Interaction between gliadins and anthocyan derivatives

The Role of Gluten in Food Products and Dietary Restriction: Exploring the Potential for Restoring Immune Tolerance

Wheat is extensively utilized in various processed foods due to unique proteins forming from the gluten network. The gluten network in food undergoes morphological and molecular structural changes during food processing, affecting the final quality and digestibility of the food. The present review introduces the formation of the gluten network and the role of gluten in the key steps of the production of several typical food products such as bread, pasta, and beer. Also, it summarizes the factors that affect the digestibility of gluten, considering that different processing conditions probably affect its structure and properties, contributing to an in-depth understanding of the digestion of gluten by the human body under various circumstances. Nevertheless, consumption of gluten protein may lead to the development of celiac disease (CD). The best way is theoretically proposed to prevent and treat CD by the inducement of oral tolerance, an immune non-response system formed by the interaction of oral food antigens with the intestinal immune system. This review proposes the restoration of oral tolerance in CD patients through adjunctive dietary therapy via gluten-encapsulated/modified dietary polyphenols. It will reduce the dietary restriction of gluten and help patients achieve a comprehensive dietary intake by better understanding the interactions between gluten and food-derived active products like polyphenols.

Effectiveness of Anthocyanin-Rich Sour Cherry Extract on Gliadin-Induced Caco-2 Barrier Damage

Several types of gluten-related disorders are known, in which the common starting point is gluten-induced zonulin release. Zonulin results in varying degrees of increased permeability in certain gluten-related disorders but is largely responsible for the development of further pathogenic processes and symptoms. Therefore, it is important to know the barrier-modulating role of individual nutritional components and to what extent the antioxidant substance supports the protection of gliadin-induced membrane damage with its radical scavenging capacity. We investigated the pH dependence of the gliadin-anthocyanin interaction using UV photometry, during which a concentration-dependent interaction was observed at pH 6.8. The barrier modulatory effect of the anthocyanin-rich sour cherry extract (AC) was analyzed on Caco-2 cell culture with pepsin-trypsin-resistant gliadin (PT-gliadin) exposure by TEER measurement, zonula occludens-1 (ZO-1), and Occludin immunohistochemistry. In addition to the TEER-reducing and TJ-rearranging effects of PT-gliadin, NF-κB activation, an increase in cytokine (TNF-α, IFN-γ, and IL-8) release, and mitochondrial ROS levels were observed. We confirmed the anti-inflammatory, stabilizing, and restoring roles of AC extract during gliadin treatment on the Caco-2 monolayer. The extract was able to significantly reduce cytokine and ROS levels despite the known interaction of the main components of the extract with PT-gliadin.

Advances in dietary proteins binding with co-existed anthocyanins in foods: Driving forces, structure-affinity relationship, and functional and nutritional properties

Anthocyanins, which are the labile flavonoid pigments widely distributed in many fruits, vegetables, cereal grains, and flowers, are receiving intensive interest for their potential health benefits. Proteins are important food components from abundant sources and present high binding affinity for small dietary compounds, e.g., anthocyanins. Protein-anthocyanin interactions might occur during food processing, ingestion, digestion, and bioutilization, leading to significant changes in the structure and properties of proteins and anthocyanins. Current knowledge of protein-anthocyanin interactions and their contributions to functions and bioactivities of anthocyanin-containing foods were reviewed. Binding characterization of dietary protein-anthocyanins complexes is outlined. Advances in understanding the structure-affinity relationship of dietary protein-anthocyanin interaction are critically discussed. The associated properties of protein-anthocyanin complexes are considered in an evaluation of functional and nutritional values.

How Do Phenolic Acids Change the Secondary and Tertiary Structure of Gliadin? Studies with an Application of Spectroscopic Techniques

The effect of the chemical structure of selected phenolic acids on the molecular organization of gliadins was investigated with the application of Fourier Transform Infrared (FTIR) technique, steady-state, and time-resolved fluorescence spectroscopy. Hydroxybenzoic (4-hydroxybenzoic, protocatechuic, vanillic, and syringic) and hydroxycinnamic (coumaric, caffeic, ferulic, sinapic) acids have been used as gliadins modifiers. The results indicated that hydroxybenzoic acids due to their smaller size incorporate into spaces between two polypeptide chains and form a hydrogen bond with them leading to aggregation. Additionally, syringic acids could incorporate into hydrophobic pockets of protein. Whereas hydroxycinnamic acids, due to their higher stiffness and larger size, separated polypeptide chains leading to gliadin disaggregation. These acids did not incorporate into hydrophobic pockets.

Effects of Physical and Chemical Factors on the Structure of Gluten, Gliadins and Glutenins as Studied with Spectroscopic Methods

This review presents applications of spectroscopic methods, infrared and Raman spectroscopies in the studies of the structure of gluten network and gluten proteins (gliadins and glutenins). Both methods provide complimentary information on the secondary and tertiary structure of the proteins including analysis of amide I and III bands, conformation of disulphide bridges, behaviour of tyrosine and tryptophan residues, and water populations. Changes in the gluten structure can be studied as an effect of dough mixing in different conditions (e.g., hydration level, temperature), dough freezing and frozen storage as well as addition of different compounds to the dough (e.g., dough improvers, dietary fibre preparations, polysaccharides and polyphenols). Additionally, effect of above mentioned factors can be determined in a common wheat dough, model dough (prepared from reconstituted flour containing only wheat starch and wheat gluten), gluten dough (lack of starch), and in gliadins and glutenins. The samples were studied in the hydrated state, in the form of powder, film or in solution. Analysis of the studies presented in this review indicates that an adequate amount of water is a critical factor affecting gluten structure.

Gliadin Sequestration as a Novel Therapy for Celiac Disease: A Prospective Application for Polyphenols

Celiac disease is an autoimmune disorder characterized by a heightened immune response to gluten proteins in the diet, leading to gastrointestinal symptoms and mucosal damage localized to the small intestine. Despite its prevalence, the only treatment currently available for celiac disease is complete avoidance of gluten proteins in the diet. Ongoing clinical trials have focused on targeting the immune response or gluten proteins through methods such as immunosuppression, enhanced protein degradation and protein sequestration. Recent studies suggest that polyphenols may elicit protective effects within the celiac disease milieu by disrupting the enzymatic hydrolysis of gluten proteins, sequestering gluten proteins from recognition by critical receptors in pathogenesis and exerting anti-inflammatory effects on the system as a whole. This review highlights mechanisms by which polyphenols can protect against celiac disease, takes a critical look at recent works and outlines future applications for this potential treatment method.

Review of Structural Features and Binding Capacity of Polyphenols to Gluten Proteins and Peptides In Vitro: Relevance to Celiac Disease

Polyphenols have been extensively studied due to their beneficial effects on human health, particularly for the prevention and treatment of diseases related to oxidative stress. Nevertheless, they are also known to have an anti-nutritional effect in relation to protein metabolism. This effect is a consequence of its binding to digestive enzymes and/or protein substrates. Dietary gluten is the main trigger of celiac disease, a common immune-based disease of the small intestine and for which the only treatment available is the adherence to a gluten-free diet. Recent studies have addressed the use of dietary polyphenols to interact with gluten proteins and avoid its downstream deleterious effects, taking the advantage of the anti-nutritive nature of polyphenols by protein sequestering. Flavonoids, coumarins and tannins have shown the ability to form insoluble complexes with gluten proteins. One of the most promising molecules has been epigallocatechin-3-gallate, which through its binding to gliadins, was able to reduce gliadins digestibility and its ability to stimulate monolayer permeability and transepithelial transport of immunodominant peptides in cell models. This review focuses on the structural features and binding capacity of polyphenols to gluten proteins and peptides, and the prospects of developing an adjuvant therapy in celiac disease.

Interaction between wheat gliadin and quercetin under different pH conditions analyzed by multi-spectroscopy methods

Polyphenols have been known to have significant binding affinity for proteins, and the specific condition (such as pH) could affect the degree of binding, the formation of covalent bond, and non-covalent interaction. In this study, characteristics of binding quercetin (Q) to wheat gliadin (G) which is a strong food allergen, were studied from pH 2.0 to pH 9.0. The results showed that Q quenched the fluorescence intensity of G by dynamic and static quenching modes and the stoichiometry of binding was close to 1. Intermolecular binding distances were smaller than 8 nm. Thermodynamic parameters suggested that hydrophobic force took charge of the formation of complexes at pH 2.0-4.0, whereas hydrogen bonds and van der Waals forces at pH 5.0-9.0. Analyses of the Fourier transform infrared and the Raman spectra along with synchronous fluorescence spectra revealed secondary and tertiary structural alterations and microenvironmental changed around protein fluorophores upon complexation with Q. The gauche-gauche-trans conformation increased at the expenses of the gauche-gauche-gauche conformation and the transition from β-turn and random coil to α-helix and β-sheet at pH 5.0 might decrease the allergenicity of G. These results provided new insights into G/Q interactions at different pH values, which may have potentials in decreasing allergen immunoreactivity.

Interaction of Protein Isolate with Anthocyanin Extracted from Black Soybean and Its Effect on the Anthocyanin Stability

The interactions between black soybean protein isolate (B-SPI) and cyanidin 3-O-glucoside (C3G), anthocyanin extracted from black soybean coat was investigated under neutral conditions. The fluorescence spectra showed that C3G had fluorescence quenching effects on B-SPI. Thermodynamic parameters showed that ∆G < 0, which demonstrated that the binding was a spontaneous reaction. Since ΔH > 0 and ΔS > 0, the interactions between C3G and B-SPI was mainly hydrophobic interactions. Fourier infrared spectroscopy results suggested that the contents of α-helix and β-sheet structure showed an increasing trend, whereas the β-angle content displayed a decreasing trend. The degradation of C3G followed first-order kinetics at 85 °C and 100 °C. After the interactions with B-SPI, the degradation rate constant was decreased and the half-life of C3G was prolonged from 70.25 ± 0.90 min to 175.64 ± 38.04 min at 85 °C, from 62.68 ± 1.1 min to 72.51 ± 2.5 min at 100 °C (p < 0.05). The results indicated that the interactions of B-SPI and C3G improved the thermal stability of C3G under heating conditions.

Effect of amino and thiol groups of wheat gluten on the quality characteristics of Chinese noodles

Wheat protein contains a large number of side chain groups, amino, hydroxyl groups and sulfydryl, which influence on the quality of Chinese noodles has not been reported. Amino and thiol groups of wheat gluten were modified by chemical reactions, and acetylated gluten (AG) and reduced gluten with anhydrous sodium sulfite (SG) were obtained. Two types of noodles were made by addition of AG and SG, and the effects of AG and SG on texture and cooking properties were investigated. With the increase of AG amount in the original flour, the sedimentation value of reconstituted flour and the tensile force of fresh and cooked noodles decreased, whereas the hardness and adhesiveness increased. The gluten index and springiness of the reconstituted flour did not vary significantly compared to those of the original flour. In addition, most of the texture and cooking quality properties of the two types of noodles decreased except the adhesiveness and tensile force of fresh noodles with a rising trend along with the increase of SG. Furthermore, the cooking yield was reduced, whereas the cooking and protein losses increased along with the elevation of modified gluten levels. Our results indicated that significant differences (p < 0.05) were present between the texture and cooking properties of Chinese noodles made by flour with AG and SG and those of unmodified samples, except for the springiness of AG noodles, and the reduction of disulfide bond was disadvantageous for the quality of noodles. Therefore, the results of the present study indicate that amino and sulfhydryl groups of wheat gluten have an important role in obtaining high-quality noodles.

The Chemical Reactivity of Anthocyanins and Its Consequences in Food Science and Nutrition

Owing to their specific pyrylium nucleus (C-ring), anthocyanins express a much richer chemical reactivity than the other flavonoid classes. For instance, anthocyanins are weak diacids, hard and soft electrophiles, nucleophiles, prone to developing π-stacking interactions, and bind hard metal ions. They also display the usual chemical properties of polyphenols, such as electron donation and affinity for proteins. In this review, these properties are revisited through a variety of examples and discussed in relation to their consequences in food and in nutrition with an emphasis on the transformations occurring upon storage or thermal treatment and on the catabolism of anthocyanins in humans, which is of critical importance for interpreting their effects on health.

Development of Pickering Emulsions Stabilized by Gliadin/Proanthocyanidins Hybrid Particles (GPHPs) and the Fate of Lipid Oxidation and Digestion

This work attempted to engineer emulsions' interface using the special affinity between proline-rich gliadin and proanthocyanidins (PA), to develop surfactant-free antioxidant Pickering emulsions with digestive-resistant properties. This binding interaction between gliadin and PA benefited the interfacial adsorption of the particles to corn oil droplets. Pickering droplets as building units assembled into an interconnected three-dimensional network structure, giving the emulsions viscoelasticity and ultrastability. Oxidative markers in Pickering emulsions were periodically monitored under thermally accelerated storage. Lipid digestion and oxidation fates were characterized using in vitro gastrointestinal (GI) models. The interfacial membrane constructed by antioxidant particles served as a valid barrier against lipid oxidation and digestion, in a PA dose-dependent manner. Briefly, lipid oxidation under storage and simulated GI tract was retarded. Free fatty acid (FFA) fraction released decreased by 55% from 87.9% (bulk oil) to 39.5% (Pickering emulsion), implying engineering interfacial architecture potentially benefited to fight obesity. This study opens a facile strategy to tune lipid oxidation and digestion profiles through the cooperation of the Pickering principle and the interfacial delivery of antioxidants.

Polyphenol Interactions Mitigate the Immunogenicity and Allergenicity of Gliadins

Wheat allergy is an IgE-mediated disorder. Polyphenols, which are known to interact with certain proteins, could be used to reduce allergic reactions. This study screened several polyphenol sources for their ability to interact with gliadins, mask epitopes, and affect basophil degranulation. Polyphenol extracts from artichoke leaves, cranberries, apples, and green tea leaves were examined. Of these extracts, the first three formed insoluble complexes with gliadins. Only the cranberry and apple extracts masked epitopes in dot blot assays using anti-gliadin IgG and IgE antibodies from patients with wheat allergies. The cranberry and artichoke extracts limited cellular degranulation by reducing mouse anti-gliadin IgE recognition. In conclusion, the cranberry extract is the most effective polyphenol source at reducing the immunogenicity and allergenicity of wheat gliadins.

Influence of glycosylation of deamidated wheat gliadin on its interaction mechanism with resveratrol

Gliadin is a main composition of wheat storage protein with unique characteristics. Polyphenol with health benefits tends to form complex with protein. In this study, glycosylation of deamidated wheat gliadin (gliadin) was carried out. Fluorescence quenching was applied to evaluate their binding mechanisms with resveratrol. Results showed that glycosylation could increase the solubility and decrease the surface hydrophobicity of gliadin. Both gliadin and glycosylated gliadin have strong affinity with resveratrol. The thermodynamic parameters of binding process indicated that complexation of resveratrol with gliadin was mainly driven by hydrophobic interaction, while by hydrogen bonds with glycosylated gliadin. The hydrosolubility of resveratrol was dramatically increased especially in the presence of glycosylated gliadin. This was consistent with the higher binding constant of glycosylated gliadin with resveratrol. Therefore, gliadin and glycosylated gliadin are both effective to carry resveratrol or other bioactive compounds, and their binding mechanisms are different due to structural difference.

Characterization of total antioxidant capacity and (poly)phenolic compounds of differently pigmented rice varieties and their changes during domestic cooking

In the recent years, the pigmented rice varieties are becoming more popular due to their antioxidant properties and phenolic content. In this study, we characterized the antioxidant capacity (TAC) and the phenolic profile in white, red and black rice varieties, and evaluated the effect of two cooking methods (i.e. "risotto" and boiling) on these compounds. Before the cooking, all the varieties contained several phenolic acids, whereas anthocyanins and flavonols were peculiar of black rice and flavan-3-ols of red rice. Among the rice varieties, the black had the highest TAC value. The content of (poly)phenolic compounds and TAC decreased after cooking in all three varieties, but to a lesser extent after the risotto method. As a consequence, the risotto cooking, which allows a complete absorption of water, would be a good cooking method to retain (poly)phenolic compounds and TAC in pigmented and non-pigmented whole-meal rice.

Study on the interaction between gliadins and a coumarin as molecular model system of the gliadins-anthocyanidins complexes

To clarify the conformational changes of gliadins (Glia) upon complexation with anthocyanidins (in particular cyanidin, Cya), the interaction of Glia with a coumarin derivative (3-ethoxycarbonylcoumarin, 3-EcC), having a benzocondensed structure similar to that of Cya, has been investigated by NMR, IR, and Raman spectroscopy under acidic and neutral conditions. Raman spectra showed that both molecules produce a similar effect on the Glia structure, i.e. an increase in the α-helix conformation and a decrease in β-sheet and β-turns content. In the presence of both molecules, this effect is more marked; the spectroscopic results showed that both Cya and 3-EcC interact with Glia and 3-EcC favors the complex formation with Glia. The results obtained in this study provide new insights into anthocyanidins-Glia interactions and may have relevance to human health, in the field of the attempts to modify gluten proteins to decrease allergen immunoreactivity.