Conformational changes and functional properties of whey protein isolate-polyphenol complexes formed by non-covalent interaction

Non-covalent interaction of rice protein and polyphenols: The effects on their emulsions

In this study, we investigated the non-covalent interaction mechanism between rice protein (RP) and three polyphenols with different concentrations (ferulic acid FA, gallic acid GA, and tannic acid TA) and their effects on the structure and emulsion stability of the proteins. Hydrophobic forces dominated the binding of RP to the polyphenols, and the reaction was heat-absorbing. The three polyphenols are bound to RP in the form of static quenching to form a non-covalent complex, and during the binding process, the RP provides one binding site. RP-polyphenol complexes, particularly RP-GA, enhanced ABTS scavenging and FRAP reduction. Polyphenols improved RP emulsion oxidative stability, inhibiting lipid oxidation and enhancing emulsion rheology and interfacial structure. RP-GA was most effective, maintaining low POV. These findings support the potential applications of RP-polyphenol noncovalent complexes in food processing.

Influence of proanthocyanidins (condensed tannins) on pulse protein polymer size and associated properties

Potential for pulse proteins in plant-based meat alternatives is limited by weak protein polymer interactions. This work examined the effects of proanthocyanidins on pulse protein crosslinking. Proanthocyanidins with degree of polymerization, mDP, 1-19.5 were reacted with soybean (control) and pulse (pea, faba, and lentil) proteins. Changes in properties, MW, and post-extrusion texture were evaluated. Pea and faba proteins exhibited stronger proanthocyanidin binding (Kd, 3.13-8.74), but lower binding capacity (Bmax, 0.29), and change in surface hydrophobicity, (ΔHo, -56 %) vs soy and lentil (Kd, 249-935, Bmax, 0.59-0.76, ΔHo, -67 %). Polymeric proanthocyanidins preferentially cross-linked high MW protein subunits, forming complexes of >600 kDa and increasing protein denaturation temperature by 2.9-12.1 °C. The proanthocyanidins increased hardness (1.8-15×) and chewiness (1.6-13×) of texturized pulse proteins, suggesting increased protein network density during extrusion. The findings highlight the potential of proanthocyanidins to enhance pulse protein polymer interactions and improve their textural properties.

Effects of high hydrostatic pressure processing on the physicochemical properties, functional characteristics, and antioxidant activity of silkworm pupae protein

With the rising demand for sustainable proteins, edible insects such as silkworm pupae are gaining recognition for their high-quality protein and essential nutrients. Advanced technologies like high hydrostatic pressure (HHP) processing have the potential to enhance the functional properties of insect proteins. This study investigated the application of HHP to silkworm pupa protein, focusing on its effects on physicochemical properties, functional characteristics, and bioactivity. HHP treatments at 400 and 600 MPa significantly enhanced emulsifying and foaming capacities, as well as antioxidant activity. Furthermore, HHP-assisted extraction facilitated protein unfolding and increased the exposure of hydrophobic groups on the protein surface, which likely contributed to improvements in protein solubility and antioxidant function. These findings provide valuable insights into the potential of HHP to enhance the quality of edible insect proteins for food applications.

Effects of grape seed proanthocyanidin on emulsifying capacity of soy protein isolate in extrusion field and its underlying mechanism

BACKGROUND

Soy protein isolate (SPI) has poor emulsifying ability because of its low molecular flexibility and compact structure, limiting its application in extruded protein-based foods. Extrusion technology has emerged as a promising way to alter the structural properties of proteins. Therefore, the impacts of grape seed proanthocyanidin (GSP) on structural and emulsifying characteristics of SPI in extrusion field were explored in this study.

RESULTS

After extrusion treatment, the molecular chains of SPI were unfolded. In comparison with extruded SPI, the interaction with GSP led to a rightward shift in particle size distribution and an enhancement in zeta potential values of the protein. As GSP concentration increased from 20 to 80 g kg-1, the free sulfhydryl content of SPI was reduced by 4.17%, 25%, 29.24% and 35.85% compared with that of extruded SPI. The addition of GSP altered the secondary structure of SPI and enhanced the microenvironment polarity. Meanwhile, SDS-PAGE results indicated that the protein presented lower molecular weight with the introduction of GSP. Compared with extruded SPI, the supplementation with GSP increased the molecular flexibility while it decreased the surface hydrophobicity of SPI. Correlation analyses demonstrated that these structural changes induced an improvement in emulsifying activity and emulsion stability of SPI. GSP mainly binds to SPI through hydrogen bonds and hydrophobic interactions under the extrusion environment.

CONCLUSION

This study demonstrated that GSP is a potential modifier, which can be applied to improve the emulsifying capacity of extruded SPI-based foods. © 2025 Society of Chemical Industry.

Preparation of soy protein isolate-ellagic acid conjugates through ultrasound-assisted metal-free Fenton reaction: Synthesis, structure, and functional properties

The grafting of polyphenols onto proteins possesses the potential to enhance their functional properties. In this study, ultrasound-assisted metal-free Fenton reaction grafting method (UMFM) was developed to efficiently prepare soy protein isolate (SPI)-ellagic acid (EA) conjugates. Under optimized conditions of 380 W, 50 °C, and 75 min, UMFM significantly improved the grafting degree of SPI with EA by 10.3 % and reduced the reaction time by 94.8 % compared to the conventional method. In addition, the results of reactive group content, multi-spectroscopy analysis, and surface hydrophobicity demonstrated the decrease in free amino and sulfhydryl groups contents, alterations in the secondary and tertiary structures of SPI, as well the ultrasonication-induced further unfolding of SPI structure, thereby facilitating the formation of covalent bonds between SPI and EA. Moreover, the functional properties of SPI, including thermal stability, emulsifying activity, and antioxidant properties, were significantly enhanced after conjugation with EA, especially in ultrasound-assisted conditions.

Preparation, structure characterization and improved thermo-reversible gel properties of covalent conjugation of marine oligosaccharides/salt-soluble pea protein induced by cold plasma treatment

Plant protein-based thermo-reversible gels are essential for meeting the dietary nutritional needs of the elderly and individuals with dysphagia. However, high hydrophobic globulin content and heat-induced denaturation often hinder gel formation. In this study, salt-soluble pea protein isolate (SPPI) was extracted via ammonium sulfate precipitation, and cold plasma (CP) was used to conjugate SPPI with marine oligosaccharides, including chito-oligosaccharides (COS), carrageenan oligosaccharides (CAS), alginate oligosaccharides (AOS) and agaric oligosaccharides (AGS). This approach achieved a maximum grafting degree of 17.89 % and facilitated the thermo-reversible gelation of SPPI. The interaction mechanisms between SPPI and marine oligosaccharides and their effects on the thermo-reversible gels' functional properties were investigated. COS/SPPI-CP exhibited enhanced solubility, conductivity, reduced particle size. Structural analyses revealed increased environmental polarity, enhanced hydrogen bonding, stronger disulfide bonds and reduced hydrophobic interactions, hence indicating a shift towards a more hydrophilic SPPI structure after oligosaccharide conjugation. CP treatment improved gel thermo-reversibility while reducing hardness, adhesiveness, and chewiness, with COS/SPPI-CP showing the lowest values for these properties. Adding 0.3 % NaCl maintained thermo-reversibility, supporting safe swallowing and adequate nutritional intake. These findings contribute to developing pea protein-based supplements for individuals with dysphagia.

Interactions between polyphenols and polysaccharides/proteins: Mechanisms, effect factors, and physicochemical and functional properties: A review

Polyphenols have attracted much attention in the food industry and nutrition because of their unique biological activities. However, the health benefits of polyphenols are compromised due to their structural instability and sensitivity to the external environment. The interaction between polyphenols and polysaccharides/proteins largely determines the stability and functional characteristics of polyphenols in food processing and storage. Hence, this topic has attracted widespread attention in recent years. This review initially outlines the basic properties of polyphenols and their applications in food. Subsequently, the interaction mechanisms between polyphenols and polysaccharides/proteins are discussed in detail including non-covalent bonding, covalent modification, and conformational changes. These interactions can display profound impacts on the nutritional value, taste, stability, and safety of food. Additionally, this article also systematically reviews the influencing factors (type, concentration, temperature, pH, and other factors) of interaction between polyphenols and proteins/polysaccharides. Finally, this paper also summarizes systematically the effects of the interaction between polyphenols and polysaccharides/proteins on the physicochemical and functional properties of polyphenols/proteins. The findings provide prospects for the application of composite materials in food preservation, functional food development, and nanocarrier development, which can provide theoretical references for the in-depth development of polyphenols in the food industry.

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.

Sea buckthorn polyphenols on gastrointestinal health and the interactions with gut microbiota

The potential health benefits of sea buckthorn polyphenols (SBP) have been extensively studied, attracting increasing attention from researchers. This paper reviews the composition of SBP, the effects of processing on SBP, its interactions with nutrients, and its protective role in the gastrointestinal tract. Polyphenols influence nutrient absorption and metabolism by regulating the intestinal flora, thereby enhancing bioavailability, protecting the gastrointestinal tract, and altering nutrient structures. Additionally, polyphenols exhibit anti-inflammatory and immunomodulatory effects, promoting intestinal health. The interaction between polyphenols and intestinal flora plays a significant role in gastrointestinal health, supporting the composition and diversity of the gut microbiota. However, further research is needed to emphasize the importance of human trials and to explore the intricate relationship between SBP and gut microbiota, as these insights are crucial for understanding the mechanisms underlying SBP's benefits for the gastrointestinal tract (GIT).

Investigating the effects of polar and non-polar polyphenols on the physicochemical properties and functional characteristics of camellia oil body emulsions

This study aimed to investigate the effects of polar catechol and non-polar α-tocopherol, either individually or in combination, on the stability and functional properties of camellia oil body emulsions. Catechol showed strong interactions with the polar surface proteins of OBs, while α-tocopherol associated with the non-polar lipid regions, collectively enhancing emulsion stability. Combined use of catechol and α-tocopherol significantly reduced droplet size (2810 to 1360 nm), increased zeta potential (5 to -42 mV), and decreased peroxide values from 45 to 12 meq/kg and TBARS values from 260 to 130 meq/kg after 14 days. Combined effect of polyphenols improved the stability of OB emulsions under stress conditions, maintaining structural integrity at elevated NaCl concentrations, high temperatures (90 °C), and after three freeze-thaw cycles. These findings demonstrate the synergistic effects of combining polar and non-polar polyphenols, offering a promising strategy for enhancing oxidative stability and functionality in food systems.

Vanillin strengthened complex coacervation behavior between gelatin and sodium carboxymethyl cellulose endowed improved mechanical properties of microcapsules

The inherent heterogeneous structure of biomass molecules usually makes the formed interfacial film prone to defects such as core material mass transfer loss, while chemical modification may be an effective means to improve the performance of biobased interfacial films. In this study, gelatin‑sodium carboxymethyl cellulose (CMC-Na) complex coacervation microcapsules were used as models and the typical aroma molecule vanillin as modifier to explore the differences in mechanical properties and other physicochemical properties of microcapsules before and after modification, as well as the potential mechanism of the differences. Results showed that the aldehyde group of vanillin formed covalent imine bond with the amino group on gelatin protein through Schiff base reaction, and the hydroxyl group on the benzene ring of vanillin formed hydrogen bonds with CMC-Na and gelatin simultaneously; these two effects were synergistically enhanced cross-linking between wall materials, thereby strengthening the mechanical properties of the microcapsules. The rupture force of microcapsules with 0.5 % vanillin was 36.60 % higher than that of blank microcapsules. In summary, this study used aroma compounds to modify biomass macromolecules, which provided a new idea for strengthening the physicochemical properties of bio-based microcapsules.

Functional, structural, and rheological properties of the complexes containing sunflower petal extract with dairy and plant-based proteins

This study aims to investigate the impact of sunflower petal extract (SFE) on the functional and structural properties of sodium caseinate and chickpea proteins. For this purpose, 3.5 % of sodium caseinate solution and 3.5 % of protein extracted from chickpea powder were prepared in phosphate buffer (pH = 7). SFE was used at different concentrations, from 1 to 3 % in different protein solutions and functional, structural and rheological properties were measured. The results revealed that complexation of SFE with different proteins can enhance the antioxidant, foaming properties, solubility, emulsion activity, emulsion stability, viscoelastic behavior, and can decrease surface hydrophobicity. FTIR and docking results showed that the most bonding type was non-covalent bonds. Major phenolic compounds containing heliannone A, B, and kaempferol had strong affinity with sodium caseinate, and then chickpea protein. Therefore, the results demonstrated that SFE and its complexes had appropriate emulsifying properties that reduces interfacial tension in the water/oil interface.

Tailoring ternary complexes of lactoferrin, EGCG, and α-lactalbumin by assembly sequence strategies: Structural characterization, assembly mechanism, and emulsification elucidation

Three distinct ternary complexes (TC-M1, TC-M2, and TC-M3) based on lactoferrin (LF), (-)-epigallocatechin-3-gallate (EGCG), and α-lactalbumin (ALA) were prepared by varying the assembly sequence and EGCG concentrations (ranging from 0 to 2.0 mM). Structural characterization was performed using various spectroscopic techniques, while the assembly mechanisms were investigated through ITC and molecular docking. These ternary complexes were further evaluated as stabilizers in Pickering emulsions. Nephelometry and DLS analysis showed that TC-M1 exhibited the highest turbidity and largest particle size, followed by TC-M2 and TC-M3. FT-IR and fluorescence spectroscopy revealed strong binding between EGCG and both ALA and LF, enhancing the hydrophilicity and extending structure of proteins. ITC and molecular docking studies indicated spontaneous interactions primarily driven by hydrogen bonding and hydrophobic forces, with LF (Ka1 = 1.9 × 105 M-1) and ALA (Ka1 = 3.6 × 104 M-1) binding approximately 3.3 and 2.9 EGCG molecules, respectively. Pickering emulsions formed by these complexes demonstrated superior emulsification properties, with TC-M1 showing the smallest CI (10.09 % ± 0.19 %), particle size (1 to 2 μm), and higher MVI (1.2) and EI (2.5) at 2.0 mM EGCG, outperforming TC-M2 and TC-M3 in stability. Overall, the assembly sequence of LF, ALA, and EGCG, along with EGCG concentration, lays the foundation for designing protein-polyphenol-protein ternary complexes, offering enhanced stability and functionality for diverse EGCG delivery applications.

Characterization of pea protein-different types of glycoside flavonoid complex interactions and functional properties

Flavonoids offer various health benefits due to their chemical properties and non-covalent interactions with food nutrients. Despite extensive research on flavonoid-protein interactions, the effects of flavonoid glycosides on pea protein (PP) remained unclear. This study explored the non-covalent interactions of luteolin (Lu), isoorientin (Iso), and cynaroside (Cyn) with PP using molecular docking and multi-spectral techniques. Results showed that Lu interacted with PP mainly through hydrophobic forces, while Iso and Cyn interacted predominantly via hydrogen bonding. At 298 K, the binding affinity of flavonoids to PP was ranked as Lu (16.98 × 104 M-1) > Iso (7.41 × 104 M-1) > Cyn (6.31 × 104 M-1). Circular dichroism analysis showed that flavonoid glycosides loosened the protein structure by inducing a change in the secondary structure of PP from an α-helix to a random coil. This resulted in improved foaming, emulsification, and antioxidant properties of PP. This study provided insights into flavonoid-protein interactions and their potential applications in functional protein foods.

Differential binding of gallic acid and epigallocatechin gallate to whey protein affects the interfacial adsorption and gastric digestion of O/W emulsion

Whey protein isolate (WPI) was reacted with 20, 120, and 240 μmol/g gallic acid (GA) or epigallocatechin gallate (EGCG) at 21 °C. Equilibrium dialysis testing indicated a stronger binding capacity of whey proteins with EGCG compared to GA. Both phenolics, especially EGCG, tended to reduce the adsorption of WPI at the oil-water interface and decreased the elasticity modulus (Ed) of the interfacial film. Yet, binding with 20 μmol/g of EGCG and GA (less so) resulted in significantly improved emulsifying activity of WPI, but the emulsion stability was decreased at all phenolic concentrations (except at 240 μmol/g). There was an overall improvement of pepsinolysis of both α-lactalbumin and β-lactoglobulin. In comparison with GA, EGCG yielded more pronounced effects on WPI interfacial adsorption, dilatational rheology, and peptic digestion.

Investigating binding mechanism between coconut globulin and tannic acid mediated by atmospheric cold plasma: Protein structure and stability

Physical methods present promising avenues for inducing covalent modifications of proteins by polyphenols, circumventing the safety and sustainability issues associated with traditional approaches. This study sought to enhance the physicochemical properties of coconut globulin (CG) by facilitating covalent cross-linking with tannic acid (TA) through atmospheric cold plasma (ACP). The ACP treatment effectively transitioned the interaction between CG and TA from non-covalent to covalent in a voltage-dependent manner at pH 6.0, resulting in structural modifications of CG. The treatment with TA enhanced the spherical structure of CG, with a reduction in particle size from 474 to 384 nm. This size reduction was further amplified by the exposure of charged groups induced by ACP treatment. Consequently, the solubility, surface hydrophobicity, and viscosity of ACP-treated CG-TA increased, leading to an elevated denaturation temperature and enhanced physical stability. These results suggest a viable approach to improving the suboptimal physicochemical properties of plant proteins.

Molecular mechanism of the interactions between coffee polyphenols and milk proteins

The interaction between coffee polyphenols and milk proteins enhances the chemical stability of coffee polyphenols; however, the mechanism underlying this interaction remains elusive, especially at the amino acid level of the proteins. This study investigated the non-covalent interactions of coffee polyphenols (chlorogenic and caffeic acids) with various milk proteins (α-casein, β-casein, κ-casein, α-lactalbumin, and β-lactoglobulin). Fluorescence spectroscopy was used to examine the affinity of the coffee polyphenols for the milk proteins. The fluorescence intensity was found to be dependent on the proline residue content in the milk proteins. Coffee polyphenols were approximately twice as soluble in proline solution as in water, indicating thermodynamically favorable interactions with proline. Molecular dynamics simulations indicated that caffeic acid interacts with the proline side chains of peptides, which is attributable to hydrophobic interaction. The present findings provide mechanistic insights into the interactions between coffee polyphenols and milk proteins at the amino acid level, thereby contributing to a deeper understanding of the enhanced chemical stability of coffee polyphenols in the presence of milk proteins. This work also presents general cautions regarding the spectroscopy of polyphenols.

Effect of rutin on the structural and functional properties of ovalbumin

Phenolic substances affect protein functionality. This study aimed to examine how rutin influences the gel properties, antioxidant activity, and structure of ovalbumin (OVA). Increasing rutin concentration enhanced the gel hardness of OVA but reduced soluble protein content with no significant effect on water retention. At 0.25 % rutin concentration, the gel hardness of OVA increased from 109.33 g to 292.60 g, while soluble protein content decreased from 1.08 mg/mL to 0.97 mg/mL. Rutin modification significantly increased the storage and loss moduli of OVA gel, making its structure more compact. At 0.25 % rutin, antioxidant analysis showed increases in the DPPH radical scavenging rate (127 %), ABTS radical scavenging rate (112 %), hydroxyl radical scavenging rate (4167 %), and reducing power (101 %) of OVA. Fluorescence spectroscopy, surface hydrophobicity, free sulfhydryl content, and circular dichroism spectra revealed that higher rutin concentrations reduced fluorescence intensity and surface hydrophobicity while increasing the free sulfhydryl content of OVA. The α-helix content of OVA decreased, while β-sheet content increased. In addition, it was confirmed that OVA and rutin were bound by hydrophobic interaction. The quenching mechanism was static quenching. Rutin alters the structure and functional properties of OVA, providing a theoretical foundation for developing antioxidant and high-gel OVA variants.

Controlled ethanol-mediated polyphenol removal from sunflower meal: Impact on physicochemical, structural, flow-behavior, and functional characteristics of isolated proteins

BACKGROUND

Polyphenols present in sunflower meal act on sunflower proteins by reacting directly with their structures and thus influencing their purity, solubility, crystallinity, and functionality. However, the effect on these properties of varying concentrations of ethanol used in dephenolization has yet to be explored. The present study aimed to explore the impact of dephenolization using varying ethanol concentrations (60%, 70%, 80%, and 90%) on the physicochemical, color, thermal, structural, functional, and flow behavior of protein isolates extracted from sunflower meal.

RESULTS

Protein isolates originating from meals that were dephenolized using higher ethanol concentrations exhibited a protein content of 836.10 g kg-1. As the concentration of ethanol increased, a reduction in crystallinity was observed from 24% to 14.15%. Fourier transform infrared (FTIR) spectroscopy revealed marked shifts in major peaks within the 1600 to 1700 cm-1 wavelength range, indicating significant structural and conformational changes. Sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) results demonstrated that dephenolization caused decline in molecular weight ranging from 25 kDa to 60 kDa. Dephenolization induced significant changes in surface morphology resulting in more heterogeneous and disordered surfaces as indicated by field emission-scanning electron microscopy (FE-SEM) micrographs. Overall improvement in the functional properties was observed, with an increase in solubility from 15.20% to 22.03%. Improvement in the flow behavior with an increase in porosity from 38% to 60% was also observed, due to dephenolization.

CONCLUSION

Dephenolization using 90% ethanol induced structural changes that enhanced physicochemical and functional characteristics of sunflower protein isolates by improving purity and solubility, reducing crystallinity, and increasing flow behavior. © 2024 Society of Chemical Industry.

Hydrodynamic cavitation induced fabrication of soy protein isolate-polyphenol complexes: Structural and functional properties

The combination of polyphenols and protein can improve the functional characteristics of protein. How to effectively promote the binding of polyphenols to protein is still a difficult topic. In this study, hydrodynamic cavitation (HC) was used to induce the fabrication of complexes between soy protein isolate (SPI) and different polyphenols (tannic acid (TA), chlorogenic acid (CGA), ferulic acid (FA), caffeic acid (CA), and gallic acid (GA)). The effect of HC on the interaction between polyphenols and SPI was investigated, and the structural and functional properties of the formed complexes were characterized. The results showed that HC treatment led to SPI structure stretching, which increased the binding level of polyphenols, especially that of TA (increased from 35.08 ± 0.73% to 66.42 ± 1.35%). The increase in ultraviolet-visible absorption intensity and quenching of fluorescence intensity confirmed that HC enhanced the interaction between polyphenols and protein. HC treatment reduced the contents of free sulfhydryl and amino groups in SPI-polyphenol complexes and altered their Fourier transform infrared spectroscopy, indicating that HC treatment promoted the formation of C-N and C-S bonds between SPI and polyphenols. Circular dichroism spectroscopy indicated that HC treatment altered the secondary structure of SPI-polyphenol complexes, inducing an increase in α-helix and random coil contents and a decrease in β-sheet content. Regarding functional properties, HC treatment improved the emulsification and antioxidant activity of SPI-polyphenol complexes. Therefore, HC is an effective technique for promoting the binding of polyphenols to protein.

Camel milk whey powder formulated using thermal (spray-drying process) and non-thermal (ultrasonication) processing methods: Effect on physicochemical, technological, and functional properties

Whey protein concentrates (WPCs) are gaining importance as a functional ingredient due to their high technological and functional properties and their diverse application in the food industry. In this study, Camel milk whey (CW) was separated from skimmed camel milk, then either spray-dried (SD) at 170, 185 and 200 °C, or treated by ultrasonication (US) (20 kHz) for 5, 10 and 15 min followed by freeze-drying to obtain camel milk whey powder (CWP). The structural analysis of CWP was carried out by Fourier-Transform Infrared Spectroscopy (FTIR) and X-Ray Diffraction (XRD) which showed no significant difference in the functional groups profile of US samples compared to control and SD samples. US samples showed some degree of crystallinity that was comparable to the control samples, while SD samples exhibited very low degree of crystallinity. The surface morphology, particle size, and surface charge of CWP were evaluated using scanning electron microscopy (SEM) and Zetasizer. The lowest particle size of 215.1 nm with surface charge of -21.6 mv was observed in SD-185 WPC. Moreover, SD samples revealed whiter color compared to the US-treated samples which were having lower L* values (P < 0.05). US-15 sample exhibited high protein solubility (100 %), whereas the SD-200 sample showed reduced solubility (92.7 %). Improvement in the emulsifying activity of CWP samples was observed after SD and US, with highest emulsifying activity index (EAI) values of 143.75 m2/g and 143.11 m2/g were reported for SD-185 and US-15 CWP samples, respectively. To conclude, SD and US were found to improve the physico-chemical, technological, and functional properties of CWP, and thus can be utilized as a promising strategy to preserve and enhance the technofunctional properties of CWP.

Ca2+-promoted free radical grafting of whey protein to EGCG: As a novel nanocarrier for the encapsulation of apigenin

Whey protein (WP) is often used as a delivery carrier due to its superior biological activity and nutritional value. Covalent binding of WP to epigallocatechin gallate (EGCG) can significantly improve the performance of WP in encapsulated materials. Nevertheless, the preparation of WP-EGCG covalent complexes still suffers from low grafting rates. Studies have shown that calcium ions (Ca2+) can modify the structure of proteins. We therefore explored the effect of calcium chloride (CaCl2) on the free radical grafting of EGCG and WP. The experimental results showed that the grafting rate of free radicals increased by 17.89% after adding Ca2+. Furthermore, the impact of WP-EGCG-Ca2+ covalent complex on the entrapment efficiency of apigenin (AP) was further examined, and the results revealed that the entrapment rate could reach 93.66% at an apigenin concentration of 0.2 mg/mL. Simulated gastrointestinal digestion showed that WP-EGCG-Ca2+ covalent complex could significantly improve the bioavailability of AP. The study provides new ideas to broaden the application of WP as a carrier for delivering bioactive substances.

Evaluating the binding mechanism, structural changes and stability of ternary complexes formed by the interaction of folic acid with whey protein concentrate-80 and L-ascorbyl 6-palmitate

In the present study, we investigated the mechanisms associated with the stabilizing effects of whey protein concentrate-80 (WPC80) and L-ascorbyl 6-palmitate (LAP) on folic acid (FA). Multispectral techniques show that WPC80 binds to FA and LAP mainly through hydrophobic interactions, and that energy is transferred from WPC80 to FA and LAP in a nonradiative form (FA/LAP); The combination of FA/LAP resulted in a change in the conformation and secondary structure content of WPC80, an increase in the absolute zeta potential of the system, and a shift in the particle size distribution towards smaller sizes. The compound system exhibits strengthened antioxidant properties and favorable binding properties. Besides, WPC80 improves the storage stability of FA under different conditions. These results demonstrated that the ternary complex formed by FA co-binding with WPC80 and LAP is an effective way to improve the stability against of FA.

Investigating the effect of whey protein isolate:proanthocyanidin complex ratio on the stability and antioxidant capacity of Pickering emulsions

Whey protein isolate (WPI) has the potential to be a Pickering stabilizer, but its applications in emulsions are restricted due to its structural susceptibility to external environments. Proanthocyanidin (PAC) is a natural antioxidant polyphenol that can improve protein properties and enhance the stability and longevity of emulsions. In the current work, PACs were employed to bind WPIs, forming a complex to stabilize Pickering emulsion. Fluorescence spectroscopy, infrared spectroscopy, confocal microscopy, quartz crystal microbalance with dissipation monitoring (QCM-D), and antioxidant stability of the emulsion were performed to characterize the structural changes of the protein/polyphenol complexes and their effects on the interfacial properties and stability of the emulsion. Results indicated that PACs and WPIs might bind through hydrogen bonding and hydrophobic interactions, effectively increasing the hydrophilicity of the complexes. QCM-D and emulsion stability showed that adsorption at the oil-water interface of the complexes was the largest, and the stability of the Pickering emulsion was optimal when the concentration ratio of PAC to WPI exceeded 1:1. The antioxidant properties of Pickering emulsions were positively correlated with the addition of PACs. These findings demonstrated that PACs could improve the properties of WPIs and enhance the stability and antioxidant properties of WPI Pickering emulsions.

Exploration of binding mechanism of whey protein isolate and proanthocyanidin: Spectroscopic analysis and molecular dynamics simulation

The non-covalent whey protein isolate-proanthocyanidin (WPI-PC) complex was constructed and possessed superior anti-muscle attenuation activity in our previous study. While the non-covalent binding mechanism of WPI and PC remains unclear. The interaction mechanism of whey protein isolate (WPI) and proanthocyanidin (PC) was explored using multispectral analysis and molecular dynamics (MD) simulation. The results indicated that the non-covalent binding of PC and WPI led to fluorescence quenching, causing the conformational changes and microenvironment changes of WPI. The surface hydrophobicity of WPI-PC complex was reduced by 42.36 % compared with WPI (P < 0.05). The hydrogen bond and hydrophobic interaction were involved in the interaction between WPI and PC, and hydrogen bond played a dominant role. The WPI-PC complex was irregular and showed a smaller sheet structure. The PC and WPI remained a stable binding mainly through 15 key residues, especially the energy contribution of LEU 39. Additionally, the flexibility and fluctuation of individual amino acid residues in WPI were altered after binding to PC. It is hoped that this study could provide theoretical basis for the application of WPI and PC in functional foods.

Unveiling the transformative influence of sonochemistry on formation of whey protein isolate and green tea extract (WPI-GTE) conjugates

This study investigated the formation of conjugates between whey protein isolate (WPI) and green tea extract (GTE) using three methods: redox-pair (R), ultrasound-assisted redox-pair (RU), and ultrasonication (UL). Ultrasonication significantly reduced the reaction time for synthesizing WPI-GTE conjugates compared to the standard R method (p < 0.05). The UL methods had the highest conjugate yield determined by polyphenol binding (p < 0.05). Fourier-transform infrared spectroscopy (FTIR) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) confirmed the conjugate formation, indicating an increased molecular weight due to protein binding with polyphenols through covalent and non-covalent bonds. Conjugates produced via ultrasonication exhibited enhanced solubility, smaller particle size, better emulsifying capacity, and improved foaming ability compared to those formed using the traditional R method (p < 0.05). However, conjugates from the R method showed higher antioxidant activity, as evidenced by DPPH•and ABTS•+ scavenging activities (p < 0.05). In conclusion, WPI-GTE conjugates created through ultrasonic treatment demonstrate potential as dual-functional ingredients, serving as both antioxidant and emulsifier.

Insight into the effect of sesamol on the structural and gel properties of yak myofibrillar proteins

Different concentrations of sesamol (0, 20, 40, 80 and 160 mg/g protein) were incorporated for evaluating the effects of sesamol on the structural and gel properties of yak myofibrillar proteins (MPs). The results manifested that the contents of active thiol and free amine diminished and the carbonyl contents elevated when the MPs modified with sesamol. The intrinsic fluorescence intensity progressively decreased and surface hydrophobic value displayed a down-up trend after binding with the increasement of sesamol. Moreover, the presence of sesamol reduced protein solubility and increased particle size of MPs. For the protein gels, inclusion of sesamol effectively improved water-holding capacity and gel strength but decremented gel whiteness and the proportion of free water, and significantly enhanced the hydrogen bonds, hydrophobic interactions and disulfide bonds in the gel matrix. Microstructure analysis revealed that a more compact microstructure was formed for the MP-sesamol gels. This study suggests that sesamol is capable of improving the functional properties of MPs, and the complexes of MP-sesamol have potential applications in the food industry.

Characteristics of pomegranate (Punica granatum L.) peel polyphenols encapsulated with whey protein isolate and β-cyclodextrin by spray-drying

Pomegranate peel polyphenols (PPPs) are recognized as promising food additives due to their diverse bioactivities; however, their application is limited by poor stability. To address this critical issue, three types of PPPs microcapsules were prepared using β-cyclodextrin (CD), whey protein isolate (WPI), and a composite material of CD-WPI through ultrasound treatment (US). Results revealed that ultrasound treatment can enhance the PPPs-wall material interaction, as evidenced by MD simulations. The encapsulation efficiency of CD-WPI-PPPs was 93.73 %, which was significantly higher than that of CD-PPPs and WPI-PPPs (p < 0.05). The degradation rate constant of CD-WPI-PPPs was reduced by 95.83 %, and its t1/2 was extended by 23-fold compared to that of unencapsulated PPPs. Furthermore, CD-WPI-PPPs exhibited greater DPPH scavenging activity and inhibited polyphenol release during oral and gastric digestion while promoting release during intestinal digestion. These outcomes were attributed to enhanced integrity and interactions between PPPs and composite materials in the microcapsules formed through ultrasound treatment, as supported by SEM images and FT-IR spectra. Consequently, the application of US in the preparation of PPPs microcapsules presents a promising strategy for developing natural nutrient additives for food applications, thereby enhancing the functional properties of food products.

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.

Effects of Protein on Green Tea Quality in a Milk-Tea Model during Heat Treatment: Antioxidant Activity, Foaming Properties, and Unbound Small-molecule Metabolome

Tea drinks/beverage has a long history and milk is often added to enhance its taste and nutritional value, whereas the interaction between the tea bioactive compounds with proteins has not been systematically investigated. In this study, a milk-tea model was prepared by mixing green tea solution with milk and then heated at 100°C for 15 min. The milk tea was then measured using biochemical assay, antioxidant detection kit, microscopy as well as HPLC-QTOF-MS/MS after ultrafiltration. The study found that as the concentration of milk protein increased in the milk-tea system, the total phenol-protein binding rate raised from 19.63% to 51.08%, which led to a decrease in free polyphenol content. This decrease of polyphenol was also revealed in the antioxidant capacity, including 2,2-diphenyl-1-picrylhydrazyl radical scavenging ability and ferric ion reducing antioxidant power, in a dose-dependent manner. Untargeted metabolomics results revealed that the majority of small-molecule compounds/polyphenols in tea, such as epigallocatechin gallate, (-)-epicatechin gallate, and Catechin 5,7,-di-O-gallate, bound to milk proteins and were removed by ultrafiltration after addition of milk and heat treatment. The SDS-PAGE and Native-PAGE results further indicated that small molecule compounds in tea formed covalent and non-covalent complexes by binding to milk proteins. All above results partially explained that milk proteins form conjugates with tea small-molecule compounds. Consistently, the particle size of the tea-milk system increased as the tea concentration increased, but the polymer dispersity index decreased, indicating a more uniform molecular weight distribution of the particles in the system. Addition of milk protein enhanced foam ability in the milk-tea system but reduced foam stability. In summary, our findings suggest that the proportion of milk added to tea infusion needs to be considered to maintain the quality of milk-tea from multiple perspectives, including stability, nutritional quality and antioxidant activity.

Modification of casein with oligosaccharides via the Maillard reaction: As natural emulsifiers

In the present study, different oligosaccharides (fructooligosaccharide (FOS), galactooligosaccharide (GOS), isomaltooligosaccharide (IMO), and xylooligosaccharide (XOS)) were modified on casein (CN) via Maillard reaction. The CN-oligosaccharide conjugates were evaluated for modifications to functional groups, fluorescence intensity, water- and oil-holding properties, emulsion foaming properties, as well as general emulsion properties and stability. The results demonstrated that the covalent combination of CN and oligosaccharides augmented the spatial repulsion and altered the hydrophobic milieu of proteins, which resulted in a diminution in water-holding capacity, an augmentation in oil-holding capacity, and an enhancement in the emulsification properties of proteins. Among them, CN-XOS exhibited the most pronounced changes, with the emulsification activity index and emulsion stability index increasing by approximately 72% and 84.3%, respectively. Furthermore, CN-XOS emulsions have smaller droplet sizes and higher absolute potential values than CN emulsions. Additionally, CN-XOS emulsions demonstrate remarkable stability when ion concentration and pH are varied. These findings indicate that oligosaccharides modified via Maillard reaction can be used as good natural emulsifiers. This provides a theoretical basis for using oligosaccharides to modify proteins and act as natural emulsifiers.

The effect of rice protein-polyphenols covalent and non-covalent interactions on the structure, functionality and in vitro digestion properties of rice protein

The characteristics of the crosslinking between rice protein (RP) and ferulic acid (FA), gallic acid (GA), or tannin acid (TA) by covalent binding of Laccase and non-covalent binding were evaluated. The RP-polyphenol complexes greatly improved the functionality of RP. The covalent effect with higher polyphenol binding equivalence showed higher emulsion activity than the non-covalent effect. The solubility, and antioxidant activity of covalent binding were higher than that of non-covalent binding in the RP-FA group, but there was a contrasting behavior in the RP-GA group. The RP-FA was most soluble in conjugates, while the RP-GA had the highest solubility in mixtures. It was found that the covalent complexes were more stable in the intestinal tract. The content of polyphenols in the RP-TA group was rapidly increased at the later intestinal digestion, which indicated the high polyphenol-protective effect in this group. Meanwhile, the RP-TA group showed high reducing power but low digestibility.

Study on the interaction mechanism between (-)-epigallocatechin-3-gallate and myoglobin: Multi-spectroscopies and molecular simulation

(-)-Epigallocatechin-3-gallate (EGCG) is remarkably efficacious in inhibiting the browning of red meat. We therefore propose a hypothesis that EGCG forms complexes with myoglobin, thereby stabilizing its structure and thus preventing browning. This study investigated the interaction mechanism between EGCG and myoglobin. EGCG induced static quenching of myoglobin. Noncovalent forces, including hydrogen bonds and van der Waals, primarily governing the interactions between myoglobin and EGCG. The interactions primarily disrupted myoglobin's secondary structure, thus significantly reducing surface hydrophobicity by 53% (P < 0.05). The modification augmented the solubility and thermal stability of myoglobin. The radius of gyration (Rg) value fluctuated between 1.47 and 1.54 nm, and the hydroxyl groups in EGCG formed an average of 2.93 hydrogen bonds with myoglobin. Our findings elucidated the formation of stable myoglobin-EGCG complexes and the myoglobin-EGCG interaction, thus confirming our initial hypothesis.

Impact of Transglutaminase-Mediated Crosslinking on the Conformational Changes in a Dual-Protein System and IgE Reactivity of Soy Protein

Transglutaminase (TGase)-catalyzed crosslinking has gained substantial traction as a novel strategy for reducing allergenic risk in food proteins, particularly within the realm of hypoallergenic food production. This study explored the impact of TGase crosslinking on conformational changes in a binary protein system composed of soy protein isolate (SPI) and sodium caseinate (SC) at varying mass ratios (10:0, 7:3, 5:5, 3:7 (w/w)). Specifically, the immunoglobulin E (IgE) binding capacity of soy proteins within this system was examined. Prolonged TGase crosslinking (ranging from 0 h to 15 h) resulted in a gradual reduction in IgE reactivity across all SPI-SC ratios, with the order of IgE-binding capability as follows: SPI > SPI5-SC5 > SPI7-SC3 > SPI3-SC7. These alterations in protein conformation following TGase crosslinking, as demonstrated by variable intrinsic fluorescence, altered surface hydrophobicity, increased ultraviolet absorption and reduced free sulfhydryl content, were identified as the underlying causes. Additionally, ionic bonds were found to play a significant role in maintaining the structure of the dual-protein system after crosslinking, with hydrophobic forces and hydrogen bonds serving as supplementary forces. Generally, the dual-protein system may exhibit enhanced efficacy in reducing the allergenicity of soy protein.

Protein-Chlorogenic Acid Interactions: Mechanisms, Characteristics, and Potential Food Applications

The interactions between proteins and chlorogenic acid (CGA) have gained significant attention in recent years, not only as a promising approach to modify the structural and techno-functional properties of proteins but also to enhance their bioactive potential in food systems. These interactions can be divided into covalent (chemical or irreversible) and non-covalent (physical or reversible) linkages. Mechanistically, CGA forms covalent bonds with nucleophilic amino acid residues of proteins by alkaline, free radical, and enzymatic approaches, leading to changes in protein structure and functionality, such as solubility, emulsification properties, and antioxidant activity. In addition, the protein-CGA complexes can be obtained by hydrogen bonds, hydrophobic and electrostatic interactions, and van der Waals forces, each offering unique advantages and outcomes. This review highlights the mechanism of these interactions and their importance in modifying the structural, functional, nutritional, and physiological attributes of animal- and plant-based proteins. Moreover, the potential applications of these protein-CGA conjugates/complexes are explored in various food systems, such as beverages, films and coatings, emulsion-based delivery systems, and so on. Overall, this literature review provides an in-depth overview of protein-CGA interactions, offering valuable insights for future research to develop novel protein-based food and non-food products with improved nutritional and functional characteristics.

Microencapsule delivery systems of functional substances for precision nutrition

Microencapsulation, a typical core-shell structure technology, encapsulates functional active ingredients for protection, controlled release, and targeted delivery. In precise nutrition, the focus is on utilizing microcapsule delivery systems for personalized dietary supplements and disease intervention. This chapter outlines the morphological structure of microcapsules, common wall materials, and preparation techniques. It discusses the characteristics of different hydrophilic and lipophilic functional factors and their function as dietary supplements. The role of microencapsulation on the controlled release, odor masking, and enhanced bioavailability of functional factors is explored. Additionally, the application of microcapsule delivery systems in nutritional interventions for diseases like inflammatory bowel disease, alcoholic/fatty liver disease, diabetes, and cancer is introduced in detail. Lastly, the chapter proposes the future developments of anticipation in responsive wall materials for precise nutrition interventions, including both challenges and opportunities.

Food-packaging applications and mechanism of polysaccharides and polyphenols in multicomponent protein complex system: A review

With the increasingly mature research on protein-based multi-component systems at home and abroad, the current research on protein-based functional systems has also become a hot spot and focus in recent years. In the functional system, the types of functional factors and their interactions with other components are usually considered to be the subjective factors of the functional strength of the system. Because this process is accompanied by the transfer of protons and electrons in the system, it has antioxidant, antibacterial and anti-inflammatory properties. Polyphenols and polysaccharides have the advantages of wide source, excellent functionality and good compatibility with proteins, and have become excellent and representative functional factors. However, polyphenols and polysaccharides are usually accompanied by poor stability, poor solubility and low bioavailability when used as functional factors. Therefore, the effect of separate release and delivery will inevitably lead to non-significant or direct degradation. After forming a multi-component composite system with the protein, the functional factor will form a stable system driven by hydrogen bonds, hydrophobic forces and electrostatic forces between the functional factor and the protein. When used as a delivery system, it will protect the functional factor, and when released, through the specific recognition of the cell membrane receptor signal, the effect of fixed-point delivery is achieved. In addition, this multi-component composite system can also form a functional composite film by other means, which has a long-term significance for prolonging the shelf life of food and carrying out specific antibacterial.

Effect of ultrasound-assisted Maillard reaction on glycosylation of goat whey protein: Structure and functional properties

Goat whey protein (GWP) has a rich amino acid profile and good techno-functional attributes but still has limited functional performance for certain applications. This study introduces an innovative ultrasound-assisted Maillard reaction to enhance GWP's functional properties by conjugating it with either gum Arabic (GA) or citrus pectin (CP). Sonication accelerated the Maillard reaction, and the glycosylation of GWP was significantly enhanced after optimization of the conjugation conditions. Gel electrophoresis examination verified the creation of GWP-polysaccharide conjugates, while scanning electron microscopy analysis revealed structural modifications caused by polysaccharide grafting and sonication. The use of ultrasound in the Maillard reaction notably enhanced the solubility, foaming capacity, and emulsifying attributes of the GWPs. Among the conjugates, the GWP-GA ones exhibited the best functional properties. Our findings suggest that this approach can notably improve the functional attributes of GWPs, thus broadening their potential uses in the food sector and beyond.

Non-covalent complexes of lutein/zeaxanthin and whey protein isolate formed at different pH levels: Binding interactions, storage stabilities, and bioaccessibilities

Lutein (Lut) and zeaxanthin (Zx) are promising healthy food ingredients; however, the low solubilities, stabilities, and bioavailabilities limit their applications in the food and beverage industries. A protein-based complex represents an efficient protective carrier for hydrophobic ligands, and its ligand-binding properties are influenced by the formulation conditions, particularly the pH level. This study explored the effects of various pH values (2.5-9.5) on the characteristics of whey protein isolate (WPI)-Lut/Zx complexes using multiple spectroscopic techniques, including ultraviolet-visible (UV-Vis), fluorescence, and Fourier transform infrared (FTIR) spectroscopies and dynamic light scattering (DLS). UV-Vis and DLS spectra revealed that Lut/Zx were present as H-aggregates in aqueous solutions, whereas WPI occurred as nanoparticles. The produced WPI-Lut/Zx complexes exhibited binding constants of 104-105 M-1, which gradually increased with increasing pH from 2.5 to 9.5. FTIR spectra demonstrated that pH variations and Lut/Zx addition caused detectable changes in the secondary WPI structure. Moreover, the WPI-Lut/Zx complexes effectively improved the physicochemical stabilities and antioxidant activities of Lut/Zx aggregates during long-term storage and achieved bioaccessibilities above 70% in a simulated gastrointestinal digestion process. The comprehensive data obtained in this study offer a basis for formulating strategies that can be potentially used in developing commercially available WPI complex-based xanthophyll-rich foods.

Roasted yerba mate (Ilex paraguariensis) infusions in bovine milk model before and after in vitro digestion: Bioaccessibility of phenolic compounds, antioxidant activity, protein-polyphenol interactions and bioactive peptides

Yerba mate is increasingly acknowledged for its bioactive properties and is currently being incorporated into various food and pharmaceutical products. When roasted, yerba mate transforms into mate tea, consumed as a hot aqueous infusion, and has gained popularity. This study investigated the bioaccessibility of phenolic compounds, protein-polyphenol interactions, antioxidant activity, and bioactive peptides in roasted yerba mate infusions, utilizing whole, semi-skimmed, and skimmed bovine milk models. The phytochemical profile of roasted yerba mate was analyzed in infusions with water and milk (whole, semi-skimmed, and skimmed), before and after in vitro digestion, identifying 18 compounds that exhibited variations in composition and presence among the samples. Bioavailability varied across different milk matrices, with milk being four times more efficient as a solvent for extraction. Gastric digestion significantly impacted (p < 0.05) the release of phenolic compounds, such as chlorogenic acid and rutin, with only chlorogenic acid remaining 100 % bioavailable in the infusion prepared with skimmed milk. Protein-polyphenol interaction did not influence protein digestion in different infusions, as there was a similarity in the hydrolysis pattern during the digestive process. Changes in antioxidant activity during digestion phases, especially after intestinal digestion in milk infusions, were related to alterations in protein structures and digestive interactions. The evaluation of total phenolic compounds highlighted that skimmed milk infusion notably preserved these compounds during digestion. Peptidomic analysis identified 253, 221, and 191 potentially bioactive peptides for whole, semi-skimmed, and skimmed milk-digested infusions, respectively, with a focus on anti-inflammatory and anticancer activities, presenting a synergistic approach to promote health benefits. The selection of milk type is crucial for comprehending the effects of digestion and interactions in bioactive compound-rich foods, highlighting the advantages of consuming plant infusions prepared with milk.

Co-assembled whey protein and proanthocyanidins as a promising biocarrier for hydrophobic pterostilbene: Fabrication, characterization, and cellular antioxidant potential

The usage of food-derived polyphenols with different polarities has been limited by their instability and incompatibility. Therefore, a biocarrier was developed by co-assembly of whey protein isolate (WPI) and hydrophilic proanthocyanidin (PC) for loading hydrophobic pterostilbene (PTE). Such biocarrier has superior affinity for PTE than WPI alone, as determined by encapsulation efficiency and loading capacity assay, fluorescence quenching analysis, and molecular docking, whereas the assembly process was characterized by particle size and zeta potential, 3-dimensional fluorescence, and scanning electron microscopy. Circular dichroism and Fourier transform infrared spectroscopy spectra confirmed the α-helix to β-sheet and random coil transition of proteins during the formation of nanocomplexes. Whey protein isolate acted as a mediator through altering the binding mode of PC and PTE, allowing them to perform significant synergistic effects in enhancing 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) and 2,2-diphenyl-1-picrylhydrazyl radical scavenging and reducing H2O2-induced cell damage. This research may serve to develop new protein/polyphenol co-loading systems and offer a reliable nutritional fortification.

Comparison of Alternative Protein Hydrogels for Delivering Myricetin: Interaction Mechanism and Stability Evaluation

Food protein carriers from different sources might have distinct stabilizing and enhancing effects on the same small molecule. To elucidate the molecular mechanism, five different sourced proteins including soy protein isolates (SPIs), whey protein isolates (WPIs), edible dock protein (EDP), Tenebrio molitor protein (TMP), and yeast protein (YP) were used to prepare protein hydrogels for delivering myricetin (Myr). The results suggested that the loading capacity order of Myr in different protein hydrogels was EDP (11.5%) > WPI (9.3%) > TMP (8.9%) > YP (8.0%) > SPI (7.6%), which was consistent with the sequence of binding affinity between Myr and different proteins. Among five protein hydrogels, EDP had an optimum loading ability since it possessed the highest hydrophobic amino acid content (45.52%) and thus provided a broad hydrophobic cavity for loading Myr. In addition, these protein-Myr composite hydrogels displayed the core-shell structure, wherein hydrogen bonding and hydrophobic interaction were the primary binding forces between proteins and Myr. Moreover, the thermal stability, storage stability, and sustained-release properties of Myr were significantly enhanced via these protein delivery systems. These findings can provide scientific guidance for deeper utilization of food alternative protein sources.

Emerging Trends in Bioavailability and Pharma-Nutraceutical Potential of Whey Bioactives

Whey, a component of milk and a useful by-product of the dairy industry's casein and cheese-making, has been used for generations to augment animal feed. It contains a range of proteins, including α-lactalbumin, β-lactoglobulin, bovine serum albumin, heavy and light chain immunoglobulins, lactoferrin, glycomacropeptide, and lactoperoxidase. Whey proteins exhibit great potential as biopolymers for creating bioactive delivery systems owing to their distinct health-enhancing characteristics and the presence of numerous amino acid groups within their structures. Whey has considerable factors such as antitumor, anti-inflammatory, antihypertensive, hypolipidemic, antiviral, and antibacterial properties in addition to chelating. The global market of whey protein stood at USD 5.33 billion in 2021, with a projected compound annual growth rate of 10.48% spanning the interval from 2022 to 2030. The escalating demand for whey protein is intrinsically linked to the amplifying consciousness surrounding healthy lifestyles. Notably, protein supplements are recurrently endorsed by fitness and sports establishments, thereby accentuating the focal point of customers toward whey protein. This review focuses on nutritional composition, whey bioactives, and their bioavailability with potential health benefits.

The inhibition mechanism of bound polyphenols extracted from mung bean coat dietary fiber on porcine pancreatic α-amylase: kinetic, spectroscopic, differential scanning calorimetric and molecular docking

The inhibitory mechanisms of purified bound polyphenols extracted from mung bean coat dietary fiber (pMBDF-BP) on porcine pancreatic α-amylase (PPA) were investigated through inhibition kinetics, fluorescence spectroscopy, circular dichroism, differential scanning calorimetry and molecular docking. It was shown that pMBDF-BP exerted significant reversible inhibition on PPA in a mixed-type inhibition manner (IC50 = 18.57 ± 0.30 μg/mL), and the combination of the three major components exhibited a synergistic inhibitory effect on PPA. Further, pMBDF-BP bound to the active site or form a polyphenol-enzyme complex at the inactive site through hydrogen bonding and hydrophobic forces, via enhancing the hydrophobicity of the microenvironment surrounding tryptophan and tyrosine residues and promoting the secondary structure of PPA towards a more stable conformation, eventually reducing the enzyme activity. This study provided theoretical evidences for the utilization of bound polyphenols extracted from mung bean coat dietary fiber as a functional component in natural inhibitors of α-amylase.

Interaction between curcumin and ultrafiltered casein micelles or whey protein, and characteristics of their complexes

This work evaluated the interaction between micellar casein (MC) or whey protein (WP) in ultrafiltration retentate with curcumin (Cur), as well as the physicochemical and functional properties of Cur-MC and Cur-WP complexes. The MC had a higher affinity for Cur than WP, shown by higher binding constants of Cur-MC at various temperatures. Thermodynamic analysis of the binding process indicated that the interaction between Cur and MC or WP was hydrophobic in nature. Cur promoted the size and polydispersity index of MC and WP at 4 mM but did not alter the morphology of spray-dried MC and WP. The Cur-MC complexes showed better aqueous solubility at pH 2-3 and 6-10 compared to free MC. Combination with MC or WP improved the 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) radical scavenging activity of Cur. In addition, combination with MC and WP promoted cumulative release of Cur during simulated gastrointestinal digestion, especially for WP. Thus, MC and WP in retentates can be good alternative protein-based carriers for Cur delivery, whereas their complexes in powder form have good functional properties that could be used as active food ingredients in several food formulations. PRACTICAL APPLICATION: Microfiltration is a cheap and convenient approach that can be used to easily produce micellar casein (MC), with whey protein (WP) as one byproduct. In this study, we proved that MC and WP in retentates have strong interaction with curcumin (Cur), whereas their complexes have good functional properties. Thus, spray-dried MC-Cur or WP-Cur complexes could be used as active food ingredients in several food formulations.

Effects of conjugated interactions between Perilla seed meal proteins and different polyphenols on the structural and functional properties of proteins

The study aims to perform alkali-induced covalent modification of perilla seed meal protein (PSMP) using different polyphenols: gallic acid (GA), protocatechuic acid (PCA), caffeic acid (CA), apigenin (API) and luteolin (LU). Covalent binding between different polyphenols and PSMP was found to occur, with PSMP-LU showing the highest binding rate of 90.89 ± 1.37 mg/g; the fluorescence spectrum of PSMP-CA showed a maximum blue shift of Δ13.4 nm; the solubility increased from 69.626 ± 1.39 % to 83.102 ± 0.98 %. In order to better understand how these covalent conjugates, stabilize -carotene in emulsions, they were utilized as emulsifiers in an emulsion delivery method. The work further reveals the formation of PSMP-polyphenol conjugates and develops a novel emulsification system to deliver readily decomposable functional factors, providing a potential scenario for the application of PSMP and bioactive conjugates.

Non-covalent interaction between hemp seed globulin and two hemp seed phenolic compounds: Mechanism and effects on protein structure, bioactivity, and in vitro simulated digestion

This study focused on elucidating the non-covalent interactions between hemp seed globulin (GLB) and two hemp seed phenolic compounds, Cannabisin A (CA) and Cannabisin B (CB), and to explore these interactions on the protein's structure, conformation, and functionality. Fluorescence quenching and thermodynamic analysis revealed that static quenching governed non-covalent interaction processes, with hydrogen bonds and van der Waals forces functioning as major forces. This was further substantiated by molecular docking studies. The binding affinity order was CA > CB, indicating that the specific phenolic compound had a notable impact on the binding affinity. Furthermore, when complexed with CA, Tyr and Trp residues were exposed to a more hydrophilic environment than when complexed with CB. It was noted that the complexation with either CA or CB consistently affects GLB's secondary structure, particle size, and ζ-potential. GLB treated with the phenolic compounds exhibited enhanced ABTS and DPPH scavenging activities and improved digestibility compared to untreated GLB. Furthermore, the non-covalent interactions significantly increased CA's water solubility, highlighting GLB as a promising natural carrier for hydrophobic bioactive components. These findings hold potential implications for enhancing hemp seed protein applications within the food industry by positively influencing its functional properties and bioactivity.

The improved bioavailability of zein/soybean protein isolate by puerarin in vitro

As the largest emitter of greenhouse gases, the livestock and poultry industry is facing the challenge of increasing production to meet global demand while reducing environmental impacts. Improving feed digestibility by optimizing feed structure (e.g., exogenous additive) is one of the green breeding measures to alleviate carbon pressure. In this study, the interaction mechanism and in vitro digestibility properties of puerarin (PUE) with feed proteins (zein and soy protein isolate (SPI)) to form Zein-PUE and SPI-PUE complexes were investigated mainly by multispectral and molecular docking techniques. Results indicated that the addition of PUE improved the physicochemical properties of proteins (e.g., solubility and disulfide bond contents). Then, the spectral results showed that the binding processes were spontaneous, and the protein structure tended to loose and disordered after binding, and more hydrophobic residues were exposed to the hydrophilic microenvironment. Moreover, on the basis of molecular docking revealed that PUE bound to zein by hydrogen bond, electrostatic and hydrophobic interactions, while with SPI by hydrogen bond and hydrophobic interaction. Finally, in vitro digestion experiments demonstrated that the bioavailability of Zein-PUE and SPI-PUE complexes increased by 1.15 % and 2.11 %, respectively. Overall, PUE is a promising feed additive beneficial for enhancing protein digestibility and bioavailability.

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.

Effects of Covalent or Noncovalent Binding of Different Polyphenols to Acid-Soluble Collagen on Protein Structure, Functionality, and Digestibility

In this study, the structure, function, and digestibility of noncovalent complexes and covalent conjugates formed by acid-soluble collagen with polyphenols of different structures (quercetin, epicatechin, gallic acid, chlorogenic acid, procyanidin, and tannic acid) were investigated. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that polyphenols were covalently bound to collagen by laccase catalytic oxidation. Biolayer interferometry revealed that the noncovalent binding strength of polyphenols to collagen from high to low was quercetin > gallic acid > chlorogenic acid > epicatechin, which was consistent with the trend of covalent polyphenol binding. Procyanidin and tannic acid had strong noncovalent binding, but their covalent binding ability was weak. Compared with the pure collagen, the complexes improved emulsification and antioxidant properties (more than 2.5 times), and the conjugates exhibited better thermal stability (99.4-106.8 °C) and antidigestion ability (reduced by more than 37%). The finding sheds new light on the use of collagen as a functional food ingredient in the food industry.