8-mg/kg/day doses of furan. In histopathological examination, enlargement of interstitial connective tissue between the thymic lobules, lymphocyte depletion, and hemorrhage were observed. We detected an increase in apoptotic cell counts in thymus of the treatment groups. In addition, we found significant differences in the distribution of fibronectin and transforming growth factor-beta in the thymus of the treatment groups. In conclusion, we suggest that furan has affected the thymus in growing male rats.

Folic Acid - The Occurrence and the Role in Human Nutrition

Folic Acid - The Occurrence and the Role in Human Nutrition Folic acid occurs naturally in the salt form of folic acid - the so-called folate. The human body cannot synthesize it, and therefore it must be supplied from outside. Folic acid is involved in the synthesis and proper functioning of RNA and DNA acids. It is essential for growth and division of all body cells, which is particularly important during active growth or in the fetal and newborn life. In children and adults, folate along with vitamin B12 are involved in the production of red blood cells. Current research indicate on the existence in Poland and in Central and Northern Europe of significant deficiencies of folic acid in the diet. Deficiency of folic acid in our diet is due to the fact that we consume more highly processed food. Stored and heat-treated food loses a large part of folates. The most common pathological processes associated with a deficiency of folic acid in the body are neural tube defects, megaloblastic anaemia, disturbances in the functioning of the nervous and cardiovascular system, as well as the development of certain types of cancer. Effective methods to increase folate intake are still being searched for.

Toxicity of food contaminant furan on liver and kidney of growing male rats

Furan is a chemical used in some industrial products and occurs naturally in heat-treated foods. We aimed to investigate the effects of orally administered furan on liver and kidney in growing Wistar male rats for 90 days. In this respect, biochemical, morphological, histopathological, and histomorphometrical examinations were performed. Three- to 4-week aged rats were divided into five groups of eight animals each; control, oil control; 2, 4, 8 mg/kg/day furan treatment groups. At the end of the experiment, antioxidant enzyme activities and serum AST, ALT, HDL, Urea, etc. levels were analyzed. Malondialdehyde (MDA) levels, superoxide dismutase (SOD), catalase (CAT), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) were also measured in liver homogenates. Also, liver and kidney were examined morphologically and histopathologically under light microscopy. According to the results of biochemical analysis, ALT, ALP, and LDL levels in treatment groups were significantly different compared with control groups. While LDL levels in treatment groups increased significantly, ALT and ALP levels decreased significantly. No significant changes were observed in liver MDA levels, superoxide dismutase and catalase activities in treatment groups. While IL-6 levels did not change in treatment groups, furan caused dose-dependent increases in liver TNF-α level of rats. In treatment groups, absolute and relative liver weights changed significantly, however, no significant changes were observed in kidney and relative kidney weights. Hyperemic blood vessels in the liver and congestion, edema, fibrosis, and tubular damage in the kidney of rats treated with furan were observed histopathologically. According to histomorphometric examinations, glomeruli diameters and glomerular volume decreased in the kidneys of rats in treatment groups.

Acrylamide in Baking Products: A Review Article

Acrylamide or 2-propenamide is a chemical compound, with chemical formula CH2=CH–CO–NH2, that can be produced at high levels in high-carbohydrate heat-treated foods. The risks of acrylamide to health and its toxic properties (neurotoxicity, genotoxicity, carcinogenicity and reproductive toxicity) were demonstrated by the Scientific Committee on Toxicity, Ecotoxicity and the Environment in 2001. Potato and bakery products account for around 50% and 20% of human exposure to acrylamide, respectively. Factors affecting acrylamide formation and degradation in foods are acrylamide precursors such as free amino acids (mainly asparagine), reducing sugars and processing conditions (i.e. baking time and temperature, moisture content and matrix of product). The aim of this review was to present some results from recent investigations of the effects of different factors affecting acrylamide formation in bakery products. Finally, recommendations are proposed as guidelines for baking manufacturers to reduce the level of acrylamide in their products.

The recognition of high molecular weight melanoidins as the main components responsible for radical-scavenging capacity of unheated and heat-treated Canadian honeys

As the Maillard reaction is known to occur in heat-treated foods, unheated and heated honey samples were subjected to the activity-guided fractionation and size-exclusion chromatography to compare the degree of browning, radical scavenging activity (ORAC) and molecular size of the fractions obtained. Heat-treatment increased browning in the fractions of light- and medium-coloured honeys ( p < 0.002), accelerated the formation of high molecular weight melanoidins (85–232 kDa) and significantly increased ORAC values ( p < 0.0001). In contrast, melanoidin content and ORAC decreased in the fractions of heat-treated dark buckwheat honey ( p < 0.001). Unheated dark honey contained a significantly higher amount of melanoidins than other honeys ( p < 0.007). Together, results showed that at low initial concentration of melanoidins, heat-treatment accelerated formation of new melanoidins and increased ORAC, while at high concentration it caused decrease and a reduction of radical scavenging activity. This study emphasises the importance of non-enzymatic browning in the prediction of the antioxidant pool in thermally processed honeys.

Hepatobiliary Toxicity of Furan: Identification of Furan Metabolites in Bile of Male F344/N Rats

Furan, which occurs in a wide variety of heat-treated foods, is a potent hepatotoxicant and liver carcinogen in rodents. In a 2-year bioassay, furan caused hepatocellular adenomas and carcinomas in mice and rats but also high incidences of bile duct tumors in rats. Furan is bioactivated by cytochrome P450 enzymes to cis-2-butene-1,4-dial, an α,β-unsaturated dialdehyde, which readily reacts with tissue nucleophiles. The objective of this study was to structurally characterize furan metabolites excreted with bile to better understand the potential role of reactive furan intermediates in the biliary toxicity of furan. Bile duct-cannulated F344/N rats (n = 3) were administered a single oral dose of 5 mg/kg b.wt. [(12)C(4)]furan or stable isotope-labeled [3,4-(13)C]furan, and bile samples collected at 30-min intervals for 4 h were analyzed by liquid chromatography-tandem mass spectrometry. A total of eight furan metabolites derived from reaction of cis-2-butene-1,4-dial with GSH and/or amino acids and subsequent enzymatic degradation were detected in bile. The main metabolite was a cyclic monoglutathione conjugate of cis-2-butene-1,4-dial, which was previously detected in urine of furan-treated rats. Furthermore, a N-acetylcysteine-N-acetyllysine conjugate, previously observed in rat urine, and a cysteinylglycine-glutathione conjugate were identified as major metabolites. These data suggest that degraded protein adducts are in vivo metabolites of furan, consistent with the hypothesis that cytotoxicity mediated through binding of cis-2-butene-1,4-dial to critical target proteins is likely to play a key role in furan toxicity and carcinogenicity.

Toxicity and carcinogenicity of furan in human diet

Furan is formed during commercial or domestic thermal treatment of food. The initial surveys of furan concentrations in heat-treated foods, published by European and US authorities, revealed the presence of relatively high furan levels in coffee, sauces, and soups. Importantly, furan is consistently found in commercial ready-to-eat baby foods. Furan induces hepatocellular tumors in rats and mice and bile duct tumors in rats with a high incidence. Epidemiological studies are not available. It is assumed that cis-2-butene-1,4-dial, the reactive metabolite of furan, is the causative agent leading to toxicity and carcinogenicity. Based on this data, furan is classified as a possible human carcinogen. The initial exposure estimates revealed a relatively small margin (~2,000) between human exposure and those furan doses, which induce liver tumors in experimental animals. As this may give rise for concern, in this review, the currently available toxicological and mechanistic data of furan are summarized and discussed with regard to its applicability in assessing the risk of furan in human diet.

Validation of a database on acrylamide for use in epidemiological studies

Acrylamide, a probable human carcinogen, was detected in various heat-treated foods such as French fries and potato crisps. Recently, positive associations have been found between dietary acrylamide intakes, as estimated with a food frequency questionnaire using an acrylamide database, and cancer risk in some epidemiological studies. As acrylamide levels vary considerably within the same type of foods, a validation study was performed to investigate whether use of an acrylamide food database containing calculated mean acrylamide content, based on extensive sampling and chemical analysis of Dutch foods (several samples per food), can classify subjects with respect to true acrylamide intake. We used the data from a 24-h duplicate diet study. The acrylamide content of 39 Dutch 24-h duplicate diets collected in 2004 was estimated using the mean acrylamide levels of foods available from the database and the menu list, on which the participants of the duplicate diet study had listed the amounts of individual foods and drinks in household units. Next, the acrylamide content of the total duplicate diets was analytically measured and correlated to the estimated acrylamide contents. The Spearman's correlation coefficient between chemically determined acrylamide content and the calculated acrylamide content of the duplicate diets was 0.82 (P<0.001). This study indicates that it is possible to classify subjects with respect to acrylamide intake if mean instead of actual content of each food is applied. The database can therefore be applied in epidemiological studies on acrylamide intake and cancer risk, such as the Netherlands Cohort Study on Diet and Cancer.

ACRYLAMIDE LEVELS IN HEAT-TREATED EGYPTIAN FOODS

This study was conducted to determine the acrylamide levels in selected heat-treated food items, commercially determine foods from the Egyptian market As with some home-prepared foods as part of the traditional ways of food preparation to study the impact of the temperature and time on formation of acrylamide which classified as a Group 2A carcinogen by the International Agency for Research on Cancer that affect the human nervous system. Acrylamide levels were determined in around 70 food samples using liquid chromatography coupled to U.V spectrometric detection LC-UV and the results were expressed in μg kg-1. The food items were also subjected to the relevant high-temperature>120°C or contain high carbohydrates and asparagines as well as those exposed during the processing to high temperatures. The investigated samples included cereal productssnack, rice, pasta noodles, tuberssweet potato, nuts almonds, pine nuts and chestnut & legume, vegetables potatoes, onion,dried fruitsraisins, dates& prunes,,sauces and beverages coffee, cocoa . Roasting and frying experiments under different process conditions were done on potatoes, sweet potato, pasta, rice, corn and noodles which represents a different preparation ways showed that acrylamide increases with the length of exposure to heat; surface color browning as an indicator of acrylamide levels in some foods; and that time has a much stronger effect on acrylamide formation than temperature. The obtained results showed that the acrylamide content ranged from < 11-1845 g/kg. Highest acrylamide concentrations were found in roasted nuts, while only moderate acrylamide contents were found in dried fruits and roasted bakery product. While the lowest value were in fried sweet and bean flafel.

The health and technological implications of a better control of neoformed contaminants by the food industry

The recent discovery of the presence of variable amounts of the carcinogenic compound acrylamide in a wide range of severely heat-treated food products, such as fried potatoes, biscuits, bread and coffee or malt, as a result of the heat process, has induced an important research in the area of the Maillard reaction in food. The interaction between a specific food composition and the heat process applied results in the development of complex oxidation and glycation reactions, which give rise to a mixture of flavoured compounds and possible neoformed contaminants (NFC). Recommendations by the European Commission aim at monitoring the content of major NFC, such as acrylamide and furan, in a list of food products commercialized in Europe. On the other hand, the Commission for European Normalization (CEN) has created recently a new workgroup (WG13) responsible for normalization of analytical method for NFC assessment. The European collective research ICARE was carried out to identify the possible health consequences of the ingestion of heat-treated products, characterize the reaction kinetics leading to NFC and evaluate some mitigation procedures proposed by the CIAA toolbox, and finally develop a simple, rapid and non destructive control method based on fluorescence acquisition on the crushed food products and chemometric analysis of the spectral information. This paper summarizes the objectives and essential results obtained in the scope of the project, highlighting the need for evaluating the distribution of NFC in food products commercialized in Europe, as well as the impact of the food formula/recipe and process on Maillard derived NFC food levels. The potential of the Fluoralys sensor regarding its ability to control food contamination with NFC is presented. A decrease in NFC concentration of heat processed food should allow significantly limiting the exposure of populations to NFC and consequently the potential related health risk.

Dietary Acrylamide Intake and Brain Cancer Risk

Acrylamide is a probable human carcinogen, which is present in several heat-treated foods. In epidemiologic studies, positive associations with endometrial, ovarian, and renal cell cancer risk have been observed. The incidence of central nervous system tumors was increased upon acrylamide administration in drinking water to rats. In the current study, the association between dietary acrylamide intake and human brain cancer risk was investigated for the first time. In 1986, 120,852 persons (ages 55-69 years) were included in the Netherlands Cohort Study on diet and cancer. At baseline, a random subcohort of 5,000 participants was randomly selected from the total cohort for a case-cohort approach. Acrylamide intake was assessed with a food frequency questionnaire at baseline and based on acrylamide analyses in relevant Dutch foods. Hazard ratios (HR) were calculated using Cox proportional hazards analysis. Subgroup analyses were done for microscopically verified brain cancer, astrocytic gliomas, high-grade astrocytic gliomas, and never-smokers. The acrylamide risk estimates were adjusted for possible brain cancer risk factors. After 16.3 years of follow-up, 216 brain cancer cases were available for analysis. The multivariable-adjusted HR per 10 microg/d increment of acrylamide intake was 1.02 (95% confidence interval, 0.89-1.16). HRs were not significantly increased either when dietary acrylamide intake was analyzed as a categorical variable. Also, there was no association in the subgroups based on histology and smoking. In this prospective cohort study, acrylamide intake was not associated with brain cancer risk.

Lung Cancer Risk in Relation to Dietary Acrylamide Intake

Acrylamide is a probable human carcinogen that is present in several heat-treated foods. In epidemiological studies, positive associations between dietary acrylamide intake and the risks of endometrial, ovarian, estrogen receptor-positive breast, and renal cell cancers have been observed. The association between dietary acrylamide intake and lung cancer risk is not known. We conducted a case-cohort study among 58 279 men and 62 573 women (aged 55-69 years) in the Netherlands Cohort Study on Diet and Cancer. Intakes of acrylamide-containing foods and risk factors for cancer were assessed with a self-administered questionnaire at baseline in 1986 and combined with acrylamide levels in relevant Dutch foods to assess total dietary acrylamide intake. The number of person-years at risk was estimated by using a random sample of participants from the total cohort that was chosen at baseline (n = 5000). Incident lung cancer cases in the total cohort were detected by computerized record linkages to the Netherlands Cancer Registry and the Netherlands Pathology Registry. Hazard ratios and 95% confidence intervals (CIs) for the risk of lung cancer associated with acrylamide intakes were estimated using Cox proportional hazards models that controlled for smoking (status, quantity, and duration) and other lung cancer risk factors. All statistical tests were two-sided. After 13.3 years of follow-up (September 17, 1986 up to January 1, 2000) there were 2649 cases of primary, histologically verified lung cancer (International Classification of Diseases for Oncology-3 code: C34) when cases with prevalent cancer at baseline (other than skin cancer) were excluded. The multivariable-adjusted hazard ratio of lung cancer for a 10-microg/d increment of acrylamide intake was 1.03 (95% CI = 0.96 to 1.11) for men and 0.82 (95% CI = 0.69 to 0.96) for women. The hazard ratio of lung cancer for the highest (median intake [microg/d]: men = 37.6 and women = 36.8) vs the lowest (median intake [microg/d]: men = 10.8 and women = 9.5) quintile of acrylamide intake was 1.03 (95% CI = 0.77 to 1.39, P(trend) = .85) for men and 0.45 (95% CI = 0.27 to 0.76, P(trend) = .01) for women. The inverse association in women was strongest for adenocarcinoma (hazard ratio for highest vs lowest tertile of intake = 0.40, 95% CI = 0.21 to 0.78; P(trend) = .01). Acrylamide intake was not associated with lung cancer risk in men but was inversely associated in women, most strongly for adenocarcinoma. This finding suggests that acrylamide is involved in human carcinogenesis through pathways other than genotoxicity.

Furan in food - a review

Furan and its derivatives were identified in a small number of heat-treated foods back in the 60’s and 70’s. In May 2004, US Food and Drug Administration published a report on the occurrence of parent furan in a number of thermally treated foods. Since furan has been classified as “possibly carcinogenic to human” by IARC, a great concern has been addressed to the analysis of this substance naturally-occurring in food. This paper gives a short overview on the mechanistic pathways of the parent furan formation in food by degradation of amino acids and/or reducing sugars, and oxidation of ascorbic acid and poly-unsaturated acids which can be induced by thermal or irradiation treatments; further, it deals with the metabolism and toxicology of furan as well as with the comparison of the methods of furan determination.

Antimicrobial Activity of Coffee Melanoidins—A Study of Their Metal-Chelating Properties

Melanoidins comprise a substantial proportion of severely heat-treated foods such as baked cereals or roasted coffee and are widely consumed dietary components. The antimicrobial activity of coffee melanoidins against different pathogenic bacteria has been studied, finding that such activity is due to their metal-chelating properties. Three different mechanisms have been observed: at low concentrations melanoidins exerted a bacteriostatic activity mediated by iron chelation from the culture medium; in the case of bacterial strains that are able to produce siderophores for iron acquisition, melanoidins chelate the siderophore-Fe3+ complex, which could decrease the virulence of such pathogenic bacteria; and, finally, coffee melanoidins also exerted a bactericide activity at high concentrations by removing Mg2+ cations from the outer membrane, promoting the disruption of the cell membrane and allowing the release of intracellular molecules.

La réaction de Maillard dans les aliments : quels enjeux pour la santé humaine ?

The Maillard reaction is a complex mixture of temperature-dependent reactions between carbonyl compounds derived from sugars, lipids, and vitamins heat degradation products, and amino groups of amino acids, proteins or DNA. Among the numerous Maillard products (MP) formed, some are considered to raise safety problems because of their carcinogenicity, or pro-oxidant and inflammatory bioactivity. MP are produced in severely heat-treated food and partially absorbed, while reaching the endogeous pool of MP formed from glucose and lipid metabolites and biological proteins or DNA. If uncompletely degraded and/or excreted, they accumulate and promote the secretion of cytokines which are involved in the development of degenerative processes. The specific contribution of dietary MP in those physiopathological phenomena remains unknown. However, risk prevention supposes to control MP formation in food, while maintaining satisfactory sensorial quality.

Dietary Acrylamide Intake Is Not Associated with Gastrointestinal Cancer Risk

Acrylamide is a probable human carcinogen that was detected in several heat-treated foods, such as French fries and crisps, in 2002. Prospective studies are needed on acrylamide and human cancer risk. We prospectively investigated the association between acrylamide and gastrointestinal cancer risk. In 1986, 120,852 men and women (aged 55–69 y) were included in the Netherlands Cohort Study on diet and cancer. At baseline, a random subcohort of 5000 participants was selected for a case-cohort approach. Acrylamide intake was assessed with a FFQ at baseline and was based on acrylamide analyses in relevant Dutch foods. After 13.3 y of follow-up, 2190, 563, 349, and 216 cases of colorectal, gastric, pancreatic, and esophageal cancer, respectively, were available for analysis. The daily acrylamide intake of the subcohort was (mean ± SD) 21.7 ± 12.1 μg. A 10-μg/d increment of acrylamide intake was associated with multivariable-adjusted Cox proportional hazard rate ratios (HR) (95% CI) of 1.00 (0.96–1.06), 1.02 (0.94–1.10), 1.06 (0.96–1.17), and 0.96 (0.85–1.09) for colorectal, gastric, pancreatic, and esophageal cancer, respectively. For former or never-smokers, the corresponding HR were: 1.03 (0.94–1.12), 1.09 (0.98–1.22), 1.07 (0.93–1.24), and 0.92 (0.76–1.11). There were some significantly increased risks within subgroups stratified by obesity, nonoccupational physical activity, and age, factors that were a priori selected based on their capacity to modify cytochrome P4502E1 activity. Overall, acrylamide intake was not associated with colorectal, gastric, pancreatic, and esophageal cancer risk, but some subgroups deserve further attention.