Soy protein isolate -(-)-epigallocatechin gallate conjugate: Covalent binding sites identification and IgE binding ability evaluation

Covalent modulation of zein surface potential by gallic acid to enhance the formation of electrostatic-driven ternary antioxidant complex coacervates with chitosan

Despite existing research on the interaction between zein (Z) and chitosan (CS), the formation and mechanisms of ternary electrostatic coacervates incorporating polyphenols remain unclear. Herein, we covalently and non-covalently modified zein with gallic acid (GA). Comparisons revealed that the covalent coupling of Z with GA (forming Z(GA)) reduced zein's surface potential, enabling them to form tightly bound coacervates with cationic polysaccharide chitosan through electrostatic attraction. Turbidity, ζ-potential, and appearance experiments indicated that the maximum yield of insoluble coacervates was achieved at a Z(GA)/CS mass ratio of 7:1 and pH 6.5. Furthermore, the coacervate properties were evaluated using Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, and microscopic structure analysis. Electrostatic attraction between the -COO- groups of Z(GA) and the -NH3+ groups of CS triggered complex coacervation, which induced structural modifications and enhanced thermal stability. This study fosters the efficient encapsulation and controlled release of nutraceuticals, enhancing human absorption.

Preparation and characterization of camellia oil body-based oleogels loaded with (-)-epigallocatechin-3-gallate (EGCG)

Growing concern for healthy diets is driving researchers to developed novel solid lipids to reduce the intake of saturated and trans fatty acids. In this study, a novel edible oleogel loaded with EGCG was prepared using camellia oil body emulsion as template under alkaline condition (pH 9.0) and the effect of EGCG concentration (10-150 μM) on the structure and physicochemical properties of the oleogels were investigated. The oil holding capacity, textural strength, and thixotropy recovery of the oleogel were enhanced by increasing EGCG concentration from 10 to 100 μM. Meanwhile, a decreasing trend was found in them at a higher EGCG concentration (150 μM). Besides, the lipid oxidative and thermal stability of the oleogel were significantly improved when EGCG were present. Microscopic observation and LF-NMR results demonstrated that OBs were directionally arranged during the freeze-drying process, forming a continuous gel network. The addition of EGCG improved the continuity of the gel structure and restricted the mobility of oil droplets, especially at an EGCG concentration of 100 μM. Front-face fluorescence spectroscopy, FTIR, and SDS-PAGE results demonstrated that EGCG acts as a bridging agent, inducing intermolecular cross-linking of oil body interfacial proteins, resulting in a significant increase in protein molecular weight, accompanied by notable reductions in α-helix and β-sheet structures, as well as fluorescence quenching. This cross-linking facilitates the aggregation of OBs, improves the anti-destruction ability of OB film, and enhances the structural continuity of COB-based oleogels. This study provides valuable insights into the use of natural OBs and water-soluble antioxidants for creating edible oleogels.

Gallic acid enhanced fiber formation in soy protein isolate-based meat analogues

This study explored the potential of gallic acid to enhance fiber formation in soy protein isolate (SPI)-based meat analogues produced from high-moisture extrusion. Specifically, the effect of gallic acid on the structure and characteristics of meat analogues was investigated. It was found that gallic acid enhanced the anisotropy index of meat analogues, with the strongest effect observed at a concentration of 0.06 mol/kg SPI. The hardness, chewiness and water binding ability of SPI-based meat analogues were also increased. Moreover, gallic acid increased the energy input to SPI during extrusion and the flow velocity difference of the SPI melt during cooling. SDS-PAGE analysis and the decrease in contents of free sulfhydryl and amino groups indicated that gallic acid induced covalent cross-linking of SPI molecules during extrusion. Also, 0.06 mol gallic acid/kg SPI had the most profound effect. Thus, it was inferred that these alterations induced promotion of fiber formation.

Allergenicity of Alternative Proteins: Reduction Mechanisms and Processing Strategies

The increasing popularity of alternative proteins has raised concerns about allergenic potential, especially for plant-, insect-, fungal-, and algae-based proteins. Allergies arise when the immune system misidentifies proteins as harmful, triggering IgE-mediated reactions that range from mild to severe. Main factors influencing allergenicity include protein structure, cross-reactivity, processing methods, and gut microbiota. Disruptions in gut health or microbiota balance heighten risks. Common allergens in legumes, cereals, nuts, oilseeds, single-cell proteins, and insect-based proteins are particularly challenging, as they often remain stable and resistant to heat and digestion despite various processing techniques. Processing methods, such as roasting, enzymatic hydrolysis, and fermentation, show promise in reducing allergenicity by altering protein structures and breaking down epitopes that trigger immune responses. Future research should focus on optimizing these methods to ensure that they effectively reduce allergenic risks while maintaining the nutritional quality and safety of alternative protein products.

Development of faba protein-tannic acid conjugate via free radical grafting: Evaluation of interaction mechanisms and antioxidative properties

A soluble fraction of faba bean protein was conjugated with tannic acid via the free-radical grafting method using a mixture of ascorbic acid and hydrogen peroxide. Surface plasmon resonance showed a strong bonding between them, while the free amino and thiol group measurements indicated tannic acid's bonding with the amino groups and cysteine residues on the proteins. Structural analysis using intrinsic fluorescence and surface hydrophobicity demonstrated tannic acid's interaction with the aromatic and hydrophobic amino acids of the protein. The conjugate showed about 77 % DPPH, 89 % ABTS, and 83 % hydroxyl radical scavenging activities and superior ferric-reducing ability compared to the protein alone and the mixture of protein and tannic acid. Electron paramagnetic resonance (EPR) spectroscopy revealed 97.8 % radical scavenging ability of the conjugate, comparable to the pure tannic acid. The exceptional antioxidative properties of conjugate can be utilized to delay lipid oxidation in protein-stabilized oil-in-water emulsions.

Rapid Covalent Bonding of Walnut Protein Isolates to EGCG: Unveiling the Ultrasound-Assisted Ratio Optimization, Binding Mechanism, and Structural-Functional Transformations

The application of walnut protein isolate (WPI) and polyphenols is usually limited by low solubility. To solve the above problem, the impact of the alkaline treatment method and the ultrasound-assisted alkaline treatment method on the structural and functional properties of protein-polyphenol covalent complexes (WPI-(-)-epigallocatechin-3-gallate (EGCG), UWPI-EGCG, respectively) was explored. Fourier transform infrared spectroscopy and fluorescence spectroscopy indicated that the covalent binding of EGCG to WPI altered the secondary and tertiary structures of the protein and increased its random coil content. In addition, the UWPI-EGCG samples had the lowest particle size (153.67 nm), the largest absolute zeta potential value (25.4 mV), and the highest polyphenol binding (53.37 ± 0.33 mg/g protein). Meanwhile, WPI-EGCG covalent complexes also possessed excellent solubility and emulsification properties. These findings provide a promising approach for WPI in applications such as functional foods.

Covalent interaction of ovalbumin with proanthocyanidins improves its thermal stability and antioxidant and emulsifying activity

BACKGROUND

The structure of proanthocyanidins (PC) contains a large number of active phenolic hydroxyl groups, which makes it have strong antioxidant capacity. This study investigated the structural and functional properties of ovalbumin (OVA) modified by its interaction with PC.

RESULTS

It was found that on increasing the concentration ratio of PC to OVA from 10:1 to 40:1, the free amino and total sulfhydryl contents of OVA decreased from 470.59 ± 38.77 and 29.81 ± 0.31 nmol mg-1 to 96.61 ± 4.55 and 21.22 ± 0.78 nmol mg-1, respectively, and the free sulfhydryl content increased from 7.65 ± 0.41 to 9.48 ± 0.58 nmol mg-1. These results indicated that CN and CS bonds were formed and PC was covalently linked with OVA. The PC content in the OVA-PC conjugates increased from 281.93 ± 12.92 to 828.81 ± 46.09 nmol mg-1 on increasing the concentration ratio of PC to OVA from 10:1 to 40:1. The contents of α-helix and β-turn of OVA decreased, and the contents of β-sheet and random coil increased, confirmed by circular dichroism. The tertiary structure of OVA was also altered according to the results of fluorescence and ultraviolet absorption spectra. The surface hydrophobicity of OVA-PC conjugates decreased with increasing bound polyphenol content. The conjugation of OVA to PC significantly improved its emulsification and antioxidant activity and denaturation temperature.

CONCLUSION

This study may provide valuable information for improving OVA's functional properties and its PC conjugates for applications in the food industry. © 2024 Society of Chemical Industry.

Soy protein-polyphenols conjugates interaction mechanism, characterization, techno-functional and biological properties: An updated review

Soy protein is a promising nutritional source with improved functionality and bioactivities due to conjugation with polyphenols (PP)-the conjugates between soy protein and PP held by covalent and noncovalent bonds. Different approaches, including thermodynamics, spectroscopy, and molecular docking simulations, can demonstrate the outcomes and mechanism of these conjugates. The soy protein, PP structure, matrix properties (temperature, pH), and interaction mechanism alter the ζ-potential, secondary structure, thermal stability, and surface hydrophobicity of proteins and also improve the techno-functional properties such as gelling ability, solubility, emulsifying, and foaming properties. Soy protein-PP conjugates also reveal enhanced in vitro digestibility, anti-allergic, antioxidant, anticancer, anti-inflammatory, and antimicrobial activities. Thus, these conjugates may be employed as edible film additives, antioxidant emulsifiers, hydrogels, and nanoparticles in the food industry. Future research is needed to specify the structure-function associations of soy protein-PP conjugates that may affect their functionality and application in the food industry.

Pea protein-p-coumaric acid conjugate-based antioxidant film: The relationship between protein structure and film properties after covalent bonding

In this study, pea protein isolates (PPI) have been used to make conjugates by covalent binding with p-coumaric acid (p-CA), and the effect of conjugation on PPI structural characteristics and the structural, optical, mechanical, and physicochemical properties of conjugate-based films were investigated. The conjugation with p-CA unfolds the tertiary structure of PPI and significantly reduces the surface charge. A tendency of aggregation with increasing p-CA addition was proposed. The conjugate-based films show stronger tensile strength (TS) and better water barrier properties than PPI-based films. However, no significant improvement of the elongation at break (EAB) and thermal stability was found for conjugate-based films. FTIR spectroscopic and zeta-potential analyses indicated that such improved film properties could be attributed to the enhancement of hydrogen bonds and weakening of electrostatic repulsion between conjugate-conjugate. Additionally, the conjugates impart the antioxidant activity to the films as confirmed by DPPH scavenging capacity. This study demonstrates the potential of using pea protein-phenolic acid conjugate to make PPI-based films with improved mechanical properties, water barrier properties, and antioxidant activity.

Effect of epicatechin gallate on the glycosylation of soybean protein isolate-lutein complexes with inulin-type fructans and the protective failure point of glycosylated proteins

In recent years, the application of natural extracts such as proteins modified to protect lutein has become a potential technology, but modified proteins lose their protective function towards lutein after a period of time. So far, very few studies have been conducted on the modified proteins after losing their protective function. Therefore, the present study investigate the effect of different polyphenols in tea polyphenols (GTP) on glycosylated soybean protein isolate-lutein (GSPI-lutein) complexes with inulin-type fructans and the GSPI after losing their protective. Screening for various types of polyphenols in tea polyphenols (GTP) revealed that epicatechin gallate (ECG) was mainly responsible for disrupting the protective efficacy of lutein and shortening the protection time from 32 to 24 h. Epicatechin (EC) exhibited the strongest protective efficacy, with the protection time prolonged to 14 days. Meanwhile, the protective efficacy of the modified proteins for lutein was lost after a period of time. Following the loss of protective ability, the a-helix and the total mercapto contents decreased, and the loose porous structure disappeared. This study explored the protective effect of modified proteins on natural pigments, but we were unable to identify the specific functional sites of the proteins involved in the reaction process.

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.

Modification of soy protein isolate and pea protein isolate by high voltage dielectric barrier discharge (DBD) atmospheric cold plasma: Comparative study on structural, rheological and techno-functional characteristics

The modification in structural, rheological, and techno-functional characteristics of soy and pea protein isolates (SPI and PPI) due to dielectric barrier discharge cold plasma (DBD-CP) were assessed. The increased carbonyl groups in both samples with cold plasma (CP) treatment led to a reduction in free sulfhydryl groups. Moreover, protein solubility of treated proteins exhibited significant improvements, reaching up to 59.07 % and 41.4 % for SPI and PPI, respectively, at 30 kV for 8 min. Rheological analyses indicated that storage modulus (G') was greater than loss modulus (G″) for CP-treated protein gels. Furthermore, in vitro protein digestibility of SPI exhibited a remarkable improvement (4.78 %) at 30 kV for 6 min compared to PPI (3.23 %). Spectroscopic analyses, including circular dichroism and Fourier Transform-Raman, indicated partial breakdown and loss of α-helix structure in both samples, leading to the aggregation of proteins. Thus, DBD-CP induces reactive oxygen species-mediated oxidation, modifying the secondary and tertiary structures of samples.

Novel a-linolenic acid emulsions stabilized by octenyl succinylated starch -soy protein-epigallocatechin-3-gallate complexes: Characterization and antioxidant analysis

In this study, octenyl succinylated starch (OSAS)-soy protein (SP)-epigallocatechin-3-gallate (EGCG) complexes were designed to enhance the physical and oxidative stability of α-linolenic acid emulsions. Formations of OSAS-SP-EGCG complexes were confirmed via particle size, ξ-potential, together with fourier transform infrared (FTIR). A mixing ratio of 1:2 for OSAS to SP-EGCG resulted in ternary complexes with the highest contact angle (59.69°), indicating the hydrophobicity. Furthermore, the characteristics of α-linolenic acid emulsions (oil phase volume fractions (φ) of 10% and 20%) stabilized by OSAS-SP-EGCG complexes were investigated, including particle size, ξ-potential, emulsion stability, oxidative stability, and microstructure. These results revealed exceptional physical stability together with enhanced oxidative stability for these emulsions. Particularly, emulsions utilizing complexes having a 1:2 OSAS to SP-EGCG ratio exhibited superior emulsion stability. These findings provide theoretical support to the development of emulsions containing high levels of α-linolenic acid and for the broader application of α-linolenic acid in food products.

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.

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.

Dual Decoration of Ferritin Nanocages by Caffeic Acid and Betanin with Covalent and Noncovalent Approaches: Structure and Stability Analyses

Ferritin is a cage-like protein with modifiable outer and inner surfaces. To functionalize ferritin with preferable carrier applications, caffeic acid was first covalently bound to the soybean ferritin outer surface to fabricate a caffeic acid-ferritin complex (CFRT) by alkali treatment (pH 9.0). A decreased content of free amino acid (0.34 μmol/mg) and increased polyphenol binding equivalent (63.76 nmol/mg) indicated the formation of CFRT (ferritin/caffeic acid, 1:80). Fluorescence and infrared spectra verified the binding of caffeic acids to the ferritin structure. DSC indicated that the covalent modification enhanced the thermal stability of CFRT. Besides, CFRT maintained the typically spherical shape of ferritin (12 nm) and a hydration radius of 7.58 nm. Moreover, the bioactive colorant betanin was encapsulated in CFRT to form betanin-loaded CFRT (CFRTB), with an encapsulation rate of 15.5% (w/w). The betanin stabilities in CFRTB were significantly improved after heat, light, and Fe3+ treatments, and its red color retention was enhanced relative to the free betanin. This study delves into the modifiable ferritin application as nanocarriers of dual molecules and gives guidelines for betanin as a food colorant.

Schiff base linkage of citral to zinc-casein hydrolysate chelates for preparing starch-based active films against L. monocytogenes on ready-to-eat foods

Listeria monocytogenes (L. monocytogenes) is a foodborne pathogen often found in ready-to-eat (RTE) foods, posing significant threats to human health. In this study, an active film based on cross-linking via Schiff base and electrostatic interaction to inactivate L. monocytogenes on RTE foods was constructed. Zinc-casein hydrolysate chelates (Zn-HCas) was prepared and blended with cationic starch (CSt) to form the substrates of the film. Then, Citral (CI) with excellent antibacterial properties was added to enhance the biological and packaging properties of the film through covalent cross-linking (Schiff base). Based on the zinc ion-activated metalloproteinases produced by L. monocytogenes, the cross-linked film could be disrupted and the release of CI was accelerated. The variation in color, FTIR, and amino group content proved that Schiff base reaction had taken place. Enhanced mechanical properties, barrier properties, thermal stability and antimicrobial activity against L. monocytogenes (exceed 99.99 %) were obtained from the CI/Zn-HCas/CSt film. The application on RTE cheese results demonstrated that the cross-linked film could be employed in active packaging field with the ability in maintaining the original chroma and texture properties of RTE cheese. In summary, the prepared cross-linked film could be used as an active packaging against L. monocytogenes contamination with great potential.

Covalent polyphenols-proteins interactions in food processing: formation mechanisms, quantification methods, bioactive effects, and applications

Proteins and polyphenols are abundant in the daily diet of humans and their interactions influence, among other things, the texture, flavor, and bioaccessibility of food. There are two types of interactions between them: non-covalent interactions and covalent interactions, the latter being irreversible and more powerful. In this review, we systematically summarized advances in the investigation of possible mechanism underlying covalent polyphenols-proteins interaction in food processing, effect of different processing methods on covalent interaction, methods for characterizing covalent complexes, and impacts of covalent interactions on protein structure, function and nutritional value, as well as potential bioavailability of polyphenols. In terms of health promotion of the prepared covalent complexes, health effects such as antioxidant, hypoglycemic, regulation of intestinal microbiota and regulation of allergic reactions have been summarized. Also, the possible applications in food industry, especially as foaming agents, emulsifiers and nanomaterials have also been discussed. In order to offer directions for novel research on their interactions in food systems, nutritional value, and health properties in vivo, we considered the present challenges and future perspectives of the topic.

Tartary buckwheat protein-phenol conjugate prepared by alkaline-based environment: Identification of covalent binding sites of phenols and alterations in protein structural and functional characteristics

Tartary buckwheat protein-rutin/quercetin covalent complex was synthesized in alkaline oxygen-containing environment, and its binding sites, conformational changes and functional properties were evaluated by multispectral technique and proteomics. The determination of total sulfhydryl and free amino groups showed that rutin/quercetin can form a covalent complex with BPI and could significantly reduce the group content. Ultraviolet-visible spectrum analysis showed that protein could form new characteristic peaks after binding with rutin/quercetin. Circular dichroism spectrum analysis showed that rutin and quercetin caused similar changes in the secondary structure of proteins, both promoting β-sheet to α-helix, β-ture and random coil transformation. The fluorescence spectrometry results showed that the combination of phenols can cause the fluorescence quenching, and the combination of rutin was stronger than the quercetin. Proteomics showed that there were multiple covalent binding sites between phenols and protein. Rutin had a high affinity for arginine, and quercetin and cysteine had high affinity. Meanwhile, the combination of rutin/quercetin and protein had reduced the surface hydrophobic ability of the protein, and improved the foaming, stability and antioxidant properties of the protein. This study expounded the mechanism of the combination of BPI and rutin/quercetin, and analysed the differences of the combination of protein and phenols in different structures. The findings can provide a theoretical basis for the development of complexes in the area of food.

Covalent and non-covalent interaction of myofibrillar protein and cyanidin-3-O-glucoside: focus on structure, binding sites and in vitro digestion properties

BACKGROUND

The aim of this study was to investigate the effects of covalent and non-covalent interactions between myofibrillar protein (MP) and cyanidin-3-O-glucoside (C3G) on protein structure, binding sites, and digestion properties. Four methods of inducing covalent cross-linking were used in the preparation of MP-C3G conjugates, including tyrosinase-catalyzed oxidation, alkaline pH shift treatment, free radical grafting, and ultrasonic treatment. A comparison was made between MP-C3G conjugates and complexes, and the analysis included sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), C3G binding ratio, liquid chromatography-tandem mass spectrometry (LC-MS/MS), protein side-chain amino acids, circular dichroism spectroscopy, three-dimensional fluorescence, particle size, and in vitro simulated digestion.

RESULTS

Covalent bonding between C3G and amino acid side chains in MP was confirmed by LC-MS/MS. In covalent bonding, tryptophan residues, free amino groups and sulfhydryl groups were all implicated. Among the 22 peptides covalently modified by C3G, 30 modification sites were identified, located in lysine, histidine, tryptophan, arginine and cysteine. In vitro simulated digestion experiments showed that the addition of C3G significantly reduced the digestibility of MP, with the covalent conjugate showing lower digestibility than the non-covalent conjugate. Moreover, the digestibility of protein decreased more during intestinal digestion, possibly because covalent cross-linking of C3G and MP further inhibited trypsin targeting sites (lysine and arginine).

CONCLUSION

Covalent cross-linking of C3G with myofibrillar proteins significantly affected protein structure and reduced protein digestibility by occupying more trypsin binding sites. © 2023 Society of Chemical Industry.

Construction of hypoallergenic microgel by soy major allergen β-conglycinin through enzymatic hydrolysis and lactic acid bacteria fermentation

Soy allergenicity is a public concern, and the combination of multiple processing methods may be a promising strategy for reducing soy allergenicity. In this study, a novel two-step enzymatic hydrolysis followed by lactic acid bacteria fermentation was proposed for the construction of hypoallergenic soybean protein microgel. β-Conglycinin was used as the main soy allergen. The effects of different enzymatic hydrolysis (Alcalase, Neutrase, and Protamex) and LAB fermentation on β-conglycinin microgel formation and its immunoreactivity were investigated. Results showed that the use of different enzymes and the attainment of different degrees of hydrolysis affected the particle distribution and zeta potential in the microgels and leads to differences in microstructure and immunoreactivity. All hydrolysates compared with intact protein accelerated the formation of gel during LAB fermentation. Among the three assayed enzymes, fermented Protamex hydrolysates at 60 min (PF-60) demonstrated a microgel with an overall reduced average particle size (741.20±7.18 nm), lower absolute values of zeta potential (10.43±0.65 mV), and regular gel network. The antigenicity and IgE-binding capacity decreased to the lowest value of 0.30 % and 6.93 %, respectively. Peptidomics and immunoinformatic analysis suggested that PF-60 disrupted 17/30, 16/44, and 23/75 epitopes in the α, α', and β subunits, respectively. Unlike the LAB-fermented unhydrolyzed β-conglycinin disrupted epitopes mostly located at the loop domain, PF-60 primarily promoted the exposure and disruption of allergen epitopes with β-sheet structure located at the core barrel domain. These findings can provide new perspectives on the preparation of hypoallergenic soybean-gel products on edible particulate systems.

All natural mussel-inspired bioadhesives from soy proteins and plant derived polyphenols with marked water-resistance and favourable antibacterial profile for wound treatment applications

HYPOTHESIS

Implementation of tissue adhesives from natural sources endowed with good mechanical properties and underwater resistance still represents a challenging research goal. Inspired by the extraordinary wet adhesion properties of mussel byssus proteins resulting from interaction of catechol and amino residues, hydrogels from soy protein isolate (SPI) and selected polyphenols i.e. caffeic acid (CA), chlorogenic acid (CGA) and gallic acid (GA) under mild aerial oxidative conditions were prepared.

EXPERIMENTS

The hydrogels were subjected to chemical assays, ATR FT-IR and EPR spectroscopy, rheological and morphological SEM analysis. Mechanical tests were carried out on hydrogels prepared by inclusion of agarose. Biological tests included evaluation of the antibacterial and wound healing activity, and hemocompatibility.

FINDINGS

The decrease of free NH2 and SH groups of SPI, the EPR features, the good cohesive strength and excellent underwater resistance (15 days for SPI/GA) under conditions relevant to their use as surgical glues indicated an efficient interaction of the polyphenols with the protein in the hydrogels. The polyphenols greatly also improved the mechanical properties of the SPI/ agarose/polyphenols hydrogels. These latter proved biocompatible, hemocompatible, not harmful to skin, displayed durable adhesiveness and good water-vapour permeability. Excellent antibacterial properties and in some cases (SPI/CGA) a favourable wound healing activity on dermal fibroblasts was obtained.

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.

Preparation, Characterization and Antioxidant Activity of Glycosylated Whey Protein Isolate/Proanthocyanidin Compounds

A glycosylated protein/procyanidin complex was prepared by self-assembly of glycosylated whey protein isolate and proanthocyanidins (PCs). The complex was characterized through endogenous fluorescence spectroscopy, polyacrylamide gel electrophoresis, Fourier infrared spectroscopy, oil-water interfacial tension, and transmission electron microscopy. The results showed that the degree of protein aggregation could be regulated by controlling the added amount of procyanidin, and the main interaction force between glycosylated protein and PCs was hydrogen bonding or hydrophobic interaction. The optimal binding ratio of protein:PCs was 1:1 (w/w), and the solution pH was 6.0. The resulting glycosylated protein/PC compounds had a particle size of about 119 nm. They exhibited excellent antioxidant and free radical-scavenging abilities. Moreover, the thermal denaturation temperature rose to 113.33 °C. Confocal laser scanning microscopy (CLSM) images show that the emulsion maintains a thick interface layer and improves oxidation resistance with the addition of PCs, increasing the application potential in the functional food industry.

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.

Identification of binding sites for Tartary buckwheat protein-phenols covalent complex and alterations in protein structure and antioxidant properties

To investigate the effects of structure, multiple binding sites and antioxidant property of Tartary buckwheat protein-phenols covalent complex, protein was combined with different concentrations of phenolic extract. Four kinds of phenols were identified by UPLC-Q/TOF-MS, which were rutin, quercetin, kaempferol and myricetin. UV-vis absorption spectroscopy and X-ray diffraction showed that the phenols can successfully bind to BPI. Fourier-transform infrared, circular dichroism and fluorescence emission spectroscopy showed that the binding of phenol can change the secondary/tertiary structure of protein. The particle distribution indicated that the binding of phenols could reduce the particle size (from 304.70 to 205.55 nm), but cross-linking occurred (435.35 nm) when the bound phenol content was too high. Proteomics showed that only rutin, quercetin and myricetin can covalently bind to BPI. Meanwhile, 4 peptides covalently bound to phenols were identified. The DPPH· scavenging capacity of complexes were from 8.38 to 33.76 %, and the ABTS·⁺ binding activity of complexes were from 19.35 to 63.99 %. The antioxidant activity of the complex was significantly higher than that of the pure protein. These results indicated that protein-phenol covalent complexes had great potential as functional components in the food field.

Soy Protein Isolate Interacted with Acrylamide to Reduce the Release of Acrylamide in the In Vitro Digestion Model

Acrylamide (AA), a common carcinogen, has been found in many dietary products.. This study aimed to explore the interaction of soybean protein isolate (SPI) with AA and further research the different effects of SPI on the AA release due to interactions in the in vitro digestion model. Analysis of variance was used to analyze the data. The results suggested that AA could bind with SPI in vitro, leading to the variation in SPI structure. The intrinsic fluorescence of SPI was quenched by AA via static quenching. The non-covalent (van der Waals forces and hydrogen bonding) and covalent bonds were the main interaction forces between SPI and AA. Furthermore, the release of AA significantly decreased due to its interaction with SPI under simulated gastrointestinal conditions. SPI had different effects on the AA release rate after different treatments. The thermal (80, 85, 90, and 95 °C for either 10 or 20 min) and ultrasound (200, 300, and 400 W for either 15, 30, or 60 min) treatments of SPI were useful in reducing the release of AA. However, the high pressure-homogenized (30, 60, 90, and 120 MPa once, twice, or thrice) treatments of SPI were unfavorable for reducing the release of AA.

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.

Effect of processing treatments on the allergenicity of nuts and legumes: A meta-analysis

The effective food processing to reduce nuts and legumes allergenicity could not be easily and directly concluded from reading a few published reports. Therefore, we conducted a meta-analysis to investigate this issue. A literature search was conducted in eight electronic databases from January 2000 to June 11, 2021. The primary outcome of interest was the allergenicity of processed nuts or legumes determined by enzyme-linked immunosorbent assay from in vitro studies. Data with the standardized mean difference (SMD) of 95% confidence interval (CI) were pooled using a random-effect model by RevMan 5.4 software. Heterogeneity was assessed using Cochran's Q (P_Q ) and I² tests. The search strategy identified 18,793 articles. However, only 61 studies met the inclusion criteria and were included in this meta-analysis. There were 21 and 15 types of respective single and combined food processing treatments analyzed for their effects on reducing allergenicity. In single processing treatment, the extrusion and fermentation had the largest reduction in allergenicity, considering their SMD value, that is, -20.19 (95% CI: -22.22 to -18.17; the certainty of evidence: moderate) and -20.8 (95% CI: -24.10 to -17.50; the certainty of evidence: moderate), respectively. Whereas in the combination, the treatment of fermentation followed by proteolytic hydrolysis showed the most significant reduction (SMD: -53.34; 95% CI: -70.18 to -36.5) and the evidence quality of this treatment was considered moderate. In conclusion, these three food processing methods showed a desirable impact in reducing nuts or legumes allergenicity. PRACTICAL APPLICATION: Nuts and legumes play an essential role as protein sources in food consumption worldwide, but they usually contain allergens. Our study has investigated the food processing methods that effectively reduce their allergenicity by meta-analysis. The result gives valuable information for further laboratory investigation on allergens and can be used by food industries in providing foods from nuts and legumes with lower allergenicity.

Reducing the potential allergenicity of amandin through binding to (-)-epigallocatechin gallate

Potential allergenicity of amandin was reduced by binding amandin with (-)-epigallocatechin gallate (EGCG) via alkaline, free radical, ultrasound-assisted alkaline, and ultrasound-assisted free radical methods. These results of total phenol content, free sulfhydryl group, free amino group, surface hydrophobicity, and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) indicated that amandin might be covalently bound to EGCG through reactive groups such as sulfhydryl and amino groups, or non-covalently through hydrophobic interactions. Fourier transformed infrared (FT-IR) spectroscopy and fluorescence spectroscopy revealed structural changes of amandin-EGCG conjugate, which also caused significant reduction in potential allergenicity of amandin. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) found that amandin bound to EGCG mainly through cysteine and glutamate residues, and linear epitope for amandin was reduced. This provided a new method and theoretical basis of hypoallergenic almond food.

Investigation of differences in allergenicity of protein from different soybean cultivars through LC/MS-MS

Soybean allergy is a health-threatening issue and identifying raw soybeans with low allergenicity is important for producing hypoallergenic soybean products. Soybean allergy is mainly triggered by soybean proteins. In this study, the protein profiles, allergen compositions, and epitopes in protein from different soybean cultivars (R1, R2 and R3) were evaluated by SDS-PAGE and LC/MS-MS, and their allergenicity was assessed by indirect ELISA and Western blot analysis using the serum IgE of patients allergic to soybeans. The lowest allergenicity was observed in R3, probably resulting from the low concentration of Gly m 4-Gly m 6. The allergenicity of soybeans is affected by multiple allergens rather than a single allergen. Venn diagram, PCA, heatmap, and peptide map analyses have shown the differences in protein and peptide profiles among soybean proteins from different soybean cultivars. Epitope analysis further demonstrated that low contents of dominant epitopes in Gly m 4 and Gly m 5 contributed to low allergenicity in R3, although R3 contained high contents of no-dominant epitopes.

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.

Impact of covalent grafting of two flavonols (kaemperol and quercetin) to caseinate on in vitro digestibility and emulsifying properties of the caseinate-flavonol grafts

Covalent grafting of one of the two flavonols (kaemperol and quercetin) to caseinate was achieved by a reaction between the heat-oxidized flavonols and caseinate at flavonol-lysine molar ratios of 1:100 and 1:200. Grafted caseinate products (GCPs) showed - NH₂ content reduction and respective kaemperol and quercetin contents of 1.08-6.13 and 3.23-6.64 mmol/kg protein. Quercetin was more reactive than kaemperol under the same conditions, while long-time flavonol heat and higher flavonol-lysine molar ratio caused greater flavonol-grafting. GCPs subjected to 180-day storage had further flavonol-grafting, -NH₂ content decrease, and weak protein crosslinking. GCPs consistently had higher surface hydrophobicity but lower emulsification and digestibility than caseinate, while greater flavonol-grafting caused a remarkable value change. Meanwhile, the Kjeldahl method was more suitable than the UV-absorption method to evaluate protein digestibility, because the grafted flavonols in this case did not interfere with data results. Collectively, the covalent flavonol-grafting of proteins can impact the assayed protein functionalities.

Non-covalent interaction of soy protein isolate and catechin: Mechanism and effects on protein conformation

Understanding the molecular mechanism behind protein-polyphenol interactions is critical for the application of protein-polyphenol compounds in foods. The purpose of this research was to investigate the non-covalent interaction mechanism between soy protein isolate (SPI) and catechin and its effect on protein conformation. We observed that particle size, ζ-potential, and polyphenol bound equivalents of SPI increased significantly after non-covalent modification with catechin. These changes caused SPI to aggregate and form a network-like structure. Fourier transform infrared spectroscopy (FTIR) indicated that increased catechin concentrations caused SPI to become looser and more disordered as its α-helix and β-sheet transformed into β-turn and random coil. Furthermore, internal structure of SPI was opened and its hydrophobic groups were exposed to a polar environment, which was demonstrated by decreased surface hydrophobicity. Thermodynamic analysis and molecular docking results showed that the main forces present between SPI and catechin were hydrophobic interactions and hydrogen bonds.

Non-covalent interaction between pea protein isolate and catechin: effects on protein structure and functional properties

The aim of this study was to investigate the effects of non-covalent interaction between pea protein isolate (PPI) and different concentrations (0.05–0.25%, w/v) of catechin (CT) on the structural and functional characteristics of protein.

Conjugation of (-)-epigallocatechin-3-gallate and protein isolate from large yellow croaker (Pseudosciaena crocea) roe: improvement of antioxidant activity and structural characteristics

BACKGROUND

Large yellow croaker (Pseudosciaena crocea) roe is the main by-product in the processing of large yellow croaker. Previous studies have found that its protein isolates are composed of vitellogenin, as well as vitellogenin B and C, having good functional properties. (-)-Epigallocatechin-3-gallate (EGCG) is a natural antioxidant component that can be combined with protein to improve antioxidant activity and structural characteristics of protein.

RESULTS

EGCG was bound with the P. crocea roe protein isolate (pcRPI) by the free radical method to prepare the conjugate. The formation of pcRPI-EGCG conjugates was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel permeation chromatography, which showed that the calculated weight-average molar masses of native-pcRPI and pcRPI-EGCG conjugates were 86.9 and 215.3 kDa, respectively. The results of fluorescence, ultraviolet, circular and infrared spectra indicated that the conjugation of EGCG with native-pcRPI changed the secondary and tertiary structure of native-pcRPI. The pcRPI-EGCG conjugates exhibited higher thermal stability than native-pcRPI. The radical scavenging and reducing power of native-pcRPI were increased by 2.0-2.5- and 1.4-fold, respectively, after the EGCG-grafting reaction.

CONCLUSION

These results indicate that the binding of pcRPI and EGCG effectively improved the antioxidant properties and structural characteristics of the pcRPI. © 2021 Society of Chemical Industry.

Inhibitory Effects of Six Types of Tea on Aging and High-Fat Diet-Related Amyloid Formation Activities

Aging and lipid metabolism disorders promote the formation and accumulation of amyloid with β-sheet structure, closely related to cardiovascular disease, senile dementia, type 2 diabetes, and other senile degenerative diseases. In this study, five representative teas were selected from each of the six types of tea, and a total of 30 teas were selected to evaluate the inhibitory activities on the formation of aging-related amyloid in vitro. The results showed that the 30 teas had a significant inhibitory effect on the formation activity on aging-related amyloid at the protein level in vitro. Although the content of catechins is relatively low, black tea and dark tea still have significant antioxidant activity and inhibit the formation of amyloid. A high-fat diet established the model of lipid metabolism disorder in premature aging SAMP8 mice, and these mice were gavaged different tea water extracts. The results showed that different tea types have a significant inhibitory effect on the formation of β-amyloid and Aβ42 mediated by age-related lipid metabolism disorders, and the in vivo activity of fully fermented teas was better than that of green tea. The action mechanism was related to antioxidation, anti-inflammatory, and improving lipid metabolism.

Enzymatic and Nonenzymatic Conjugates of Lactoferrin and (-)-Epigallocatechin Gallate: Formation, Structure, Functionality, and Allergenicity

The impact of covalent attachment of (-)-epigallocatechin gallate (EGCG) to lactoferrin (LF) on the structure, morphology, functionality, and allergenicity of the protein was studied. These polyphenol-protein conjugates were formed using various enzymatic (laccase- and tyrosinase-catalyzed oxidation) and nonenzymatic (free radical grafting and alkali treatment) methods. The preparation conditions for forming the enzymatic conjugates were optimized by exploring the influence of order-of-addition effects: protein, polyphenols, and enzymes. The total phenol content of the LF-EGCG conjugates was quantified using the Folin-Ciocalteu method. The nature of the conjugates formed was determined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Fourier transform infrared (FTIR) spectroscopy analyses. These studies showed that enzymatic cross-linking was a highly effective means of forming LF-EGCG conjugates. Analysis of these conjugates using various spectroscopic methods showed that conjugation to EGCG changed the molecular structure of LF. Atomic force microscopy showed that the four covalent cross-linking methods affected the size and morphology of these LF-EGCG conjugates formed. The antioxidant activity and emulsifying stability of LF were significantly improved by conjugation to EGCG. Finally, an enzyme-linked immunosorbent assay (ELISA) and a western blot assay indicated that conjugation of EGCG reduced the binding capacity of LF to immunoglobulin E (IgE) and immunoglobulin G (IgG), which is consistent with a decrease in allergenicity. Overall, this study suggests that LF-EGCG conjugates formed using enzymatic or nonenzymatic methods have potential applications as functional ingredients in foods.