Molecular interaction of soybean glycinin and β-conglycinin with (−)-epigallocatechin gallate induced by pH changes

Development and characterization of adhesives constructed by soy protein isolate and tea polyphenols for enhanced tensile strength in plant-protein meat applications

The study aimed to evaluate a food adhesive developed using tea polyphenols (TPs) with soybean protein isolate (SPI) to create a cohesive bond between soy protein gel and simulated fat. Upon the addition of 5.0 % TPs, significant increases in viscosity, thermal stability, and crystallinity were noted in adhesives, suggesting the formation of a cohesive network. Furthermore, TPs effectively enhanced adhesion strength, with the optimal addition being 5.0 %. This enhancement can be attributed to hydrogen bonding, hydrophobic and electrostatic interactions between TPs and SPI molecules. TPs induced a greater expansion of the protein structure, exposing numerous buried hydrophobic groups to a more hydrophilic and polar environment. However, excessive TPs were found to diminish adhesion strength. This can be attributed to enhanced reactions between TPs and SPI, where high molecular weight SPI-TPs cooperatively aggregate to form agglomerates that eventually precipitated, rendering the adhesive network inhomogeneous, less stable, and more prone to disruption.

Characterization of the covalent binding of cyanidin-3-glucoside to bovine serum albumin and its inhibition mechanism for advanced nonenzymatic glycosylation reactions

Nonenzymatic glycosylation of proteins can generate advanced glycosylation end products, which are closely associated with the pathogenesis of certain chronic physiological diseases and aging. In this study, we characterized the covalent binding of cyanidin-3-glucoside (C3G) to bovine serum albumin (BSA) and investigated the mechanism by which this covalent binding inhibits the nonenzymatic glycosylation of BSA. The results indicated that the covalent interaction between C3G and BSA stabilized the protein's secondary structure. Through liquid chromatography-electrospray ionization tandem mass spectrometry analysis, we identified the covalent binding sites of C3G on BSA as lysine, arginine, asparagine, glutamine, and cysteine residues. This covalent interaction significantly suppressed the nonenzymatic glycosylation of BSA, consequently reducing the formation of nonenzymatic glycosylation products. C3G competitively binds to nonenzymatic glycosylation sites (e.g., lysine and arginine) on BSA, thereby impeding the glycosylation process and preventing the misfolding and structural alterations of BSA induced by fructose. Furthermore, the covalent attachment of C3G to BSA preserves the secondary structure of BSA and hinders subsequent nonenzymatic glycosylation events.

Unraveling the binding mechanism between soybean protein isolate and selected bioactive compounds

The present study was aimed to investigate the interactions between soybean protein isolate (SPI) with resveratrol (RESV) and lutein (LUT). The binding forces, molecular interactions and functional properties were explored by multi-spectroscopic analysis, molecular docking and functional property indexes between SPI and RESV/LUT. The RESV/LUT quenched SPI chromophore residues with static mechanism and the endothermic reaction. The SPI- RESV/LUT complexes were formed through hydrogen bond, electrostatic and hydrophobic interactions. Molecular docking confirmed van-der-Waals force as one of the important forces. The interaction of RESV/LUT led to SPI's secondary structure alterations with a decrease in α-helix and random coil and an increase in β-sheet and β-turns. RESV/LUT developed foaming and emulsifying properties of SPI and showed a significant decrease of the surface hydrophobicity with RESV/LUT concentrations increase attributed to SPI's partial unfolding. Our study exposed molecular mechanisms and confirmations to understand the interactions in protein- RESV/LUT complexes for protein industrial base promotion.

Formation mechanism of quinoa protein hydrolysate-EGCG complexes at different pH conditions and its effect on the protein hydrolysate-lipid co-oxidation in emulsions

This study aimed to investigate the interaction, structure, antioxidant, and emulsification properties of quinoa protein hydrolysate (QPH) complexes formed with (-)-epigallocatechin gallate (EGCG) at pH 3.0 and 7.0. Additionally, the effect of pH conditions and EGCG complexation on protein hydrolysate-lipid co-oxidation in QPH emulsions was explored. The results indicated that QPH primarily interacted with EGCG through hydrophobic interactions and hydrogen bonds. This interaction led to alterations in the secondary structure of QPH, as well as a decrease in surface hydrophobicity and free SH content. Notably, the binding affinity between QPH and EGCG was observed to be higher at pH 7.0 compared to pH 3.0. Consequently, QPH-EGCG complexes exhibited more significant enhancement in antioxidant and emulsification properties at pH 7.0 than pH 3.0. The pH level also influenced the droplet size, ζ-potential, and interfacial composition of emulsions formed by QPH and QPH-EGCG complexes. Compared to QPH stabilized emulsions, QPH-EGCG stabilized emulsions were more capable of mitigating destabilization during storage and displayed fewer lipid oxidation products, carbonyl generation, and sulfhydryl groups and fluorescence loss, which implied better oxidative stability of the emulsions. Furthermore, the QPH-EGCG complexes formed at pH 7.0 exhibited better inhibition of protein hydrolysate-lipid co-oxidation. Overall, these findings provide valuable insights into the potential application of QPH and its complexes with EGCG in food processing systems.

pH-regulated Tannic acid and soybean protein isolate adhesive for enhanced performance in plant-based meat analogues

A food adhesive comprising tannic acid (TA) and soybean protein isolate (SPI) was developed to establish a cohesive bond between soy protein gel and simulated fat. The impact of varying TA concentrations and pH levels on the adhesive's rheology, thermal stability, chemical structure, and tensile strength were investigated. Rheological results revealed a gradual decrease in adhesive viscosity with increasing TA content. Differential scanning calorimetry (DSC) and thermal gravimetric (TG) results indicated that the stability of the adhesive improved with higher TA concentrations, reaching its peak at 0.50% TA addition. The incorporation of TA resulted in the cross-linking of amino group in unfolded SPI molecules, forming a mesh structure. However, under alkaline conditions (pH 9), adhesive viscosity and stability increased compared to the original pH. This shift was due to the disruption of the SPI colloidal charge structure, an increase in the stretching of functional groups, further unfolding of the structure, and an enhanced binding of SPI to TA. Under the initial pH conditions, SPI reacted with TA's active site to form covalent crosslinked networks and hydrogen bonds. In alkaline condition, beyond hydrogen and ionic bonding, the catechol structure was oxidized, forming an ortho-quinone that crosslinked SPI and created a denser structure. Tensile strength measurements and freeze-thaw experiments revealed that the adhesive exhibited maximum tensile strength and optimal adhesion with 0.75% TA at pH 9, providing the best overall performance. This study provides a new formulation and approach for developing plant-based meat analogues adhesives.

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.

Comparison of pH-induced protein-polyphenol self-assembly methods: Binding mechanism, structure, and functional characteristics

Herein, we used pH-shifted and pH-driven methods to assemble kidney-bean protein isolate (KPI) and luteolin (Lut) into a nanocomplex and subsequently investigated their binding mechanism, structure, and functional properties. Results showed that the nanocomplex prepared by the pH-driven method exhibited a better encapsulation effect and controlled release of Lut. Fluorescence spectroscopy and molecular docking analysis showed that the binding affinities under alkaline conditions were higher than those under acidic and neutral conditions. Various spectral techniques were used to determine the structural changes in the KPI-Lut nanocomplex, including the transformation of α-helices and β-sheets and alteration of specific amino acid microenvironments, which were more pronounced in the pH-driven nanocomplex. The structural changes in the nanocomplex further affected their surface hydrophobicity and thermal stability. Additionally, the combination of KPI and Lut significantly improved the antioxidant activity and α-glucosidase inhibitory ability of the resultant nanocomplexes, particularly the one prepared by the pH-driven method.

Insight into the binding characteristics of epigallocatechin-3-O-gallate and alcohol dehydrogenase: Based on the spectroscopic and molecular docking analysis

Alcohol dehydrogenase (ADH) is one of the pivotal enzymes for alcohol metabolism, which plays an important role in many physiological processes. In this study, the activation effects of epigallocatechin-3-O-gallate (EGCG) on ADH and the characteristics of the interaction were investigated via biochemical method, spectroscopy methods, and molecular docking. The results demonstrated that EGCG significantly increased the catalytic activity of ADH with a 33.33% activation rate and that EGCG blending slightly altered the microenvironment surrounding ADH aromatic amino acids, with an increase in the quantity of β-sheet and a decrease in the α-helix. Through the thermal stability analysis, it is further shown that the interaction of the two affects the intra-molecular hydrogen bond formation of the protein, and the conformation is partially extended. Besides, a total of 8 residues in ADH participated in the docking with EGCG, among which Asp-227, Lys-231, Glu-234, Gly-365 and Glu-366 participated in the formation of hydrogen bonds. At the same time, EGCG and amino group of Lys-231 form a noncovalent bond through cation-π interaction. In particular, hydrogen bonding was beneficial to keep the stability of EGCG-ADH, which was the primary driver of ADH activity activation. The results supply a new way for EGCG to activate ADH and a theoretical basis for the development of anti-alcoholism products.

Effect of enzymolysis combined with Maillard reaction treatment on functional and structural properties of gluten protein

In this work, the modified gluten was prepared by enzymolysis combined with Maillard reaction (MEG), and its functional and structural properties were investigated. The result showed that the maximum foamability of MEG was 19.58 m2/g, the foam stability was increased by 1.8 times compared with gluten, and the solubility and degree of graft were increased to 44.4 % and 28.1 % at 100 °C, whereas the content of sulfhydryl group decreased to 0.81 μmol/g. The scavenging ability on ABTS+radical and DPPH radical of MEG was positively correlated with reaction temperature, and the maximum values were 86.57 % and 71.71 % at 140 °C, respectively. Furthermore, the fluorescence quenching effect of tryptophan and tyrosine residues was enhanced, while the fluorescence intensity decreased with the temperature increase. Scanning electron microscopy revealed that the surface of enzymatically hydrolyzed-gluten became smooth and the cross section became straightened, while MEG turned smaller and irregular approaching a circular structure. FT-IR spectroscopy showed that enzymatic hydrolysis promoted the occurrence of more carbonyl ammonia reactions and the formation of precursors of advanced glycosylation end products. These results provide a feasible method for improving the structure and functional properties of gluten protein.

Pickering emulsions stabilized by ternary complexes involving curcumin-modified zein and polysaccharides with different charge amounts for encapsulating β-carotene

In this research, zein was modified with curcumin to obtain covalent and non-covalent complexes. They were further covered with polysaccharides (gum arabic or gum karaya) possessing different surface charge amounts to obtain ternary nanoparticles for preparing novel antioxidant Pickering emulsions. The addition of curcumin to the zein-polysaccharide system significantly retarded the UV degradation of the encapsulated β-carotene (maximum retention ∼ 97%) and effectively inhibited the lipid oxidation of the emulsions. In vitro gastrointestinal digestion assays showed that gum karaya significantly delayed the release of free fatty acids, thereby improving the bioaccessibility of β-carotene (the highest bioavailability ∼ 38%). By comparing the performance of the complex particles, the weakly charged polysaccharides were superior to the highly charged ones, while zein-curcumin covalent binding was superior to non-covalent binding in the above experiments. This study provides innovative perspectives on the use of novel Pickering emulsions to provide ideal protection and bioavailability of lipophilic nutraceuticals.

Comparative study of dietary phenols with Tartary buckwheat protein (2S/13S): impact on structure, binding sites and functionality of protein

BACKGROUND

This research was to investigate the interaction mechanism between 2S albumin and 13S globulin (2S and 13S, the most important storage proteins in Tartary buckwheat seeds) and three phenols (rutin, quercetin and myricetin) regarding the structural and antioxidant properties of their complexes.

RESULTS

There are differences in the binding affinity of phenols for 2S and 13S. Rutin had a higher binding affinity for 2S, myricetin had a higher binding affinity for 13S, and 13S exhibited a higher affinity toward phenols than did 2S. Binding with phenols significantly changed the secondary and tertiary structures of 2S and 13S, decreased the surface hydrophobic value and enhanced the antioxidant capacity. Molecular docking and isothermal titration calorimetry showed that the binding processes were spontaneous and that there were hydrogen bonds, hydrophobic bonds and van der Waals force interactions between phenols and proteins.

CONCLUSION

These findings could provide meaningful guidance for the further application of buckwheat protein complex. © 2023 Society of Chemical Industry.

Interactions of ferulic acid and ferulic acid methyl ester with endogenous proteins: Determination using the multi-methods

Ferulic acid (FA) and ferulic acid methyl ester (FAM) are important phenolic compounds in Baijiu. In this study, the interaction of FA and FAM with human serum albumin (HSA) and lysozyme (LZM) was investigated using multispectral methods and molecular dynamics simulation. FA and FAM could interact with HSA and LZM, changing the conformation and hydrophilicity of the protein. The quenching mechanisms of FA-HSA, FA-LZM, FAM-HSA, and FAM-LZM were all static-quenching. In the FA-HSA, FAM-HSA, and FA-LZM systems, the interaction forces were mainly hydrophobic interactions and hydrogen bonding. In the FAM-LZM system, the interaction forces were mainly hydrophobic interactions, hydrogen bonding, and van der Waals force. Common metal ions such as K+, Ca2+, Cu2+, Mg2+, and Mn2+ could affect the binding ability of FA and FAM to HSA and LZM. Moreover, FA and FAM could increase the stability of HSA and LZM, and the protein bound to FA/FAM was more stable than the free protein. FA and FAM had varying degrees of impact on the physiological activities of HSA and LZM. This study provides relevant information on the interactions and metabolic mechanisms of FA and its derivatives with endogenous proteins.

Regulation of interfacial mechanics of soy protein via co-extraction with flaxseed protein for efficient fabrication of foams and emulsions

Enrichment of plant proteins with functionality is of great importance for expanding their application in food formulations. This study proposed an innovation to co-enrich soy protein and flaxseed protein to act as efficient interfacial stabilizers for generating foams and emulsions. The structure, interfacial properties, and functionalities of the soy protein-flaxseed protein natural nanoparticles (SFNPs) obtained by alkali extraction-isoelectric precipitation (AE) and salt extraction-dialysis (SE) methods were investigated. Overall, the foamability of AE-SFNPs (194.67 %) was 1.45-fold that of SE-SFNPs, due to their more flexible structure, smaller particle size, and suitable surface wettability, promoting diffusion and adsorption at the air-water interface. AE-SFNPs showed higher emulsion stability (140.89 min), probably because the adsorbed AE-SFNPs with smaller size displayed soft particle-like properties and stronger interfacial flexibility, and therefore could densely and evenly arrange at the interface, facilitating the formation of a stiff and solid-like interfacial layer, beneficial for more stable emulsion formation. The findings may innovatively expand the applications of SFNPs as food ingredients.

ε-Polylysine and soybean protein isolate form nanoscale to microscale electrostatic complexes in solution: properties, interactions and as antimicrobial edible coatings on citrus

A feasible approach to enhance the antimicrobial efficacy of ε-polylysine (PL) in applications is to form delivery complexes with delicate structures and good dispersion properties. This work aims to study the multiscale structures, properties and interactions, and edible coating applications of the electrostatic complex formed by PL and soy protein isolate (SPI). When the mass ratio of SPI to PL (SE) was between 5 and 15, especially 11, microscale solid-liquid phase separation occurred in the system due to the small absolute zeta potential. When the SE was in the range of 15-20, the system formed a stable nanoscale suspension, the average particle size and zeta potential were 191 nm and -20 mV, respectively. The physicochemical properties of the complexes were investigated including the colloidal properties, spectroscopy and interactions analysis, viscosity, contact angle, and antimicrobial activities against Escherichia coli, Staphylococcus aureus, and Penicillium expansum. Finally, the in vivo application on citrus demonstrated that the nanoscale PL/SPI electrostatic complex (SE = 20) as functional coatings has both barrier and antimicrobial activities. The study provides a novel application strategy for PL and nanoscale electrostatic complexes as postharvest coatings.

Effect of polysaccharides on conformational changes and functional properties of protein-polyphenol binary complexes: A comparative study

This study aimed to investigate the effect of different polysaccharides on the binding behavior and functional properties of soybean protein isolate (SPI)-quercetin (Que) complex. The binding behavior was assessed using multi-spectral technique with the Stern-Volmer equation, which confirmed the presence of static fluorescence quenching in Que and SPI. The addition of sodium alginate (SA) resulted in a reduction of the binding affinity between SPI and Que, while dextran (DX) exhibited some promoting effect. A slight blue shift was observed in amide I and amide II bands, indicating the presence of hydrophobic and electrostatic interactions. Circular dichroism spectra revealed the ordered structures transformed into a more disordered state when polysaccharides were added, leading to an increase in random coils (SA: 18.5 %, DX: 15.4 %). Docking and dynamic simulations demonstrated that SA displayed greater stability within the hydrophobic compartments of SPI than DX, increased rigidity and stability of the SPI structure in SPI-Que-SA complexes. Electrostatic forces played a significant role between SPI and SA, while van der Waals forces were the main driving forces in SPI-DX complexes. Overall, the introduction of SA led to a looser and stable structure of SPI-Que complexes, resulting in an improvement of their emulsifying, foaming, and antioxidant properties.

Deciphering the interaction mechanism and binding mode between chickpea protein isolate and flavonoids based on experimental studies and molecular simulation

Chickpea protein isolate (CPI) is a promising novel plant protein, and protein-flavonoid system has also been applied in various food products. However, the interaction mechanism between CPI and flavonoids remains to be elucidated. In this paper, the affinity behavior between flavonoids and CPI was explained by constructing the three-dimensional quantitative structure-activity relationship (R2 = 0.988, Q2 = 0.777). Subsequently, four representative flavonoids were selected for further study. Multi-spectroscopy analysis showed that the sequence of affinity for CPI was puerarin > apigenin > naringenin > epigallocatechin gallate. Meanwhile, flavonoids altered the secondary structure and spatial conformation of CPI, leading to the static quenching of CPI. Additionally, thermodynamic analysis indicated that hydrogen bonding and van der Waals forces were the main driving forces for complex binding. Molecular docking and molecular dynamics simulations further explored the binding sites and conformations of complexes. This study provides theoretical guidance for in-depth research on the interaction patterns between biomacromolecules and small molecules in food matrices.

Importance of binary and ternary complex formation on the functional and nutritional properties of legume proteins in presence of phytic acid and calcium

Nowadays, legumes are considered as a good source of plant-based proteins to replace animal ones. They are more favorable regarding environmental aspects and health benefits, therefore many people consider moving toward a greener diet. Interestingly, recent consumer trends are promoting pea and faba bean as alternatives to soybean. Both are rich in protein and a good source of essential nutrients and minerals (calcium). However, these advantages can be partially impaired due to their high phytic acid content. This natural polyphosphate is a major antinutrient in plant-based foods, as it can bind minerals (particularly calcium) and proteins, thereby reducing their digestibility and subsequent bioavailability. Indeed, complexes formed are insoluble and limiting the absorption of nutrients, thus lowering the nutritional value of pulses. To understand and overcome these issues, the present review will refine specific mechanisms involved in assemblies between these three essential compounds in legumes as soluble/insoluble binary or ternary complexes. Molecular interactions are influenced by the environmental medium including pH, ionic strength and molar concentrations modulating the stability of these complexes during protein extraction. Protein/phytic acid/calcium complexes stability is of high relevance for food processing affecting not only structure but also functional and nutritional properties of proteins in legume-based foods.

Development of protein-polyphenol particles to stabilize high internal phase Pickering emulsions by polyphenols' structure

Protein-polyphenol colloidal particles are promising stabilizers for high internal phase Pickering emulsions (HIPPEs). However, the relationship between the structure of the polyphenols and its ability to stabilize HIPPEs has not been studied thus far. In this study, bovine serum albumin (BSA)-polyphenols (B-P) complexes were prepared, and their ability to stabilize HIPPEs was investigated. The polyphenols were bound to BSA via non-covalent interactions. Optically isomeric polyphenols formed similar bonds with BSA, whereas a greater number of trihydroxybenzoyl groups or hydroxyl groups in the dihydroxyphenyl moieties of polyphenols increased the B-P interactions. Polyphenols also reduced the interfacial tension and enhanced the wettability at the oil-water interface. The HIPPE stabilized by BSA-tannic acid complex exhibited the highest stability among the B-P complexes and resisted demixing and aggregation during centrifugation. This study promotes the potential applications of polyphenol-protein colloidal particles-stabilized HIPPEs in the food industry.

Suppression mechanism of L-lysine on the Epigallocatechin-3-gallate-induced loss of myofibrillar protein gelling potential

As a natural antioxidant, Epigallocatechin-3-gallate (EGCG) needed to be added in high doses to maintain the quality of meat products. However, high doses of EGCG caused the excessive aggregation of myofibrillar protein (MP), which damaged the gel properties of MP gels. Therefore, the purpose of this study was to investigate the mitigation of EGCG-induced loss of MP gelling potential by L-Lysine (L-Lys). The results showed that the addition of 20 mM L-Lys induced excessive unfolding and loose aggregation of MP at 10 µmol/g EGCG, and hence, reducing the solubility (14.5%) and the tryptophan fluorescence, and forming a network structure with a large aperture. Therefore, the cooking loss was decreased from 29.20% to 15.13%, and the strength of MP gels was decreased from 0.35 N to 0.17 N. However, L-Lys hindered the hydrogen bonding interactions and hydrophobic interactions between MP and EGCG by competing the binding sites of MP at 50 µmol/g EGCG, which was supported by the Zeta potential, surface hydrophobicity, FTIR and molecular docking analysis. Thus L-Lys mitigated the protein aggregation caused by 50 µmol/g EGCG, improved the solubility (23.02%∼86.99%) and apparent viscosity, which were beneficial for the formation of a continuous network structure in MP gels. Therefore, the cooking loss of MP gels was decreased from 52.40% to 41.30%, and the gel strength was enhanced from 0.13 N to o.22 N with 20 mM L-Lys addition. The present study could provide a new strategy for increasing the amounts of EGCG in meat products without damaging the gel properties of meat products.

Formation, characterization, and antigenicity of lecithin-β-conglycinin complexes

Lipid binding has been proposed to represent a functional property of many allergenic proteins. This study investigated the formation, characterization, and antigenicity of lecithin-β-conglycinin complexes. The results indicate that lecithin was combined with β-conglycinin via static quenching and primarily driven by hydrogen bonds and van der Waals forces. In addition, heat treatment reduced the antigenicity of complexes, as evidenced by changes in molecular weight and secondary and tertiary structures. It revealed that large aggregates developed and more hydrophobic regions were exposed for complexes after heat treatment, as well as a decrease in the β-sheet contents and an increase in the β-turn and random coil contents. Furthermore, the average particle size of the complexes increased with increased temperature treatment, and the morphology of the complexes exhibited an amorphous polymer. These findings shedlight on the interaction between lecithin and β-conglycinin and help us understand the role of lecithin in allergic reactions.

Fabrication of a novel antioxidant emulsifier through tuning the molecular interaction between soy protein isolates and young apple polyphenols

Soy protein isolates (SPI) exhibit weaker emulsifying properties than those of animal proteins, thereby limiting their wide applicability. In this study, a novel plant-based antioxidant emulsifier was developed using SPI and young apple polyphenols (YAP), and its underlying interaction mechanisms were discovered using multispectral technology and molecular docking. YAP physically bound to SPI through hydrogen bonds and hydrophobic interactions, which significantly enhanced the free radicals scavenging, reducing, and metal ion chelating abilities of SPI by introducing free hydroxyl groups. Moreover, SPI modified by YAP exerted better emulsifying performance owing to a looser protein structure, reflected by a higher random coil and a lower α-helix content. In addition, YAP may bridge adjacent SPI molecules, promoting the adsorption and anchoring of SPI at the oil-water interface. SPI-YAP complexes are promising antioxidant emulsifiers that can be used to nano-deliver functional oils and nutrients, thereby broadening SPI and YAP applications in the food industry.

Esterified Soy Proteins with Enhanced Antibacterial Properties for the Stabilization of Nano-Emulsions under Acidic Conditions

Soy protein isolate (SPI), including β-conglycinin (7S) and glycinin (11S), generally have low solubility under weakly acidic conditions due to the pH closed to their isoelectric points (pIs), which has limited their application in acidic emulsions. Changing protein pI through modification by esterification could be a feasible way to solve this problem. This study aimed to obtain stable nano-emulsion with antibacterial properties under weakly acidic conditions by changing the pI of soy protein emulsifiers. Herein, the esterified soy protein isolate (MSPI), esterified β-conglycinin (M7S), and esterified glycinin (M11S) proteins were prepared. Then, pI, turbidimetric titration, Fourier transform infrared (FTIR) spectra, intrinsic fluorescence spectra, and emulsifying capacity of esterified protein were discussed. The droplet size, the ζ-potential, the stability, and the antibacterial properties of the esterified protein nano-emulsion were analyzed. The results revealed that the esterified proteins MSPI, M7S, and M11S had pIs, which were measured by ζ-potentials, as pH 10.4, 10.3, and 9.0, respectively, as compared to native proteins. All esterified-protein nano-emulsion samples showed a small mean particle size and good stability under weakly acidic conditions (pH 5.0), which was near the original pI of the soy protein. Moreover, the antibacterial experiments showed that the esterified protein-based nano-emulsion had an inhibitory effect on bacteria at pH 5.0.

Complex plant protein prepared from rice protein and pea protein: Improve the thermal stability of betanin

Betanin (BN) is a kind of edible natural red pigment with a variety of biological activities, but the thermal instability of BN has critically restricted its application in food industry. In this study, complex plant protein (RP-PP) was constructed by rice protein (RP) and pea protein (PP) to study the thermal protection effect and protective mechanism on BN. Thermal degradation results indicated RP-PP significantly improved thermal protection effect, and the degradation rate of BN was decreased from 93.74 % to 56.48 % after heating at 80 ℃ for 60 min. The main interaction between RP-PP and BN was hydrophobic force based on the result of fluorescence spectroscopy, FTIR and molecular docking. In addition, a porous network structure of RP-PP was observed by SEM, and the pore structure gradually decreased at the presence of BN, which speculated BN was trapped in it. TEM observation showed that RP-PP gradually aggregated with the increasing BN concentration, leading to a significant increase in particle size and the formation of network structure. The BN acted as a bridge to the surrounding proteins in the aggregated complex and was encapsulated within it. The interaction and encapsulation may be the key reasons for the improved thermal stability of BN.

Complexation of soybean protein isolate with β-glucan and myricetin: Different affinity on 7S and 11S globulin by QCM-D and molecular simulation analysis

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The ternary complex of SPI, β-glucan and myricetin was prepared, and the interaction mechanism was studied.

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QCM-D was used to explore the binding affinity of 7S and 11S to β-glucan and myricetin.

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Molecular docking analysis indicated that 11S protein has a stronger binding capacity compared with 7S.

The complexation of soybean protein isolate (SPI) with β-glucan (DG) and myricetin (MC) was focused in this study. UV-Vis, circular dichroism and 3D fluorescence analysis jointly proved that interaction with DG and MC altered the structures of SPI, whose β-sheet decreased to 29 % and random coil increased to 35 %, respectively. Moreover, the microenvironment of tryptophan and tyrosine from protein were changed. The ternary complex performed a different molecular weight distribution, showing a larger molecular weight of 1.17×10⁶ g/mol compared with SPI verified by gel permeation chromatography (GPC). And it was further evidenced by Quartz Crystal Microbalance with Dissipation (QCM-D) and molecular docking that glycinin (11S) possessed a better affinity toward DG and MC compared with β-conglycinin (7S), which indicated stronger binding ability through hydrogen bonds. The successful preparation of SPI-DG-MC complex will advance the application of soybean resource as a functional food ingredient.

Increased sulfur-containing amino acid content and altered conformational characteristics of soybean proteins by rebalancing 11S and 7S compositions

Soybean proteins are limited by their low contents of methionine and cysteine. Herein, 7S globulin accumulation was reduced using RNA interference to silence CG-β-1 expression, and the content of the A2B1a subunit was largely increased under the soybean seed-specific oleosin8 promoter. The results showed that the sulfur-containing amino acid content in soybean seeds drastically improved, reaching 79.194 nmol/mg, and the 11S/7S ratio had a 1.89-fold increase compared to the wild-type acceptor. The secondary structures of 11S globulin were also altered, and the β-sheet content increased with decreasing β-turn content, which was confirmed by Fourier transform infrared spectroscopy, Raman spectroscopy and circular dichroism analysis. Our findings suggested that raising the accumulation of 11S glycinin at the expense of reducing the content of 7S globulin is an attractive and precise engineering strategy to increase the amount of sulfur-containing amino acids, and soybean proteins with A2B1a subunits of 11S isolates improved, and β-subunits of 7S fractions reduced simultaneously might be an effective new material for food production.

Zein enhanced the digestive stability of five citrus flavonoids via different binding interaction

BACKGROUND

Zein is commonly used to construct food flavonoid delivery systems. This study investigated the effect and mechanism of zein on the digestive stability of five citrus flavonoids, namely hesperetin (HET), hesperidin (HED), neohesperidin (NHD), naringenin (NEN), and naringin (NIN).

RESULTS

Zein enhanced the digestive stability of the five citrus flavonoids, especially that of HET and NEN, during digestion in the stomach and small intestine. Fluorescence spectroscopy results suggested that citrus flavonoids spontaneously quenched the endogenous fluorescence of zein in static quenching mode. The binding of HET, HED and NHD to zein was driven respectively by electrostatic, hydrophobic and electrostatic interaction. However, Van der Waals' force and hydrogen (H)-bond interaction represented the primary driving force for binding NEN, and NIN to zein to form complexes. The binding of the five citrus flavonoids to zein also caused a diverse bathochromic shift in ultraviolet absorbance. Analysis using Fourier-transform infrared and Raman spectroscopy revealed that the binding behavior of the five citrus flavonoids had different effects on changes in the secondary structures, disulfide bonds, and tyrosine exposure of zein. The results were also partially verified by molecular dynamic simulation.

CONCLUSIONS

Zein enhanced the digestive stability of the five citrus flavonoids via different binding interactions that was due to the difference in molecular structure of citrus flavonoids. © 2022 Society of Chemical Industry.

Changes on the conformational and functional properties of soybean protein isolate induced by quercetin

The conformational changes and functional properties of SPI induced by quercetin was investigated via fourier transform infrared (FTIR) spectroscopy, fluorescence spectroscopy, circular dichroism (CD) spectroscopy and molecular docking. A decrease in the fluorescence intensity and a blue shift in the maximum wavelength were observed due to the binding process with fluorescent residues. The analysis of Stern-Volmer equation showed that the fluorescence quenching induced by quercetin took the form of static quenching, and the binding stoichiometry between SPI and quercetin was 1:1. The values of ΔH and ΔS were both positive illustrating that hydrophobic interaction was the primary binding force between quercetin and SPI. Results of FTIR and CD indicated that the binding with quercetin changed the secondary structure of SPI, resulting in a partially unfolded and more flexible structure. SDS-PAGE confirmed there was no covalent interaction between the two constituents. Molecular docking demonstrated that there were stable configurations and high matching degrees in both 11S and 7S proteins with quercetin via hydrogen bonds and hydrophobic interactions. Meanwhile, modification by quercetin enhanced the foaming and emulsifying capacities of SPI. These findings might provide theory reference for elucidation the mechanism of polyphenols-proteins interaction and development of related food additive products in future.

Different interactions driving the binding of soy proteins (7S/11S) and flavonoids (quercetin/rutin): Alterations in the conformational and functional properties of soy proteins

The purpose of this research was to comparatively investigate the interactions between bioactive flavonoids (quercetin and rutin) and two predominant soy proteins (β-conglycinin and glycinin), and the structural and functional properties of their complexes. The binding affinities of quercetin/rutin toward 7S/11S were structure-dependent, in that rutin had a higher binding affinity than that of quercetin, and 11S exhibited higher affinity toward quercetin/rutin than that of 7S. The interactions in the 7S/11S-quercetin complexes were driven by van der Waals forces and hydrogen-bonding interactions, whereas the 7S/11S-rutin complexes exhibited hydrophobic interactions. Binding to quercetin or rutin altered the secondary structures (decrease in the α-helix and random coil contents and increase in the β-sheet content), decreased the surface hydrophobicity and thermal stability, and enhanced the antioxidant capacity of 7S and 11S. These findings provide valuable information that can facilitate the design of custom-tailored protein-flavonoid macromolecules.

Dual stabilization of Pickering emulsion with epigallocatechin gallate loaded mesoporous silica nanoparticles

Oxidation in food emulsions remains challenging to keep food quality and shelf-life. In this paper, a dual stabilization to both oil phase and antioxidant in Pickering emulsion is presented. Mesoporous silica nanospheres (MSN) were prepared to incorporate epigallocatechin gallate (EGCG), a typical plant-based antioxidant. EGCG loaded MSN were used to emulsify Litsea cubeba essential oil, a model oil, with olfactory investigation of the chemical stability. The emulsions improved the physical and chemical stabilization. The emulsions were uniformly stable with various parameters with one-month observation. Olfactory evaluation and GC-MS-O investigation reveal that the odors and odorous compounds of essential oil were well preserved in Pickering emulsions and much better than those in conventional emulsion with Tween 80. EGCG loaded MSN Pickering emulsion efficiently protect essential oil from oxidation. EGCG was also well retained in Pickering emulsion. This strategy could inspire new designs for food functional Pickering emulsions with efficient protective effect.

An insight into the changes in conformation and emulsifying properties of soy β-conglycinin and glycinin as affected by EGCG: Multi-spectral analysis

The binding mechanisms between soy β-conglycinin/glycinin and (-)-epigallocatechin-3-gallate (EGCG) were evaluated using multi-spectral techniques and molecular modeling. Additionally, the emulsifying properties of β-conglycinin/glycinin were investigated in their interactions with EGCG. Fluorescence analysis revealed that the quenching of β-conglycinin/glycinin by EGCG was static quenching. Specifically, EGCG to β-conglycinin/glycinin resulted in the conformation changes of the Trp and Tyr residues, around which the polarity toward more hydrophilic. The dominated binding between β-conglycinin and EGCG was hydrogen bonding, whereas was mainly hydrophobic force between glycinin and EGCG. Such affinity induced a more organized protein confirmation with decreased random coil and increased α-helix and β-structures. The docking data indicated the better affinity between glycinin and EGCG, compared to β-conglycinin. The emulsifying ability and capacity of β-conglycinin were enhanced with involvement EGCG, however no effect was found for glycinin. Our findings deliver insights in understanding of the interaction mechanisms between β-conglycinin/glycinin and EGCG.

Effects of preheat treatment and polyphenol grafting on the structural, emulsifying and rheological properties of protein isolate from Cinnamomum camphora seed kernel

In this study, protein isolate (PI) and purified polyphenol extract (PPE) were prepared from Cinnamomum camphora seed kernel (CCSK). The effects of preheat treatment (50-90 °C) combined with polyphenol grafting (5 % PPE, w/w) on the structural, emulsifying and rheological properties of PI were investigated. Results demonstrated the preheat treatments at 80 and 90 °C significantly increased the extent of protein aggregation of PI. Fluorescence spectra and thermal behavior analysis revealed that preheat-treated PI exhibited more compact structure and higher thermal stability. Moreover, the emulsifying stability and apparent viscosity of PI were enhanced after preheat treatments at 50, 60 and 70 °C. After modification by PPE, the secondary structural changes of preheat-treated PI were confirmed by FTIR. PPE modification improved the thermal stability and antioxidant activities of preheat-treated PI. These results provide a novel way to combine the advantages of preheat treatment and polyphenol grafting in developing a novel protein ingredient.

Isolation and characterization of the anthocyanins derived from red radishes (Raphanus sativus L.) and the protective ability of β-lactoglobulin against heat-induced oxidation

This study employed the "two-step dialysis" method and AB-8 or D101 macroporous resin chromatography to isolate the anthocyanins in red radishes (ARR). The red radish juice was dialyzed twice at 3000 and 500 Da, respectively. UHPLC-QqQ-MS/MS revealed 24 types of ARRs, of which pelargonidin (Pg)-3-diglucoside-5-(malonyl)glucoside (P3D5MG), Pg-3-diglucoside-5-glucoside (P3D5G), Pg-3-(feruloyl)diglucoside-5-(malonyl)glucoside (P3FD5MG), Pg, and malvidin (Mv) represented the main compounds. The total anthocyanin content in the ARR prepared via the "two-step dialysis" method was 29.69% and 18.44% higher than that obtained using AB-8 and D101 macroporous resins, respectively. The ARRs inhibited heat-induced β-lactoglobulin (β-Lg) oxidation. The amino acid residue microenvironment and secondary β-Lg structure were modified via ARR binding. The energy involved in P3D5MG and β-Lg binding was -392 kJ/mol, which was significantly lower than that during the binding process of P3D5M, P3FD5MG, Pg, and Mv to β-Lg (-338 to -168 kJ/mol). These results indicated that "two-step dialysis" was a promising method for deriving natural pigment with strong antioxidant activity from red radishes. PRACTICAL APPLICATION: As a natural food colorant, anthocyanins have attracted increasing attention in the food industry in recent years. This study used "two-step dialysis" to effectively separate ARRs. Moreover, the anthocyanins in ARR can bind to β-Lg to protect against heating-induced oxidation. Therefore, ARRs may not only act as a food pigment but also as antioxidants.

Formation of soybean protein isolate-hawthorn flavonoids non-covalent complexes: Linking the physicochemical properties and emulsifying properties

In recent years, more and more attention had been paid to the combination of proteins and flavonoids, and several flavonoids had been reported to improve the physicochemical and emulsifying properties of proteins. This study investigated the effects of ultrasonic treatment (450 W for 10 min, 20 min, and 30 min) on the physicochemical properties, antioxidant activity, and emulsifying properties of soy protein isolate (SPI) -hawthorn flavonoids (HF) non-covalent complexes. The results showed that the addition of HF to SPI and 20 min of ultrasound could reduce α-helix and random coil, increase β-sheet and β-turn, and enhance fluorescence quenching. In addition, it decreased the particle size, zeta potential, surface hydrophobicity, and turbidity to 88.43 or 95.27 nm, -28.80 mV, 1250.42, and 0.23, respectively. The protein solubility, free sulfhydryl group, antioxidant activity, emulsifying activity index, and emulsifying stability index all increased to 73.93%, 15.07 μmol/g, 71.00 or 41.91%, 9.81 m²/g, and 67.71%, respectively. Moreover, high-density small and low-flocculation droplets were formed. Therefore, the combined ultrasound treatment and addition of HF to SPI is a more effective method for protein modification compared to ultrasound treatment alone. It provides a theoretical basis for protein processing and application in the future.

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.

Preparation of Pickering emulsion based on soy protein isolate-gallic acid with outstanding antioxidation and antimicrobial

This study investigated a novel antioxidant and antimicrobial Pickering emulsion stabilized by soy protein isolate (SPI) and gallic acid (GA) as an excellent protective delivery medium for lipophilic functional food. SPI-GA complex nanoparticles were fabricated by a covalent cross-linking mechanism under alkaline conditions with a small particle size (42.93-24.91 nm) and high zeta potential (26.92-38.58 -mV), which led to improved stability at high GA concentrations. Without the addition of preservatives, it was found that SPI-GA complex nanoparticles have a certain antimicrobial ability. Using these nanoparticles as the only stabilizers, outstanding antioxidant and antimicrobial Pickering emulsions could be easily prepared, and they had a small droplet size (948.09-457.82 nm), great stability and inhibited lipid peroxidation and antibacterial ability. Oxidation and microbial protection proceeded in a GA concentration-dependent manner. This study provides a novel way to prepare functionalized Pickering emulsions as delivery media for functional lipophilic raw materials.