Immunochemical determination of gluten in malts and beers

Characteristics of Oat and Buckwheat Malt Grains for Use in the Production of Fermented Foods

Malted gluten-free cereal grains and pseudo-cereals are interesting raw materials for producing fermented foods. The aim of the work was to assess selected technological quality characteristics and antioxidant properties of special malts in terms of use in the production of fermented foods. The research material consisted of malts made from oat, buckwheat, and brewing barley. Malting was performed on a microtechnical scale according to the standard scheme for brewing barley grain. The basic quality parameters of cereal grains obtained malts, and laboratory wort were assessed according to methods applicable in brewing. Atypical brewing malts were characterized by parameters such as malt extractability, protein solubilization, diastatic force, mash filtration time, and wort viscosity. The best results, comparable to barley malt, were obtained for naked oat malt. Malted buckwheat grains turned out to be the least biochemically modified, although their use in the production of beer and/or other fermented beverages is supported by the high content of bioactive substances and antioxidant potential. As the malting process of cereal plants improves their antioxidant properties and increases their nutritional value, oat and buckwheat malts can be successfully used to produce gluten-free fermented beverages or as an addition to fermented products, e.g., in baking and confectionery.

Low Gluten Beers Contain Variable Gluten and Immunogenic Epitope Content

Gluten content labels inform food choice and people practicing a gluten-free diet rely upon them to avoid illness. The regulations differ between jurisdictions, especially concerning fermented foodstuffs such as beer. Gluten abundance is typically measured using ELISAs, which have come into question when testing fermented or hydrolysed foodstuffs such as beer. Mass spectrometry can be used to directly identify gluten peptides and reveal false negatives recorded by ELISA. In this survey of gluten in control and gluten-free beers, gluten protein fragments that contain known immunogenic epitopes were detected using liquid chromatography-mass spectrometry in multiple beers that claim to be gluten-free and have sufficiently low gluten content, as measured by ELISA, to qualify as being gluten-free in some jurisdictions. In fact, several purportedly gluten-free beers showed equivalent or higher hordein content than some of the untreated, control beers. The shortcomings of ELISAs for beer gluten testing are summarised, the mismatch between ELISA and mass spectrometry results are explored, and the suitability of existing regulations as they pertain to the gluten content in fermented foods in different jurisdictions are discussed.

Safety Assessment of Foods and Drinks Consumed by People on a Gluten-Free Diet

Naturally gluten-free foods and processed foods that do not contain information about the potential presence of gluten in them pose a hypothetical threat to people with food allergies and celiac disease. Patients who should follow a strict gluten-free diet do not always do so. Therefore, the aim of this research was to analyze certified “gluten-free” and naturally gluten-free products without labeled “may contain gluten” information in terms of their content of gluten proteins. The enzyme immunoassay AgraQuant Gluten G12 ELISA test kit was used for the analysis. Of all the products used in the research, only 5.8% were found to contain gluten above 20 ppm. Only one product labeled “gluten-free” was contaminated with gluten at 79.3 ppm (cider cake). In addition, our research also examined the gluten content of commercial beers containing barley malt not labeled as “gluten-free”. Research has shown that 60% of samples are not safe for those on a strict gluten-free diet. Our research clearly shows that many manufacturers, although they do not monitor their products for the presence of gluten in them, offer safe products, although they cannot be recommended in a gluten-free diet. Therefore, there is a strong need to increase the frequency of testing by food manufacturers for the presence of gluten in their products, so that the number of products approved for people on a gluten-free diet continues to increase.

Beer and Allergens

Food allergies are an important global health concern, with many countries following the World Health Organisation’s guidelines with regards to due labelling of foods and, as such, providing forewarning about the presence of potential allergens to potential consumers. While for some produce, the link to specific allergens might be very clear to most consumers, this is not the case for all produce. People with specific food-related allergies usually know what to look out for, but occasionally, unexpected allergens are present in trusted produce. Beer is known to most to contain barley, which will contain gluten-like proteins that can cause allergic reactions in some people. Similarly, beer might contain sulphites and other potential allergens traditionally associated with beers. This review aims to examine a wide range of allergens that have entered the beer production process in recent years. As a result, examples of beers that contain one or more of the 14 EU-UK listed allergens are described, different allergen regulations in different countries are emphasised and their impact explained, and a number of case studies involving allergic reactions following exposure to and the ingestion of beer are highlighted.

Recent innovations in the production of selected specialty (non-traditional) beers

Customer demand for product diversity is the key driving force for innovations in the brewing industry. Specialty beers are regarded as a distinct group of beers different from two major types, lagers and ales, without established definitions or boundaries. Specialty beers, including low- to no-alcohol beer, low carbohydrate beer, gluten-free beer, sour beer, probiotic beer, and enriched beer, are exclusively brewed and developed keeping in mind their functionality, the health and wellbeing of the consumer, and emerging market trends. Compared with conventional beer-brewing, the production of specialty beers is technologically challenging and usually requires additional process steps, unique microorganisms, and special equipment, which in turn may incur additional costs. In addition, the maintenance of quality and stability of the products as well as consumer acceptability of the products are major challenges to successful commercialization. A harmonious integration of traditional brewing practices and modern technological approaches may hold potential for future developments. In the present review, latest developments in the fermentative production of selected specialty beers are discussed.

Tracking Gluten throughout Brewing Using N-Terminal Labeling Mass Spectrometry

Gluten-containing grains cause adverse health effects in individuals with celiac disease. Fermentation of these grains results in gluten-derived polypeptides with largely uncharacterized sizes and sequences, which may still trigger an immune response. This research used N-terminal labeling mass spectrometry to characterize protein hydrolysates during each stage of bench-scale brewing, including malting, mashing, boiling, fermentation, and aging. Gluten hydrolysates from each brewing step were tracked, and the immunotoxic potential was evaluated by sequence comparison with peptides known to stimulate celiac immune responses. The results indicate that proteolysis and precipitation of gliadins occurring during brewing differ by protein region and brewing stage. The termini of gliadins were hydrolyzed throughout the entire brewing process, but the central regions remained relatively stable. Most hydrolysis occurred during malting, and most precipitation occurred during boiling. The addition of yeast yielded new cleavage sites but did not result in complete hydrolysis. Consistent detection of peptides within the clinically important regions of gliadin corroborated the hydrolytic resistance of this region. N-terminal labeling mass spectrometry served as a novel approach to track the fate of gliadin/gluten throughout bench-scale brewing. Consistently identified fragments could serve as improved targets for the detection of hydrolyzed gluten in fermented products.

Peptidomics of an industrial gluten-free barley malt beer and its non-gluten-free counterpart: Characterisation and immunogenicity

Recent research suggests that gluten-free beers by prolyl-endopeptidase treatment may not be safe for coeliac disease (CD) patients. Therefore, the gluten peptidome of an industrial gluten-free prolyl-endopeptidase treated malt beer (<10 ppm gluten) was compared to its untreated counterpart (58 ppm gluten) as a reference. NanoLC-HRMS analysis revealed the presence of 155 and 158 gluten peptides in the treated and reference beer, respectively. Characterisation of the peptides in treated beer showed that prolyl-endopeptidase activity was not complete with many peptides containing (multiple) internal proline-residues. Yet, prolyl-endopeptidase treatment did eliminate complete CD-immunogenic motifs, however, 18 peptides still contained partial, and potentially unsafe, motifs. In the reference beer respectively 7 and 37 gluten peptides carried (multiple) complete and/or partial CD-immunogenic motifs. Worrying is that many of these partial immunogenic gluten peptides do not contain a recognition epitope for the R5-antibody and would be overlooked in the current ELISA analysis for gluten quantification.

Compositional and immunogenic evaluation of fractionated wheat beers using mass spectrometry

The safety and regulatory status of fermented products derived from gluten-containing grains for patients with celiac disease remains controversial. Bottom-up mass spectrometry (MS) has complemented immunoassays for the compositional and immunogenic analyses of wheat beers. However, uncharacterized proteolysis during brewing followed by the secondary digestion for MS has made the analysis and data interpretation complicated. In this study, the composition and immunogenic potential of seven commercially available wheat beers were evaluated using bottom-up MS with the aid of fractionation and a multi-step peptide search strategy to identify peptides generated by various types of proteolysis. Gluten-derived peptides accounted for approximately 50% and 20% of the total number of wheat-derived and barley-derived peptides, respectively, in the investigated beers. Although relatively large polypeptides cannot be thoroughly characterized using traditional bottom-up proteomics, up to 50% of peptides identified contained celiac-immunogenic motifs, and consumption of wheat beers would pose risks for celiac patients.

Potential ways for gluten contamination of gluten-free grain and gluten-free foods: the buckwheat case

Buckwheat has been reported to be responsible for gluten contamination in manufactured gluten-free foods (mGFFs) although it is inherently gluten-free (GF). It could happen through buckwheat grains contacting gluten-containing (GC) grains and surfaces contacted by GC grains during pre-manufacturing practices. To simulate grain contact, whole and broken GC grains (wheat, rye, barley, and oat) were mixed into buckwheat grains at the ratio of 2.5-10.0%. Grains were agitated in vessels with inner surfaces covered with buckwheat grain. Gluten was not detected in buckwheat grains contacting whole GC grains at all mixing ratios. It was not detected in the case of broken GC grains at the mixing ratio of 2.5% and oat grains at all mixing ratios. Gluten concentration increased with the increasing mixing ratio and the natural gluten concentration of broken GC grains. To simulate surface contact, GC grains were first agitated in galvanised steel vessels and then buckwheat grains were agitated together under the same conditions. Gluten was detected on galvanised steel surfaces contacted by whole and broken GC grains. It was not detected in buckwheat grains contacting the surfaces contaminated by whole GC grains. Gluten was detected in buckwheat grain in the case of the broken GC grains except for oats. Gluten concentrations increased with increasing natural gluten concentration of GC grains. Contamination of mGFFs could be linked to potential contact with buckwheat grain. This contamination issue could be resolved through regulations mandating the proof of being GF for ingredients used in the production of mGFFs.

Functional Beer—A Review on Possibilities

The expansion of the beer industry has enabled many possibilities for improvement regarding the taste, aroma and functionality of this drink. Health-related issues and a general wish for healthier lifestyles has resulted in increased demand for functional beers. The addition of different herbs or adjuncts in wort or beer has been known for centuries. However, today’s technologies provide easier ways to do this and offer additional functional properties for the health benefits and sensory adjustments of classical beer. Medicinal, religious or trendy reasons for avoiding certain compounds in beer or the need to involve new ones in the brewing recipe has broadened the market for the brewing industry and made beer more accessible to consumers who, till now, avoided beer.

Immunogenic Potential of Beer Types Brewed With Hordeum and Triticum spp. Malt Disclosed by Proteomics

The protein/peptide composition of five beer kinds, including two experimental beer-like products brewed with einkorn (Triticum monococcum), a beer labeled as “gluten-free,” a traditional all-barley malt and a wheat (T. aestivum) containing beer, was characterized with HPLC-ESI MS/MS-based proteomics. To enlarge the characterization of the components, the polypeptides were fractionated according to their molecular size (cut-off 6 kDa). All the beer types contained a variety of polypeptides arising from all the gliadin subfamilies (α-/β-, γ-, and ω-gliadins) able to induce an immune response in celiac disease (CD) patients in addition to a panel of IgE-reactive food allergens. Wheat storage proteins were heavily hydrolyzed in the beer samples brewed with einkorn. The presence of gluten-like fragments, also including the 25-mer and 33-mer-like of α-gliadin, was confirmed in beer brewed with barley and wheat malt as well as in the gluten-free beer. Both CD-toxic and allergenic peptides of all beer samples were drastically degraded when subjected to a simulated gastroduodenal (GD) digestion. After in vitro digestion, the level of gluten-like peptides assayed with the G12 competitive ELISA, was below the threshold (20 ppm) for a food to be considered as “gluten-free.” A few gliadin-derived epitopes occurred in the digests of beers crafted with wheat or Norberto-ID331 line of einkorn. In contrast, digests of all barley malt and gluten-free beers did not contain detectable gluten-like epitopes, but only minor fragments of hordeins and IgE-reactive food allergens. All beer samples evoked a weak immune response on gliadin-reactive celiac T cells isolated from intestinal biopsies of celiac patients. Compared to undigested polypeptides, the response was markedly reduced by GD digestion. Although the consumption of a moderate amount of beer brewed with barley or einkorn could deliver a relatively low amount of CD-toxic epitopes, the findings of this study emphasize the urgent need of a reliable and accurate quantification of gluten epitopes in all types of beer, also including the gluten-free one, to compute realistically the contribution of beer to the overall gluten intake, which can be responsible of intestinal tissue damages in celiacs.

Detection and Quantitation of Gluten in Fermented-Hydrolyzed Foods by Antibody-Based Methods: Challenges, Progress, and a Potential Path Forward

Celiac disease (CD) affects ~1 in 141 individuals in the United States, requiring adherence to a strict gluten-free diet. The Codex Standard and the European Commission states that gluten level of gluten-free foods must not exceed 20 ppm. The FDA requires food bearing the labeling claim “gluten-free” to contain <20 ppm gluten. Accurate quantitation of gluten in fermented-hydrolyzed foods by antibody-based methods is a challenge due to the lack of appropriate reference materials and variable proteolysis. The recent uses of proteases (e.g., proline endopeptidases or PEP) to hydrolyze immunopathogenic sequences of gluten proteins further complicates the quantitation of immunopathogenic gluten. The commercially available antibody-based methods routinely used to detect and quantitate gluten are not able to distinguish between different hydrolytic patterns arising from differences in fermentation processes. This is a severe limitation that makes accurate quantitation and, ultimately, a detailed evaluation of any potential health risk associated with consuming the food difficult. Utilizing gluten-specific antibodies, a recently developed multiplex-competitive ELISA along with western blot analysis provides a potential path forward in this direction. These complimentary antibody-based technologies provide insight into the extent of proteolysis resulting from various fermentation processes and have the potential to aid in the selection of appropriate hydrolytic calibration standards, leading to accurate gluten quantitation in fermented-hydrolyzed foods.

Effectiveness of proteolytic enzymes to remove gluten residues and feasibility of incorporating them into cleaning products for industrial purposes

The development of protocols for efficient gluten elimination is one of the most critical aspects of any allergen management strategy in the industry. The suitability of different proteolytic enzymes to be included in a cleaning formulation that allows the effective elimination of gluten residues was studied. Alcalase (ALC), neutrase (NEUT) and flavourzyme (FLAV) were selected from in silico analysis. The presence of 1% (v/v) of linear alkylbenzene sulphonate (LAS), a common anionic detergent, improved the gluten solubility, which may favour its elimination. Chromatographic analysis showed that the three enzymes studied were able to hydrolyse gluten in the presence of LAS. The highest percentage of short peptides (< 5 kDa) was achieved with ALC, what increases the probability of reducing the gluten antigenicity. Besides, in the presence of ALC and detergent LAS have detected the lowest levels of gluten with ELISA kits. So, effective amounts of ALC and LAS were added to a cleaning formulation, where its proteolytic activity was maintained above 90% after 37 days at 4 °C and 25 °C (under dark). Preliminary validation of the effectiveness enzymatic cleaning formulation to hydrolyse gluten was performed in a ready-to-eat/frozen food company, in which previous episodes of cross-contamination with gluten have been detected. The gluten content decreased to values below 0.125 μg/100 cm² when the cleaning formulation was tested on different surfaces with different cleaning protocols, demonstrating the high suitability of the enzymatic cleaning formulation developed.

Gluten Immunogenic Peptides as Standard for the Evaluation of Potential Harmful Prolamin Content in Food and Human Specimen

Gluten is a complex mixture of storage proteins in cereals like wheat, barley, and rye. Prolamins are the main components of gluten. Their high content in proline and glutamine makes them water-insoluble and difficult to digest in the gastrointestinal tract. Partial digestion generates peptide sequences which trigger immune responses in celiac and gluten-sensitive patients. Gluten detection in food is challenging because of the diversity, in various food matrices, of protein proportions or modifications and the huge number of immunogenic sequences with differential potential immunoactivity. Attempts to develop standard reference materials have been unsuccessful. Recent studies have reported the detection of a limited number of dominant Gluten Immunogenic Peptides (GIP) that share similarities to epitopes presented in the α-gliadin 33-mer, which showed to be highly proteolytic resistant and is considered to be the most immunodominant peptide within gluten in celiac disease (CD). GIP were detectable and quantifiable in very different kind of difficult to analyze food, revealing the potential immunogenicity by detecting T-cell activity of celiac patients. But GIP were also found in stool and urine of celiac patients on a supposedly gluten-free diet (GFD), showing the capacity to resist and be absorbed and excreted from the body, providing the first simple and objective means to assess adherence to the GFD. Methods to specifically and sensitively detect the most active GIP in food and biological fluids are rational candidates may use similar analytical standard references for determination of the immunopathological risk of gluten exposure in gluten-related diseases.

Liquid Chromatography-Mass Spectrometry Analysis Reveals Hydrolyzed Gluten in Beers Crafted To Remove Gluten

During brewing, gluten proteins may be solubilized, modified, complexed, hydrolyzed, and/or precipitate. Gluten fragments that persist in conventional beers render them unsuitable for people with celiac disease (CD) or gluten intolerance. Barley-based beers crafted to remove gluten using proprietary precipitation and/or application of enzymes, e.g. prolyl endopeptidases (PEP) that degrade the proline-rich gluten molecules, are available commercially. Gluten measurement in fermented products remains controversial. The industry standard, a competitive ELISA, may indicate gluten values <20 mg/kg, which is deemed safe for people with CD. However, in this study, liquid chromatography-mass spectrometry analyses revealed gluten peptides derived from hydrolyzed fragments, many >30 kDa in size. Barley gluten (hordeins) were detected in all beers analyzed with peptides representing all hordein classes detected in conventional beers but also, alarmingly, in many gluten-reduced beers. It is evident that PEP digestion was incomplete in several commercial beers, and peptides comprising missed cleavages were identified, warranting further optimization of PEP application in an industrial setting.

A multiplex competitive ELISA for the detection and characterization of gluten in fermented-hydrolyzed foods

A novel competitive ELISA was developed utilizing the G12, R5, 2D4, MIoBS, and Skerritt antibody-HRP conjugates employed in nine commercial ELISA test kits that are routinely used for gluten detection. This novel multiplex competitive ELISA simultaneously measures gliadin-, deamidated gliadin-, and glutenin-specific epitopes. The assay was used to evaluate 20 wheat beers, 20 barley beers, 6 barley beers processed to reduce gluten, 15 soy sauces, 6 teriyaki sauces, 6 Worcestershire sauces, 6 vinegars, and 8 sourdough breads. For wheat beers, the apparent gluten concentration values obtained by the G12 and Skerritt antibodies were typically higher than those obtained using the R5 antibodies. The sourdough bread samples resulted in higher apparent gluten concentration values with the Skerritt antibody, while the values generated by the G12 and R5 antibodies were comparable. Although the soy-based sauces showed non-specific inhibition with the multiple R5 and G12 antibodies, their overall profile was distinguishable from the other categories of fermented foods. Cluster analysis of the apparent gluten concentration values obtained by the multiplex competitive ELISA, as well as the relative response of the nine gluten-specific antibodies used in the assay to different gluten proteins/peptides, distinguishes among the different categories of fermented-hydrolyzed foods by recognizing the differences in the protein/peptide profiles characteristic of each product. This novel gluten-based multiplex competitive ELISA provides insight into the extent of proteolysis resulting from various fermentation processes, which is essential for accurate gluten quantification in fermented-hydrolyzed foods. Graphical abstract A novel multiplex competitive ELISA for the detection and characterization of gluten in fermented-hydrolyzed foods.

Effects of moderate beer consumption on health and disease: A consensus document

A large evidence-based review on the effects of a moderate consumption of beer on human health has been conducted by an international panel of experts who reached a full consensus on the present document. Low-moderate (up to 1 drink per day in women, up to 2 in men), non-bingeing beer consumption, reduces the risk of cardiovascular disease. This effect is similar to that of wine, at comparable alcohol amounts. Epidemiological studies suggest that moderate consumption of either beer or wine may confer greater cardiovascular protection than spirits. Although specific data on beer are not conclusive, observational studies seem to indicate that low-moderate alcohol consumption is associated with a reduced risk of developing neurodegenerative disease. There is no evidence that beer drinking is different from other types of alcoholic beverages in respect to risk for some cancers. Evidence consistently suggests a J-shaped relationship between alcohol consumption (including beer) and all-cause mortality, with lower risk for moderate alcohol consumers than for abstainers or heavy drinkers. Unless they are at high risk for alcohol-related cancers or alcohol dependency, there is no reason to discourage healthy adults who are already regular light-moderate beer consumers from continuing. Consumption of beer, at any dosage, is not recommended for children, adolescents, pregnant women, individuals at risk to develop alcoholism, those with cardiomyopathy, cardiac arrhythmias, depression, liver and pancreatic diseases, or anyone engaged in actions that require concentration, skill or coordination. In conclusion, although heavy and excessive beer consumption exerts deleterious effects on the human body, with increased disease risks on many organs and is associated to significant social problems such as addiction, accidents, violence and crime, data reported in this document show evidence for no harm of moderate beer consumption for major chronic conditions and some benefit against cardiovascular disease.

Effects of a Proline Endopeptidase on the Detection and Quantitation of Gluten by Antibody-Based Methods during the Fermentation of a Model Sorghum Beer

The effectiveness of a proline endopeptidase (PEP) in hydrolyzing gluten and its putative immunopathogenic sequences was examined using antibody-based methods and mass spectrometry (MS). Based on the results of the antibody-based methods, fermentation of wheat gluten containing sorghum beer resulted in a reduction in the detectable gluten concentration. The addition of PEP further reduced the gluten concentration. Only one sandwich ELISA was able to detect the apparent low levels of gluten present in the beers. A competitive ELISA using a pepsin-trypsin hydrolysate calibrant was unreliable because the peptide profiles of the beers were inconsistent with that of the hydrolysate calibrant. Analysis by MS indicated that PEP enhanced the loss of a fragment of an immunopathogenic 33-mer peptide in the beer. However, Western blot results indicated partial resistance of the high molecular weight (HMW) glutenins to the action of PEP, questioning the ability of PEP in digesting all immunopathogenic sequences present in gluten.

Detection and Quantification of Gluten during the Brewing and Fermentation of Beer Using Antibody-Based Technologies

In 2013 the U.S. Food and Drug Administration (FDA) defined the term ''gluten-free'' and identified a gap in the analytical methodology for detection and quantification of gluten in foods subjected to fermentation and hydrolysis. To ascertain the ability of current enzyme-linked immunosorbent assays (ELISAs) to detect and quantify gluten in fermented and hydrolyzed products, sorghum beer was spiked in the initial phases of production with 0, 20, and 200 μg/ml wheat gluten, and samples were collected throughout the beer production process. The samples were analyzed using five sandwich ELISAs and two competitive ELISAs and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis with Western analysis employing four antibodies (MIoBS, R5, G12, and Skerritt). The sensitivity of the MIoBS ELISA (0.25 ppm) enabled the reliable detection of gluten throughout the manufacturing process, including fermentation, when the initial concentration of 20 μg/ml dropped to 2 μg/ml. The R5 antibody-based and G12 antibody-based sandwich ELISAs were unable to reliably detect gluten, initially at 20 μg/ml, after the onset of production. The Skerritt antibody-based sandwich ELISA overestimated the gluten concentration in all samples. The R5 antibody-based and G12 antibody-based competitive ELISAs were less sensitive than the sandwich ELISAs and did not provide accurate results for quantifying gluten concentration. The Western analyses were able to detect gluten at less than 5 μg/ml in the samples and confirmed the results of the ELISAs. Although further research is necessary before all problems associated with detection and quantification of hydrolyzed and fermented gluten are resolved, the analytical methods recommended by the FDA for regulatory samples can detect ≥ 20 μg/ml gluten that has undergone brewing and fermentation processes associated with the manufacture of beer.

Portable gliadin-immunochip for contamination control on the food production chain

Celiac disease (CD) is one of the most common digestive disorders caused by an abnormal immune reaction to gluten. So far there are no available therapies, the only solution is a strict gluten-free diet, which however could be very challenging as gluten can be hidden in many food products. Furthermore an additional problem is related to cross-contamination of nominal gluten-free foods with gluten-based ones during manufacturing. Here we propose a lab on chip platform as a powerful tool to help food manufacturers to evaluate the real amount of gluten in their products by an accurate in-situ control of the production chain and maybe to specify the real gluten content in packages labeling. Our portable gliadin-immunochips, based on an electrochemical impedance spectroscopy transduction method, were first calibrated and then validated for both liquid and solid food matrixes by analyzing different beers and flours. The high specificity of our assay was also demonstrated by performing control experiments on rice and potatoes flours containing prolamin-like proteins. We achieved limit of quantification of 0.5 ppm for gliadin that is 20 times lower than the worldwide limit established for gluten-free food while the method of analysis is faster and cheaper than currently employed ELISA-based methods. Moreover our results on food samples were validated through a mass spectrometry standard analysis.

The gluten-free diet and its current application in coeliac disease and dermatitis herpetiformis

BACKGROUND

A gluten-free diet (GFD) is currently the only available therapy for coeliac disease (CD).

OBJECTIVES

We aim to review the literature on the GFD, the gluten content in naturally gluten-free (GF) and commercially available GF food, standards and legislation concerning the gluten content of foods, and the vitamins and mineral content of a GFD.

METHODS

We carried out a PubMed search for the following terms: Gluten, GFD and food, education, vitamins, minerals, calcium, Codex wheat starch and oats. Relevant papers were reviewed and for each topic a consensus among the authors was obtained.

CONCLUSION

Patients with CD should avoid gluten and maintain a balanced diet to ensure an adequate intake of nutrients, vitamins, fibre and calcium. A GFD improves symptoms in most patients with CD. The practicalities of this however, are difficult, as (i) many processed foods are contaminated with gluten, (ii) staple GF foods are not widely available, and (iii) the GF substitutes are often expensive. Furthermore, (iv) the restrictions of the diet may adversely affect social interactions and quality of life. The inclusion of oats and wheat starch in the diet remains controversial.

Immunological characterization of the gluten fractions and their hydrolysates from wheat, rye and barley

Gluten proteins in wheat, rye and barley cause celiac disease, an autoimmune disorder of the small intestine, which affects approximately 1% of the world population. Gluten is comprised of prolamin and glutelin. Since avoidance of dietary gluten is the only option for celiac patients, a sensitive gluten detection and quantitation method is warranted. Most regulatory agencies have set a threshold of 20 ppm gluten in foods labeled gluten-free, based on the currently available ELISA methods. However, these methods may exhibit differences in gluten quantitation from different gluten-containing grains. In this study, prolamin and glutelin fractions were isolated from wheat, rye, barley, oats and corn. Intact and pepsin-trypsin (PT)-digested prolamin and glutelin fractions were used to assess their immunoreactivity and gluten recovery by three sandwich and two competitive ELISA kits. The Western blots revealed varied affinity of ELISA antibodies to gluten-containing grain proteins and no reactivity to oat and corn proteins. ELISA results showed considerable variation in gluten recoveries from both intact and PT-digested gluten fractions among different kits. Prolamin fractions showed higher gluten recovery compared to their respective glutelin fractions. Among prolamins, barley exhibited higher recovery compared to wheat and rye with most of the ELISA kits used. Hydrolysis resulted in reduced gluten recovery of most gluten fractions. These results suggest that the suitability of ELISA for accurate gluten quantitation is dependent upon various factors, such as grain source, antibody specificity, gluten proteins and the level of their hydrolysis in foods.

Accuracy of ELISA detection methods for gluten and reference materials: a realistic assessment

The determination of prolamins by ELISA and subsequent conversion of the resulting concentration to gluten content in food appears to be a comparatively simple and straightforward process with which many laboratories have years-long experience. At the end of the process, a value of gluten, expressed in mg/kg or ppm, is obtained. This value often is the basis for the decision if a product can be labeled gluten-free or not. On the basis of currently available scientific information, the accuracy of the obtained values with commonly used commercial ELISA kits has to be questioned. Although recently several multilaboratory studies have been conducted in an attempt to emphasize and ensure the accuracy of the results, data suggest that it was the precision of these assays, not the accuracy, that was confirmed because some of the underlying assumptions for calculating the gluten content lack scientific data support as well as appropriate reference materials for comparison. This paper discusses the issues of gluten determination and quantification with respect to antibody specificity, extraction procedures, reference materials, and their commutability.

Immunological determination of gliadin 33-mer equivalent peptides in beers as a specific and practical analytical method to assess safety for celiac patients

BACKGROUND

Cereals used for beer manufacturing contain gluten, which is immunotoxic for celiac patients. The gluten remaining after processes of malting and brewing is mostly hydrolyzed, which makes practical evaluation of the immunotoxicity of the gluten pools challenging.

RESULTS

We analyzed the presence of gluten peptides equivalent to the major immunotoxic protease-resistant gliadin 33-mer in 100 Belgium beers, using monoclonal antibodies (G12/A1). Immunochromatographic strips and enzyme-linked immonosorbent assay G12/A1 methods estimated at least 20 ppm gluten equivalents in 90 beers and gluten-free in 10 beers. The G12/A1 reactivity of beer high-performance liquid chromatographic fractions correlated to the presence of T-cell-reactive epitopes identified by peptide sequencing.

CONCLUSION

The determination of equivalent gliadin 33-mer epitopes in beers has been shown to be practical, specific, and sensitive for the measurement of potential immunotoxicity for celiac patients.

Quantification of Hordeins by ELISA: the correct standard makes a magnitude of difference

BACKGROUND

Coeliacs require a life-long gluten-free diet supported by accurate measurement of gluten (hordein) in gluten-free food. The gluten-free food industry, with a value in excess of $6 billion in 2011, currently depends on two ELISA protocols calibrated against standards that may not be representative of the sample being assayed.

AIM

The factors affecting the accuracy of ELISA analysis of hordeins in beer were examined.

RESULTS

A simple alcohol-dithiothreitol extraction protocol successfully extracts the majority of hordeins from barley flour and malt. Primary hordein standards were purified by FPLC. ELISA detected different classes of purified hordeins with vastly different sensitivity. The dissociation constant (Kd) for a given ELISA reaction with different hordeins varied by three orders of magnitude. The Kd of the same hordein determined by ELISA using different antibodies varied by up to two orders of magnitude. The choice of either ELISA kit or hordein standard may bias the results and confound interpretation.

CONCLUSIONS

Accurate determination of hordein requires that the hordein standard used to calibrate the ELISA reaction be identical in composition to the hordeins present in the test substance. In practice it is not feasible to isolate a representative hordein standard from each test food. We suggest that mass spectrometry is more reliable than ELISA, as ELISA enumerates only the concentration of particular amino-acid epitopes which may vary between different hordeins and may not be related to the absolute hordein concentration. MS quantification is undertaken using peptides that are specific and unique enabling the quantification of individual hordein isoforms.

Measuring hordein (gluten) in beer--a comparison of ELISA and mass spectrometry

BACKGROUND

Subjects suffering from coeliac disease, gluten allergy/intolerance must adopt a lifelong avoidance of gluten. Beer contains trace levels of hordeins (gluten) which are too high to be safely consumed by most coeliacs. Accurate measurement of trace hordeins by ELISA is problematic.

METHODS

We have compared hordein levels in sixty beers, by sandwich ELISA, with the level determined using multiple reaction monitoring mass spectrometry (MRM-MS).

RESULTS

Hordein levels measured by ELISA varied by four orders of magnitude, from zero (for known gluten-free beers) to 47,000 µg/mL (ppm; for a wheat-based beer). Half the commercial gluten-free beers were free of hordein by MS and ELISA. Two gluten-free and two low-gluten beers had zero ELISA readings, but contained significant hordein levels (p<0.05), or near average (60-140%) hordein levels, by MS, respectively. Six beers gave false negatives, with zero ELISA readings but near average hordein content by MS. Approximately 20% of commercial beers had ELISA readings less than 1 ppm, but a near average hordein content by MS. Several barley beers also contained undeclared wheat proteins.

CONCLUSIONS

ELISA results did not correlate with the relative content of hordein peptides determined by MS, with all barley based beers containing hordein. We suggest that mass spectrometry is more reliable than ELISA, as ELISA enumerates only the concentration of particular amino-acid epitopes; this may vary between different hordeins and may not be related to the absolute hordein concentration. MS quantification is undertaken using peptides that are specific and unique, enabling the quantification of individual hordein isoforms. This outlines the problem of relying solely on ELISA determination of gluten in beverages such as beer and highlights the need for the development of new sensitive and selective quantitative assay such as MS.

Significant differences in coeliac immunotoxicity of barley varieties

SCOPE

The only treatment available for coeliac disease (CD) is a strict diet in which the intake of wheat, barley, rye, or oats is avoided. Barley is a major cereal crop, grown mainly for its use in brewing, and it has high nutritional value. The identification of varieties with a reduced toxicity profile may contribute to improve the diet, the quality of life and health of CD patients.

METHODS AND RESULTS

Searching for harmless barleys, we investigated accessions of malting and wild barley, used for developing new cultivated cereals. The CD toxicity profile of barleys was screened using G12 antibody and cell proliferation and IFN-γ release from peripheral blood mononuclear cells and intestinal biopsies from CD patients. We found a direct correlation between the reactivity with G12 and the immunogenicity of the different barleys.

CONCLUSION

The malting barleys were less immunogenic, with reduced levels of toxic gluten, and were possibly less harmful to CD patients. Our findings could raise the prospect of breeding barley species with low levels of harmful gluten, and the attractive goal of developing nontoxic barley cultivars, always taking into account the Codex standard for foods for special dietary use for persons intolerant to gluten.

Shotgun proteome analysis of beer and the immunogenic potential of beer polypeptides

The majority of beer proteins originate from barley (Hordeum vulgare) which is used for brewing. Barley is known to contain celiacogenic gliadin-like prolamins (hordeins) along with other immunogenic proteins which endure malt proteases and the harsh conditions of brewing. In addition, a multitude of peptides that may retain or even amplify the immune-stimulating potential is released in beer because of proteolysis. The comprehensive annotation of the beer proteome is challenged both by the high concentration range of the protein entities and by a severe degree of processing-induced modifications. Overcoming the pitfalls of the classical two-dimensional electrophoresis approach coupled to mass spectrometry (MS), the gel-free shotgun proteomic analysis expanded the current inventory of a popular Italian beer to 33 gene products, including traces of intact B- and D-hordeins and 10 proteins from Saccharomyces spp. The high performance liquid chromatography-electrospray MS/MS peptidomic analysis of the low-molecular weight beer components disclosed a panel of hordein-derived peptides that encrypt gluten-like sequence motifs, potentially harmful to celiacs. The presence of antigliadin IgA-immunoresponsive prolamins was assayed by Western and dot blot using sera of N=4 celiac patients. Gliadin-reactive T-cell lines isolated from the intestine of N=5 celiacs activated an IFN-γ response when challenged with deamidated beer polypeptides.

Celiac disease, gluten-free diet, and oats

Oats in a gluten-free diet increase the diet's nutritional value, but their use remains controversial. Contamination with prolamins of other cereals is frequent, and some clinical and experimental studies support the view that a subgroup of celiac patients may be intolerant to pure oats. Thus, this issue is more complex than previously suggested. In order to produce oats that are safe for all celiac patients, the following topics should be addressed: selection of oat cultivars with low avenin content, research on such recombinant varieties of oats, development of assay methods to detect avenins in oat products, guidelines for the agricultural processing of oats and the manufacture of oat products, as well as guidelines for following up with celiac patients who consume oats.