Functional and conformational changes to soy proteins accompanying anthocyanins: Focus on covalent and non-covalent interactions

Structural modulation of eggshell membrane hydrolysates by tannic acid: Simultaneous enhancement of antioxidant and emulsifying properties

In this study, eggshell membrane hydrolysate (ESMH) and tannic acid (TA) complexes were prepared through both covalent and non-covalent interactions, with their structural properties, antioxidant activity and emulsifying properties being evaluated. The results revealed that the covalent complexes have lower sulfhydryl content (5.3 μmol/g) and higher TA binding capacity (0.15 mg/mL Protein) than the non-covalent complexes at the same TA concentration. FTIR and fluorescence analyses indicated that the structure of ESMH changed after binding with TA. Antioxidant assays demonstrated that TA significantly enhanced the free radical scavenging ability and Fe2+chelating ability of ESMH. Furthermore, when the ESMH-TA covalent complex was applied to a storage test of fresh mayonnaise, the rate of lipid oxidation was effectively slowed down. In addition, the covalent complexes successfully prepared emulsions with smaller particle sizes (8.5 μm) and provided improved stability against lipid oxidation by altering the protein conformation.

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.

Revealing the non-enzymatic covalent interaction between neo-/crypto-chlorogenic acid and beta-lactoglobulin under nonthermal process and potential delivery capability

Several studies have shown that the protein-chlorogenic acid covalent complex has better function and stability than the non-covalent. The degree of binding between the proteins and chlorogenic acids (CQA) can be enhanced by the ultrasound process. Herein, the effects of ultrasound-assisted non-enzymatic covalent binding (the free radical induction (Vc)-ultrasound combination and the alkali treatment (Alkali)-ultrasound combination) of two chlorogenic acids (neochlorogenic acid (3-CQA), cryptochlorogenic acid (4-CQA)) and β-lactoglobulin (β-LG) on proteins structure and properties were investigated. Results showed that ULG-Alkali-4CQA exhibited a 5.1 % reduction in α-helices, a 6.8 % increase in random curl and proteins structures becoming loose and disordered. The hydrophilicity and thermal stability of β-LG were effectively enhanced by the addition of 4-CQA and the effect of alkali treatment-ultrasound combination. Curcumin (CUR) and lycopene (LYC) were successfully delivered by the covalent complexes as delivery vehicles. The encapsulation efficiencies of the ULG-Vc/Alkali-4CQA + CUR and ULG-Vc/Alkali-4CQA + LYC complexes were 82.81 %, 84.16 %, 89.56 % and 90.51 %, respectively. The stabilities of CUR and LYC in the ULG-Vc/Alkali-4CQA + CUR/LYC ternary complexes were superior to those of all the measured complexes delivery systems. The study hopes to establish a theoretical foundation and serve as a reference for the advancement of a highly stable food-grade delivery system.

Edible blueberry anthocyanin-loaded soybean protein nanofibers/sodium alginate hydrogel beads: Freshness detection of high protein drinks

In this study, blueberry anthocyanins were embedded in soybean protein nanofibers/sodium alginate hydrogel (SNF/SA) to prepare an edible pH-responsive chromogenic hydrogel bead for freshness monitoring of milk, soybean milk and dual protein drinks. The results showed that the encapsulation rate of blueberry anthocyanins was 87.43 %. The loading of blueberry anthocyanins achieved the pH-response color development of SNF/SA hydrogel beads. SS/B3 hydrogel beads (SNF/SA loaded with 0.1 g anthocyanins) showed good color stability when stored in different environments for 96 h. When the SS/B3 hydrogel beads were used for detecting the protein drinks freshness, fresh drinks and spoiled drinks could be clearly distinguished by color of hydrogel beads. In addition, SS/B3 hydrogel beads promoted protein digestibility of protein drinks and protected anthocyanins from degradation in the stomach environment. Therefore, the hydrogel bead was accessible and edible, it could provide a possibility for monitoring the quality changes of fresh protein drinks.

Amphipathic regulation of cottonseed protein with the conjugation of bayberry tannin for efficient surface decontamination of uranium

Radioactive substances (Uranium) on the human body or facility surfaces are easy to diffuse in nuclear activity, posing a severe threat to ecological security and human health, especially for personnel working in and around uranium mining and nuclear facilities. In this work, a green protein-based surfactant was synthesized using the free-radical conjugating method to graft bayberry tannin (BT) onto cottonseed protein (CPI) for regulating its amphipathy and removing uranyl ions (UO₂²⁺) in both aqueous environments and solid surfaces. FTIR, CD spectroscopy, intrinsic fluorescence, conductometric titration, and SEM-EDX characterization techniques confirmed the successful covalent conjugation of BT onto CPI, inducing unfolding, conformational changes, and enhanced hydrophilicity of CPI. Thus, leading to improved foaming and emulsifying properties. Notably, the surfactant exhibited high efficiency in UO₂²⁺ removal and selectivity from an aqueous environment, achieving a removal rate of 93 % within 30 minutes and a maximum adsorption capacity of 310.15 mg/g. Additionally, it also demonstrated effectiveness in decontaminating different simulated uranium-contaminated solid surfaces. The synergistic interaction between BT's phenolic-hydroxyl groups and CPI's structural versatility and functional groups facilitated the effective UO₂²⁺ complexation. This study demonstrates the feasibility of using agro-industrial waste-derived CPI-BT as an eco-friendly, sustainable, and cost-effective alternative to synthetic surfactants for mitigating uranium contamination in environments near uranium mining operations and nuclear facilities.

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.

A comprehensive review of the impact of anthocyanins from purple/black Rice on starch and protein digestibility, gut microbiota modulation, and their applications in food products

This review explores the impact of anthocyanins derived from purple and black rice on starch and protein digestibility, gut microbiota modulation, and their applications in food production. Anthocyanins are shown to reduce starch digestibility by forming complexes with starch, thereby inhibiting key digestive enzymes. Additionally, they can influence protein digestion by inducing structural changes that enhance resistance to digestive processes. Evidence suggests that black rice anthocyanins positively modulate gut microbiota composition, potentially improving overall gut health. The incorporation of anthocyanin-rich extracts into various food products, such as bread and beverages, underscores their potential as functional ingredients. This review provides valuable insights into the health benefits associated with rice anthocyanins and identifies areas for future research to optimize their application in functional foods aimed at managing metabolic health.

Stabilization of calcium-fortified soy protein emulsions by calcium chelating agent sodium tripolyphosphate

Calcium-fortified soy protein emulsions stabilized by sodium tripolyphosphate are of considerable importance for the development of calcium-fortified soymilk products. This study aimed to investigate the characteristics and stabilities of calcium-fortified soy protein emulsions stabilized by sodium tripolyphosphate. When the concentration of sodium tripolyphosphate ranged from 0 to 0.6%, the emulsion potential and emulsification activity index gradually increased to 35.5 mV and 71.7 ± 0.8%, while the particle size and flocculation index progressively decreased to 756.2 ± 41.3 nm and 16.21%, respectively. However, when the concentration exceeded 0.6%, these characterization data plateaued. Microstructural analysis revealed a uniform distribution of droplets. Raman spectroscopy showed an increase in the ordered structure of proteins in the emulsion. Additionally, the centrifugal, thermal, and storage stabilities of the emulsion were enhanced. These findings offer insights into the properties of calcium-fortified soy protein emulsions stabilized by sodium tripolyphosphate and may contribute to expanding their utilization in emulsions and soy products.

Graphical abstract

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.

Casein-grape seed proanthocyanidins complexes stabilized Pickering emulsion gels based on Lycium Barbarum seed oil with excellent mechanical properties and oxidation resistance

Pickering emulsion gels received extensive attention in encapsulating fat-soluble substances such as Lycium barbarum seed oil (LBSO). However, the gels presented poor mechanical properties, otherwise, their physical encapsulation cannot inhibit lipid peroxidation. Herein, grape seed proanthocyanidins (OPCs) and casein (CAS) complexes interacted through hydrogen and covalent bonds were proposed to build Pickering emulsion gels and encapsulate LBSO, which changed the secondary structures of CAS and further enhanced emulsifying ability, oxidation resistance, and gelling performance. The CAS-OPCs gels had better microstructures and mechanical properties due to the enhancement of hydrogen and covalent interactions. Furthermore, gels with OPC contents of 8.00 mg/mL had performance in 3D printing. And gels reduced the peroxide value of LBSO (9.33±0.20 to 1.39±0.22 mmol/kg) after heating. This study helps reveal the possible mechanisms of OPCs on gels and provides a reference for the application and research of OPCs and CAS composites in Pickering emulsion gels.

Differential Enzymatic Hydrolysis: A Study on Its Impact on Soy Protein Structure, Function, and Soy Milk Powder Properties

Protein constitutes the primary nutrient in soy, and its modifications are intricately linked to the properties of the soy milk powder. This study employed six main commercial enzymes (bromelain, neutrase, papain, trypsin, flavourzyme, and alcalase) to investigate the impact of enzymatic hydrolysis on the structural and functional properties of soy protein isolate (SPI), as well as its influence on the physicochemical properties of soy milk powder. The findings indicated that each of enzymes exhibits distinct specificity, with the degree of hydrolysis following the order: alcalase > flavourzyme > papain > bromelain > neutrase > trypsin. Enzymatic hydrolysis facilitates the unfolding of SPI, leading to the exposure of chromogenic fluorophores and hydrophobic amino acid residues, which in turn promotes an increase in free sulfhydryl content. Concurrently, this process induces the transformation of α-helix and β-sheet into β-turn and random coil. The enzyme modification enhances the solubility, emulsification, and foaming activities of SPI and significantly augment its antioxidant properties (p < 0.05). However, this enzymatic treatment adversely affects the stability of its emulsification and foaming properties. Subsequent to enzymatic hydrolysis, soy milk powder demonstrated a reduction in particle size and an improvement in solubility, which significantly enhanced its flavor profile. In summary, alcalase offers substantial advantages in augmenting the functional properties of SPI and increasing the solubility of soy milk powder. However, this process adversely affects the flavor profile of soy milk powder, a consequence attributed to the broad hydrolysis specificity of alcalase.

High-moisture extrusion of rice bran-peanut proteins: Changes in structural properties and antioxidant activity simulating gastrointestinal digestion

In this experiment, we investigated the structural properties, digestibility, and variations in antioxidant activity of rice bran-tissue peanut protein (RB-TPP), which was created through high-moisture extrusion between peanut protein powder (PPP) and various additions (0 %, 5 %, 10 %, 15 %, and 20 %) of rice bran (RB). The disulfide bonding and hydrophobic interactions were strengthened, and the hydrogen bonding in the RB-TPP was weakened by adding 5-10 % RB. Additionally, the β-sheet content reached its maximum at RB-10 %, which allowed the hydrophobic groups to be encapsulated ina stable protein network fiber structure, enhancing degree of organization, the thermal stability and digestibility of RB-TPP. On the other hand, RB-10 % showed increased total phenolic content and antioxidant activity, in which the ABTS radical scavenging rate was increased by 22.14 % compared with that of RB-0 %, while the DPPH radical scavenging rate in simulated gastric digestion was increased by 10.59 %. RB addition at 15-20 % hindered the aggregation of proteins, which was not conducive to the rearrangement of protein molecules, and the increase in the irregular curls made the RB-TPP structure loose and disordered. This study provides valuable information for producing tissue proteins with stable fiber network structure and better nutritional and functional properties by adding RB.

The role of Maillard reaction in increasing affinity between soybean protein isolate and phloretin and its effects on protein functionality

This study investigated the effects of the Maillard reaction on the interaction between soybean protein isolate (SPI) and phloretin (PHL), along with its impact on the functional properties of soybean protein isolate. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) results showed that sodium alginate (SA) was successfully grafted onto SPI. The fluorescence results indicated that the red shift and fluorescence burst of the ternary complexes were more pronounced, indicating that the proteins in the complexes had a more compact tertiary structure. The molecular docking showed that phloretin formed shorter hydrogen bonds with surrounding active amino acid residues after the Maillard reaction, suggesting that the Maillard reaction enhanced the stability of Phloretin's binding to proteins. The slight blue shifts observed in the amide I and amide II bands suggested hydrogen bonding and electrostatic interactions are also present. A decrease in α-helix and β-sheet content, along with an increase in irregular curl content, indicating protein unfolding. Also, the functional properties of SPI were improved due to the unfolding of the protein structure. These findings will provide valuable insights for the subsequent study of Maillard reaction products in the construction of nutrient delivery systems.

Fabrication, characterization and gastrointestinal fate of curcumin-loaded emulsions stabilized by soy protein-based ternary composite nanoparticles

To design a novel emulsifier capable of enhancing the bioavailability of curcumin (Cur)-loaded emulsions in the gastrointestinal tract, soy protein-based ternary composite nanoparticles (SEPn) were fabricated by transacylation reaction. The results showed that SEPn was formed by the covalent binding of the carboxyl groups in PGA to the amino groups in SEC through multiple forces. SEPn-1:1 was determined to be the optimal condition for preparing Cur-loaded emulsions. Additionally, SEPn-1:1 had superior emulsifying capacity as formed plastic-state emulsion gel with φ as low as 0.5. Moreover, the rise in oil content promoted the development of gel, thus increasing the apparent viscosity, gel strength, and stability of Cur-loaded emulsions. Furthermore, SEPn-1:1 emulsion exhibited excellent gastric stability and higher free fatty acid (FAA) release rates in the small intestine phase compared with that of SECcon (SEC control sample) and Mixture emulsion, thus leading to the highest bioavailability of Cur (28.57 ± 1.91 %).

Effects of C-ring structures on the formations of flavonoid semiquinones and their binding behavior with β-lactoglobulin as revealed by experimental and modeling approaches

The present study investigated the covalent binding behavior of the flavonoids, catechin, eriodictyol, luteolin and quercetin with β-lactoglobulin (βlg). Since the four flavonoids possess the identical A- and B-ring structures, effects of the C-rings on the properties of flavonoids and the corresponding semiquinones are revealed. Experimental methods including DLS and CD spectra indicated that with quercetin at room temperature did not induce aggregation of βlg, whilst binding with the other three flavonoids resulted in aggregation of βlg. Proteomic and LC-MS/MS analysis indicated that lysine (Lys/K), tryptophan (Trp/W) and cysteine (Cys/C) exhibited high propensity to bind with flavonoids. Catechin exhibited the highest binding with βlg while eriodictyol had the lowest and showed no tendency to bind with tryptophan (Trp/W). Quantum chemistry calculations showed that the corresponding semiquinones with the deprotonations occurring on the A-rings exhibited higher reactivity than those with radicals on the B-rings. Behavior of flavonoid semiquinones formed after deprotonation influenced the protein stability as revealed by MD simulations. Assemblies of quercetin semiquinones were found to protect βlg from unfolding and aggregation. The modeling provided explanations for experimental observations, and provided new insights and understanding of covalent interactions between proteins and flavonoids.

Interactions with peanut protein isolate regulate the bioaccessibility of cyanidin-3-O-glucoside: Multispectral analysis, simulated digestion, and molecular dynamic simulation

Anthocyanins are susceptible to degradation owing to environmental factors. Combining them with proteins can improve their stability; however, the interaction mechanism is difficult to elucidate. This study used multispectral and molecular dynamics simulations and molecular docking methods to investigate the interaction mechanism between peanut protein isolate (PPI) and cyanidin-3-O-glucoside (C3G). The UV absorption peak and PPI turbidity increased, while the fluorescence intensity decreased with greater C3G content. Protein secondary structure changes suggested that PPI and C3G coexisted in spontaneous covalent and non-covalent interactions via static quenching. The complex structures were stable over time and C3G stably bound to the peanut globulin Ara h 3 cavity through hydrogen bonding and hydrophobic interactions. Furthermore, PPI enhanced the C3G antioxidant activity and bioaccessibility by increasing its retention rate during in-vitro simulated digestion. This study elucidates the binding mechanism of PPI and C3G and provides insight into applications of the complex in food development.

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

The Effect of Lipids on the Structure and Function of Egg Proteins in Response to Pasteurization

In recent years, the consumption of liquid eggs has failed to meet the expectations of the public due to growing concerns regarding food safety and health. It is well known that there are interactions between the components in liquid eggs, and the interaction effect on the structure and functional properties of the proteins and antigenicity remains unclear. To investigate egg component interactions, we focused on four major egg lipids, namely phosphatidylcholine, palmitic acid, oleic acid, and linoleic acid, as well as four major egg proteins, including ovalbumin, ovotransferrin, ovomucoid, and lysozyme. The protein structural changes were analyzed using polypropylene gel electrophoresis, circular dichroism, ultraviolet absorption spectra, and exogenous fluorescence spectra, and the functional properties were assessed through solubility measurements and particle size analysis, while protein antigenicity was evaluated using an enzyme-linked immunosorbent assay. All the results revealed that oleic acid had the most significant effect on proteins' secondary and tertiary structures, particularly affecting ovalbumin and ovotransferrin. Linoleic acid substantially increased the solubility of ovalbumin and ovomucoid, while palmitic acid significantly influenced the particle size of ovalbumin and lysozyme. Thus, we found that different lipids exhibit distinct effects on egg protein properties during pasteurization conditions, with oleic acid showing the most substantial impact on protein structure and antigenicity.

Enhancement of soy protein functionality by conjugation or complexation with polysaccharides or polyphenols: A review

Soy proteins have good nutritional quality and exhibit a range of useful functional attributes, making them a viable option for replacing animal proteins in the development of more sustainable and eco-friendly plant-based food products. Nevertheless, soy proteins are prone to denaturation and/or aggregation under conditions they encounter in some food and beverage products (including certain pH, ionic, and thermal conditions), which adversely impact their functional performance. This problem can often be overcome by covalently (conjugation) or noncovalently (complexation) linking the soy proteins to polysaccharides or polyphenols, thereby expanding their application scope. Compared to soy proteins alone, these conjugates or complexes exhibit enhanced technofunctional performance, including improved solubility, emulsification, foaming, gelling, antimicrobial properties, and antioxidant capacities. Conjugates are typically more stable than complexes, which may be an advantage for some food applications. However, complexes do not require additional regulatory approval, which makes them more suitable for most food applications. This review aims to comprehensively examine the enhancement of soy protein functionality through conjugation or complexation with polysaccharides or polyphenols. The research focuses on how these modifications enhance solubility, emulsification potential, foaming, gelling, and antioxidant properties, reduce the allergenicity of soy proteins, and enable their potential applications in plant-based food development, 3D food printing, fat substitutes, functional food carriers, and hypoallergenic foods.

Comparison of Interactions Between Soy Protein Isolate and Three Folate Molecules: Effect on the Stabilization, Degradation, and Oxidization of Folates and Protein

This study selected three approved folate sources-folic acid (FA), L-5-methyltetrahydrofolate (MTFA), and calcium 5-methyltetrahydrofolate (CMTFA)-to explore their interaction mechanisms with soy protein isolate (SPI) through spectrofluorometric analysis and molecular docking simulations. We investigated how these interactions influence the structural and physicochemical stability of folates and SPI. Three folates spontaneously bound to SPI, forming complexes, resulting in a decrease of approximately 30 kJ·mol-1 in Gibbs free energy and an association constant (Ka) of 105 L·mol-1. The thermodynamic parameters and molecular docking study revealed the unique binding mechanisms of FA and MTFA with SPI. FA's planar pteridine ring and conjugated double bonds facilitate hydrophobic interactions, whereas MTFA's reduced ring structure and additional polar groups strengthen hydrogen bonding. Although the formation of SPI-folate complexes did not result in substantial alterations to the SPI structure, their binding has the potential to enhance both the physical and thermal stability of the protein by stabilizing its conformation. Notably, compared with free FA, the FA-SPI complexes significantly enhanced FA's stability, exhibiting 71.1 ± 1.2% stability under light conditions after 9 days and 63.2 ± 2.6% stability in the dark after 60 days. In contrast, no similar effect was observed for MTFA. This discrepancy can be ascribed to the distinct degradation pathways of the Fa and MTFA molecules. This study offers both theoretical and experimental insights into the development of folate-loaded delivery systems utilizing SPI as a matrix.

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

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

Modification of the texture of 3D printing soy protein isolate-based foods with proper nozzle sizes: A swallowing oriented strategy for dysphagia diet

3D printing could provide swallowing-friendly food with high nutrition for a dysphagia diet. The effects of printing nozzle size on texture modification were studied using the soy protein isolate (SPI)-beeswax (BWX)-based bigel ink system enriched with bio-actives. Smaller nozzle sizes (0.4 to 0.8 mm) decrease while bigger ones (1.6 to 2.0 mm) increase the texture profiles. Fortunately, the 1.0 mm nozzle size helps to regulate the rheology of mechanical strength and soften the texture of hardness, as well as maintain a higher proportion of semi-solid water. Consequently, the 1.0 mm nozzle achieved the highest printability and the product was classified as level-5 or level-6 minced and moist food. The decreasing nozzle sizes apply higher shearing force to the bigel ink, which leads to the aggregation of oleogel particles, crystal clusters, and the broken of the SPI hydrogel network. Increasing the nozzle sizes maintained structure stability but resulted in the fabrication of harder textures and slower release of bio-actives. The 1.00 mm kept the balance between the large and small nozzle effect, which might help to keep the microstructure stable and show high bio-accessibility of bio-actives. This work provides a novel insight into texture modification with 3D printing parameters.

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.

Sanxan-Protein Complex Particles for Stabilization of Pickering Emulsions: Improving Emulsification Properties

Sanxan (SAN) is a novel microbial polysaccharide that is both safe and edible and represents a promising new source of food resources. It exhibits gelling properties and certain emulsifying properties. To date, there have been few studies published on the enhancement of protein emulsification by sanxan. In this study, three widely used proteins were used: casein (CS), pea protein isolate (PPI), and soy protein isolate (SPI). SAN-protein composite particles were prepared by non-covalent interactions to evaluate the availability of SAN in Pickering emulsions. The effect of SAN on the ability of the complexes to stabilize the emulsion was investigated by measuring and characterizing the physicochemical properties of three SAN-protein complexes. Fourier transform infrared (FTIR) and fluorescence spectroscopy analyses showed that SAN was able to bind to three proteins to form complexes. All three complexes formed by SAN with SPI, PPI and CS had good emulsification properties, with PPI-SAN being the best. Storage results showed better stability of the composite particle-stabilized emulsion. These results indicate that the complexation of SAN with proteins improves the emulsification of proteins and increases the stability of Pickering emulsions. The findings of this study provide valuable information for the utilization of SAN in emulsions.

Co-encapsulation of hydrophilic and hydrophobic bioactives stabilized in nanostarch-assisted emulsion for inner core gel of coaxial 3D printing

3D printing technology, especially coaxial 3D mode of multiple-component shaping, has great potential in the manufacture of personalized nutritional foods. However, integrating and stabilizing functional objectives of different natures remains a challenge for 3D customized foods. Here, we used starch nanoparticle (SNP) to assisted soy protein (SPI) emulsion to load hydrophilic and hydrophobic bioactives (anthocyanin, AC, and curcumin, Cur). The addition of SNP significantly improved the storage stability of the emulsion. Xanthan gum (XG) was also added to the SNP/SPI system to enhance its rheology and form an emulsion gel as inner core of coaxial 3D printing. Low field nuclear magnetic resonance and emulsification analyses showed that AC/Cur@SNP/SPI/XG functional inner core had a strong water binding state and good stability. After printing with outer layer, the SNP/SPI coaxial sample had the lowest deviation rate of 0.8 %. Also, SNP/SPI coaxial sample showed higher AC (90.2 %) and Cur (90.8 %) retention compared to pure starch (S), pure SNP, pure SPI, and S/SPI samples as well as SNP/SPI sample printed without outer layer. In summary, this study provides a new perspective for the manufacture of customized products as multifunctional foods, feeds and even potential delivery of drugs.

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.

The Effect of Dihydromyricetin (DMY) on the Mechanism of Soy Protein Isolate/Inulin/Dihydromyricetin Interaction: Structural, Interfacial, and Functional Properties

The combination of proteins with polysaccharides and polyphenols is expected to improve their physicochemical and functional properties. In this study, a novel plant-based antioxidant emulsifier was formed by soybean protein isolate (SPI), inulin (INU), and dihydromyricetin (DMY). Based on the binary system of SPI/INU, we focused on exploring the effect of the DMY concentration (0.5 mg/mL~2.5 mg/mL) on the formation and properties of the ternary complex. The structure, interaction mechanism, and interfacial and functional properties of the ternary complex were investigated. The results indicate that compared to the SPI/INU binary complex, the SPI/INU/DMY ternary complex had a significant decrease in particle size (~100 nm) and a slight decrease in absolute zeta potential. The SPI/INU binary complex with DMY mainly interacted by hydrogen bonding and hydrophobic interactions. Due to the incorporation of DMY, the structure of SI was denser and more flexible. The ternary complex exhibited an ideal three-phase contact angle and demonstrated better foaming and antioxidant ability. Additionally, compared to SPI/INU, the ternary complex had a significant improvement in EAI. These results provide a strategy for polyphenols to modify the structure, interfacial properties, and functions of protein/polysaccharide complexes. This provides a potential reference for the preparation of more ternary complexes with excellent emulsifying and antioxidant properties for application in emulsions.

Optimization and Preparation of Ultrasound-Treated Whey Protein Isolate Pickering Emulsions

This study aimed to create Pickering emulsions with varying oil fractions and assess the impact of ultrasonic treatment on the properties of Whey Protein Isolates (WPIs). At 640 W for 30 min, ultrasound reduced WPI aggregate size, raised zeta potential, and improved foaming, emulsifying, and water-holding capacities. FTIR analysis showed structural changes, while fluorescence and hydrophobicity increased, indicating tertiary structure alterations. This suggests that sonication efficiently modifies WPI functionality. Under ideal conditions, φ = 80 emulsions were most stable, with no foaming or phase separation. Laser scanning revealed well-organized emulsions at φ = 80. This study provides a reference for modifying and utilizing WPI.

Protein-phenolic interactions and reactions: Discrepancies, challenges, and opportunities

Although noncovalent interactions and covalent reactions between phenolic compounds and proteins have been investigated across diverse scientific disciplines, a comprehensive understanding and identification of their products remain elusive. This review will initially outline the chemical framework and, subsequently, delve into unresolved or debated chemical and functional food-related implications, as well as forthcoming challenges in this topic. The primary objective is to elucidate the multiple aspects of protein-phenolic interactions and reactions, along with the underlying overwhelming dynamics and possibilities of follow-up reactions and potential crosslinking between proteins and phenolic compounds. The resulting products are challenging to identify and characterize analytically, as interactions and reactions occur concurrently, mutually influencing each other. Moreover, they are being modulated by various conditions such as the reaction parameters and, obviously, the chemical structure. Additionally, this review delineates the resulting discrepancies and challenges of properties and attributes such as color, taste, foaming, emulsion and gel formation, as well as effects on protein digestibility and allergenicity. Ultimately, this review is an opinion paper of a group of experts, dealing with these challenges for quite a while and aiming at equipping researchers with a critical and systematic approach to address current research gaps concerning protein-phenolic interactions and reactions.

Preparation of oil-in-water emulsions stabilized by faba bean protein-grape leaf polyphenol conjugates: pH-, salt-, heat-, and freeze-thaw-stability

BACKGROUND

Plant proteins are being increasingly utilized as functional ingredients in foods because of their potential health, sustainability, and environmental benefits. However, their functionality is often worse than the synthetic or animal-derived ingredients they are meant to replace. The functional performance of plant proteins can be improved by conjugating them with polyphenols. In this study, the formation and stability of oil-in-water emulsions prepared using faba bean protein-grape leaf polyphenol (FP-GLP) conjugates as emulsifiers. Initially, FP-GLP conjugates were formed using an ultrasound-assisted alkali treatment. Then, corn oil-in-water emulsions were prepared using high-intensity sonication (60% amplitude, 10 min) and the impacts of conjugate concentration, pH, ionic strength, freezing-thawing, and heating on their physicochemical properties and stability were determined.

RESULTS

Microscopy and light scattering analysis showed that oil-in-water emulsions containing small oil droplets could be formed at conjugate concentrations of 2% and higher. The addition of salt reduced the electrostatic repulsion between the droplets, which increased their susceptibility to aggregation. Indeed, appreciable droplet aggregation was observed at ≥ 50 mmol/L sodium chloride. The freeze-thaw stability of emulsions prepared with protein-polyphenol conjugates was better than those prepared using the proteins alone. In addition, the emulsions stabilized by the conjugates had a higher viscosity than those prepared by proteins alone.

CONCLUSION

This study showed that FP-GLP conjugates are effective plant-based emulsifiers for forming and stabilizing oil-in-water emulsions. Indeed, emulsions formed using these conjugates showed improved resistance to pH changes, heating, freezing, and salt addition. © 2024 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

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

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

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.

Structural, physicochemical and digestive properties of non-covalent and covalent complexes of ultrasound treated soybean protein isolate with soybean isoflavone

The non-covalent and covalent complexes of ultrasound treated soybean protein isolate (SPI) and soybean isoflavone (SI) were prepared, and the structure, physicochemical properties and in vitro digestion characteristics of SPI-SI complexes were investigated. Ultrasonic treatment increased the non-covalent and covalent binding degree of SPI with SI, and the 240 W ultrasonic covalent complexes had higher binding efficiency. Appropriate ultrasonic treatment caused more uniform particle size distribution, lower average particle size and higher surface charge, which enhanced the free sulfhydryl groups and surface hydrophobicity, thus improving the stability, solubility and emulsifying properties of complexes. Ultrasonic treatment resulted in more disordered secondary structure, tighter tertiary conformation, higher thermal stability and stronger SPI-SI covalent interactions of complexes. These structural modifications of particles had important effects on the chemical stability and gastrointestinal digestion fate of SI. The ultrasonic covalent complexation had a greater resistance to heat-induced chemical degradation of SI and improved its chemical stability. Furthermore, the 240 W ultrasonic covalent complexes showed lower protein digestibility during digestion, and provided stronger protection for SI, which improved the digestion stability and antioxidant activity. Therefore, appropriate ultrasound promoted SPI-SI interactions to improve the stability and functional properties of complexes, which provided a theoretical basis for the development of new complexes and their applications in functional foods.

Insight into the solubilization mechanism of wheat gluten by protease modification from conformational change and molecular interaction perspective

The low solubility limits the utilization of other functional characteristics of wheat gluten (WG). This study effectively improved the solubility of WG through protease modification and explored the potential mechanism of protease modification to enhance the solubility of WG, further stimulating the potential application of WG in the food industry. Solubility of WG modified with alkaline protease, complex protease, and neutral protease was enhanced by 98.99%, 54.59%, and 51.68%, respectively. Notably, the content of β-sheet was reduced while the combined effect of hydrogen bond and ionic bond were increased after protease modification. Meanwhile, the reduced molecular size and viscoelasticity as well as the elevated surface hydrophobicity, thermostability, water absorption capacity, and crystallinity were observed in modified WG. Moreover, molecular docking indicated that protease was specifically bound to the amino acid residues of WG through hydrogen bonding, hydrophobic interaction, and salt bridge.

Covalent Interactions of Anthocyanins with Proteins: Activity-Based Protein Profiling of Cyanidin-3-O-glucoside

Anthocyanins are common natural pigments with a variety of physiological activities. Traditional perspectives attribute their molecular mechanism to noncovalent interactions influencing signaling pathways. However, this ignores the nature of its benzopyrylium skeleton, which readily reacts with the electron-rich groups of proteins. Here, we modified cyanidin-3-O-glucoside (C3G) via activity-based protein profiling technology by our previous synthesis route and prepared the covalent binding probe (C3G-Probe) and the noncovalent photoaffinity probe (C3G-Diazirine). The properties of C3G's covalent binding to proteins were also discovered by comparing the labeling of the two probes to the whole HepG2 cell proteome. We further explored its target proteins and enriched pathways in HepG2 and HeLa cells. Western blot analysis further confirmed the covalent binding of C3G to four target proteins: insulin-degrading enzyme, metal cation symporter ZIP14, spermatid perinuclear RNA-binding protein, and Cystatin-B. Pathway analysis showed that covalent targets of C3G were concentrated in metabolic pathways and several ribonucleoprotein complexes that were also coenriched. The results of this study provide new insights into the interaction of the naturally active molecule C3G with proteins.

Interaction of soy protein isolate with hydroxytyrosol based on an alkaline method: Implications for structural and functional properties

This study investigated the effect of different concentrations of hydroxytyrosol (HT) covalently bound to soy protein isolate (SPI) by the alkaline method on the structure and function of the adducts. The amount of polyphenol bound to SPI first increased to a maximum of 42.83 % ± 1.08 % and then decreased. After the covalent binding of HT to SPI, turbidity and in vitro protein digestibility increased and decreased significantly with increasing concentrations of HT added, respectively, and the structure of SPI was changed. The adducts had a maximum solubility of 52.52 % ± 0.33 %, and their water holding capacity reached a maximum of 8.22 ± 0.11 g/g at a concentration of 50 μmol/g of HT. Covalent modification with HT significantly increased the emulsifying and foaming properties and antioxidant activity of SPI; the DPPH and ABTS radical scavenging rates increased by 296.89 % and 33.80 %, respectively, at a concentration of 70 μmol/g of HT.

Preparation and functional properties of rice bran globulin-chitooligosaccharide-quercetin-resveratrol covalent complex

BACKGROUND

As the major protein (approximately 36%) in rice bran, globulin exhibits excellent foaming and emulsifying properties, endowing its useful application as a foaming and emulsifying agent in the food industry. However, the low water solubility restricts its commercial potential in industrial applications. The present study aimed to improve this protein's processing and functional properties.

RESULTS

A novel covalent complex was fabricated by a combination of the Maillard reaction and alkaline oxidation using rice bran globulin (RBG), chitooligosaccharide (C), quercetin (Que) and resveratrol (Res). The Maillard reaction improved the solubility, emulsifying and foaming properties of RBG. The resultant glycosylated protein was covalently bonded with quercetin and resveratrol to form a (RBG-C)-Que-Res complex. (RBG-C)-Que-Res exhibited higher thermal stability and antioxidant ability than the native protein, binary globulin-chitooligosaccharide or ternary globulin-chitooligosaccharide-polyphenol (only containing quercetin or resveratrol) conjugates. (RBG-C)-Que-Res exerted better cytoprotection against the generation of malondialdehyde and reactive oxygen species in HepG2 cells, which was associated with increased activities of antioxidative enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) through upregulated genes SOD1, CAT, GPX1 (i.e. gene for glutathione peroxidase-1), GCLM (i.e. gene for glutamate cysteine ligase modifier subunit), SLC1A11 (i.e. gene for solute carrier family 7, member 11) and SRXN1 (i.e. gene for sulfiredoxin-1). The anti-apoptotic effect of (RBG-C)-Que-Res was confirmed by the downregulation of caspase-3 and p53 and the upregulation of B-cell lymphoma-2 gene expression.

CONCLUSION

The present study highlights the potential of (RBG-C)-Que-Res conjugates as functional ingredients in healthy foods. © 2024 Society of Chemical Industry.

Analytical approaches for assessing protein structure in protein-rich food: A comprehensive review

This review focuses on changes in nutrition and functional properties of protein-rich foods, primarily attributed to alterations in protein structures. We provide a comprehensive overview and comparison of commonly used laboratory methods for protein structure identification, aiming to offer readers a convenient understanding of these techniques. The review covers a range of detection technologies employed in food protein analysis and conducts an extensive comparison to identify the most suitable method for various proteins. While these techniques offer distinct advantages for protein structure determination, the inherent complexity of food matrices presents ongoing challenges. Further research is necessary to develop and enhance more robust detection methods to improve accuracy in protein conformation and structure analysis.

Research Progress on the Extraction and Purification of Anthocyanins and Their Interactions with Proteins

Anthocyanins, as the most critical water-soluble pigments in nature, are widely present in roots, stems, leaves, flowers, fruits, and fruit peels. Many studies have indicated that anthocyanins exhibit various biological activities including antioxidant, anti-inflammatory, anti-tumor, hypoglycemic, vision protection, and anti-aging. Hence, anthocyanins are widely used in food, medicine, and cosmetics. The green and efficient extraction and purification of anthocyanins are an important prerequisite for their further development and utilization. However, the poor stability and low bioavailability of anthocyanins limit their application. Protein, one of the three essential nutrients for the human body, has good biocompatibility and biodegradability. Proteins are commonly used in food processing, but their functional properties need to be improved. Notably, anthocyanins can interact with proteins through covalent and non-covalent means during food processing, which can effectively improve the stability of anthocyanins and enhance their bioavailability. Moreover, the interactions between proteins and anthocyanins can also improve the functional characteristics and enhance the nutritional quality of proteins. Hence, this article systematically reviews the extraction and purification methods for anthocyanins. Moreover, this review also systematically summarizes the effect of the interactions between anthocyanins and proteins on the bioavailability of anthocyanins and their impact on protein properties. Furthermore, we also introduce the application of the interaction between anthocyanins and proteins. The findings can provide a theoretical reference for the application of anthocyanins and proteins in food deep processing.

Decoding the Duality of Antinutrients: Assessing the Impact of Protein Extraction Methods on Plant-Based Protein Sources

This review aims to provide an updated overview of the effects of protein extraction/recovery on antinutritional factors (ANFs) in plant protein ingredients, such as protein-rich fractions, protein concentrates, and isolates. ANFs mainly include lectins, trypsin inhibitors, phytic acid, phenolic compounds, oxalates, saponins, tannins, and cyanogenic glycosides. The current technologies used to recover proteins (e.g., wet extraction, dry fractionation) and novel technologies (e.g., membrane processing) are included in this review. The mechanisms involved during protein extraction/recovery that may enhance or decrease the ANF content in plant protein ingredients are discussed. However, studies on the effects of protein extraction/recovery on specific ANFs are still scarce, especially for novel technologies such as ultrasound- and microwave-assisted extraction and membrane processing. Although the negative effects of ANFs on protein digestibility and the overall absorption of plant proteins and other nutrients are a health concern, it is also important to highlight the potential positive effects of ANFs. This is particularly relevant given the rise of novel protein ingredients in the market and the potential presence or absence of these factors and their effects on consumers' health.

Unveiling the impact of high-pressure processing on anthocyanin-protein/polysaccharide interactions: A comprehensive review

Anthocyanins, natural plant pigments responsible for the vibrant hues in fruits, vegetables, and flowers, boast antioxidant properties with potential human health benefits. However, their susceptibility to degradation under conditions such as heat, light, and pH fluctuations necessitates strategies to safeguard their stability. Recent investigations have focused on exploring the interactions between anthocyanins and biomacromolecules, specifically proteins and polysaccharides, with the aim of enhancing their resilience. Notably, proteins like soy protein isolate and whey protein, alongside polysaccharides such as pectin, starch, and chitosan, have exhibited promising affinities with anthocyanins, thereby enhancing their stability and functional attributes. High-pressure processing (HPP), emerging as a non-thermal technology, has garnered attention for its potential to modulate these interactions. The application of high pressure can impact the structural features and stability of anthocyanin-protein/polysaccharide complexes, thereby altering their functionalities. However, caution must be exercised, as excessively high pressures may yield adverse effects. Consequently, while HPP holds promise in upholding anthocyanin stability, further exploration is warranted to elucidate its efficacy across diverse anthocyanin variants, macromolecular partners, pressure regimes, and their effects within real food matrices.

Effects of preheat treatment and syringic acid modification on the structure, functional properties, and stability of black soybean protein isolate

This study investigated preheated (25-100°C) black soybean protein isolate (BSPI) conjugated with syringic acid (SA) (25 and 50 µmol/g protein) under alkaline conditions, focusing on the structure, functional properties, and storage stability. The results revealed that the SA binding equivalent and binding rate on BSPI increased continuously as the preheat temperature increased. Additionally, preheating positively impacted the surface hydrophobicity (H0) of BSPI, with further enhancement observed upon SA binding. Preheating and SA binding altered the secondary and tertiary structure of BSPI, resulting in protein unfolding and increased molecular flexibility. The improvement in BSPI functional properties was closely associated with both preheating temperature and SA binding. Specifically, preheating decreased the solubility of BSPI but enhanced the emulsifying activity index (EAI) and foaming capacity (FC) of BSPI. Conversely, SA binding increased the solubility of BSPI with an accompanying increase in EAI, FC, foaming stability, and antioxidant activity. Notably, the BSPI100-SA50 exhibited the most significant improvement in functional properties, particularly in solubility, emulsifying, and foaming attributes. Moreover, the BSPI-SA conjugates demonstrated good stability of SA during storage, which positively correlated with the preheating temperature. This study proposes a novel BSPI-SA conjugate with enhanced essential functional properties, underscoring the potential of preheated BSPI-SA conjugates to improve SA storage stability. PRACTICAL APPLICATION: Preheated BSPI-SA conjugates can be used as functional ingredients in food or health products. In addition, preheated BSPI shows potential as a candidate for encapsulating and delivering hydrophobic bioactive compounds.

The Effect of Nanoscale Modification of Nisin by Different Milk-Derived Proteins on Its Physicochemical Properties and Antibacterial Activity

Nisin is used as a natural food preservative because of its broad-spectrum antimicrobial activity against Gram-positive bacteria. However, free nisin is susceptible to various factors that reduce its antimicrobial activity. Milk protein, a protein derived from milk, has self-assembly properties and is a good carrier of bioactive substances. In this study, lactoferrin-nisin nanoparticles (L-N), bovine serum albumin-nisin nanoparticles (B-N), and casein-nisin nanoparticles (C-N) were successfully prepared by a self-assembly technique, and then their properties were investigated. The studies revealed that lactoferrin (LF) and nisin formed L-N mainly through hydrophobic interactions and hydrogen bonding, and L-N had the best performance. The small particle size (29.83 ± 2.42 nm), dense reticular structure, and good thermal stability, storage stability, and emulsification of L-N laid a certain foundation for its application in food. Further bacteriostatic studies showed that L-N enhanced the bacteriostatic activity of nisin, with prominent inhibitory properties against Listeria monocytogenes, Staphylococcus aureus, and Bacillus cereus, which mainly disrupted the cell membrane of the bacteria. The above results broaden our understanding of milk protein-nisin nanoparticles, while the excellent antibacterial activity of L-N makes it promising for application as a novel food preservative, which will help to improve the bioavailability of nisin in food systems.

Enhancing the properties of soy protein isolate and dialdehyde starch films for food packaging applications through tannic acid crosslinking

The utilization of naturally derived biodegradable polymers, including proteins, polysaccharides, and polyphenols, holds significant promise in addressing environmental concerns and reducing reliance on nonrenewable resources. This study aimed to develop films with enhanced UV resistance and antibacterial capabilities by covalently cross-linking soy protein isolate (SPI) with dialdehyde starch (DAS) through the incorporation of tannic acid (TA). The covalent crosslinking of TA with DAS and SPI was shown to establish a stable chemical cross-linking network. The tensile strength of the resulting SPI/DAS/15TA film exhibited a remarkable increase of 208.27 % compared to SPI alone and 52.99 % compared to SPI/DAS film. Notably, the UV absorption range of SPI/DAS/10TA films extended from 200 nm to 389 nm. This augmentation can be attributed to the oxidation of TA's phenolic hydroxyl groups to quinone under alkaline conditions, which then facilitated cross-linking with the SPI chain via Michael addition and Schiff base reactions. Furthermore, the film demonstrated robust antibacterial properties due to the incorporation of TA. Collectively, the observed properties highlight the significant potential of the SPI/DAS/10TA film for applications in food packaging, where its enhanced mechanical strength, UV resistance, and antibacterial characteristics can contribute to improved product preservation and safety.

Remodeling mechanism of gel network structure of soy protein isolate amyloid fibrils mediated by cellulose nanocrystals

The differences in the gelling properties of soy protein isolate (SPI) and soy protein isolate amyloid fibrils (SAFs) as well as the role of cellulose nanocrystals (CNC) in regulating their gel behaviors were investigated in this study. The binding of CNC to β-conglycinin (7S), glycinin (11S), and SAFs was predominantly driven by non-covalent interactions. CNC addition reduced the particle size, turbidity, subunit segments, and crystallinity of SPI and SAFs, promoted the conversion of α-helix to β-sheet, improved the thermal stability, exposed more tyrosine and tryptophan residues, and enhanced the intermolecular interactions. A more regular and ordered lamellar network structure was formed in the SAFs-CNC composite gel, which could be conducive to the improvement of gel quality. This study would provide theoretical reference for the understanding of the regulatory mechanism of protein amyloid fibrils gelation as well as the high-value utilization of SAFs-CNC complex as a functional protein-based material or food ingredient in food field.

General approaches to biopolymer-based Pickering emulsions

Pickering emulsion is a type of emulsion that uses solid particles or colloidal particles as emulsifiers rather than surfactants to adhere at oil-water interface. Pickering emulsions have gathered significant research attention recently due to their excellent stability and wide range of potential uses compared to traditional emulsions. Major advancements have been made in development of innovative Pickering emulsions using different colloidal particles by various techniques including homogenization, emulsification and ultrasonication. Use of biopolymer particles gives Pickering emulsions a more escalating possibilities. In this review paper, we seek to present a critical overview of development in food-grade particles that have been utilized to create Pickering emulsions with a focus on techniques and application of Pickering emulsions. Particularly, we have evaluated protein, lipid, polysaccharide-based particles and microalgal proteins that have emerged in recent years with respect to their potential to stabilize and add novel functionalities to Pickering emulsions. Some preparation methods of Pickering emulsions in brief, applications of Pickering emulsions are also highlighted. Encapsulation and delivery of bioactive compounds, fat substitutes, film formation and catalysis are potential applications of Pickering emulsions. Pickering double emulsions, nutraceutical and bioactive co-delivery, and preparation of porous materials are among research trends of food-grade Pickering emulsions.