Cereals for developing gluten-free products and analytical tools for gluten detection

Tef: The Rising Ancient Cereal: What do we know about its Nutritional and Health Benefits?

This review covers the nutritional significance of tef cereal as compared to other common cereals with emphasis on carbohydrate content and starch digestibility, protein content, iron and zinc bioavailability and antioxidant potentials. Tef is a gluten free cereal and contains the highest iron and calcium among other cereals. It has high micro- and macro- nutritional profile and is becoming globally popular in the healthy grain food chain. Tef starch has a high gelatinization temperature, an essential precondition in the preparation of low glycemic index foods. There are significantly conflicting reports of iron content of tef ranging from 5 to 150 mg/100 g dm. The traditional fermentation of injera reduced majority of the phytic acid but no significant change to mineral bioavailability was observed. This review indicated that studies on starch digestibility, protein characterization, amylase and protease inhibitors, mineral bioavailability and antioxidant potentials are needed to further explore the nutritional and health benefits of tef.

Current Trends in Ancient Grains-Based Foodstuffs: Insights into Nutritional Aspects and Technological Applications

For centuries, ancient grains fed populations, but due to their low yield, they were abandoned and replaced by high-yielding species. However, currently, there is a renewed interest in ancient wheat and pseudocereal grains from consumers, farmers, and manufacturers. Ancient wheat such as einkorn, emmer, spelt, and Kamut®, are being reintegrated because of their low fertilizer input, high adaptability and important genetic diversity. New trends in pseudocereal products are also emerging, and they are mostly appreciated for their nutritional outcomes, particularly by the gluten-free market. Toward healthier lifestyle, ancient grains-based foodstuffs are a growing business and their industrialization is taking 2 pathways, either as a raw ingredient or a functional ingredient. This paper deals with these grain characteristics by focusing on the compositional profile and the technological potential.

Comparative proteomic analysis of two transgenic low-gliadin wheat lines and non-transgenic wheat control

Gluten proteins are major determinants of the bread making quality of wheat, but also of important wheat-related disorders, including coeliac disease (CD), and allergies. We carried out a proteomic study using the total grain proteins from two low-gliadin wheat lines, obtained by RNAi, and the untransformed wild type as reference. The impact of silencing on both target and on non-target proteins was evaluated. Because of the great protein complexity, we performed separate analyses of four kernel protein fractions: gliadins and glutenin subunits, and metabolic and CM-like proteins, by using a classical 2D electrophoresis gel based approach followed by RP-HPLC/nESI-MS/MS. As a result of the strong down-regulation of gliadins, the HMW-GS, metabolic and chloroform/methanol soluble proteins were over-accumulated in the transgenic lines, especially in the line D793, which showed the highest silencing of gliadins. Basing on these data, and considering that metabolic proteins and chloroform/methanol soluble proteins (CM-like), such as the α-amylase/trypsin inhibitor family, β-amylase and serpins, were related to wheat allergens, further in vivo analysis will be needed, especially those related to clinical trials in controlled patients, to determine if these lines could be used for food preparation for celiac or other gluten intolerant groups.

BIOLOGICAL SIGNIFICANCE

Several enteropathies and allergies are related to wheat proteins. Biotechnological techniques such as genetic transformation and RNA interference have allowed the silencing of gliadin genes, providing lines with very low gliadin content in the grains. We report a proteomic-based approach to characterize two low-gliadin transgenic wheat lines obtained by RNAi technology. These lines harbor the same silencing fragment, but driven by two different endosperm specific promoters (γ-gliadin and D-hordein). The comprehensive proteome analysis of these transgenic lines, by combining two-dimensional electrophoresis and RP-HPLC/nESI-MS/MS, provided a large number of spots differentially expressed between the control and the transgenic lines. Hence, the results of this study will facilitate further safety evaluation of these transgenic lines.

Evaluation of the physicochemical properties of gluten-free pasta enriched with resistant starch

BACKGROUND

The objective was to examine the potential use of resistant starch (RS) as a fibre-enriching ingredient in gluten-free pasta. Pasta was enriched with commercial RS type II (Hi-Maize™ 260) at 100-200 g kg^-1 substitution of rice flour. The effects on the rheological properties of dough and pasta quality as a result of RS addition and the loss in RS due to the process were evaluated.

RESULTS

Dough water absorption was not influenced by the addition of RS. The cooking loss (CL) of RS-enriched samples was 30% lower than reference without fibre. The addition of RS significantly increased firmness of cooked pasta, and above 100 g kg^-1 RS level of substitution samples showed a lower stickiness value. Dynamic rheological tests on pasta dough showed a higher storage modulus for fibre samples, indicating a higher number of elastically physical interactions. Loss in RS in uncooked pasta was about 31% compared with the initial amount added to the product.

CONCLUSIONS

The addition of RS improved the quality of gluten-free pasta owing to its ability to increase the firmness and decrease the CL and stickiness of cooked pasta. The product enriched with 200 g kg^-1 RS can be considered a source of DF. © 2016 Society of Chemical Industry.

Doubled Haploid Transgenic Wheat Lines by Microspore Transformation

Microspores are preferred explant choice for genetic transformation, as their use shortens the duration of obtaining homozygous transformants. All established gene-delivery methods of particle bombardment, electroporation, and cocultivation with Agrobacterium tumefaciens were optimized on androgenic microspores or derived tissues. In the biolistic gene delivery method 35-40 days old haploid microspore embryoids were used for genetic transformation, whereas freshly isolated androgenic microspores were used for genetic transformation in the electroporation and Agrobacterium cocultivation-based methods. The genetic transformation methods of biolistic gene-delivery and electroporation gave rise to the chimeric plants, whereas the method involving cocultivation with Agrobacterium yielded homozygous transformants. These methods were tested on a large number of cultivars belonging to different market classes of wheat, and found to be fairly independent of the explant genotype. Other benefits of using microspores or derived tissues for transformation are: (1) a few explant donors are required to obtain desired transformants and (2) the time required for obtaining homozygous transformants is about 8 months in case of spring wheat genotypes and about a year in case of winter wheat genotypes.

Novel approaches for enzymatic gluten degradation to create high-quality gluten-free products

Celiac disease (CD), a chronic enteropathy of the small intestine caused by ingestion of gluten, is one of the most prevalent food hypersensitivities worldwide. The essential treatment is a strict lifelong gluten-free diet based on the avoidance of gluten-containing products from wheat, rye, barley and, in rare cases, oats. Products made from naturally gluten-free raw materials often have inferior nutritional, textural and sensory properties compared to the corresponding gluten-containing products. Therefore, the incorporation of wheat, rye and barley flours after efficient removal of the harmful component gluten into gluten-free products would be beneficial. Gluten modification resulting in decreased CD-immunoreactivity may be achieved via the formation of crosslinks using microbial transglutaminase. To effectively eliminate CD-immunoreactivity, plant, fungal, bacterial, animal or engineered peptidases are capable of degrading gluten proteins and peptides into harmless fragments. The application of peptidases from germinated cereal grains, fungal peptidases and/or lactic acid bacteria during food processing yielded high-quality sourdough wheat breads, pasta, wheat starch and bran, rye products and beer, all with gluten contents below the Codex Alimentarius threshold of 20mg/kg for gluten-free products. As with all gluten-free products, the legislative compliance of such treated materials needs to be monitored closely. Provided that all safety requirements are met, gluten-containing raw materials treated in an adequate way to remove CD-active gluten fragments may be used together with naturally gluten-free ingredients to create an extended choice of high-quality gluten-free products.

Incorporation of carrot pomace powder in wheat flour: effect on flour, dough and cookie characteristics

Carrot pomace powder (CPP) of 72 and 120 mesh sizes was incorporated in wheat flour at 10, 15 and 20 % level and its impact on flour, dough and cookie characteristics was evaluated. Protein content of the flour blends (8.84-7.88 %) decreased and fibre content (4.63-6.68 %) increased upon blending of CPP in wheat flour. Wheat flour containing 120 mesh CPP showed better functional properties [water absorption (1.16-1.47 %), oil absorption (1.11-1.39 %), solubility index (41-50 %) and swelling power (1.34-1.39)] than those containing 72 mesh. Water solvent retention capacity and sucrose solvent retention capacity increased while lactic acid solvent retention capacity and sodium carbonate solvent retention capacity decreased with blending of CPP. Water absorption, dough development time and degree of softening increased whereas, dough stability and mixing tolerance decreased with increasing CPP. The highest decrease in pasting was observed flour containing 72 mesh CPP. Rheology of dough containing 120 mesh CPP closely resembled the control. Color of flour and cookies increased with blending of CPP irrespective of mesh size. Antioxidant activity of cookies was higher than the flour blends. The cookies containing CPP of 72 mesh showed the lowest hardness. However, cookies containing CPP of 120 mesh showed the best sensory properties. Incorporation of 120 mesh CPP produced low gluten cookies with manageable flour and dough characteristics and better antioxidant and sensory properties.

Rapid Detection of Food Allergens by Microfluidics ELISA-Based Optical Sensor

The risks associated with the presence of hidden allergens in food have increased the need for rapid, sensitive, and reliable methods for tracing food allergens in commodities. Conventional enzyme immunosorbent assay (ELISA) has usually been performed in a centralized lab, requiring considerable time and sample/reagent consumption and expensive detection instruments. In this study, a microfluidic ELISA platform combined with a custom-designed optical sensor was developed for the quantitative analysis of the proteins wheat gluten and Ara h 1. The developed microfluidic ELISA biosensor reduced the total assay time from hours (up to 3.5 h) to 15-20 min and decreased sample/reagent consumption to 5-10 μL, compared to a few hundred microliters in commercial ELISA kits, with superior sensitivity. The quantitative capability of the presented biosensor is a distinctive advantage over the commercially available rapid methods such as lateral flow devices (LFD) and dipstick tests. The developed microfluidic biosensor demonstrates the potential for sensitive and less-expensive on-site determination for rapidly detecting food allergens in a complex sample system.

Targeting of prolamins by RNAi in bread wheat: effectiveness of seven silencing-fragment combinations for obtaining lines devoid of coeliac disease epitopes from highly immunogenic gliadins

Gluten proteins are responsible for the viscoelastic properties of wheat flour but also for triggering pathologies in susceptible individuals, of which coeliac disease (CD) and noncoeliac gluten sensitivity may affect up to 8% of the population. The only effective treatment for affected persons is a strict gluten-free diet. Here, we report the effectiveness of seven plasmid combinations, encompassing RNAi fragments from α-, γ-, ω-gliadins, and LMW glutenin subunits, for silencing the expression of different prolamin fractions. Silencing patterns of transgenic lines were analysed by gel electrophoresis, RP-HPLC and mass spectrometry (LC-MS/MS), whereas gluten immunogenicity was assayed by an anti-gliadin 33-mer monoclonal antibody (moAb). Plasmid combinations 1 and 2 downregulated only γ- and α-gliadins, respectively. Four plasmid combinations were highly effective in the silencing of ω-gliadins and γ-gliadins, and three of these also silenced α-gliadins. HMW glutenins were upregulated in all but one plasmid combination, while LMW glutenins were downregulated in three plasmid combinations. Total protein and starch contents were unaffected regardless of the plasmid combination used. Six plasmid combinations provided strong reduction in the gluten content as measured by moAb and for two combinations, this reduction was higher than 90% in comparison with the wild type. CD epitope analysis in peptides identified in LC-MS/MS showed that lines from three plasmid combinations were totally devoid of CD epitopes from the highly immunogenic α- and ω-gliadins. Our findings raise the prospect of breeding wheat species with low levels of harmful gluten, and of achieving the important goal of developing nontoxic wheat cultivars.

Selective capture of most celiac immunogenic peptides from hydrolyzed gluten proteins

The available immunomethods for gluten quantitation could underestimate or overestimate the net immunoactivity of foods and beverages if the chosen analytical antibody is not specific to the relevant gluten immunogenic peptides (GIP). Accurate detection of the most active GIP is desirable to assess the potential celiac toxicity of food. We evaluated the capacity of the G12 monoclonal antibody for selectively depleting GIP in samples from two different gluteomes. Samples of hydrolyzed gliadin from wheat and a barley beer were used. The input (starting peptide digest of prolamins), the flow-through (unbound peptides), and the output (captured peptides) were analyzed by G12 and R5 competitive ELISA as well as by stimulation assays of T-cells from celiac patients. Most of the GIP were retained by the G12-agarose and represented the largest part of the immunogenicity of the gluten peptidome. G12 immunodepletion experiments with hydrolyzed gluten showed that this antibody reacted with those with the highest immunoactivity for celiac patients.

Improving wheat to remove coeliac epitopes but retain functionality

Coeliac disease is an intolerance triggered by the ingestion of wheat gluten proteins. It is of increasing concern to consumers and health professionals as its incidence appears to be increasing. The amino acid sequences in gluten proteins that are responsible for triggering responses in sensitive individuals have been identified showing that they vary in distribution among and between different groups of gluten proteins. Conventional breeding may therefore be used to select for gluten protein fractions with lower contents of coeliac epitopes. Molecular breeding approaches can also be used to specifically down-regulate coeliac-toxic proteins or mutate coeliac epitopes within individual proteins. A combination of these approaches may therefore be used to develop a “coeliac-safe” wheat. However, this remains a formidable challenge due to the complex multigenic control of gluten protein composition. Furthermore, any modified wheats must retain acceptable properties for making bread and other processed foods. Not surprisingly, such coeliac-safe wheats have not yet been developed despite over a decade of research.

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Coeliac disease is of increasing concern as its incidence appears to be increasing.

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Over 30 amino acid sequences (coeliac epitopes) have been defined.

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Coeliac epitopes differ in their distribution between wheat gluten proteins.

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Transgenesis can be used to reduce coeliac-toxic proteins and coeliac epitopes.

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This can be exploited to develop “coeliac-safe” wheats.

Multiplex liquid chromatography-tandem mass spectrometry for the detection of wheat, oat, barley and rye prolamins towards the assessment of gluten-free product safety

Celiac patients should feel confident in the safety of foods labelled or expected to be gluten-free. In this context, a targeted proteomic approach based on liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) technique was proposed to assess the presence of celiotoxic cereals, namely wheat, oats, barley and rye, in raw and processed food products. To this aim, unique marker peptides were properly selected in order to distinguish between the different cereal types. A revised cocktail solution based on reducing and denaturing agents was exploited for prolamin extraction from raw and processed food; in addition, defatting with hexane was carried out for sample clean-up, allowing to largely reduce problems related to matrix effect. Method validation on fortified rice flour showed good analytical performance in terms of sensitivity (limits of detection in the 2-18 mg kg(-1) range). However, poor trueness was calculated for self-made incurred bread (between 3 and 30% depending on the peptide), probably due to baking processes, which reduce gluten extractability. Thus, it is evident that in the case of processed foods further insights into sample treatment efficiency and reference materials for protein calibration are required to obtain accurate gluten determination. Finally, the developed method was applied for the analysis of market food products, offering the possibility to discriminate among cereals, with good agreement with labelled ingredients for gluten-containing foodstuffs.

Structure and quality of pasta enriched with functional ingredients

In this article we review current knowledge on the fate of those functional components that have been more widely studied, how they may interact during pasta processing and what impact they may have on quality pasta attributes.

Control of β-carotene bioaccessibility using starch-based filled hydrogels

β-Carotene was incorporated into three types of delivery system: (i) "emulsions": protein-coated fat droplets dispersed in water; (ii) "hydrogels": rice starch gels; and (iii) "filled hydrogels": protein-coated fat droplets dispersed in rice starch gels. Fat droplets in filled hydrogels were stable in simulated mouth and stomach conditions, but aggregated under small intestinal conditions. Fat droplets in emulsions aggregated under oral, gastric, and intestinal conditions. β-Carotene bioaccessibility was higher when encapsulated in filled hydrogels than in emulsions or hydrogels, which was attributed to increased aggregation stability of the fat droplets leading to a larger exposed lipid surface area. β-Carotene bioaccessibility in starch hydrogels containing no fat was very low (≈1%) due to its crystalline nature and lack of mixed micelles to solubilise it. The information presented may be useful for the design of rice-starch based gel products fortified with lipophilic nutraceuticals.