Whey protein-polyphenol conjugates and complexes: Production, characterization, and applications

Algae: A promising and sustainable protein-rich food ingredient for bakery and dairy products

The consumer demand for protein rich foods urges the exploration for novel products of natural origin. Algae can be considered as a gold mine of different bioactive compounds, among which protein is distributed in significant amounts i.e., around 30% and can even reach to 55-60% in some cyanobacteria. Bakery and dairy products are extensively consumed worldwide due to product diversification and innovation. However, incorporation of algae biomass can lead to the development of green colour and fishy flavour that usually is not accepted in such products. Therefore, isolation and application of algae-derived proteins opens a new door for food industry. The present review provides a comprehensive understanding of incorporation of algae as a protein-rich ingredient in bakery and dairy products. The paper provides a deep insight for all the possible recent trends related to production and extraction of algae proteins accompanied by their incorporation in bakery and dairy foods.

Effects of purple cabbage anthocyanin extract on the gluten characteristics and the gluten network evolution of high-gluten dough

BACKGROUND

Anthocyanins are polyphenolic pigments that have hypoglycemic, antioxidation, anti-aging, and other effects. Research has shown that polyphenols can optimize the processing of dough and improve the texture and nutritional characteristics of dough products. The formation of gluten networks is decisive for the quality of flour products. The effects of purple cabbage anthocyanin (PCA) extract on the structure, microscopic morphology, and network formation of gluten protein were studied, and the types of cross-linking between PCA and gluten protein are discussed.

RESULTS

The results show that PCA extract increased the free sulfhydryl (SH) group content and the free amino group of gluten proteins, stimulated an increase in the β-sheet ratio and the decrease of α-helix ratio, and increased the gluten index significantly (P < 0.05). The PCA extract also induced gluten protein aggregation, increased the height of protein molecular chains, and stimulated the formation of gluten networks. When PCA extract concentrations were 4 g kg-1 and 8 g kg-1, the gluten network was more homogeneous, continuous, and dense.

CONCLUSION

Appropriate anthocyanins have a positive effect on the properties of gluten and promote the formation of gluten networks. Excessive anthocyanins destroy gluten protein interaction and harm gluten cross-linking. This study may provide a useful source of data for the production of functional flour products rich in anthocyanins. © 2024 Society of Chemical Industry.

Spasmolytic, Antimicrobial, and Antioxidant Activities of Spray-Dried Extracts of Gentiana asclepiadea L. with In Silico Pharmacokinetic Analysis

This study aimed to evaluate the spasmolytic activity of an underground parts extract of Gentiana asclepiadea L. (Gentianaceae), assess its antioxidant and antimicrobial activities, and explore the impact of extract encapsulation on the aforementioned bioactivities. An extract encapsulated by spray drying with whey protein, pure extract, and pure whey protein were comparatively tested. The main compounds identified via HPLC-DAD analysis underwent in silico ADME assessment. The spasmolytic effect was tested on a model of spontaneous rat ileum contractions, and the mechanism of action was further evaluated on acetylcholine-, KCl-, CaCl2-, BaCl2-, histamine-, N(ω)-nitro-L-arginine methyl ester-, and glibenclamide-modified contractions. The most abundant compounds were secoiridoids (dominantly gentiopicroside), followed by C-glycosylated flavonoids and xanthones. Both pure and encapsulated extracts achieved significant spasmolytic effects, despite the spasmogenic activity of pure whey protein. The extract may exert its spasmolytic effect through multiple pathways, predominantly by antagonizing the Ca2+ channel and opening the K+ channel, while the nitric oxide pathway appears not to be involved. The antimicrobial and antioxidant activities of the pure extract were moderate. The extract stabilized by encapsulation retained all of the tested bioactivities of the unencapsulated extract. The obtained results suggest that G. asclepiadea has potential for use in the treatment of some gastrointestinal complaints and that the encapsulated extract could be a valuable functional ingredient in pharmaceutical and food products.

Covalent conjugation of Inca peanut albumin and polyphenols with different phenolic hydroxyl numbers through laccase catalysis to improve functional properties

BACKGROUND

Enzymatic crosslinking is a method that can be used to modify Inca peanut albumin (IPA) using polyphenols, and provides desirable functionalities; however, the effect of polyphenol structures on conjugate properties is unclear. In this study, we selected four polyphenols with different numbers of phenolic hydroxyl groups [para-hydroxybenzoic acid (HBA), protocatechuic acid (PCA), gallic acid (GA), and epigallocatechin gallate (EGCG)] for covalent modification of IPA by enzymatic crosslinking, and explored the structure-function changes of the IPA-polyphenol conjugates.

RESULTS

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analysis showed that laccase successfully promoted covalent crosslinking of IPA with polyphenols, with the order of degree of conjugation as EGCG > GA > PCA > HBA, the IPA-EGCG conjugate showed the highest polyphenol binding equivalents (98.35 g kg-1 protein), and a significant reduction in the content of free amino, sulfhydryl, and tyrosine group. The oxidation of polyphenols by laccase forms quinone or semiquinone radicals that are covalently crosslinked to the reactive groups of IPA, leading to significant changes in the secondary and tertiary structures of IPA, with spherical structures transforming into dense lamellar structures. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging ability and emulsification stability of IPA-EGCG conjugates improved by almost 6-fold and 2.7-fold, respectively, compared with those of unmodified IPA.

CONCLUSION

These data suggest that the higher the number of polyphenol hydroxyl groups, the higher the degree of IPA-polyphenol conjugation; additionally, enzymatic crosslinking can significantly improve the functional properties of IPA. © 2024 Society of Chemical Industry.

In Vitro Gastrointestinal Digestion of Various Sweet Potato Leaves: Polyphenol Profiles, Bioaccessibility and Bioavailability Elucidation

The chemical composition discrepancies of five sweet potato leaves (SPLs) and their phenolic profile variations during in vitro digestion were investigated. The results indicated that Ecaishu No. 10 (EC10) provided better retention capacity for phenolic compounds after drying. Furthermore, polyphenols were progressively released from the matrix as the digestion process proceeded. The highest bioaccessibility of polyphenols was found in EC10 intestinal chyme at 48.47%. For its phenolic profile, 3-, 4-, and 5-monosubstituted caffeoyl quinic acids were 9.75%, 57.39%, and 79.37%, respectively, while 3,4-, 3,5-, and 4,5-disubstituted caffeoyl quinic acids were 6.55, 0.27 and 13.18%, respectively. In contrast, the 3,4-, 3,5-, 4,5-disubstituted caffeoylquinic acid in the intestinal fluid after dialysis bag treatment was 62.12%, 79.12%, and 62.98%, respectively, which resulted in relatively enhanced bioactivities (DPPH, 10.51 μmol Trolox/g; FRAP, 8.89 μmol Trolox/g; ORAC, 7.32 μmol Trolox/g; IC50 for α-amylase, 19.36 mg/g; IC50 for α-glucosidase, 25.21 mg/g). In summary, desirable phenolic acid release characteristics and bioactivity of EC10 were observed in this study, indicating that it has potential as a functional food ingredient, which is conducive to the exploitation of the sweet potato processing industry from a long-term perspective.

Structural and functional properties of whey protein isolate-inulin conjugates prepared with ultrasound or wet heating method

BACKGROUND

Whey protein isolate (WPI) generally represents poor functional properties such as thermal stability, emulsifying activity and antioxidant activity near its isoelectric point or high temperatures, which limit its application in the food industry. The preparation of WPI-polysaccharide covalent conjugates based on Maillard reaction is a promising method to improve the physical and chemical stability and functional properties of WPI. In this research, WPI-inulin conjugates were prepared through wet heating method and ultrasound method and their structural and functional properties were examined.

RESULTS

In conjugates, the free amino acid content was reduced, the high molecular bands were emerged at sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), new C-N bonds were formed in Fourier-transform infrared (FTIR) spectroscopy, and fluorescence intensity was reduced compared with WPI. Furthermore, the result of circular dichroism (CD) spectroscopy also showed that the secondary structure of conjugates was changed. Conjugates with ultrasound treatment had better structural properties compared with those prepared by wet heating treatment. The functional properties such as thermal stability, emulsifying activity index (EAI), emulsion stability (ES) and antioxidant activity of conjugates with wet heating treatment were significantly improved compared with WPI. The EAI and ES of conjugates with ultrasound treatment were the highest, but the thermal stability and antioxidant activity were only close to that of the conjugates with wet heating treatment for 2 h.

CONCLUSION

This study revealed that WPI-inulin conjugates prepared with ultrasound or wet heating method not only changed the structural characteristics of WPI but also could promote its functional properties including thermal stability, EAI, ES and antioxidant activity. © 2024 Society of Chemical Industry.

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.

Characterization and emulsifying ability evaluation of whey protein-pectin conjugates formed by glycosylation

Glycosylation is a method that enhances the functional properties of proteins by covalently attaching sugars to them. This study aimed at preparing three conjugates (WP-HG, WP-SBP, and WP-RGI) by dry heating method to research the influence of different pectin structures on the functional properties of WP and characterize properties and structures of these conjugates. The research results manifested that the degree of glycosylation (DG) of HG, SBP and RGI were 13.13 % ± 0.07 %, 23.27 % ± 0.3 % and 36.39 % ± 0.3 % respectively, suggesting that the increase of the number of branch chains promoted the glycosylation reaction. The formation of the conjugate was identified by the FT-IR spectroscopy technique. And SEM showed that WP could covalently bind to pectin, resulting in a smoother and denser surface of the conjugates. The circular dichroism analysis exhibited that the glycosylation reaction altered the secondary structure of WP and decreased the α-Helix content. This structural change in the protein spatial conformation led to a decrease in the hydrophobicity of protein surface. But the addition of pectin further regulated the hydrophilic-hydrophobic ratio on the surface of the protein, thus improving the emulsification properties of WP. In addition, the glycosylation could improve the stability of the emulsion, giving it a smaller droplet size, higher Zeta-potential and more stable properties. In a word, this study pointed out the direction for the application of different pectin structures in the development of functional properties of glycosylation products in food ingredients.

Simultaneous ultrasound and microwave application in myosin-chlorogenic acid conjugation: Unlocking enhanced emulsion stability

This study investigated the grafting chlorogenic acid (CA) onto myosin, utilizing various techniques including conventional method, ultrasound, microwave, and combination of ultrasound and microwave (UM). The grafting efficiency was as follows: conventional method < microwave < ultrasound < UM. The UM technique manifested the highest CA-binding capacity (80.26 μmol/g myosin) through covalent bonding, and a much shorter time was required for conjugation than conventional method. The conjugation of polyphenol significantly increased the solubility of myosin with reduced aggregation behavior, which was accompanied by structural alterations from ordered structures (α-helix and β-sheet) to disordered forms. The emulsion stabilized by UM-myosin-CA conjugate exhibited the most homogeneous microstructure with favorable creaming stability. Moreover, the resulting emulsion presented strong oxidation resistance and storage stability. These results illustrate the promising potential of employing CA-grafted myosin, especially when processed using the UM technique, in the development of highly efficient emulsifiers.

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

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

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

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

Modifications of whey proteins for emulsion based applications: Current status, issues and prospectives

Whey proteins are a major group of dairy proteins with high potential for various food based applications. Whey protein isolate has a limited range of functionalities. This functional range can be expanded using diverse modification methods to suit specific applications. This review summarizes the recent advances in the modifications of whey proteins using chemical, physical, and enzymatic methods and their combinations as well as the modification effects on the physicochemical properties. The uses of these modified whey proteins in emulsion based food and beverage systems are described. The limitations in the studies summarized are critically discussed, while future research directions are suggested on how to better utilize whey proteins for emulsion based uses through modifications.

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.

Animal derived biopolymers for food packaging applications: A review

It is essential to use environment-friendly, non-toxic, biodegradable and sustainable materials for various applications. Biopolymers are derived from renewable sources like plants, microorganisms, and agricultural wastes. Unlike conventional polymers, biopolymer has a lower carbon footprint and contributes less to greenhouse gas emission. All biopolymers are biodegradable, meaning natural processes can break them down into harmless products such as water and biomass. This property is of utmost importance for various sustainable applications. This review discusses different classifications of biopolymers based on origin, including plant-based, animal-based and micro-organism-based biopolymers. The review also discusses the desirable properties that are required in materials for their use as packaging material. It also discusses the different processes used in modifying the biopolymer to improve its properties. Finally, this review shows the recent developments taking place in using specifically animal origin-based biopolymer and its use in packaging material. It was observed that animal-origin-based biopolymers, although they possess unique properties however, are less explored than plant-origin biopolymers. The animal-origin-based biopolymers covered in this review are chitosan, gelatin, collagen, keratin, casein, whey, hyaluronic acid and silk fibroin. This review will help in renewing research interest in animal-origin biopolymers. In summary, biopolymer offers a sustainable and environment-friendly alternative to conventional polymers. Their versatility, biocompatibility will help create a more sustainable future.

Unravelling the interaction between α-SOH and myofibrillar protein based on spectroscopy and molecular dynamics simulation

This work systematically investigated the dose-response interaction between hydroxy-α-sanshool (α-SOH) and pork myofibrillar proteins (MPs) via spectroscopy, molecular docking, and molecular dynamics simulation methods. Results showed that MPs bound with low α-SOH can enhance the surface hydrophobicity and particle size of MPs, whereas high concentrations were exactly the opposite. The main interaction force in α-SOH/MPs complex changed from hydrophobic to hydrogen bonding with increased α-SOH. α-SOH causes tryptophan quenching and bring about a red shift at low concentration, as well as to promote α-helix conversion into β-sheet in MPs. Simultaneously, molecular docking and dynamics simulations verified that hydrogen bonding and hydrophobic forces were the main contributors to α-SOH/MPs complex, indicating that the binding of α-SOH with MPs proceeded spontaneously with high intensity, in which TYR286 contributed the most significant energy. Therefore, revealing the binding mechanism of α-SOH and MPs can contribute to the deep processing of numbing meat products.

Structure Characterization and Functional Properties of Flaxseed Protein-Chlorogenic Acid Complex

This study aimed to investigate the effects of the covalent binding of flaxseed protein (FP) and chlorogenic acid (CA) on the structure and functional properties of FP-CA complexes fabricated using the alkali method. The results suggested that the encapsulation efficiency of CA encapsulated by FP ranged from 66.11% to 72.20% and the loading capacity of CA increased with an increasing addition ratio of CA with a dose-dependent relationship, which increased from 2.34% to 10.19%. The particle size, turbidity, zeta potential and PDI of FP and the FP-CA complexes had no significant discrepancy. UV-Vis and fluorescence spectra showed the existence of the interaction between FP and CA. SEM images showed that the surface of the FP-0.35%CA complex had more wrinkles compared to FP. Differential scanning calorimetry analysis indicated the decomposition temperature of FP at 198 °C was higher than that (197 °C) of the FP-0.35%CA complex, implying that the stability of the FP-CA complexes was lower than FP. The functional properties suggested that the FP-CA complex with 1.40% CA had a higher water holding capacity (500.81%), lower oil holding capacity (273.495%) and lower surface hydrophobicity. Moreover, the FP-CA complexes had better antioxidant activities than that of FP. Therefore, this study provides more insights for the potential application of FP-CA covalent complexes in functional food processing.

Protein-polysaccharide-based delivery systems for enhancing the bioavailability of curcumin: A review

In recent years, a wide attention has been paid to curcumin in medicine due to its excellent physiological activities, including anti-inflammatory, antioxidant, antibacterial, and nerve damage repair. However, the low solubility, poor stability, and rapid metabolism of curcumin make its bioavailability low, which affects its development and application. As a unique biopolymer structure, protein-polysaccharide (PRO-POL)-based delivery system has the advantages of low toxicity, biocompatibility, biodegradability, and delayed release. Many scholars have investigated PRO-POL -based delivery systems to improve the bioavailability of curcumin. In this paper, we focus on the interactions between different proteins (e.g. casein, whey protein, soybean protein isolate, pea protein, zein, etc.) and polysaccharides (chitosan, sodium alginate, hyaluronic acid, pectin, etc.) and their effects on complexes diameter, surface charge, encapsulation drive, and release characteristics. The mechanism of the PRO-POL-based delivery system to enhance the bioavailability of curcumin is highlighted. In addition, the application of PRO-POL complexes loaded with curcumin is summarized, aiming to provide a reference for the construction and application of PRO-POL delivery systems.

The Effect of a High-Protein Diet Supplemented with Blackthorn Flower Extract on Polyphenol Bioavailability and Antioxidant Status in the Organs of C57BL/6 Mice

The health benefits of polyphenols are based on their bioavailability, which is why a significant portion of research focuses on factors that affect their bioavailability. Previous studies suggest that the intake of polyphenols along with macronutrients in food represents one of the key factors influencing the bioavailability of polyphenols and, consequently, their biological activity in the organism. Since polyphenols in the human diet are mainly consumed in food together with macronutrients, this study investigated the in vivo absorption, metabolism, and distribution of polyphenolic compounds from the water extract of blackthorn flower (Prunus spinosa L.) in combination with a protein-enriched diet in the organs (small intestine, liver, kidney) of C57BL/6 mice. The bioaccumulation of polyphenol molecules, biologically available maximum concentrations of individual groups of polyphenol molecules, and their effect on the oxidative/antioxidative status of organs were also examined. The results of this study indicate increased bioabsorption and bioavailability of flavan-3-ols (EC, EGCG) and reduced absorption kinetics of certain polyphenols from the groups of flavonols, flavones, and phenolic acids in the organs of C57BL/6 mice after intragastric administration of the water extract of blackthorn flower (Prunus spinosa L.) in combination with a diet enriched with whey proteins. Furthermore, subchronic intake of polyphenols from the water extract of blackthorn flower (Prunus spinosa L.) in combination with a diet enriched with whey proteins induces the synthesis of total glutathione (tGSH) in the liver and superoxide dismutase (SOD) in the liver and small intestine. The results of this study suggest potential applications in the development of functional foods aimed at achieving the optimal health status of the organism and the possibility of reducing the risk of oxidative stress-related disease.

Molecular Mechanisms and Applications of Polyphenol-Protein Complexes with Antioxidant Properties: A Review

Proteins have been extensively studied for their outstanding functional properties, while polyphenols have been shown to possess biological activities such as antioxidant properties. There is increasing clarity about the enhanced functional properties as well as the potential application prospects for the polyphenol-protein complexes with antioxidant properties. It is both a means of protein modification to provide enhanced antioxidant capacity and a way to deliver or protect polyphenols from degradation. This review shows that polyphenol-protein complexes could be formed via non-covalent or covalent interactions. The methods to assess the complex's antioxidant capacity, including scavenging free radicals and preventing lipid peroxidation, are summarized. The combination mode, the type of protein or polyphenol, and the external conditions will be the factors affecting the antioxidant properties of the complexes. There are several food systems that can benefit from the enhanced antioxidant properties of polyphenol-protein complexes, including emulsions, gels, packaging films, and bioactive substance delivery systems. Further validation of the cellular and in vivo safety of the complexes and further expansion of the types and sources of proteins and polyphenols for forming complexes are urgently needed to be addressed. The review will provide effective information for expanding applications of proteins and polyphenols in the food industry.

Protocatechuic acid and gallic acid improve the emulsion and thermal stability of whey protein by covalent binding

This study aimed to explore the impacts of gallic acid (GA)/protocatechuic acid (PA) on the structural and functional characteristics of whey proteins (WP) through covalent binding. To this purpose, the covalent complexes of WP-PA and WP-GA at different concentration gradients were prepared by the alkaline method. SDS-PAGE indicated that PA/GA was cross-linked by covalent bonds. The decreased contents of free amino and sulfhydryl groups suggested that WP formed covalent bonds with PA/GA by amino and sulfhydryl groups, and the structure of WP became slightly looser after covalent modification by PA/GA. When the concentration of GA was added up to 10 mM, the structure of WP was slightly loosened with a reduction of α-helix content by 2.3% and an increase in random coil content by 3.0%. The emulsion stability index of WP increased by 14.9 min after interaction with GA. Moreover, the binding of WP and 2-10 mM PA/GA increased the denaturation temperature by 1.95 to 19.87 °C, indicating the improved thermal stability of the PA/GA-WP covalent complex. Additionally, the antioxidant capacity of WP was increased with increasing GA/PA concentration. This work may offer worthful information for enhancing the functional properties of WP and the application of the PA/GA-WP covalent complexes in food emulsifiers.

Designing ultra-stable linseed oil-in-water Mickering emulsions using whey protein isolate cold-set microgels containing marjoram aqueous extract: Effect of pH and extract on rheological, physical, and chemical properties

In this study, whey protein isolate (WPI) cold-set microgels containing marjoram (Origanum majorana) aqueous extract (MAE) were prepared at different pHs (4.0, 5.0, and 6.0). After characterization, the microgel dispersion was used to stabilize linseed oil-in-water Mickering emulsions (MEs). The resultant MEs were then characterized in terms of physicochemical and rheological properties under the effect of pH and MAE addition. The morphology, particle size, zeta potential, and interfacial tension of microgels were affected by pH and MAE. XRD patterns showed the amorphous structure. Microgel-stabilized MEs did not reveal any significant sign of instability under gravity during 6 months of storage. All MEs had dominant elastic character. Despite the lowest zeta potential values, MEs prepared at pH 4 showed the highest physical stability against gravity but the lowest centrifugal stability against oiling off, which indicated that both viscous and elastic components are required for MEs stability. This sample had the highest apparent viscosity and the strongest viscoelastic properties. Rheological data were best fitted with Herschel-Bulkley and Power Law models. An increase in pH and presence of MAE improved the oxidative stability of MEs. The results of this study showed that WPI microgels are appropriate candidate for long-term stabilization of linseed oil-in-water MEs. The presence of MAE is useful in designing special emulsions in which the aqueous phase is partially replaced by the aqueous extract of medicinal plants.

Characterization of a Dihydromyricetin/α-Lactoalbumin Covalent Complex and Its Application in Nano-emulsions

A dihydromyricetin (DMY)/α-lactoalbumin (α-La) covalent complex was prepared and characterized, and its application in nano-emulsions was also evaluated in this study. The results suggested that the covalent complex could be obtained using the alkaline method. The UV and IR spectra confirmed the formation of the covalent complex, and the amount of DMY added was positively correlated with the total phenol content of the complex. The complex had an outstanding 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS)-radical-scavenging ability, reducing power and α-glucosidase inhibitory activity, which were positively related to its total phenol content. The complex could be used as an emulsifier to stabilize the β-carotene-loaded nano-emulsion. The stability and β-carotene-protective capacity of the nano-emulsion stabilized by the complex were also positively related to the total phenol content of the complex, being higher than those of the nano-emulsion developed using α-La. Our results provide a reference for the construction of a new food delivery system and extend the applications of α-La and DMY in foods.

Processing Enhances Coix Seed Prolamins Structure and Releases Functional Peptides after Digestion: In Silico and In Vitro Studies

Dipeptidyl peptidase-IV (DPP-IV) is a key target for the treatment of type 2 diabetes mellitus. It is possible that peptides that precisely regulate DPP-IV could be released from coix seed prolamins (CSP), but whether this happens has not yet been investigated. We performed the in silico digestion of CSP and predicted the bioactivity, absorption, transport, toxicity, and allergenicity of the resulting peptides. The simulation predicted that 47 non-toxic bioactive peptides would be released. After screening these, we found that 64.58% of them could possess DPP-IV inhibitory activity. The effect of thermal processing on the amino acid composition and structural properties of CSP was determined, and the DPP-IV inhibitory activity of its digestion-derived peptides was also assessed. The results showed that processing could change the flavour of coix seed and the supply of amino acids. After processing, the spatial conformation of CSP changed from ordered to disordered, and the peptide content and the DPP-IV inhibitory activity of its digestion products significantly increased by 19.89-30.91% and 36.84-42.02%, respectively. These results support the hypothesis that processing can change the protein structure and increase the probability that bioactive peptides will be released. They also have important implications for the development of bioactive peptides and the intensive processing of coix seeds.

Modification of the Structural and Functional Characteristics of Mung Bean Globin Polyphenol Complexes: Exploration under Heat Treatment Conditions

During the storage and processing of mung beans, proteins and polyphenols are highly susceptible to interactions with each other. Using globulin extracted from mung beans as the raw material, the study combined it with ferulic acid (FA; phenolic acid) and vitexin (flavonoid). Physical and chemical indicators were combined with spectroscopy and kinetic methods, relying on SPSS and peak fit data to statistically analyze the conformational and antioxidant activity changes of mung bean globulin and two polyphenol complexes before and after heat treatment and clarify the differences and the interaction mechanism between globulin and the two polyphenols. The results showed that, with the increase in polyphenol concentration, the antioxidant activity of the two compounds increased significantly. In addition, the antioxidant activity of the mung bean globulin-FA complex was stronger. However, after heat treatment, the antioxidant activity of the two compounds decreased significantly. The interaction mechanism of the mung bean globulin-FA/vitexin complex was static quenching, and heat treatment accelerated the occurrence of the quenching phenomenon. Mung bean globulin and two polyphenols were combined through a hydrophobic interaction. However, after heat treatment, the binding mode with vitexin changed to an electrostatic interaction. The infrared characteristic absorption peaks of the two compounds shifted to different degrees, and new peaks appeared in the areas of 827 cm^-1, 1332 cm^-1, and 812 cm^-1. Following the interaction between mung bean globulin and FA/vitexin, the particle size decreased, the absolute value of zeta potential increased, and the surface hydrophobicity decreased. After heat treatment, the particle size and zeta potential of the two composites decreased significantly, and the surface hydrophobicity and stability increased significantly. The antioxidation and thermal stability of the mung bean globulin-FA were better than those of the mung bean globulin-vitexin complex. This study aimed to provide a theoretical reference for the protein-polyphenol interaction mechanism and a theoretical basis for the research and development of mung bean functional foods.

Influence of environmental pH on the interaction properties of WP-EGCG non-covalent nanocomplexes

BACKGROUND

Whey protein-epigallocatechin gallate (WP-EGCG) covalent conjugates and non-covalent nanocomplexes were prepared and compared using Fourier-transform infrared spectra. The effect of pH (at 2.6, 6.2, 7.1, and 8.2) on the non-covalent nanocomplexes' functional properties and the WP-EGCG interactions were investigated by studying antioxidant activity, emulsification, fluorescence quenching, and molecular docking, respectively.

RESULTS

With the formation of non-covalent and covalent complexes, the amide band decreased; the -OH peak disappeared; the antioxidant activity of WP-EGCG non-covalent complexes was 2.59- and 2.61-times stronger than WP-EGCG covalent conjugates for 1-diphenyl-2-picryl-hydrazyl (DPPH) and ferric reducing ability of plasma (FRAP), respectively (particle size: 137 versus 370 nm). The antioxidant activity (DPPH 27.48-44.32%, FRAP 0.47-0.63) was stronger at pH 6.2-7.1 than at pH 2.6 and pH 8.2 (DPPH 19.50% and 26.36%, FRAP 0.39 and 0.41). Emulsification was highest (emulsifying activity index 181 m²  g^-1 , emulsifying stability index 107%) at pH 7.1. The interaction between whey protein (WP) and EGCG was stronger under neutral and weakly acidic conditions: K_SV (5.11-8.95 × 10²  L mol^-1 ) and K_q (5.11-8.95 × 10¹⁰  L mol s^-1 ) at pH 6.2-7.1. Binding constants (pH 6.2 and pH 7.1) increased with increasing temperature. Molecular docking suggested that hydrophobic interactions played key roles at pH 6.2 and pH 7.1 (∆H > 0, ∆S > 0). Hydrogen bonding was the dominant force at pH 2.6 and pH 8.2 (∆H < 0, ∆S < 0).

CONCLUSION

Environmental pH impacted the binding forces of WP-EGCG nanocomplexes. The interaction between WP and EGCG was stronger under neutral and weakly acidic conditions. Neutral and weakly acidic conditions are preferable for WP-EGCG non-covalent nanocomplex formation. © 2023 Society of Chemical Industry.

Influence of rose anthocyanin extracts on physicochemical properties and in vitro digestibility of whey protein isolate sol/gel: Based on different pHs and protein concentrations

Protein-polyphenol interactions can improve the physicochemical properties of proteins. The objective of this study was to investigate the influence of rose anthocyanin extracts (RAEs) on the physicochemical properties and digestibility of whey protein isolate (WPI) sol/gel at different pHs and protein concentrations. Hydrophobicity interaction and ionic bonding were the main forces for the formation of acidic WPI and WPI-RAEs sol/gel. When pH was higher than 2.4, sol/gel became unstable, which may be related to hydrophobicity, ζ-potential value, total sulfhydryl and free sulfhydryl content changes. In addition, RAEs had positive effects on the color and water distribution of all WPI sol/gel. Moreover, RAEs improved the viscoelasticity of WPI sol/gel with protein content ≥ 12 % (w/v) at pH 2.4. More importantly, the addition of RAEs could reduce the digestibility of WPI sol/gel. We hope our works can provide promising strategies for developing WPI-RAEs foods.

Targeting Interfacial Location of Phenolic Antioxidants in Emulsions: Strategies and Benefits

It is important to have larger proportions of health-beneficial polyunsaturated lipids in foods, but these nutrients are particularly sensitive to oxidation, and dedicated strategies must be developed to prevent this deleterious reaction. In food oil-in-water emulsions, the oil-water interface is a crucial area when it comes to the initiation of lipid oxidation. Unfortunately, most available natural antioxidants, such as phenolic antioxidants, do not spontaneously position at this specific locus. Achieving such a strategic positioning has therefore been an active research area, and various routes have been proposed: lipophilizing phenolic acids to confer them with an amphiphilic character; functionalizing biopolymer emulsifiers through covalent or noncovalent interactions with phenolics; or loading Pickering particles with natural phenolic compounds to yield interfacial antioxidant reservoirs. We herein review the principles and efficiency of these approaches to counteract lipid oxidation in emulsions as well as their advantages and limitations.

Novel Colloidal Food Ingredients: Protein Complexes and Conjugates

Food proteins, polysaccharides, and polyphenols are natural ingredients with different functional attributes. For instance, many proteins are good emulsifiers and gelling agents, many polysaccharides are good thickening and stabilizing agents, and many polyphenols are good antioxidants and antimicrobials. These three kinds of ingredients can be combined into protein, polysaccharide, and/or polyphenol conjugates or complexes using covalent or noncovalent interactions to create novel multifunctional colloidal ingredients with new or improved properties. In this review, the formation, functionality, and potential applications of protein conjugates and complexes are discussed. In particular, the utilization of these colloidal ingredients to stabilize emulsions, control lipid digestion, encapsulate bioactive ingredients, modify textures, and form films is highlighted. Finally, future research needs in this area are briefly proposed. The rational design of protein complexes and conjugates may lead to the development of new functional ingredients that can be used to create more nutritious, sustainable, and healthy foods.

Caseinate-reinforced pectin hydrogels: Efficient encapsulation, desirable release, and chemical stabilization of (-)-epigallocatechin

(-)-Epigallocatechin (EGC) has good health benefits, but its chemical stability is low. Pectin hydrogels have potential for the encapsulation and delivery of EGC, but they are limited by porous networks and poor mechanical properties. In this study, protein (whey protein isolate and caseinate)-reinforced pectin hydrogel beads (HB_PEC-WPI and HB_PEC-CAS) were developed to overcome these limitations. The results showed that HB_PEC-CAS was a superior delivery system for EGC. HB_PEC-CAS had a compact network structure, mainly because of the hydrogen bonds that formed between caseinate and pectin. Moreover, the EGC encapsulation efficiency of HB_{PEC-CAS (2.4%)} reached 92.23 %; HB_{PEC-CAS (2.4%)} could also delay the release of EGC in an aqueous environment, while ensuring its sufficient release in a simulated gastrointestinal environment. Notably, EGC was chemically stabilized in HB_{PEC-CAS (2.4%)} during a 6-day storage period at 37 °C through the inhibition of its epimerization, oxidation, dimerization, and trimerization. The numerous hydroxyl groups in EGC readily interacted with the exposed amino acid residues in caseinate and created more protective sites. This study developed a strategy for protein-reinforced pectin hydrogel development and approaches for the protection of tea polyphenols; the findings offer useful insights for the tea-based food and beverage industry.

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

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

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

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

Design and characterization of whey protein nanocarriers for thyme essential oil encapsulation obtained by freeze-drying

Innovative coating powders, based on whey protein concentrate (10-15 wt%) as native (WPC) or denatured protein (d-WPC), solely or in combination with alginate (0.75 wt%, AL), containing thyme essential oil, were produced using the freeze-drying technique. The impact of individual components (protein, alginate and oil) as well as the effect of heat-induced protein denaturation, was resolved regarding physicochemical, thermal and morphological properties of powders. High product yield (∼100%), particle size (223-257 nm), low moisture content (0.10-0.13%) and zeta potential (-19 to -25.6 mV) were determined for all samples. Strong antimicrobial activity of thyme oil nanocarriers against foodborne pathogens was demonstrated. Thermogravimetric analysis (TGA) indicated enhanced thermal stability of encapsulated oil. The most specific bands of structural compounds were identified in Raman spectra of the tested formulations, but principal component analysis (PCA) on recorded spectra was necessary to show the differences between carriers of different wall materials.

Chemistry of Protein-Phenolic Interactions Toward the Microbiota and Microbial Infections

Along with health concerns, interest in plants as food and bioactive phytochemical sources has been increased in the last few decades. Phytochemicals as secondary plant metabolites have been the subject of many studies in different fields. Breakthrough for research interest on this topic is re-juvenilized with rising relevance in this global pandemics' era. The recent COVID-19 pandemic attracted the attention of people to viral infections and molecular mechanisms behind these infections. Thus, the core of the present review is the interaction of plant phytochemicals with proteins as these interactions can affect the functions of co-existing proteins, especially focusing on microbial proteins. To the best of our knowledge, there is no work covering the protein-phenolic interactions based on their effects on microbiota and microbial infections. The present review collects and defines the recent data, representing the interactions of phenolic compounds -primarily flavonoids and phenolic acids- with various proteins and explores how these molecular-level interactions account for the human health directly and/or indirectly, such as increased antioxidant properties and antimicrobial capabilities. Furthermore, it provides an insight about the further biological activities of interacted protein-phenolic structure from an antiviral activity perspective. The research on the protein-phenolic interaction mechanisms is of great value for guiding how to take advantage of synergistic effects of proteins and polyphenolics for future medical and nutritive approaches and related technologies.

Advances in dietary proteins binding with co-existed anthocyanins in foods: Driving forces, structure-affinity relationship, and functional and nutritional properties

Anthocyanins, which are the labile flavonoid pigments widely distributed in many fruits, vegetables, cereal grains, and flowers, are receiving intensive interest for their potential health benefits. Proteins are important food components from abundant sources and present high binding affinity for small dietary compounds, e.g., anthocyanins. Protein-anthocyanin interactions might occur during food processing, ingestion, digestion, and bioutilization, leading to significant changes in the structure and properties of proteins and anthocyanins. Current knowledge of protein-anthocyanin interactions and their contributions to functions and bioactivities of anthocyanin-containing foods were reviewed. Binding characterization of dietary protein-anthocyanins complexes is outlined. Advances in understanding the structure-affinity relationship of dietary protein-anthocyanin interaction are critically discussed. The associated properties of protein-anthocyanin complexes are considered in an evaluation of functional and nutritional values.

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

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

Fabrication, characterization and in vitro digestion of camellia oil body emulsion gels cross-linked by polyphenols

This study was designed to investigate the formation of camellia oil body (OB) emulsion gels covalently cross-linked by oxidized polyphenols: catechin (OCT), caffeic acid (OCF), chlorogenic acid (OCA), and tannic acid (OTA). The structural characteristics, thermal stabilities, antioxidant activities, rheological properties, and lipid digestion kinetics of the cross-linked OB-polyphenol emulsion gels were studied. The results of free sulfhydryl and amino group contents, FT-IR, fluorescence spectroscopy, surface hydrophobicity and thermal stability analyses confirmed the formation of covalent interactions between polyphenols and OB emulsions. Based on the second-order structural kinetic model, OB emulsion gel cross-linked by OTA had stronger intermolecular interactions and more developed 3-D network structures than those of OCA, OCF and OCT. Furthermore, lipid digestion kinetics showed that the cross-linking of polyphenols with the OBs slowed down the disintegration of protein matrix under gastric conditions, resulting in delay the release of free fatty acid, which was confirmed by CLSM observations.

The non-covalent interactions between whey protein and various food functional ingredients

In daily diet, Whey protein (WP) is often coexisted with various Food functional ingredients (FFI) such as proteins, polyphenols, polysaccharides and vitamins, which inevitably affect or interact with each other. Generally speaking, they may be interact by two different mechanisms: non-covalent and covalent interactions, of which the former is more common. We reviewed the non-covalent interactions between WP and various FFI, explained the effect of each WP-FFI interaction, and provided possible applications of WP-FFI complex in the food industry. The biological activity, physical and chemical stability of FFI, and the structure and functionalities of WP were enhanced through the non-covalent interactions. The development of non-covalent interactions between WP and FFI provides opportunities for the design of new ingredients and biopolymer complex, which can be applied in different fields. Future research will further focus on the influence of external or environmental factors in the food system and processing methods on interactions.

Ultrasound-assisted assembly of β-lactoglobulin and chlorogenic acid for non covalent nanocomplex: fabrication, characterization and potential biological function

It is essential to understand the ultrasound-induced changes in assembly of proteins and polyphenols into non covalent nanocomplex. β-Lactoglobulin (LG) and chlorogenic acid (CA) with various biological activities can be combined to form food-grade nanocomplexes. This study systematically explored the role of high-intensity ultrasound pretreatment on the binding mechanisms of LG and CA, and the potential biological function for embedding curcumin (Cur). The scanning electron microscopy (SEM) revealed that ultrasound treatment could destroy the structure of LG, and the particle size of the protein was reduced to<50 nm. The change in secondary structure of the protein by ultrasound treatment could be revealed by the fourier transform infrared (FTIR) and fluorescence spectra. Besides, it was found that LG and CA were combined to form a complex under the hydrophobic interaction, and CA was bound in the internal cavity of LG with a relatively extended conformation. The result demonstrated that the ratio of Cur embedded in the ultrasonic sample could be effectively increased by 7% - 10%, the particle size in the emulsion was smaller, and the dispersion was more stable. This work contributes to the development of protein-polyphenol functional emulsion systems with the ability to deliver Cur.

Soluble Aggregates of Myofibrillar Proteins Engineered by Gallic Acid: Colloidal Structure and Resistance to In Vitro Gastric Digestion

Myofibrillar protein (MP)-soluble aggregates can be made by tactics of gallic acid (GA) modification during pH shifting, and this work aimed to disclose their aggregation pattern and in vitro digestion behavior. GA modification dissociated the filamentous structure of myofibrils and caused structural reassembly to form small-sized aggregates. These aggregates were evidenced to contain GA-bridged dimers and oligomers of myosin or actin, having a molecular weight of ∼1225 kDa. Additionally, the structural rearrangement significantly decreased the surface hydrophobicity while substantially increased the surface charge. As a result, the obtained colloidal solution was translucent and heat-resistant. Intriguingly, MP-soluble aggregates exhibited a retarded digestive behavior. Further evaluation by a quartz crystal microbalance suggested that the reduced binding affinity of soluble aggregates toward gastric pepsin could be the underlying reason. This work may foster the engineering advances of modulating the MP structure-digestion for the tailor manufacturing of muscle protein-based beverages.