Milk whey protein modification by coffee-specific phenolics: effect on structural and functional properties

Polyphenol oxidase mediates (-)-epigallocatechin gallate to inhibit endogenous cathepsin activity in Apostichopus japonicus

Apostichopus japonicus (A. japonicus) has rich nutritional value and is an important economic crop. Due to its rich endogenous enzyme system, fresh A. japonicus is prone to autolysis during market circulation and storage, resulting in economic losses. In order to alleviate this phenomenon, we investigated the effect of polyphenol oxidase (PPO) mediated (-)-epigallocatechin gallate (EGCG) on the activity and structure of endogenous cathepsin series protein (CEP) from A. japonicus. Research on cathepsin activity showed that PPO mediated EGCG could significantly reduce enzyme activity, resulting in a decrease in enzymatic reaction rate. SDS-PAGE and scanning electron microscopy results showed that PPO mediates EGCG could induce CEP aggregation to form protein aggregates. Various spectral results indicated that EGCG caused changes in the structure of CEP. Meanwhile, the conjugates formed by PPO mediated EGCG had lower thermal stability. In conclusion, PPO mediated EGCG was an effective method to inhibit the endogenous enzyme activity.

Formation of Cysteine Adducts with Chlorogenic Acid in Coffee Beans

The post-harvest processing of coffee beans leads to a wide range of reactions involving proteins. The formation of crosslinks between proteins and phenolic compounds present in high concentrations of coffee beans represents one of the most challenging and still not fully characterized reactions. The aim of this work was to assess the presence of products from such reactions in coffee samples, focusing on the adducts between cysteine and chlorogenic acids (CQAs). For this purpose, 19 green and 15 roasted coffee samples of the Coffea arabica, Coffea canephora, and Coffea liberica varieties were selected for this study and basically characterized. Then, targeted liquid chromatography mass spectrometry (LC-MS/MS) methods were developed to assess the formation of adducts between CQA and cysteine, glutathione, and N-acetylcysteine as the amino acid and peptide models, and quantified such adducts in coffee samples. The results of the characterization showed a heterogeneous distribution of the protein content (8.7-14.6%), caffeine (0.57-2.62 g/100 g), and antioxidant capacity (2-4.5 g ascorbic acid/100 g) in Arabica, Canephora, and Liberica samples. Glutamic acid, arginine, and proline were found to be the major amino acids, while 5-CQA (38-76%), 3-CQA (4-13%), and 4-CQA (4-13%) were the most abundant CQA derivatives of all coffee varieties. The model experiments for adduct formation demonstrated that cysteine binds to CQA via thiol groups and 5-CQA initially isomerizes to 3- and 4-CQA, depending on the conditions, allowing cysteine to bind to two different sites on 3-, 4- or 5-CQA molecules, thus, forming six different Cys-CQA adducts with m/z 476. The reaction was more favored at pH 9, and the adducts proved to be stable up to 90 °C for 10 min and up to 28 days at room temperature. The relative quantification of adducts showed peak area values ranging from 1100 to 3000 in green coffee bean samples, while no adducts were detected in roasted coffee beans. Overall, this work was the first attempt to demonstrate the presence of Cys-CQA adducts in coffee beans and paves the way for further investigations of such adduct formation at the protein level.

Reactivity and mechanism of the reactions of 4-methylbenzoquinone with amino acid residues in β-lactoglobulin: A kinetic and product investigation

Quinones, produced by the oxidation of phenolic compounds, covalently bind to nucleophilic groups on amino acids or proteins. In this study, the reactions of 4-methylbenzoquinone (4MBQ) with β-lactoglobulin (β-LG) and amino acids at neutral pH were investigated. LC-MS analysis revealed that Cys121 was likely the most modified residue in β-LG. Identification of reaction products by LC-MS/MS showed that Michael addition occurred in all reactions with amino acids tested. The formation of Schiff base and a di-adduct was found in His and Trp samples. Apparent second-order rate constants (k2) were determined at 25 °C and pH 7.0 by stopped-flow spectrophotometry. The rate of reactions decreased in the order: β-LG > His > Trp > Arg > Nα-acetyl His > Nα-acetyl Arg > Nα-acetyl Trp. The rate constants correlated with the pKa values of the amino acids, showing that the amount of unprotonated amine is the major factor determining the reactivity.

Ultrasound-assisted macroporous resin treatment improves the color and functional properties of sunflower meal protein

Sunflower meal protein (SMP) has been considered as a high-quality source of plant protein. However, because the chlorogenic acid (CA) contained in sunflower seed meal was prone to oxidation reactions under traditional alkali extraction conditions, the extracted protein has a dark color and some poor functional properties. To this end, this study used ultrasound-assisted macroporous resin treatment to extract SMP. The improvement effects and potential mechanisms of ultrasonic-assisted macroporous resin treatment with different powers (100, 300, and 500 W) on the color and functional properties of SMP were studied. The results showed that compared with untreated sunflower meal protein (USMP), the lightness value (L*), solubility, emulsification, and gel elasticity were significantly enhanced when treated with 100 W and 300 W ultrasonic-assisted macroporous resin. However, when the ultrasonic power was increased to 500 W, the L* value, solubility, emulsification, and gel elasticity decreased instead, indicating that lower power (100 W and 300 W) ultrasonic-assisted macroporous resin treatment significantly improved the color and functional properties of SMP. Further research found that ultrasound-assisted macroporous resin treatment changed the secondary and tertiary structures of SMP, transformed β-sheet into α-helix and β-turn through rearrangement, and significantly improved surface hydrophobicity. It shows that ultrasonic-assisted macroporous resin treatment expands the SMP structure and exposes hydrophobic groups, thereby improving the color and functional properties of SMP. This study provides a potential strategy for extracting SMP with light color and good functional properties. It also provides a theoretical basis for the wide application of SMP in food processing.

Polyphenol removal with ultrasound-assisted ethanol extraction from defatted walnut powder: optimization of conditions and effect on functional properties of protein isolates

BACKGROUND

Walnut kernels are high in polyphenols (PPs), which cause low protein solubility, limiting the use of walnut protein in the food industry. To obtain the best technical parameters of the dephenolization treatment, the defatted walnut powder was dephenolized using ultrasound-assisted ethanol extraction (UAE), and the response surface optimization was performed on the basis of single factor. On this basis, the effects of dephenolization on the solubility, emulsifying properties and foaming properties of walnut protein isolates (WPIs) were compared to those of defatted walnut powder without dephenolization.

RESULTS

The results showed that PP extraction in the UAE could significantly increase PP yield. The optimal process parameters were as follows: 51% (v/v) ethanol concentration, 140 W ultrasound power, 10 min extraction time, 30 °C ultrasound temperature, and a material-liquid ratio of 1:30 (w/v). The results revealed that the UAE dephenolization treatment significantly improved the functionality of WPI and that the functionality of the dephenolized WPI by UAE was superior to that of the protein without dephenolization, and that the functionality of both walnut proteins was the worst at pH 5, with solubility of 5.31% and 4.86%, emulsifying activity index (EAI) of 24.95 and 19.91 m2 /g, and foaming capacity (FC) of 3.66% and 2.94%, respectively; and the best at pH 11, with solubility of 82.35% and 73.55%, EAI of 46.35 and 37.28 m2 /g, and FC of 35.85% and 18.87%, respectively.

CONCLUSION

The study found that dephenolization by UAE can significantly improve the functionality of WPI, and this method should be promoted and used in walnut and walnut protein processing industries. © 2023 Society of Chemical Industry.

Covalent polyphenol modification of a reactive cysteine in the major apple allergen Mal d 1

Naturally occurring polyphenols can modify the molecular properties of food allergens. For the major apple allergen Mal d 1 it has been postulated that chemical reactions with polyphenols cause permanent changes in the tertiary structure, causing a loss of conformational IgE epitopes and reducing allergenicity. In our study, we investigated the effect that reactions with oxidized polyphenols have on the structure of Mal d 1 by mass spectrometry and NMR spectroscopy. We showed that a surface-exposed cysteine residue in this allergen spontaneously reacts with oxidized polyphenols under formation of a defined covalent adduct. Chemical modification of Mal d 1 did not destabilize or perturb the three-dimensional fold, nor did it interfere with ligand binding to its internal pocket. A structural model of the chemically modified apple allergen is presented, which reveals that the bound polyphenol partially covers a conformational IgE epitope on the protein surface.

Dairy-Protein-Based Aggregates as Additives Enriched with Tart Cherry Polyphenols and Flavor Compounds

Nowadays, the development of innovative food products with positive health effects is on the rise. Consequently, the aim of this study was a formulation of aggregates based on tart cherry juice and dairy protein matrix to investigate whether different amounts (2% and 6%) of protein matrix have an impact on the adsorption of polyphenols as well as on the adsorption of flavor compounds. Formulated aggregates were investigated through high-performance liquid chromatography, spectrophotometric methods, gas chromatography and Fourier transform infrared spectrometry. The obtained results revealed that with an increase in the amount of protein matrix used for the formulation of aggregates, a decrease in the adsorption of polyphenols occurred, and, consequently, the antioxidant activity of the formulated aggregates was lower. The amount of protein matrix additionally affected the adsorption of flavor compounds; thus the formulated aggregates differed in their flavor profiles in comparison with tart cherry juice. Adsorption of both phenolic and flavor compounds caused changes in the protein structure, as proven by recording IR spectra. Formulated dairy-protein-based aggregates could be used as additives which are enriched with tart cherry polyphenols and flavor compounds.

A model study on the site-specificity of (-)-epicatechin-induced reactions in β-lactoglobulin by high-resolution mass spectrometry in combination with bioinformatics

Polyphenol-protein reactions in model solutions of β-lactoglobulin (β-LG) incubated with (-)-epicatechin at 37 °C and 60 °C were monitored by microLC-timsTOF Pro-MS/MS combined with bioinformatics strategies. The addition of (-)-epicatechin to the model solutions resulted in changes in tryptic peptide profiles. Covalent bond formation between (-)-epicatechin o-quinones and β-LG was identified for the residues S27, S30, K60, C66, K69, and C160, with C160 being the predominant binding site. Furthermore, the incubation of β-LG with (-)-epicatechin significantly promoted oxidation, especially for the residues M7 and M24. The reaction of monomeric (-)-epicatechino-quinone at C160 was also identified in the milk chocolate sample. The adaptation of this study by extending the scope of the reaction products offers significant potential for comprehensive food profiling strategies.

Phenolic Acid-Amino Acid Adducts Exert Distinct Immunomodulatory Effects in Macrophages Compared to Parent Phenolic Acids

Caffeic acid (CA) and chlorogenic acid (CGA) are commonly found phenolic acids in plant-derived foods and beverages. Their corresponding adducts with cysteine (Cys) have been detected in coffee-containing beverages. However, despite the well-documented antioxidant and anti-inflammatory activity of CA and CGA, the immunomodulatory activities of the Cys adducts (CA-Cys and CGA-Cys) are unknown. The adducts were therefore synthesized, and their immunomodulatory effects were studied in lipopolysaccharide (LPS)-treated RAW 264.7 cells and compared to the activity of the parent phenolic acids. CA and CGA generally down-regulated the inflammatory responses. However, RNA-sequencing showed that the LPS-induced pathways related to Toll-like receptor signaling, chemokine signaling, and NOD-like receptor signaling, and JAK-STAT/MAPK signaling pathways were upregulated in adduct-treated cells relative to parent phenolic acids, while neurodegenerative disorder-related pathways and metabolic pathways were downregulated. Production of prostaglandin E₂ (PGE₂), interleukin-6, tumor necrosis factor-α (TNF-α), and reactive oxygen species (ROS) was all inhibited by CA and CGA (P < 0.05). PGE₂ and TNF-α were further suppressed in adduct-stimulated cells (P < 0.05), but ROS production was increased. For example, TNF-α produced by 100 μM CGA-stimulated cells and 100 μM CGA-Cys adduct-stimulated cells were 4.46 ± 0.23 and 1.61 ± 0.18 ng/mL, respectively. Thus, the addition of the Cys moiety drastically alters the anti-inflammatory activity of phenolic compounds.

Limited enzymatic hydrolysis of green coffee protein as a technique for preparing new functional food components

Valorisation of side-streams in food production has become an important booster for increased sustainability in food production. The objective of this work was to study and improve the functional properties of green coffee (GC) protein. Extraction of defatted GC meal by using PVPP slightly increased protein yield and significantly decreased the amount of covalently and non-covalently bound CQA, therefore decreasing the antioxidant activity of the meal. Peptic hydrolysis at pH 1.5 led to a significantly higher degree of hydrolysis (DH) than at pH 3. Sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that the molecular weights of peptides of GC protein hydrolysates were in the range of 11-60 kDa, while peptides were in the range of 500-5000 Da using matrix-assisted laser desorption/ionization-time of flight mass spectroscopy (MALDI-TOF MS). Additionally, the enzymatic hydrolysis significantly improved the antioxidant activity of the GC protein. Finally, the results suggest that enzymatic hydrolysis with pepsin is an effective technique to provide bioactive compounds. The works presented in our manuscript may help in further exploiting the potential use of green coffee beans for food, cosmetic or pharmaceutical industry.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-022-05646-3.

Decolorization and detoxication of plant-based proteins using hydrogen peroxide and catalase

The gap between the current supply of meat and its predicted future demand is widening, increasing the need to produce plant-based meat analogs. Despite ongoing technical developments, one of the unresolved challenges of plant-based meat analogs is to safely and effectively decolor plant proteins that originally exhibit yellow-brown or strong brown color. This study aimed to develop an effective and safe decoloring system for soy-based protein products using food-grade hydrogen peroxide and catalase. First, soy-based protein isolate (PI) and textured vegetable protein (TVP) were treated with hydrogen peroxide, and then the residual hydrogen peroxide was degraded using catalase. This process caused notable decolorization of PI and TVP, and residual hydrogen peroxide was not detected in these products. These findings indicate that this process could safely and effectively decolorize soy-based proteins. Interestingly, this decoloring process enhanced the solubility, water- and oil-holding capacities, foaming capacity, and emulsifying stability of decolored soy-based PI. Additionally, cooking loss and juiciness of decolored TVP-based foods were improved compared to those of non-treated foods. These findings indicate that the decoloring process also enhances the physical properties of soy-based protein products.

Digestive stability and transport ability changes of β-lactoglobulin–catechin complexes by M cell model in vitro

The current research on interaction between catechin and protein has focused on non-covalent crosslinking, however, the mechanism of free radical-induced crosslinking between catechin and β-lactoglobulin (BLG) is not known. In this study, BLG bound to four catechins [epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG), and epigallocatechin gallate (EGCG)]. The structure change of complex was investigated by circular dichroism spectroscopy, ultraviolet-visible (UV-vis) spectroscopy and Acid and 8-Anilino-1-naphthalenesulfonic acid (ANS) fluorescence spectroscopy. M cell model was constructed to evaluate the transintestinal epithelial transport capacity of complex digestive products. The results showed that catechins were covalently bound to BLG by C-S and C-N bonds and their binding content was EGCG&gt;EGC&gt;ECG&gt;EC. Moreover, catechins could change the secondary structure of BLG, with the decrease of α-helix and reduction of the irregular coilings, which leads to the loose spatial structure of the protein. Moreover, the catechin could enhance further the digestibility of BLG. Transport capacity of digestive products of M cell model was about twice of that of the Caco-2 cell model, indicating that M cell model had better antigen transport capacity. The difference between groups indicated that the transport efficiency of digestive products was decreased with the presence of catechin, in which BLG-EGCG and BLG-EGC groups were transported more strong than those of BLG-EC and BLG-ECG groups. The transport efficiency of BLG-catechin complexes were lower than that of BLG, indicating that catechin had the protective and repair roles on intestinal barrier permeability.

Suppression of Pepper mild mottle virus (PMMoV) by Modified Whey Proteins

Modified whey proteins with quercetin (WPI-QU) and onion extract (WPI-OE), as a control approach, could be applicable because it is available, safe and cheap. The modified whey protein isolate (WPI) with quercetin dihydrate and onion extract powder rich with quercetin were evaluated for induction of systemic resistance against Pepper mild mottle virus (PMMoV) in pepper plants. Data of mass spectrometry illustrated that one or more of Qu isomers covalently attached to WPI. Unmodified whey protein (UWPI), WPI-QU and WPI-OE significantly decreased PMMoV concentration and severity at two weeks after inoculation. Plant height, number of leaves, and shoot fresh and dry weights were substantially increased in WPI-QU- and WPI-OE-treated pepper plants compared to the control. Total antioxidant status (TAS) and vitamin C contents were highly increased in WPI-OE-treated plants compared with other treatments. The expression levels of defense related genes (PR4, PR9, TIN1 and PIN2) were enormously elevated in WPI-OE and WPI-QU treatments using qRT-PCR. In conclusion, the results give novel insights to possible applications of the WPI–quercetin bioconjugates in designing a wide range of functional products. Moreover, this study is the first to establish the effective control of PMMoV by modified whey proteins.

The structure, antioxidant and antibacterial properties of thiol-modified soy protein isolate induced by allicin

This study investigated the effect of allicin binding on the structure, antioxidant and antibacterial properties of soy protein isolate (SPI). Results showed that allicin bound to 82.6 % free thiol groups of SPI at a molar ratio of 0.5. The combination of allicin and SPI significantly affected the structure of protein. Result of circular dichroism showed that the content of α-helix decreased by 26.9 % and the content of β-sheet increased by 12.2 % over control when the molar ratio was 0.5. The result of surface hydrophobicity signified the unfolding of SPI with the action of allicin. These results implied that allicin binding might be a suitable method for the modification of SPI. Furthermore, the antibacterialand antioxidant experiments indicated that allicin-SPI conjugates not only had the capacity to inhibit the growth of Escherichia coli and Staphyloccocus aureus, but also had DPPH and ABTS radicals scavenging activities.

Altering functional properties of rice protein hydrolysates by covalent conjugation with chlorogenic acid

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Rice protein hydrolysate was covalently conjugated to chlorogenic acid by three methods.

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Covalent conjugation resulted in an unfolded structure of rice protein hydrolysate.

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LYS might be the binding sites for chlorogenic acid grafted on rice protein hydrolysate.

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Conjugates formed by alkaline method exhibited highest functional property.

Proteins and phenolic compounds are common components in foods that readily interact with each other to yield complexes, leading to changes in the functional properties. In this study, we investigated the effect of covalent conjugation of rice protein hydrolysates (RPH) with chlorogenic acid (CA) on the structural and functional properties of RPH. Three RPH-CA conjugates were prepared by the alkaline, enzyme, and free radical methods, respectively. Covalent conjugation decreased the content of free amino, thiol, and tyrosine groups, and increased in the amount of CA bounds from 15.23 to 21.11 nmol/mg. Moreover, the circular dichroism analysis revealed that covalent conjugation resulted in an increase of random coils. The emulsifying activity and antioxidant capacity of RPH were also improved by the covalent conjugation with CA. This work provides a better understanding of the formation of hydrolysates-chlorogenic acid conjugates, contributing to improving the functional properties of foods.

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

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

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

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

In vitro phenolic bioaccessibility of coffee beverages with milk and soy subjected to thermal treatment and protein-phenolic interactions

The effect of skimmed bovine milk and soy protein on the in vitro bioaccessibility of polyphenols in coffee beverages under thermal treatment (25, 90, and 121 °C) and the protein-phenolic interaction was investigated. Thermal treatment at 90 °C and 121 °C reduced the in vitro bioaccessibility of total and individual phenolic. Skimmed milk and soy protein addition increased the total (by 37.01%-64.21% and 24.74%-47.32%, respectively) and individual phenolic in vitro bioaccessibility (by 4.40%-27.29% and 12.02%-28.61%, respectively) of coffee beverages subjected to thermal treatment at 25, 90 and 121 °C. Compared with soy protein, skimmed milk significantly enhanced the in vitro bioaccessibility of coffee polyphenols, possibly owing to the presence of different types and strengths of noncovalent protein-phenolic interactions. These findings can provide certain theoretical knowledge for optimizing the processing technology and formula of the food industry to help improve the health benefits of milk coffee beverages.

Protein-polyphenol conjugates: Preparation, functional properties, bioactivities and applications in foods and nutraceuticals

Protein is a crucial nutritional ingredient in the daily human diet. Polyphenols (PPNs) are the abundant phytochemicals in plants, which are associated with health promotion as well as affect functionality in food systems. Both ingredients possess different types of functionalities (crosslinking, gelling, emulsifying, film-forming, etc.) and bioactivities (antioxidant, antimicrobial, anti-inflammatory, etc.). In the past decade, various methods have been implemented to enhance the functionalities and bioactivities of foods. Conjugation or grafting methods has been introduced widely. Conjugations of PPNs with proteins through various methods have been performed for the synthesis of the protein-polyphenol conjugate. Those potential grafting methods are alkaline associated, free-radical mediated, enzyme catalyzed, and chemical coupling methods. Several factors such as reaction conditions, type of proteins, and PPNs also influenced the conjugation efficiency. Various technologies, e.g., mass spectroscopy, fluorescence spectroscopy, UV spectroscopy, Fourier transform infrared spectroscopy, circular dichroism, and sodium dodecyl sulfate polyacrylamide gel electrophoresis have been used to elucidate conjugation and structural alternation of proteins and some properties of resulting conjugates. The prepared protein-PPN conjugates have been documented to enhance the bioactivities and functional properties of an initial protein. Moreover, conjugates have been employed in emulsions or as nanoparticles for nutraceutical delivery. Edible-films for food packaging and hydrogels for controlled drug release have been developed using protein-PPN conjugates. This chapter focuses on the methodologies and characteristics of protein-PPN conjugates and their applications in various food systems and nutraceutical field.

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

Whey proteins are widely used as functional ingredients in various food applications owing to their emulsifying, foaming, and gelling properties. However, their functional attributes are limited in some applications because of the dependence of their performance on pH, mineral levels, and temperature. Several approaches have been investigated to enhance the functional performance of whey proteins by interacting them with polyphenols via covalent bonds (conjugates) or non-covalent bonds (complexes). The interaction of the polyphenols to the whey proteins alters their molecular characteristics, techno-functional attributes, and biological properties. Analytical methods for characterizing the properties of whey protein-polyphenol complexes and conjugates are highlighted, and a variety of potential applications within the food industry are discussed, including as antioxidants, emulsifiers, and foaming agents. Finally, areas for future research are highlighted.

Bovine β-Lactoglobulin Covalent Modification by Flavonoids: Effect on the Allergenicity and Human Intestinal Microbiota

The present study aims to investigate the structure of covalent conjugates of bovine β-lactoglobulin (BLG) and flavonoids (luteolin, myricetin, and hyperoside), and their effect on the allergenicity and human intestinal microbiota. Covalent modification of amino acids in BLG by flavonoids was confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and o-phthaldialdehyde assay. The secondary and conformational structures of BLG were changed by the covalent modification, which were determined by the circular dichroism, Fourier transform infrared spectroscopy, fluorescence spectroscopy, and UV spectroscopy. The enzyme-linked immunosorbent assay (ELISA) and cell experiments indicated that BLG covalent conjugates could reduce IgE/IgG binding capacities and suppress the allergy reactivity of RBL-2H3 cells, suggesting that the covalent modification modulated the balance of T cells. Meanwhile, covalent modification of BLG with these flavonoids can alter the diversity of human intestinal microbiota and the community abundance at phylum, family, and genus levels. The results revealed that covalent modification of BLG with flavonoids alters human intestinal microbiota, might result in the reduction of allergenicity, which could provide information for confirming the relationship between food allergy and the intestinal microbial ecosystem.

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

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

Effects of different dietary polyphenols on conformational changes and functional properties of protein-polyphenol covalent complexes

In this study, conjugates of whey protein isolate (WPI) and four polyphenols (epigallocatechin gallate [EGCG], quercetin [QC], apigenin [AG], and naringenin [NG]) were prepared through free-radical grafting. The results for polyphenol binding equivalents and content of free amino and sulfhydryl groups as well as those from sodium dodecyl sulfate-polyacrylamide gel electrophoresis confirmed the covalent interaction between WPI and the polyphenols. Fourier transform infrared spectroscopy and fluorescence spectrum analysis identified the potential binding sites of the complexes and determined changes in the protein structure. The particle size distribution and scanning electron microscopy data demonstrated increases in conjugate particle sizes and surface changes in the complexes. The conjugation process significantly increased the polyphenols' antioxidant properties and thermal stabilities, whereas surface hydrophobicity was substantially reduced. WPI-EGCG had the best functional properties, followed by WPI-QC, WPI-AG, and WPI-NG.

Effect of non-covalent binding of phenolic derivatives with scallop (Patinopecten yessoensis) gonad protein isolates on protein structure and in vitro digestion characteristics

The present study was aimed to investigate the effects of non-covalent interactions between scallop gonad protein isolates (SGPIs) and different concentrations (20, 120 and 240 μmol/g, protein basis) of four phenolic compounds, such as (-)-epigallocatechin gallate (EGCG), epicatechin 3-gallate (ECG), epigallocatechin (EGC), and catechin (C), regarding the structural and functional properties of the complex. Total sulfhydryl and surface hydrophobicity in SGPIs decreased by nearly 72% and 65% with 240 μmol/g EGCG, similar but less appreciable changes were produced by EGC, ECG and C. Fluorescence quenching and thermodynamic parameters suggested that hydrogen bond and van der Waals dominated the interaction process between SGPIs and EGCG, and the interaction was further studied by molecular docking. Moreover, EGCG-treated SGPIs digests exerted higher ABTS+• scavenging activity than that of ECG and EGC-treated SGPIs. These findings are helpful to reveal the binding mechanism of phenolics and SGPIs, and provide a theoretical basis for the application of SGPIs-phenolic complexes as functional food additives.

Whey protein addition and its increased light absorption and tinctorial strength of model solutions colored with anthocyanins

Anthocyanins (ACN) are pigments with vivid colors, but their application as food colorants is restricted by their limited stability and color expression. Anthocyanins exhibit higher stability in dairy systems than in buffers at similar pH, suggesting that pigments may be able to interact with dairy components such as proteins, resulting in improved performance as colorants. Our objective was to determine the type of interaction between whey proteins (WP) and ACN leading to color enhancements and to determine the role of the ACN chemical structure in this interaction. Model solutions colored with semipurified pigments from sources with different ACN profiles (Berberis boliviana, grape skin, purple corn, black carrot, and red cabbage) were mixed with different concentrations of whey protein isolate (WPI) in pH 3 buffer. Absorption spectra of these solutions were acquired using an absorbance microplate reader, and color parameters were calculated from spectral data. Isolated ACN 3-glucosides were used to determine the role of the aglycone structure in the WP-ACN interaction using visible and fluorescence spectroscopy. In silico modeling was used to visualize potential differences in the interaction between β-lactoglobulin and ACN. Addition of WPI resulted in hyperchromic shifts at the wavelength of maximum absorption in the visible range (λ_vis-max) of up to 19%, and a significant increase in tinctorial strength for all ACN sources (ΔE > 5). Moreover, ACN acylation did not seem to play a significant role in the WP-ACN interaction. When using isolated ACN, WPI addition resulted in hyperchromic shifts at the λ_vis-max only for methoxylated ACN such as petunidin-3-glucoside (up to 24%), and malvidin-3-glucoside (up to 97%). The bimolecular quenching constant values (K_q > 10¹⁰M^-1s^-1) strongly suggested that the predominant type of quenching interaction was static. Analysis of enthalpy, entropy, and Gibbs free energy showed that this binding was spontaneous; depending on the chemical structure of the ACN, the predominant binding forces could be hydrophobic interactions or hydrogen bonding. Modeling suggested that methoxylations in the B ring of the aglycon structure promoted interactions with electron acceptor amino acids. Overall, WP could be used to enhance the tinctorial strength of select ACN depending on their structural characteristics. Therefore, ACN source selection may play a key role for specific applications in dairy products.

Addition of milk to coffee beverages; the effect on functional, nutritional, and sensorial properties

To date, there exists a debate on the effect of milk added to coffee infusions/beverages concerning the nutritional quality of coffee and the functional properties of its phenolic compounds. Yet, the full nutritional quality and functional properties of a coffee beverage without a significant negative impact on its sensorial profile are highly desired by the consumers. Negative/masking, positive, and neutral effects of milk on the antioxidant activity and bioavailability of coffee phenolics (particularly, chlorogenic acids) have been reported. Some potential factors including the type and amount of milk added, type of coffee beverage, the composition of both milk (protein and fat) and coffee (phenolic compounds), preparation method, assays used to measure antioxidant properties, and sampling size may account for the various reported findings. Interactions between phenolic compounds in coffee and milk proteins could account as the main responsible aspect for the reported masking/negative impact of milk on the antioxidant activity and bioaccessibility/bioavailability of coffee bioactives. However, considering the interactions between milk components and coffee phenolics, which result in the loss of their functionality, the role of milk fat globules and the milk fat globule membrane can also be crucial, but this has not been addressed in the literature so far.HighlightsIn most cases, milk is added to the coffee beverages in several various ways.Effect of milk on the nutritional/functional properties of coffee is controversial.Enough evidence suggests negative effects of milk addition on properties of coffee.Interactions of coffee phenolics and milk proteins could account as the main aspect.The role of milk fat globules and milk fat globule membrane may also be crucial.

Physicochemical properties, antioxidant activities, and binding behavior of 3,5-di-O-caffeoylquinic acid with beta-lactoglobulin colloidal particles

Milk proteins and polyphenols are increasingly being studied as functional ingredients due to the epidemiologically-proved health benefits. In this study, composite β-lactoglobulin (β-lg) or β-lactoglobulin nanoparticles (β-lgNPs)-3,5-di-O-caffeoylquinic acid (3,5diCQA) with superior physicochemical and antioxidant activity (AA) were produced using β-lg and 3,5-di-O-caffeoylquinic acid. The main interactions between β-lg or β-lgNPs with 3,5diCQA were hydrogen bonding and hydrophobic effects. The 3,5diCQA caused a decrease in α-helix and β-sheet structure with a corresponding increase in unordered structure. Compared to β-lg alone, composite β-lg or β-lgNPs-3,5diCQA slightly decreased the particle size but increased their negative surface potentials especially for β-lg or β-lgNPs at a molar ratio of 5:1. The addition of 3,5diCQA appreciably improved the AA in a dose-dependent manner. These results shed light on the structural, physicochemical, and AA of composite β-lg or β-lgNPs-3,5diCQA non-covalent complexes, important for application as functional ingredients in food solutions as well as in the pharmaceutical industry.

Improvement of protein emulsion stability through glycosylated black bean protein covalent interaction with (-)-epigallocatechin-3-gallate

This study investigated the effects of covalent conjugates combined by glycosylated black bean protein isolate (BBPI-G) and (−)-epigallocatechin-3-gallate (EGCG) on the emulsion stability. Fourier transform infrared (FTIR) spectroscopy showed that covalent binding of EGCG with BBPI-G made the protein molecule unfolded. Besides, the emulsifying properties of BBPI-G were increased after combined with EGCG. BBPI-G–EGCG emulsion had lower mean particle size and higher content of interfacial protein adsorption (AP), which resulted in thicker and more impact oil–water interface. Therefore, the stability of emulsions was significantly improved. Furthermore, the emulsions prepared by BBPI-G–EGCG compounds exhibited considerable stability in storage, oxidation, thermal treatments, freeze–thaw and freeze-dried powders resolubility. This study demonstrated that the covalent bond of glycosylated protein and polyphenols could advance the emulsifying performance of protein, and BBPI-G–EGCG covalent complex was an effective emulsifier for preparing high stability emulsions.

Stability improvement of emulsions stabilized by covalent conjugation with glycosylated black bean protein and EGCG (BBPI-G–EGCG) was studied through structure changes of proteins and emulsion properties.

Changes in structure and allergenicity of shrimp tropomyosin by dietary polyphenols treatment

Here, the potential allergenicity of shrimp tropomyosin (TM) after conjugation with chlorogenic acid (CA) and (-)-epigallo-catechin 3-gallate (EGCG) was assessed. Conformational structures of TM-polyphenol complexes were detected using SDS-PAGE, circular dichroism (CD), and fluorescence. Potential allergenicity was assessed by immunological methods, a rat basophil leukemia cell model (RBL-2H3), and in vivo assays. Indirect ELISA showed that TM-polyphenol complexes caused a conformational change to TM structure, with decreased IgG/IgE binding capacity significantly fewer inflammatory mediators were released with EGCG-TM and CA-TM in a mediator-releasing RBL-2H3 cell line. Mice model showed low allergenicity to serum levels of TM-specific antibody and T-cell cytokine production. EGCG-TM and CA-TM might reduce the potential allergenicity of shrimp TM, which could be used to produce hypoallergenic food in the food industry.

Comprehensive Characterization and Relative Quantification of α-Amylase/Trypsin Inhibitors from Wheat Cultivars by Targeted HPLC-MS/MS

The α-amylase/trypsin inhibitors (ATIs) are discussed as being responsible for non-celiac wheat sensitivity (NCWS), besides being known as allergenic components for baker’s asthma. Different approaches for characterization and quantification including proteomics-based methods for wheat ATIs have been documented. In these studies generally the major ATIs have been addressed. The challenge of current study was then to develop a more comprehensive workflow encompassing all reviewed wheat-ATI entries in UniProt database. To substantially test proof of concept, 46 German and Turkish wheat samples were used. Two extractions systems based on chloroform/methanol mixture (CM) and under buffered denaturing conditions were evaluated. Three aspects were optimized, tryptic digestion, chromatographic separation, and targeted tandem mass spectrometric analysis (HPLC-MS/MS). Preliminary characterization with sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) documented the purity of the extracted ATIs with CM mixture and the amylase (60–80%)/trypsin (10–20%) inhibition demonstrated the bifunctional activity of ATIs. Thirteen (individual/common) biomarkers were established. Major ATIs (7–34%) were differently represented in samples. Finally, to our knowledge, the proposed HPLC-MS/MS method allowed for the first time so far the analysis of all 14 reviewed wheat ATI entries reported.