Viscoelastic properties of wheat gliadin and glutenin suspensions

Linear and non-linear rheological properties of wheat gliadin and glutenin suspensions were investigated at various concentrations. Linear dynamic viscoelastic properties for both gliadin and glutenin were strongly dependent on concentration. For gliadins, the storage moduli (G′), loss moduli (G″), and phase shifts dramatically changed within a narrow concentration range, indicating that gliadin suspension properties changed from viscous to viscoelastic. Glutenins exhibited viscoelastic solid behaviour at all measured concentrations. The non-linear shear viscoelastic properties of gliadin and glutenin also depended on concentration. Viscosities of gliadins displayed shear-thinning behaviour; viscosities for glutenins showed shear-thickening behaviour at low shear rates, and shear-thinning behaviour at higher shear rates. Our results indicate that gliadin’s structure in suspension changes over a small concentration range, and suggest that gliadin is important in adjusting and controlling gluten’s viscoelastic behaviour, and not only as a diluent of gluten’s functional properties.     

Phenolic profiles and antioxidant activities of commercial beers

The phenolic profiles and corresponding antioxidant activities of 34 commercial beers in Chinese markets were evaluated. Results found remarkable variations in total and individual phenolic contents as well as antioxidant activity across beer brands. Gallic and ferulic acids were the dominant phenolic compounds identified in the tested beer samples and both of them accounted for >50% of the total phenolic compounds. Results from Pearson correlation analysis suggested that five antioxidant activity assays positively correlated well (p < 0.01) with each other and showed significant positive correlations (p < 0.05) with (+)-catechin, protocatechuic, and caffeic acids contents. Stepwise linear regression further demonstrated that different phenolic components responsible for beer antioxidant activity were dependent on the method used, and that ferulic acid, syringic acid, (+)-catechin, caffeic acid, protocatechuic acid and (−)-epicatechin together made 55.0–88.1% of contribution to the antioxidant activity of beer.     

Assay of gliadin by real‐time immunopolymerase chain reaction

Patients with coeliac disease (gluten‐sensitive enteropathy) are intolerant against gliadins from wheat and the respective proteins from related cereals and have to keep a lifelong gluten‐free diet. For control of gliadin in gluten‐free food sensitive assay techniques are necessary. We developed an immunopolymerase chain reaction (iPCR) assay for gliadin. In this technique immunological detection of gliadin by a monoclonal antibody R5 conjugated with an oligonucleotide is amplified by PCR. For quantification, iPCR was performed as real‐time PCR (real‐time iPCR) in one step. By means of real‐time iPCR, the sensitivity of gliadin analysis was increased more than 30‐fold above the level reached by enzyme immunoassay. Real time‐iPCR using R5 directly conjugated with oligonucleotide was clearly more sensitive than real time‐iPCR applying sequentially biotinylated R5, streptavidin, and biotinylated oligonucleotide. With directly conjugated R5 gliadin was detected at a concentration as low as 0.16 ng/mL corresponding to 16 μg gliadin/100 g food or 0.16 ppm (corresponding to 0.25 g of food extracted in 10 mL of solvent and 25‐fold dilution of the extract prior to analysis). This is the first report applying the highly sensitive technique of iPCR for gliadin analysis. Furthermore, this is the first approach to perform real‐time iPCR in one step without changing the reaction vessels after enzyme immunoassay for subsequent PCR analysis thus minimizing risks of contamination and loss of sensitivity.     

The effect of microwave treatment on the immunoreactivity of gliadin and wheat flour

Commercial gliadins and wheat flour were exposed to microwaves at power distribution of 70, 200, and 500 W for different time periods to achieve a level of applied energy doses up to 150 kJ. Ethanolic extracts (40 vol.% ethanol/water) of microwave treated samples were analyzed by ELISA with the use of either monoclonal antibodies against -gliadin or polyclonal anti-gliadin antibodies and by electrophoresis followed by immunoblotting. A significant increase in reactivity, almost 210% over the untreated control sample, was observed for gliadins exposed to the energy dose of 40 kJ. Gliadins treated with higher energy doses showed a drop in an immune response independent of monoclonal or polyclonal antibodies used in ELISA. Gliadin fractions extracted from wheat flour treated with microwaves demonstrated similar immunoreactivity changes vs applied energy, although the maximum of reactivity appeared at 30 kJ. The increase in immune response of microwave irradiated gliadins was also confirmed by immunoblotting assay with the use of sera of patients susceptible to wheat flour allergy. Reversed phase HPLC elution profiles of treated gliadins showed that the content of all gliadin fractions in microwave treated samples decreased with the increase of the dose of applied energy.     

Oxidative modification of a proline-rich gliadin peptide

Prolamins are proline-rich proteins occurring in cereal grains. Prolamins of wheat, barley and rye, or gluten protein, can cause coeliac disease in individuals not tolerating gluten. Degrading harmful prolamins can reduce their toxicity. A model peptide sequenced in α-gliadin, 33-mer (LQLQPFPQPQLPYPQPQLPYPQPQLPYPQPQPF), was chosen for our study. The metal-catalysed oxidation of 33-mer was studied, instead of enzymatic hydrolysis. Peptide 33-mer was treated in several oxidative systems. Iron-catalysed hydrogen peroxide-induced oxidation showed the greatest modification of 33-mer. Carbonyl groups and dityrosine cross-links were readily formed. At best, the immunological activity of 33-mer was reduced to 18% of its initial level after 24 h of oxidation. Oxidative treatment can be further applied for the modification of cereal prolamin proteins, since it appears to be a potential alternative for reduction of coeliac immunological activities in gluten proteins.     

Interference of denaturing and reducing agents on the antigen/antibody interaction. Impact on the performance of quantitative immunoassays in gliadin analysis

Immunoassays are the most commonly used quantitative techniques to determine the gliadin content of food aimed at coeliac patients. Though the minimal amount of gliadins inducing the typical histopathological changes at the intestinal mucosa in coeliacs is still a matter of debate, current research is focussed on the development of methods having higher sensitivities. One of the main drawbacks in gliadin analysis is the low efficiency of the conventional extraction procedure using 60% ethanol. The use of reducing (2-mercaptoethanol) and denaturing (guanidinium chloride) agents has been recommended to improve the extraction efficiency. Owing to the well-known effects of these agents on native conformation of proteins, and their widely reported interference on the antigen/antibody interaction in other systems, we assessed whether gliadin detection by immunoassays is affected by the presence of those agents. Using two ELISA formats with a panel of polyclonal and monoclonal antibodies, we found that recognition by specific antibodies of partially or totally denatured gliadins is severely impaired. The magnitude of the interference depends on the antibodies used and the ELISA format. The impact of such interference was analysed for each step of the immunoassays. 2-mercaptoethanol had a stronger effect than guanidinium chloride, and the antigen became almost undetectable for some assays when both reagents were used in combination. Remarkably, since quantitative results are obtained by comparison with a calibration curve using a native antigen, there is no equivalence between the antigen/antibody interaction occurring in the sample and that in the standard gliadin, leading to underestimation of the actual gliadin content. Therefore, we suggest that not only the effects of reducing and denaturing agents on the antigen during the extraction procedure, but also the effects of residual amounts of these agents on the antigen/antibody interaction should be considered when a quantitative immunoassay is performed. V.V. D is postgraduate fellow of CONICET. C.A.F. and F.G.Ch. are members of the Researcher Career of CONICET. This study was supported by the Grant PICT 9800 from ANPCyT and a Grant from the Comisión Investigaciones Científicas de la Provincia de Buenos Aires.     

Mycotoxins in South African traditionally brewed beers

Traditionally brewed alcoholic beverages are regularly consumed by most ethnic black South Africans. Maize and barley, both of which are used for producing locally brewed alcoholic beer, are frequently contaminated by mycotoxin-producing moulds. The study was undertaken to investigate whether these toxins are present in raw grains and the traditional beers imbibed by the local black African population. It was established that the raw ingredients (sorghum, sorghum malt grains, maize grits), commercially produced traditional beers (Utshwala and Utshwala special) and home-brewed beers (Umqombotha, Isiqatha, Imfulamfula) were contaminated by bacteria and fungi (both yeasts and moulds). The contaminating moulds were isolated and identified. The contaminated samples were analysed for aflatoxins B 1 , B 2 , G 1 and G 2 , zearalenone, citrinin, deoxynivalenol, and ochratoxin A using a multi-mycotoxin thin-layer chromatography screening method and the toxins were quantified by high-performance liquid chromatography. Grain samples were infected by Aspergillus flavus , A. alliaceus , A. clavatus , Penicillium spp., Rhizopus spp. and Mucor spp. Sorghum malt grain samples contained the toxin zearalenone. No mycotoxin-producing fungi were present in the fermented beers but two of six commercial beer samples contained aflatoxins (200 and 400 μgl -1 ) and 45% (13 of 29) of the home-brewed beers had zearalenone (range 2.6-426 μg l -1 ) and/or ochratoxin A (3-2340 μg l -1 ).     

Presence and distribution of arsenical species in beers

The total content of arsenic and of its inorganic (As(III) and As(V)) and organic (monomethylarsonic acid, MMAA, and dimethylarsinic acid, DMAA) species were determined in a set of 21 alcoholic and alcohol-free beer samples using the technique of Hydride Generation Atomic Absorption Spectrometry. For total arsenic analysis, beer samples were dried and then microwave digested with nitric acid in polytetrafluoroethylene containers. For the speciation analysis, beers were previously subjected to ion exchange chromatography to elute the mentioned inorganic and organic arsenical species. Both microwave digestion and chromatographic separation methods were validated from certified reference materials and prepared standard solutions, respectively. The results obtained are presented in terms of the distribution and occurrence of arsenical species in the samples. The As levels of the beer samples were in the range of 1.5-12.4mug/l. The influence of the production process for the alcoholfree beers in the speciation of arsenic is discussed. In alcoholic beers MMAA was the most abundant species, and for non-alcoholic beers inorganic As(III) was similar to the organic species. An estimated intake of total As of 0.47mug/person/day and 11.4mug/person/day was obtained for average consumers and for heavy drinkers, respectively.     

Aluminium content of beers

 The aluminium (Al) concentration in different brands of beers packaged in Al cans and glass bottles was measured at the end of the shelf-life of the beer, by the Zeeman graphite furnace atomic absorption spectrophotometry (ZGFAAS) method. The results show that in all cases a brand of beer packaged in an Al can has a higher Al content than the same brand bottled in glass. The measurements of the Al concentration in some Al-canned beers throughout 12 months of storage show that a relatively small increase of the Al concentration in beers occurs throughout storage. All these results indicate that some Al is taken up by the beer in Al cans, presumably through the slight and slow dissolution of Al from the can wall, due to some defects in the protective lacquer layer. The evaluated daily intake of Al (0.256 mg) possible through the consumption of beer was practically negligible in relation to both the total daily dietary Al intake and the tolerable daily Al intake. Thus, beers are an insignificant source of dietary Al intake and it appears that the Al intake from beers (due to the low content of Al in beers and its low bioavailability) should not be a cause for concern with regard to Al toxicity for the human body. Received: 22 April 1996     

Aluminium content of beers

 The aluminium (Al) concentration in different brands of beers packaged in Al cans and glass bottles was measured at the end of the shelf-life of the beer, by the Zeeman graphite furnace atomic absorption spectrophotometry (ZGFAAS) method. The results show that in all cases a brand of beer packaged in an Al can has a higher Al content than the same brand bottled in glass. The measurements of the Al concentration in some Al-canned beers throughout 12 months of storage show that a relatively small increase of the Al concentration in beers occurs throughout storage. All these results indicate that some Al is taken up by the beer in Al cans, presumably through the slight and slow dissolution of Al from the can wall, due to some defects in the protective lacquer layer. The evaluated daily intake of Al (0.256 mg) possible through the consumption of beer was practically negligible in relation to both the total daily dietary Al intake and the tolerable daily Al intake. Thus, beers are an insignificant source of dietary Al intake and it appears that the Al intake from beers (due to the low content of Al in beers and its low bioavailability) should not be a cause for concern with regard to Al toxicity for the human body. Received: 22 April 1996     

Rheological behavior of heat-induced wheat gliadin gel

Wheat gliadin gel is prepared for the first time through heating alkaline solution of propanol/water (50/50, v/v) at pH = 9.3 and 50 °C. Dynamic rheological tests were performed to characterize the gelation time and the number of elastically effective chains of the gliadin gel. Scanning electron microscope was used to observe the morphology of the freeze-dried gel.     

面筋蛋白与面条品质关系研究

通过分离添加方法研究面筋蛋白、麦谷蛋白、麦醇溶蛋白对面条质构品质影响。结果表明:添加不同量面筋蛋白、麦谷蛋白后,面条硬度、咀嚼性、粘合性增大,而添加麦醇溶蛋白却减小;麦醇溶蛋白赋予面条粘附性;麦谷蛋白能增强熟面条内部强度即耐煮性;面筋蛋白对拉伸特性影响最大。     

Improvement of an emotional lexicon for the evaluation of beers

Emotional response has been the subject of many studies during the last years. Many studies have shown the importance of using consumers to generate emotional lexicons. Chaya et al. (2015) developed a consumer defined (CD) lexicon to assess emotional response elicited by beer products. Shortly after, van Zyl and Meiselman (2015) presented a procedure to ensure that emotional lists were fully composed by emotions. The present research was developed to improve and test the lexicon developed by Chaya et al. (2015) following the approach proposed by van Zyl and Meiselman (2015). The proposed procedure allowed an easy filtering of terms for the study of emotional response. As a consequence, the test was shorter, clearer, and easier to understand and to complete by consumers. The improved emotional lexicon of beer favoured 1) the efficiency of the research in terms of discrimination among samples, 2) the simplicity of use by the consumers.     

Application of a commercial immunoassay to the direct determination of insecticide imidacloprid in fruit juices

An ELISA was used to directly determine residual imidacloprid in fruit juices. Imidacloprid could be determined by only diluting samples without any pre-treatments such as filtration, centrifugation, and clean-up procedures. The ELISA enabled imidacloprid to accurately determine down to about 5 μg/L in apple and grape juice samples and down to about 20 μg/L in orange juice sample. Recovery and precision of the ELISA were evaluated by spiking fruit juice samples with imidacloprid in the 10–400 μg/L ranges. Coefficients of variation were lower than 20% in all cases, and average recoveries were 94.2%, 113.2%, and 104.2% for apple, grape, and orange juice samples, respectively. No false positive results were found. The results obtained with the proposed ELISA well correlated with the reference HPLC for each fruit juice sample (r > 0.99).     

Microstructure of hydrated gluten network

The present work reviews the microstructure of hydrated gluten network and its protein fractions i.e., gliadin and glutenin. We summarize microstructural imaging of the last forty years as observed by various techniques such as atomic force or electron microscopy. Furthermore, rheological and calorimetric modeling that provides additional information on the microstructural features of the network is also discussed. Combining most of the available evidence it is suggested that the building blocks of gluten network are gluten-sheets with embedded aggregates. The sheets are arranged in parallel fashion to give rise to a nanoporous ultrastructure.     

Impact of colour adjustment on flavour stability of pale lager beers with a range of distinct colouring agents

The impact of colour adjustment on the flavour stability of five pale lager beers with a range of colouring agents such as specialty malts, colouring beer and artificial caramel colourant was investigated. The research focused on determination of the endogenous anti-oxidative potential (EAP) of the beer samples using a novel Electron Spin Resonance (ESR) method. The results were correlated with the concentration levels of a portfolio of compounds formed during beer ageing, which were detected and quantified by GC–MS. The beer samples were also assessed by the ICBD sensory panel. Additionally, the quantification of organic radicals of the specialty malts and the roasted barley were conducted by ESR (whole intact kernel and milling fraction measurement). Based on the results of this holistic approach, a colouring agent was identified that enhanced the flavour stability of pale lagers based on the final beer’s physical-, chemical-, and sensory-properties.     

Phenolics and related substances in alcohol-free beers

 The present study examines and compares the phenolic compositions of several commercially available alcohol-free and standard beers. In general, the values for the contents of the phenolic components in the alcohol-free beers are lower than the values for the standard beers; this is attributable to differences in the duration of fermentation and the yeast strains employed in brewing alcohol-free beers (e.g., the case of tyrosol) and to losses brought about by the dealcoholization processes employed (e.g., p-coumaric acid, caffeic acid, vanillic acid, etc.). The values for the other low-molecular-weight compounds considered, such as 5-(hydroxymethyl)furfural and tryptophol, are also lower in the alcohol-free than in the standard beers. Received: 16 July 1999     

Comparative investigations of gluten proteins from different wheat species

The only commercially available immunoassay for gliadin determination in gluten-free food which has been ring-tested and in use for many years, is a test kit based on monoclonal antibodies against -gliadins. Various studies of the literature have shown that different gliadin standards resulted in different calibration curves, and it has been proposed that the affinity of -gliadins to the monoclonal antibodies varied among wheat varieties. To clarify this fundamental problem, total gliadins and the -gliadins from a winter wheat ("Rektor"), a spring wheat ("CWRS"), a wheat rye hybrid ("Herzog") and varieties of spelt, durum wheat, emmer and einkorn, were isolated and analyzed by means of an enzyme-linked immunoabsorbent assay (ELISA) kit based on antibodies against -gliadins. Additionally, single - and -gliadins of Rektor wheat were studied. The results demonstrated that the calibration curves derived for total gliadins differed, in parts, strongly from that of the kit gliadin standard; only the curves for the durum wheat and spelt gliadins were in congruence with the kit gliadin. Single -gliadins revealed strong differences between and within wheat species and ELISA equivalents had a range from 10 to 220% according to kit gliadin. The affinity of -gliadins was not correlated with the calibration curves of total gliadins. Some of the -gliadins of Rektor wheat showed ELISA equivalents similar to those of -gliadins. Because the proportions of -gliadins in total gliadins were significantly higher than those of -gliadins, the unspecific binding of -gliadins contributed much more to the total affinity of gliadins than the specific binding of -gliadins. -Gliadins, however, did not show any detectable affinity.     

Monoclonal antibody R5 for detection of putatively coeliac-toxic gliadin peptides

Monoclonal antibody R5 against rye secalin was recently suggested to be useful in analysis of gluten in food. The epitope specificity of R5 was characterized and compared with those of eight other monoclonal antibodies (mabs) against gliadins (gli) and secalins. Mabs were tested for binding to synthetic peptides spanning in overlapping manner sequences of gli. In a luminescence assay R5 bound to all peptides from the N-terminal part of α-type gli hitherto known to induce in sensitive patients with coeliac disease after in vivo instillation. Thus, R5 proves to be very useful for gluten analysis. Sequences QQPFP, QQQFP, LQPFP, and QLPFP were bound most strongly. Substitution of glutamine by glutamic acid in the epitope may decrease binding of R5 dependent on surrounding amino acids. One of the positions of the substitutions diminishing antibody binding was a typical site of attack of tissue transglutaminase, the enzyme converting by deamidation cereal prolamins into their disease active form. Investigation of eight other mabs against gli and secalins showed binding properties very similar to R5. We speculate the sequence QQQ/PFP seems to represent an immunodominant structure in prolamins. An erratum to this article can be found at