Covalent conjugation with (-)-epigallo-catechin 3-gallate and chlorogenic acid changes allergenicity and functional properties of Ara h1 from peanut

Ultrasound-enhanced covalent reaction of gliadin: the inhibition of antigenicity and its potential mechanisms

BACKGROUND

Wheat proteins can be divided into water/salt-soluble protein (albumin/globulin) and water/salt-insoluble protein (gliadins and glutenins (Glu)) according to solubility. Gliadins (Glia) are one of the major allergens in wheat. The inhibition of Glia antigenicity by conventional processing techniques was not satisfactory.

RESULTS

In this study, free radical oxidation was used to induce covalent reactions. The effects of covalent reactions by high-intensity ultrasound (HIU) of different powers was compared. The enhancement of covalent grafting effectiveness between gliadin and (-)-epigallo-catechin 3-gallate (EGCG) was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, matrix-assisted laser desorption/ionization-time-of-flight-mass spectrometry and Folin-Ciocalteu tests. HIU caused protein deconvolution and disrupted the intrastrand disulfide bonds that maintain the tertiary structure, causing a shift in the side chain structure, as proved by Fourier, fluorescence and Raman spectroscopic analysis. Comparatively, the antigenic response of the conjugates formed in the sonication environment was significantly weaker, while these conjugates were more readily hydrolyzed and less antigenic during simulated gastrointestinal fluid digestion.

CONCLUSION

HIU-enhanced free radical oxidation caused further transformation of the spatial structure of Glia, which hid or destroyed the antigenic epitope, effectively inhibiting protein antigenicity. This study widened the application of polyphenol modification in the inhibition of wheat allergens. © 2024 Society of Chemical Industry.

Epigallocatechin gallate modification of physicochemical, structural and functional properties of egg yolk granules

The aim of this study was to prepare protein-polyphenol covalent complexes by treating egg yolk granules (EYG) with alkali in the presence of epigallocatechin gallate (EGCG) and characterize the physicochemical, structural, and functional properties of these covalent complexes. Results revealed that the optimal covalent binding occurred when the concentration of EGCG reached 0.15% (w/w), resulting in a grafting rate of 1.51 ± 0.03%. As the amount of EGCG increased, corresponding increases were observed in the particle size and ζ-potential of the complexes, thereby enhancing their stability. Furthermore, our analysis using fluorescence spectroscopy, FTIR, SEM, and SDS-PAGE collectively demonstrated the formation of a covalent complex between EYG and EGCG. Notably, the covalent complexes exhibited improved antioxidant activity and emulsifying properties. Overall, this study establishes a theoretical framework for the future practical application of EYG, emphasizing the potential of EGCG to modify its structural and functional characteristics.

Reducing the Allergenicity of β-Lactoglobulin by Covalent Modification with Different Contents of Epigallocatechin Gallate (EGCG): In Vitro and In Vivo Studies

β-Lactoglobulin (βLG) is a major allergen in bovine milk protein. This study was designed to investigate changes in βLG structure, digestibility, and allergenicity induced by covalent binding modification with different contents of (-)-epigallocatechin 3-gallate (EGCG). The reaction of EGCG conjugation with βLG reached saturation at a molar ratio of 1:60 βLG:EGCG. Conjugation with EGCG altered the βLG structure, decreased IgE-binding capacity, and increased digestibility in a dose-dependent manner. In vivo studies showed that covalent conjugation with EGCG can reduce βLG-induced allergic symptoms with reducing levels of IgE, histamine, and mast cell protease-1 (mMCP-1) and the percentage of sensitized mast cells. Allergenicity was reduced more effectively in saturated βLG-EGCG conjugates compared to semisaturated conjugates. Observed changes in IFN-γ, IL-4, IL-5, IL-10, and TGF-β levels suggested that βLG-EGCG conjugates were able to promote Th1/Th2 immune balance. These findings further our understanding of the relationship between the degree of polyphenol conjugation and the allergenicity of food allergens.

Effect of the Combined Ultrasound with Other Technologies on Food Allergenicity: Ultrasound before, under, and after Other Technologies

Food allergies are a main public health disease in the world. Ultrasound is an environmentally friendly technology that typically leads to protein unfolding and loss of protein structure, which means it has the potential to be combined with other technologies to achieve a great reduction of allergenicity in foods. This review concludes the effects of the combined ultrasound with other technologies on food allergenicity from three combinations: ultrasound before other technologies, ultrasound under other technologies, and ultrasound after other technologies. Each combination affects food allergenicity through different mechanisms: (1) as for ultrasound before other technologies, ultrasound pretreatment can unfold and lose the protein structure to improve the accessibility of other technologies to epitopes; (2) as for ultrasound under other technologies, ultrasound can continuously affect the accessibility of other technologies to epitopes; (3) as for ultrasound after other technologies, ultrasound further induces structural changes to mask and disrupt the epitopes. The reduction of allergenicity is related to the ultrasound/other technologies conditions and food types/cultivars, etc. The comparison of ultrasound before, under, and after other technologies to decrease food allergenicity should be further investigated in the future. The combination of ultrasound with other technologies is promising to produce hypoallergenic foods.

Emerging Chemical, Biochemical, and Non-Thermal Physical Treatments in the Production of Hypoallergenic Plant Protein Ingredients

Allergies towards gluten and legumes (such as, soybean, peanut, and faba bean) are a global issue and, occasionally, can be fatal. At the same time, an increasing number of households are shifting to plant protein ingredients from these sources, which application and consumption are limited by said food allergies. Children, the elderly, and people with immune diseases are particularly at risk when consuming these plant proteins. Finding ways to reduce or eliminate the allergenicity of gluten, soybean, peanut, and faba bean is becoming crucial. While thermal and pH treatments are often not sufficient, chemical processes such as glycation, polyphenol conjugation, and polysaccharide complexation, as well as controlled biochemical approaches, such as fermentation and enzyme catalysis, are more successful. Non-thermal treatments such as microwave, high pressure, and ultrasonication can be used prior to further chemical and/or biochemical processing. This paper presents an up-to-date review of promising chemical, biochemical, and non-thermal physical treatments that can be used in the food industry to reduce or eliminate food allergenicity.

Atmospheric cold plasma reduces Ara h 1 antigenicity in roasted peanuts by altering the protein structure and amino acid profile

Ara h 1 is the major allergen in peanuts. To enhance the unique flavor, peanuts are usually roasted at high temperatures. However, roasting can increase the allergenic potential, owing to glycation of allergens. Atmospheric cold plasma (ACP) is a non-thermal processing technology that generates reactive species, enabling protein structural changes. Herein, glucose was also added to the ACP-treated peanut protein before roasting. The content and antigenicity of the advanced glycation end products were measured. The antigenicity was evaluated by ELISA and in vitro digestion assays. The amino acid profile and secondary and tertiary protein structures were also assessed. The antigenicity of Ara h 1 decreased by 91 % and 76 % after 30 min of air and nitrogen plasma treatment, respectively. The glycation degree and thermal and digestive stabilities were also reduced. These results correlated with the structural changes, denaturation, and aggregation. Therefore, cold plasma may reduce the allergic effects of peanuts.

Effects of Chlorogenic Acid on Lowering IgE-Binding Capacity of Soybean 7S: Comparison between Covalent and Noncovalent Interaction

Allergenicity of soybean 7S protein (7S) troubles many people around the world. However, many processing methods for lowering allergenicity is invalid. Interaction of 7S with phenolic acids, such as chlorogenic acid (CHA), to structurally modify 7S may lower the allergenicity. Hence, the effects of covalent (C-I, periodate oxidation method) and noncovalent interactions (NC-I) of 7S with CHA in different concentrations (0.3, 0.5, and 1.0 mM) on lowering 7S allergenicity were investigated in this study. The results demonstrated that C-I led to higher binding efficiency (C-0.3:28.51 ± 2.13%) than NC-I (N-0.3:22.66 ± 1.75%). The C-I decreased the α-helix content (C-1:21.06%), while the NC-I increased the random coil content (N-1:24.39%). The covalent 7S-CHA complexes of different concentrations had lower IgE binding capacity (C-0.3:37.38 ± 0.61; C-0.5:34.89 ± 0.80; C-1:35.69 ± 0.61%) compared with that of natural 7S (100%), while the noncovalent 7S-CHA complexes showed concentration-dependent inhibition of IgE binding capacity (N-0.3:57.89 ± 1.23; N-0.5:46.91 ± 1.57; N-1:40.79 ± 0.22%). Both interactions produced binding to known linear epitopes. This study provides the theoretical basis for the CHA application in soybean products to lower soybean allergenicity.

Dietary Polyphenols, Plant Metabolites, and Allergic Disorders: A Comprehensive Review

Given the ongoing rise in the occurrence of allergic disorders, alterations in dietary patterns have been proposed as a possible factor contributing to the emergence and progression of these conditions. Currently, there is a significant focus on the development of dietary therapies that utilize natural compounds possessing anti-allergy properties. Dietary polyphenols and plant metabolites have been intensively researched due to their well-documented anti-inflammatory, antioxidant, and immunomodulatory characteristics, making them one of the most prominent natural bioactive chemicals. This study seeks to discuss the in-depth mechanisms by which these molecules may exert anti-allergic effects, namely through their capacity to diminish the allergenicity of proteins, modulate immune responses, and modify the composition of the gut microbiota. However, further investigation is required to fully understand these effects. This paper examines the existing evidence from experimental and clinical studies that supports the idea that different polyphenols, such as catechins, resveratrol, curcumin, quercetin, and others, can reduce allergic inflammation, relieve symptoms of food allergy, asthma, atopic dermatitis, and allergic rhinitis, and prevent the progression of the allergic immune response. In summary, dietary polyphenols and plant metabolites possess significant anti-allergic properties and can be utilized for developing both preventative and therapeutic strategies for targeting allergic conditions. The paper also discusses the constraints in investigating and broad usage of polyphenols, as well as potential avenues for future research.

Covalent conjugation with polyphenol reduced the sensitization of walnut and ameliorated allergy by enhancing intestinal epithelial barrier in mice

In order to reduce the sensitization of walnut protein (WP), the effects of the interaction between WP and (-)-Epigallocatechin gallate (EGCG), quercetin, trans-ferulic acid, and resveratrol were investigated. Covalent and non-covalent conjugations were compared. The results suggested that covalent conjugation reduced the free amino acid content, sulfhydryl content, and surface hydrophobicity. When compared to non-covalent conjugation, covalent modification showed a lower IgE binding capacity, accompanied by changes in protein conformation. Moreover, animal experiments revealed that there were up-regulation of transforming growth factor-β, T-box expressed in t cells, and forkhead transcription factor Foxp3 mRNA expression, and down-regulation of IL-4, IL-17, GATA binding protein 3 and retinoid-related orphan nuclear receptor γt mRNA expression in the conjugate groups. These results suggested that covalent conjugation of polyphenols, especially EGCG, likely ameliorated allergy by promoting Th1/Th2 and Treg/Th17 balance and alleviating allergy-induced intestinal barrier damage, which might be a support in reducing the allergenicity of WP.

Solubilization strategy of myofibrillar proteins in low-ionic media (prototype soup): The effect of high-intensity ultrasound combined with non-covalent or covalent modification of polyphenols on myosin molecular assembly

This study investigated the effect of (-)-Epigallocatechin-3-gallate (EGCG) non-covalent/covalent grafting onto myofibrillar protein (MP) by high-intensity ultrasound (HIU) on its water-solubility and filament forming behavior. The results showed that the introduction of EGCG, especially in the case of covalent grafting, could inhibit the molecular assembly of myosin and improve the MP water solubility from 2.7% to 53.1% (P < 0.05). The HIU pretreatment provided more opportunities for EGCG grafting onto the ultrasound-treated protein (UMP) by disrupting the filamentous polymerization of myosin and thus further facilitated MP dissolution. Additionally, compared with the UMP-EGCG non-covalent complexes, the covalent complexes with a yellow appearance exhibited a higher absolute zeta potential (35.9 mV) and a lower particle size (53.7 μm) (P < 0.05). Overall, the combination of HIU pretreatment and EGCG covalent modification may provide a promising method for improving the solubility and processing properties of MP in low ionic media (prototype soup).

Reducing the allergenicity of tropomyosin in shrimp by covalent conjugation with quercetin and chlorogenic acid

The study aimed to assay the allergenicity of shrimp tropomyosin (TM) following covalent conjugation with quercetin (QR) and chlorogenic acid (CA). The structure of the TM-polyphenol covalent conjugates was examined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), circular dichroism (CD), fluorescence, differential scanning calorimetry (DSC), and Fourier Transform infrared spectroscopy (FTIR). Potential allergenicity was evaluated using in vitro and in vivo methods. The results showed that QR and CA induced structural changes in TM through aggregation. RBL-2H3 cell results showed that TM-QR and TM-CA covalent conjugates reduced the release of β-hexosaminidase and histamine, respectively. In the mice model, TM-QR and TM-CA covalent conjugates reduced the level of IgE, IgG, IgG1, histamine, and mMCP-1 in sera. Furthermore, the allergenicity was reduced by suppressing Th2-related cytokines (IL-4, IL-5, IL-13) and promoting Th1-related cytokines (IFN-γ). These research findings demonstrate that the covalent binding of TM with QR and CA, modifies the allergenic epitopes of shrimp TM, thereby reducing its potential allergenicity. This approach holds practical applications in the production of low-allergenicity food within the food industry.

Regulation of ovalbumin allergenicity and structure-activity relationship analysis based on pulsed electric field technology

The study focused on the regulation of ovalbumin (OVA) allergenicity using pulsed electric field (PEF) technology and examined the structure-activity link. Following PEF treatment, the ability of OVA to bind to IgE and IgG1 at 6 kHz was inhibited by 30.41 %. According to the microstructure, PEF caused cracks on the OVA surface. Spectral analysis revealed a blue shift in the amide I band and a decrease in α-helix and β-sheet content indicating that the structure of OVA was unfolded. The disulfide bond conformation was transformed and the structure tended to be disordered. The increased fluorescence intensity indicated that tryptophan and tyrosine were exposed which led an increase in hydrophobicity. In addition, the results of molecular dynamics (MD) simulations confirmed that the stability of OVA was reduced after PEF, which was related to the reduction of hydrogen bonding and the sharp fluctuation of aspartic acid. Therefore, PEF treatment induced the exposure of hydrophobic amino acids and the transformation of disulfide bond configuration which in turn masked or destroyed allergenic epitopes, and ultimately inhibited OVA allergenicity. This study provided insightful information for the production of hypoallergenic eggs and promoted the use of PEF techniques in the food field.

Investigation of peanut allergen-procyanidin non-covalent interactions: Impact on protein structure and in vitro allergenicity

Interactions between plant polyphenols and food allergens may be a new way to alleviate food allergies. The non-covalent interactions between the major allergen from peanut (Ara h 2) with procyanidin dimer (PA2) were therefore characterized using spectroscopic, thermodynamic, and molecular simulation analyses. The main interaction between the Ara h 2 and PA2 was hydrogen bonding. PA2 statically quenched the intrinsic fluorescence intensity and altered the conformation of the Ara h 2, leading to a more disordered polypeptide structure with a lower surface hydrophobicity. In addition, the in vitro allergenicity of the Ara h 2-PA2 complex was investigated using enzyme-linked immunosorbent assay (ELISA) kits. The immunoglobulin E (IgE) binding capacity of Ara h 2, as well as the release of allergenic cytokines, decreased after interacting with PA2. When the ratio of Ara h 2-to-PA2 was 1:50, the IgE binding capacity was reduced by around 43 %. This study provides valuable insights into the non-covalent interactions between Ara h 2 and PA2, as well as the potential mechanism of action of the anti-allergic reaction caused by binding of the polyphenols to the allergens.

Electrochemically assisted DNA and thioaromatic assembly as sensing and antifouling interface for food allergens

Food allergies have become a global issue and are estimated to affect approximately 220 million people worldwide. Allergy to peanuts can easily become life-threatening and induce anaphylactic reactions. Mislabeling and cross-contamination during food processing can occur in the frame of world population growth and pose a serious health issue. As the mandatory allergen list is not uniform worldwide, the development of routine analytical strategies with high specificity and sensitivity is a demanding task to aid in the rapid identification of allergenic foods. In this work, an electrochemical aptasensor for Ara h1 peanut allergen was developed by immobilizing the specific aptamer by the inserting method. First, a layer of p-aminothiophenol (p-ATP) was immobilized on the gold surface of screen-printed electrodes (GSPE) to improve the aptamer insertion and reduce the fouling effects at the electrode surface. The grafting of the p-ATP and Ara h1 aptamer on the GSPE surface was monitored by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The resulting disposable aptasensor allowed for indirect electrochemical detection of Ara h1 protein in the presence of 5 mM ferro/ferricyanide as a redox probe. The electrochemical response upon aptamer-target interaction was monitored in the concentration range 1-250 nM, and two limits of detection in the nanomolar range were estimated based on DPV (2.78 nM Ara h1) and EIS (0.82 nM Ara h1) measurements. The aptasensor was successfully applied to real sample analysis.

Dietary Polyphenols-Natural Bioactive Compounds with Potential for Preventing and Treating Some Allergic Conditions

In light of the constantly increasing prevalence of allergic diseases, changes in dietary patterns have been suggested as a plausible environmental explanation for the development and progression of these diseases. Nowadays, much attention has been paid to the development of dietary interventions using natural substances with anti-allergy activities. In this respect, dietary polyphenols have been studied extensively as one of the most prominent natural bioactive compounds with well-documented anti-inflammatory, antioxidant, and immunomodulatory properties. This review aims to discuss the mechanisms underlying the potential anti-allergic actions of polyphenols related to their ability to reduce protein allergenicity, regulate immune response, and gut microbiome modification; however, these issues need to be elucidated in detail. This paper reviews the current evidence from experimental and clinical studies confirming that various polyphenols such as quercetin, curcumin, resveratrol, catechins, and many others could attenuate allergic inflammation, alleviate the symptoms of food allergy, asthma, and allergic rhinitis, and prevent the development of allergic immune response. Conclusively, dietary polyphenols are endowed with great anti-allergic potential and therefore could be used either for preventive approaches or therapeutic interventions in relation to allergic diseases. Limitations in studying and widespread use of polyphenols as well as future research directions are also discussed.

Casein-phenol interactions occur during digestion and affect bioactive peptide and phenol bioaccessibility

Casein (CN) represents many proline residues that may bind polyphenols. Some evidence exists of CN-polyphenols interaction in model systems. The formation of such interactions upon digestion and the effects on CN digestibility and potential functionality due to the release of bioactive peptides are obscure. This study aimed to explore the interactions of CN with different phenol compounds under digestive conditions and monitor how they affect the bioaccessibility of phenol compounds and bioactive peptides. CN or CN hydrolysate and phenol compounds such as chlorogenic acid, ellagic acid, catechin, green tea extract, and tea extract, singularly or in combination with CN were digested in vitro. Total antioxidant capacity (TAC), degree of hydrolysis, and bioactive peptide formation were assessed in the samples collected through the digestion. The results showed that bioaccessible TAC was 1.17 to 1.93-fold higher in CN co-digested with phenol compounds than initially due to a higher release of antioxidant peptides in the presence of phenolic compounds. However, TAC values in the intestinal insoluble part of CN-phenol digests were higher than the initial, indicating that such interactions may be functional to transport phenols to the colon. Bioactive peptide release was affected by the phenol type (catechins were the most effective) as well as phenol concentration. As an opioid peptide released from β-CN, β-casomorphin formation was significantly influenced by the co-digestion of CN with phenol compounds. This study confirmed the possible CN-phenol interaction during digestion, affecting bioactive peptide release.

Comparison of proanthocyanidins A2 and B2 on IgE-reactivity and epitopes in Gly m 6 using multispectral, LC/MS-MS and molecular docking

This study comparatively analyzed the changes in IgE-reactivity and epitopes in proanthocyanidins A2- (PA-Gly m 6) and B2-Gly m 6 (PB-Gly m 6) conjugates prepared by alkali treatment at 80 °C for 20 min. Similar to the western blot, ELISA also showed a higher reduced IgE-reactivity in PA-Gly m 6 (70.12 %) than PB-Gly m 6 (63.17 %). SDS-PAGE demonstrated that proanthocyanidins A2 caused more formation of >180 kDa polymers than proanthocyanidins B2. Multispectral analyses revealed that PA-Gly m 6 exhibited more structural alteration (e.g., a decrease of α-helical content and ANS fluorescence intensity) to unfold protein structure than proanthocyanidins B2, improving the accessibility to modify Gly m 6 for shielding or destroying conformational epitopes. LC/MS-MS revealed that PA-Gly m 6 conjugates had a lower abundance of allergens, peptides and linear epitopes than PB-Gly m 6 conjugates. Molecular docking showed that proanthocyanidins A2 and B2 reacted with Gln-317 and Asn-94 of epitopes, respectively. Overall, proanthocyanidins A2 is more effective than proanthocyanidins B2 to decrease the IgE-reactivity of Gly m 6 due to more shielding or destruction of conformational epitopes and lower content allergens and linear epitopes, which was attributed to more protein-crosslinks formation and structural changes in PA-Gly m 6 conjugates.

Reducing Antigenicity and Improving Antioxidant Capacity of β-Lactoglobulin through Covalent Interaction with Six Flavonoids

β-lactoglobulin (β-LG) is a pivotal nutritional and functional protein. However, its application is limited by its antigenicity and susceptibility to oxidation. Here, we explore the impact of covalent modification by six natural compounds on the antigenicity and antioxidant characteristics of β-LG to explore the underlying interaction mechanism. Our findings reveal that the covalent interaction of β-LG and flavonoids reduces the antigenicity of β-LG, with the following inhibition rates: epigallocatechin-3-gallate (EGCG) (57.0%), kaempferol (42.4%), myricetin (33.7%), phloretin (28.6%), naringenin (26.7%), and quercetin (24.3%). Additionally, the β-LG-flavonoid conjugates exhibited superior antioxidant capacity compared to natural β-LG. Our results demonstrate that the significant structural modifications from α-helix to β-sheet induced by flavonoid conjugation elicited distinct variations in the antigenicity and antioxidant activity of β-LG. Therefore, the conjugation of β-LG with flavonoids presents a prospective method to reduce the antigenicity and enhance the antioxidant capacity of β-LG.

Modulating the allergenicity and functional properties of peanut protein by covalent conjugation with polyphenols

Peanut protein is a common food allergen. Our previous study demonstrated that the allergenicity of Ara h1 declines after covalent conjugation with polyphenols in vitro; however, how polyphenols affect the structure, function, and allergenicity of peanut protein extract (PPE) after covalent conjugating needs clarifying. Here, we assessed how the structure, function, and allergenicity of PPE changed after covalent conjugation with epigallocatechin-3-gallate (PPE-EGCG) and chlorogenic acid (PPE-CA). PPE covalently conjugated with EGCG and CA using the alkali treatment method. Multi-spectroscopy showed that the structure of PPE-EGCG/CA conjugate changed, becoming less folded. In contrast, the functional properties of PPE significantly improved. The allergenicity of PPE-EGCG/CA significantly declined in vitro and in vivo experiments. Our findings confirm that covalent conjugation of PPE with EGCG and CA reduces the allergenicity and improves the functional properties of PPE by changing the structure of the protein.

Unraveling the effects of low protein-phenol binding affinity on the structural properties of beta-lactoglobulin

Non-covalent interactions of phenolics with proteins cannot always be readily identified, often leading to contradictory results described in the literature. This results in uncertainties as to what extent phenolics can be added to protein solutions (for example for bioactivity studies) without affecting the protein structure. Here, we clarify which tea phenolics (epigallocatechin gallate (EGCG), epicatechin and gallic acid) interact with the whey protein β-lactoglobulin by combining various state-of-the-art-methods. STD-NMR revealed that all rings of EGCG can interact with native β-lactoglobulin, indicating multidentate binding, as confirmed by the small angle X-ray scattering experiments. For epicatechin, unspecific interactions were found only at higher protein:epicatechin molar ratios and only with ¹H NMR shift perturbation and FTIR. For gallic acid, none of the methods found evidence for an interaction with β-lactoglobulin. Thus, gallic acid and epicatechin can be added to native BLG, for example as antioxidants without causing modification within wide concentration ranges.

Mechanistic studies of polyphenols reducing the trypsin inhibitory activity of ovomucoid: Structure, conformation, and interactions

Ovomucoid (OVM) is a critical anti-nutritional factor in egg, which may reduce nutrient utilization. In this study, the effects of polyphenols on the trypsin inhibitory activity (TIA) of OVM were investigated by exploring the structural changes and interaction mechanisms. The results found that TIA decreased to 62.34% and 90.41% as epigallocatechin gallate (EGCG) and gallic acid (GA) were added individually. EGCG and GA interacted with OVM via static quenching and hydrophobic interaction. They induced a transition of OVM conformation from disorder to order. Infrared and fluorescence quenching analysis showed that the interaction between EGCG or GA and OVM was spontaneous, and hydrophobic interaction was the predominant force. The mechanism suggested that polyphenols affect the protein conformation by spontaneously binding to OVM in hydrophobic interactions, and lowering the TIA through reduced hydrophobicity. In summary, EGCG may be a promising OVM trypsin activity inactivator, which could also guarantee safety of egg products.

Effects of covalent conjugation with quercetin and its glycosides on the structure and allergenicity of Bra c p from bee pollen

Profilin family members are potential pan-allergens in foods, presenting public health hazards. However, studies on the allergenicity modification of profilin allergens are limited. Herein, quercetin and its glycosides (isoquercitrin and rutin) were applied to modify the allergenicity of a profilin allergen (Bra c p) from Brassica campestris bee pollen. Results showed that only quercetin can be closely covalently bound to Bra c p among the three, and the binding site was located at the Cys98 residue. After covalently conjunction, the relative content of α-helix structure in Bra c p was reduced by 40.05%, while random coil was increased by 42.89%; moreover, the Tyr and Phe residues in Bra c p were masked. These structural changes could alter the conformational antigenic epitopes of Bra c p, resulting in its allergenicity reduction. Our findings might provide a technical foundation for reducing the allergenicity of bee pollen and foods containing profilin family allergens.

The alteration of composition, conformation, IgE-reactivity and functional attributes in proanthocyanidins-soy protein 7S conjugates formed by alkali-heating treatment: Multi-spectroscopic and proteomic analyses

This study assessed the alteration of IgE-reactivity and functional attribute in soy protein 7S-proanthocyanidins conjugates (7S-80PC) formed by alkali-heating treatment (pH 9.0, 80 °C, 20 min). SDS-PAGE demonstrated that 7S-80PC exhibited the formation of >180 kDa polymers, although the heated 7S (7S-80) had no changes. Multispectral experiments revealed more protein unfolding in 7S-80PC than in 7S-80. Heatmap analysis showed that 7S-80PC showed more alteration of protein, peptide and epitope profiles than 7S-80. LC/MS-MS demonstrated that the content of total dominant linear epitopes was increased by 11.4 % in 7S-80, but decreased by 47.4 % in 7S-80PC. As a result, Western-blot and ELISA showed that 7S-80PC exhibited lower IgE-reactivity than 7S-80, probably because 7S-80PC exhibited more protein-unfolding to increase the accessibility of proanthocyanidins to mask and destroy the exposed conformational epitopes and dominant linear epitopes induced by heating treatment. Furthermore, the successful attachment of PC to soy 7S protein significantly increased antioxidant activity in 7S-80PC. 7S-80PC also showed higher emulsion activity than 7S-80 owing to its high protein flexibility and protein unfolding. However, 7S-80PC exhibited lower foaming properties than 7S-80. Therefore, the addition of proanthocyanidins could decrease IgE-reactivity and alter the functional attribute of the heated soy 7S protein.

Sonochemical Effects on the Preparation, Structure and Function of Gliadin-(-)-Epigallo-Catechin 3-Gallate Conjugates

It is essential to understand the mechanism of action of ultrasound synergistic free radical oxidation to promote covalent reactions between proteins and polyphenols. (-)-epigallo-catechin 3-gallate (EGCG) with rich bioactivity could be used to increase the functional properties of cereal protein-gliadin (GL). This study systematically explored the role of ultrasound treatment (US) on the binding mechanisms of GL and EGCG. Electrophoresis and high-performance liquid chromatography (HPLC) confirmed the greater molecular mass of the covalent complexes in the ultrasound environment. Quantitative analysis by the phenol content revealed that the ultrasound environment increased the EGCG content in the covalent complex by 15.08 mg/g of protein. The changes in the spatial structure of the proteins were indicated by Fourier infrared and ultraviolet spectroscopy. Additionally, scanning electron microscopy (SEM) and atomic force microscopy (AFM) found that US disrupted the aggregation of GL and the clustered structure of the covalent complexes. The results demonstrated that the water solubility of ultrasonic conjugates was significantly increased by 8.8-64.19%, the digestion rate was more efficient, and the radical scavenging capacity was twice that of GL. This research contributes to the theoretical basis for broadening the application of polyphenols in modifying protein.

A review of the structure, function, and application of plant-based protein-phenolic conjugates and complexes

Interactions between plant-based proteins (PP) and phenolic compounds (PC) occur naturally in many food products. Recently, special attention has been paid to the fabrication of PP-PC conjugates or complexes in model systems with a focus on their effects on their structure, functionality, and health benefits. Conjugates are held together by covalent bonds, whereas complexes are held together by noncovalent ones. This review highlights the nature of protein-phenolic interactions involving PP. The interactions of these PC with the PP in model systems are discussed, as well as their impact on the structural, functional, and health-promoting properties of PP. The PP in conjugates and complexes tend to be more unfolded than in their native state, which often improves their functional attributes. PP-PC conjugates and complexes often exhibit improved in vitro digestibility, antioxidant activity, and potential allergy-reducing activities. Consequently, they may be used as antioxidant emulsifiers, edible film additives, nanoparticles, and hydrogels in the food industry. However, studies focusing on the application of PP-PC conjugates and complexes in real foods are still scarce. Further research is therefore required to determine the structure-function relationships of PP-PC conjugates and complexes that may influence their application as functional ingredients in the food industry.

Multi-spectral and proteomic insights into the impact of proanthocyanidins on IgE binding capacity and functionality in soy 11S protein during alkali-heating treatment

This study evaluated the impact of proanthocyanidins on immunoglobulin E (IgE) binding capacity, antioxidant, foaming and emulsifying properties in soy 11S protein following alkali treatment at 80 °C for 20 min. The formation of >180 kDa polymer was observed in the combined heating and proanthocyanidins-conjugation treatment sample (11S-80PC) rather than in the heating treated sample (11S-80) using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The structural analyzes demonstrated that 11S-80PC exhibited more protein unfolding than 11S-80. Heatmap analysis revealed that 11S-80PC had more alteration of peptide and epitope profiles in 11S than in 11S-80. Molecular docking showed that PC could well react with soy protein 11S. Liquid chromatography tandem MS analysis (LC/MS-MS) demonstrated that there was a 35.6 % increase in 11S-80, but a 14.5 % decrease in 11S-80PC for the abundance of total linear epitopes. As a result, 11S-80PC exhibited more reduction in IgE binding capacities than 11S-80 owing to more obscuring and disruption of linear and conformational epitopes induced by structural changes. Moreover, 11S-80PC exhibited higher antioxidant capacities, foaming properties and emulsifying activity than 11S-80. Therefore, the addition of proanthocyanidins could decrease allergenic activity and enhance the functional properties of the heated soy 11S protein.

Investigation of the differences in the effect of (-)-epigallocatechin gallate and proanthocyanidins on the functionality and allergenicity of soybean protein isolate

In this study, the differences in effects of (-)-epigallocatechin gallate (EGCG) and proanthocyanidins (PC) on the functionality and allergenicity of soybean protein isolate (SPI) were studied. SDS-PAGE demonstrated that SPI-PC conjugates exhibited more high-molecular-weight polymers (>180 kDa) than SPI-EGCG conjugates. Structural analysis showed that SPI-PC conjugates exhibited more disordered structures and protein-unfolding, improving the accessibility of PC to modify SPI, compared to SPI-EGCG conjugates. LC/MS-MS demonstrated that PC caused more modification of SPI and major soybean allergens than EGCG, resulting in a lower abundance of epitopes. The successful attachment of EGCG and PC to SPI significantly increased antioxidant capacity in conjugates. Furthermore, SPI-PC conjugates exhibited greater emulsifying activity and lower immunoglobulin E (IgE) binding capacity than SPI-EGCG conjugates, which was attributed to more disordered structure and protein-unfolding in SPI-PC conjugates. It is implied that proanthocyanidins may be promising compounds to interact with soybean proteins to produce functional and hypoallergenic foods.

Phenolic compounds in walnut pellicle improve walnut (Juglans regia L.) protein solubility under pH-shifting condition

This study focused on the interaction of walnut protein with phenolic extracts of walnut pellicle (PEWP) under alkaline condition, leading to enhancement of protein solubility under neutral condition. First, the change of PEWP under alkaline condition was determined by RP-HPLC and mass spectrometry, and the results showed that most ellagitannins in PEWP could be retained under alkaline condition within 3 h. Interaction between PEWP and walnut protein under pH-shifting condition resulted in the remarkable increase of protein solubility (above 90%) at neutral pH. The results from SDS-PAGE and SEC showed that the improved solubility lied in the formation of large and soluble protein aggregates due to the covalent interaction among walnut protein and polyphenols. A significant change in tertiary structure of protein-phenolic complex was witnessed by fluorescence spectrum and near-UV circular dichroism. Meanwhile, walnut protein-polyphenol interaction led to a slight increase in β-turn while a slight decrease in β-sheet. Combined with amino acid composition, it could be illustrated that the covalent bonding for walnut protein with polyphenol mainly occurred at Lysine residues.

Covalent and Noncovalent Complexation of Phosvitin and Gallic Acid: Effects on Protein Functionality and In Vitro Digestion Properties

To investigate the effects of different binding modes on the structure, function, and digestive properties of the phosvitin (Pv) and gallic acid (GA) complex, Pv was covalently and noncovalently combined with different concentrations of GA (0.5, 1.5, and 2.5 mM). The structural characterization of the two Pv-GA complexes was performed by Fourier transform infrared, circular dichroism, and LC-MS/MS to investigate the covalent and noncovalent binding of Pv and GA. In addition, the microstructure of the two Pv-GA complexes was investigated by super-resolution microscopy and transmission electron microscopy. The particle size and zeta potential results showed that the addition of GA increased the particle size and the absolute potential of Pv. The determination of protein digestibility, polyphenol content, SH and S-S group levels, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and antioxidant capacity of the digests indicated that noncovalent complexes had greater antioxidant and protective effects on polyphenols. Molecular docking revealed that GA was conjugated with Pv through hydrogen bond interactions.

Ultrasound-assisted preparation of lactoferrin-EGCG conjugates and their application in forming and stabilizing algae oil emulsions

The aim of this study was to prepare lactoferrin-epigallocatechin-3-gallate (LF-EGCG) conjugates and to determine their ability to protect emulsified algal oil against aggregation and oxidation. LF-EGCG conjugates were formed using an ultrasound-assisted alkaline treatment. The ultrasonic treatment significantly improved the grafting efficiency of LF and EGCG and shortened the reaction time from 24 h to 40 min. Fourier transform infrared spectroscopy and circular dichroism spectroscopy analyses showed that the covalent/non-covalent complexes could be formed between LF and EGCG, with the CO and CN groups playing an important role. The formation of the conjugates reduced the α-helix content and increased the random coil content of the LF. Moreover, the antioxidant activity of LF was significantly enhanced after conjugation with EGCG. LF-EGCG conjugates as emulsifiers were better at inhibiting oil droplet aggregation and oxidation than LF alone. This study demonstrates that ultrasound-assisted formation of protein-polyphenol conjugates can enhance the functional properties of the proteins, thereby extending their application as functional ingredients in nutritionally fortified foods.

Functional and Allergenic Properties Assessment of Conalbumin (Ovotransferrin) after Oxidation

Conalbumin (CA) is an iron-binding egg protein that has various bioactivities and causes major allergenicity in humans. This study investigated how oxidation affects the multiple functional properties of CA. The lipid peroxidation method was used to prepare treated CA [2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH)-CA and acrolein-CA] complexes. CA induced structural changes through oxidation. These changes enhanced the digestibility, rate of endocytosis in dendritic cells, and emulsifying and foaming properties of CA. ELISA and immunoblot analysis showed that the complexes reduced the IgE-binding ability of CA through lipid oxidation. KU812 cell assays showed that modification by AAPH and acrolein caused the release of IL-4 and histamine to decline. In conclusion, oxidation treatment modified the functional and structural properties of CA, reducing allergenicity during processing and preservation.

The Biological Activity Mechanism of Chlorogenic Acid and Its Applications in Food Industry: A Review

Chlorogenic acid (CGA), also known as coffee tannic acid and 3-caffeoylquinic acid, is a water-soluble polyphenolic phenylacrylate compound produced by plants through the shikimic acid pathway during aerobic respiration. CGA is widely found in higher dicotyledonous plants, ferns, and many Chinese medicine plants, which enjoy the reputation of “plant gold.” We have summarized the biological activities of CGA, which are mainly shown as anti-oxidant, liver and kidney protection, anti-bacterial, anti-tumor, regulation of glucose metabolism and lipid metabolism, anti-inflammatory, protection of the nervous system, and action on blood vessels. We further determined the main applications of CGA in the food industry, including food additives, food storage, food composition modification, food packaging materials, functional food materials, and prebiotics. With a view to the theoretical improvement of CGA, biological activity mechanism, and subsequent development and utilization provide reference and scientific basis.

Covalent modification of zein with polyphenols: A feasible strategy to improve antioxidant activity and solubility

Covalent modification of protein with polyphenols is an attractive research topic, since it is an effective way to improve the properties and broaden the applications of protein. However, the majority of prolamin-polyphenol reactions were carried out in alcohol aqueous solution, and this study aimed to investigate the covalent interaction of zein and polyphenols in water. Chlorogenic acid (CGA), gallic acid (GA), and caffeic acid (CA) were used as polyphenol models. The grafting ratio revealed that zein interacted more strongly with CGA and CA than with GA, which was probably due to the larger molecular weight of CGA and the hydroxycinnamic acid structure of CA. Afterward, the differences in structural and functional properties between control zein and zein-polyphenol complexes were compared. Covalent interaction with polyphenols induced great changes in the morphology and secondary structure of zein. Compared with control zein and non-covalent complexes, covalent zein-polyphenol complexes exhibited better solubility, antioxidant activity, and thermal stability. PRACTICAL APPLICATION: Covalent modification of zein with polyphenols in water is a simple and efficient method, which can ameliorate the antioxidant activity as well as the hydrophilicity of zein and improve its application value. The findings of this research carry important implications for using zein-polyphenol complexes as novel food additives, or to design more efficient delivery systems.

A review on polyphenols and their potential application to reduce food allergenicity

This review summarized recent studies about the effects of polyphenols on the allergenicity of allergenic proteins, involving epigallocatechin gallate (EGCG), caffeic acid, chlorogenic acid, proanthocyanidins, quercetin, ferulic acid and rosmarinic acid, etc. Besides, the mechanism of polyphenols for reducing allergenicity was discussed and concluded. It was found that polyphenols could noncovalently (mainly hydrophobic interactions and hydrogen bonding) and covalently (mainly alkaline, free-radical grafting, and enzymatic method) react with allergens to induce the structural changes, resulting in the masking or/and destruction of epitopes and the reduction of allergenicity. Oral administration in murine models showed that the allergic reaction might be suppressed by regulating immune cell function, changing the levels of cytokines, suppressing of MAPK, NF-κb and allergens-presentation pathway and improving intestine function, etc. The outcome of reduced allergenicity and suppressed allergic reaction was affected by many factors such as polyphenol types, polyphenol concentration, allergen types, pH, oral timing and dosage. Moreover, the physicochemical and functional properties of allergenic proteins were improved after treatment with polyphenols. Therefore, polyphenols have the potential to produce hypoallergenic food. Further studies should focus on active concentrations and bioavailability of polyphenols, confirming optimal intake and hypoallergenic of polyphenols based on clinical trials.

A new method to reduce allergenicity by improving the functional properties of soybean 7S protein through covalent modification with polyphenols

The 7S fraction contains several major allergens of soybean protein. Here, the effects of covalent modification by chlorogenic acid (CHA) and (-)-epigallo-catechin 3-gallate (EGCG) on the allergenicity and functional properties of soybean 7S protein were investigated. Conjugation with EGCG and CHA resulted in the formation of cross-linked protein polymers and changes to the structures of the protein, which might mask or destroy the epitopes on it. In vitro analysis revealed that modification by polyphenols noticeably reduced IgE binding activity and histamine release. In vivo analysis showed that modification led to milder anaphylactic shock symptoms and minor damage of the intestine in mice, with reducing IgG, IgE, IgG1, mMCP-1, and histamine levels. The allergic response was also suppressed by the repression of IFN-γ, IL-4, and IL-5 and the up-regulation of IL-10 and TGF-β in the conjugate groups. Furthermore, modification enhanced antioxidant, emulsion, foaming capacity, and foam stability of the protein.

Protein-polyphenol conjugates: Preparation, functional properties, bioactivities and applications in foods and nutraceuticals

Protein is a crucial nutritional ingredient in the daily human diet. Polyphenols (PPNs) are the abundant phytochemicals in plants, which are associated with health promotion as well as affect functionality in food systems. Both ingredients possess different types of functionalities (crosslinking, gelling, emulsifying, film-forming, etc.) and bioactivities (antioxidant, antimicrobial, anti-inflammatory, etc.). In the past decade, various methods have been implemented to enhance the functionalities and bioactivities of foods. Conjugation or grafting methods has been introduced widely. Conjugations of PPNs with proteins through various methods have been performed for the synthesis of the protein-polyphenol conjugate. Those potential grafting methods are alkaline associated, free-radical mediated, enzyme catalyzed, and chemical coupling methods. Several factors such as reaction conditions, type of proteins, and PPNs also influenced the conjugation efficiency. Various technologies, e.g., mass spectroscopy, fluorescence spectroscopy, UV spectroscopy, Fourier transform infrared spectroscopy, circular dichroism, and sodium dodecyl sulfate polyacrylamide gel electrophoresis have been used to elucidate conjugation and structural alternation of proteins and some properties of resulting conjugates. The prepared protein-PPN conjugates have been documented to enhance the bioactivities and functional properties of an initial protein. Moreover, conjugates have been employed in emulsions or as nanoparticles for nutraceutical delivery. Edible-films for food packaging and hydrogels for controlled drug release have been developed using protein-PPN conjugates. This chapter focuses on the methodologies and characteristics of protein-PPN conjugates and their applications in various food systems and nutraceutical field.

A mussel-inspired film for adhesion to wet buccal tissue and efficient buccal drug delivery

Administration of drugs via the buccal route has attracted much attention in recent years. However, developing systems with satisfactory adhesion under wet conditions and adequate drug bioavailability still remains a challenge. Here, we propose a mussel-inspired mucoadhesive film. Ex vivo models show that this film can achieve strong adhesion to wet buccal tissues (up to 38.72 ± 10.94 kPa). We also demonstrate that the adhesion mechanism of this film relies on both physical association and covalent bonding between the film and mucus. Additionally, the film with incorporated polydopamine nanoparticles shows superior advantages for transport across the mucosal barrier, with improved drug bioavailability (~3.5-fold greater than observed with oral delivery) and therapeutic efficacy in oral mucositis models (~6.0-fold improvement in wound closure at day 5 compared with that observed with no treatment). We anticipate that this platform might aid the development of tissue adhesives and inspire the design of nanoparticle-based buccal delivery systems.