Interactions between milk proteins and polyphenols: Binding mechanisms, related changes, and the future trends in the dairy industry

Revealing binding mechanism of β-casein to chrysin, apigenin, and luteolin and locating its binding pockets by molecular docking and molecular dynamics

Revealing the interaction mechanism of proteins with bioactive molecules and the location of their binding pockets is crucial for predicting the structure-function relationship of proteins in drug discovery and design. Despite some published papers on the interaction of β-casein with small bioactive molecules, the ambiguity of the location and constituent amino acids of β-casein binding pockets prompted us to identify them by in silico simulation of its interaction with three polyphenols, chrysin, apigenin, and luteolin. Molecular docking revealed that the primary β-casein binding pocket for chrysin consists of five nonpolar amino acids (Leu73, Phe77, Pro80, Ile89, and Pro196), three polar neutral amino acids (Ser137, Gln138, and Gln197), and two polar charged amino acids (Glu136, and Arg198). For β-casein/apigenin and β-casein/luteolin complexes, Asn83 also contributes to forming the pocket. Molecular dynamics provided more details, such as the relative contribution of determinative amino acids and the role of various forces. For example, we found that Glu210, Glu132, and Glu35 are the most destructive residues in the binding of chrysin, apigenin, and luteolin to β-casein, respectively. Also, we observed that hydrophobic forces mainly stabilize β-casein/chrysin and β-casein/apigenin, and polar solvation (including hydrogen bonds) stabilizes β-casein/luteolin, all by spontaneous processes.

Characterization of Alginate-Crystalline Nanocellulose Composite Hydrogel as Polyphenol Encapsulation Agent

Alginate hydrogel is broadly known for its potential as an encapsulation agent due to its compatibility and versatility. Despite its predominance, alginate hydrogel naturally has macropores and a less rigid structure, which leads to syneresis and uncontrolled diffusion of bioactive compounds from the gel network. Combining alginate with other biopolymers has been considered to improve its properties as an encapsulation agent. This research aimed to evaluate the effect of Crystalline Nanocellulose (CNC) to the physical properties and the diffusion of gallic acid (GA), as a water-soluble polyphenol model, through the alginate-CNC composite hydrogels performed as an encapsulation agent. The hydrogel mixtures were made from 1:0, 1:1, 2:0, 2:1, 2:2, and 2:3 solid-basis ratio of sodium alginate:crystalline nanocellulose and evaluated for syneresis, gel strength and stiffness, rehydration properties and gel porosity. Alginate-CNC and GA interaction was observed through zeta-potential analysis and Fourier Transform Infrared (FTIR) spectroscopy. Results showed that composite hydrogel with the highest proportion of CNC increased the gel rehydration capacity (87.33 %), gel strength and stiffness as well as reduced the gel syneresis (14.72 %) and dried gel porosity (0.62). GA pre-loaded gel with 2:2 and 2:3 S-C ratios reduced the diffusion of gallic acid by 92.07-92.27 %. FTIR showed hydrogen bonding between GA and the alginate-CNC hydrogel. Alginate-CNC hydrogel had a fibrous and compact structure as shown in the cryo-SEM and confocal microscope images.

Using multi-modal spectroscopy technology and microscopic analysis to explore the regulation of ultra-high pressure heat-assisted treatment on the texture of ready-to-eat shrimp during storage

This study employed multi-modal spectroscopy technology and microscopic analysis to investigate the effects of various treatments on the texture of ready-to-eat (RTE) shrimps during storage. The results indicated that ultra-high pressure heat-assisted treatment (UHP-HAT) significantly improved the texture properties of RTE shrimps while simultaneously reducing the carbonyl and trichloroacetic acid-soluble properties associated with protein oxidative degradation. Furthermore, UHP-HAT resulted in a denser and more ordered protein structure, which contributed to an increased content of bound and immobile water. A partial least squares regression model for texture prediction was developed using data obtained from hyperspectral imaging, demonstrating a strong correlation between spectral information and texture parameters. Additionally, infrared imaging was utilized to elucidate the distribution of functional groups (OH, CO, CH) and carbonyl compounds within the proteins. Overall, the findings suggested that UHP-HAT could effectively delay the deterioration of texture by mitigating protein degradation.

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

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

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

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

Process-Induced Molecular-Level Protein-Carbohydrate-Polyphenol Interactions in Milk-Tea Blends: A Review

The rapid increase in the production of powdered milk-tea blends is driven by a growing awareness of the presence of highly nutritious bioactive compounds and consumer demand for convenient beverages. However, the lack of literature on the impact of heat-induced component interactions during processing hinders the production of high-quality milk-tea powders. The production process of milk-tea powder blends includes the key steps of pasteurization, evaporation, and spray drying. Controlling heat-induced interactions, such as protein-protein, protein-carbohydrate, protein-polyphenol, carbohydrate-polyphenol, and carbohydrate-polyphenol, during pasteurization, concentration, and evaporation is essential for producing a high-quality milk-tea powder with favorable physical, structural, rheological, sensory, and nutritional qualities. Adjusting production parameters, such as the type and the composition of ingredients, processing methods, and processing conditions, is a great way to modify these interactions between components in the formulation, and thereby, provide improved properties and storage stability for the final product. Therefore, this review comprehensively discusses how molecular-level interactions among proteins, carbohydrates, and polyphenols are affected by various unit operations during the production of milk-tea powders.

Identifying the temporal contributors and their interactions during dynamic formation of black tea cream

Tea cream formed in hot and strong tea infusion while cooling deteriorates quality and health benefits of tea. However, the interactions among temporal contributors during dynamic formation of tea cream are still elusive. Here, by deletional recombination experiments and molecular dynamics simulation, it was found that proteins, caffeine (CAF), and phenolics played a dominant role throughout the cream formation, and the contribution of amino acids was highlighted in the early stage. Furthermore, CAF was prominent due to its extensive binding capacity and the filling complex voids property, and caffeine-theaflavins (TFs) complexation may be the core skeleton of the growing particles in black tea infusion. In addition to TFs, the unidentified phenolic oxidation-derived products (PODP) were confirmed to contribute greatly to the cream formation.

Exploring the potential utilization of copigmented barberry anthocyanins in ice cream: Focusing on foaming aspects, and melting attributes

Anthocyanins have emerged as promising substitutes for synthetic dyes owing to their color profiles, and potential health-boosting properties. The primary aim of this investigation was to assess the impact of copigmented, and un-copigmented barberry anthocyanins, employed at different concentrations (1, 3, and 5% w/w) as colorants in ice cream. The secondary goal was to investigate the influence of barberry anthocyanins on ice cream foaming characteristics, and melting point. The samples' physicochemical, textural, and organoleptic characteristics, total phenolic, and anthocyanin content, and antioxidant activity were determined. By increasing barberry extract concentrations in the samples, the pH levels (5.81) decreased, and overrun increased(30.0 ± 1.15%), respectively. Furthermore, the textural analysis showed that increasing barberry anthocyanins within the ice cream formulation correlated with an increase in sample hardness (113.72 ± 1.34 N). The control sample (vanilla ice cream) had the highest value of melting rate (1.09 ± 0.03 g/min), whereas the specimen containing 5% of copigmented barberry anthocyanins exhibited the lowest rate of melting (0.50 ± 0.01 g/min). The start time of melting of control sample was 1098 s and by increasing the concentration of copigmented barberry anthocyanins from 1 to 5%, this time increased from 1405.2 s to 1831.2 s (P < 0.05). In conclusion, barberry anthocyanins reduced the melting rate as a crucial attribute for ice cream.

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

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

Investigating the Formation of In Vitro Immunogenic Gluten Peptides after Covalent Modification of Their Structure with Green Tea Phenolic Compounds under Alkaline Conditions

Celiac disease is an autoimmune disorder triggered by immunogenic gluten peptides produced during gastrointestinal digestion. To prevent the production of immunogenic gluten peptides, the stimulation of covalent-type protein-polyphenol interactions may be promising. In this study, gluten interacted with green tea extract (GTE) at pH 9 to promote the covalent-type gluten-polyphenol interactions, and the number of immunogenic gluten peptides, 19-mer, 26-mer, and 33-mer, was monitored after in vitro digestion. Treatment of gluten with GTE provided an increased antioxidant capacity, decreased amino group content, and increased thermal properties. More importantly, there was a remarkable (up to 73%) elimination of immunogenic gluten peptide release after the treatment of gluten with 2% GTE at 50 °C and pH 9 for 2 h. All of these confirmed that gluten was efficiently modified by GTE polyphenols under the stated conditions. These findings are important in developing new strategies for the development of gluten-free or low-gluten food products with reduced immunogenicity.

The roles of Saccharomyces cerevisiae on the bioaccessibility of phenolic compounds

Phenolic compounds are a group of non-essential dietary compounds that are widely recognized for their beneficial health effects, primarily due to their bioactive properties. These compounds which found in a variety of plant-based foods, including fruits, vegetables, and grains are known to possess antimicrobial, antioxidant, anti-inflammatory, and anti-carcinogenic properties. However, the health effects of these compounds depend on their bioaccessibility and bioavailability. In recent years, there has been growing interest in the use of probiotics for promoting human health. Saccharomyces cerevisiae is a yeast with potential probiotic properties and beneficial health effects. Biosorption of phenolic compounds on Saccharomyces cerevisiae cell walls improves their bioaccessibility. This characteristic has also allowed the use of this yeast as a biosorbent in the biosorption process due to its low cost, safety, and easy availability. S. cerevisiae enhances the bioaccessibility of phenolic compounds as a delivery system under in vitro digestion conditions. The reason for this phenomenon is the protective effects of yeast on various phenolic compounds under digestion conditions. This article shows the role of S. cerevisiae yeast on the bioaccessibility of various phenolic compounds and contributes to our understanding of the potential impact of yeasts in human health.

Comparison of Non-Covalent and Covalent Interactions between Lactoferrin and Chlorogenic Acid

Adding polyphenols to improve the absorption of functional proteins has become a hot topic. Chlorogenic acid is a natural plant polyphenol with anti-inflammatory, antioxidant, and anticancer properties. Bovine lactoferrin is known for its immunomodulatory, anticancer, antibacterial, and iron-chelating properties. Therefore, the non-covalent binding of chlorogenic acid (CA) and bovine lactoferrin (BLF) with different concentrations under neutral conditions was studied. CA was grafted onto lactoferrin molecules by laccase catalysis, free radical grafting, and alkali treatment. The formation mechanism of non-covalent and covalent complexes of CA-BLF was analyzed by experimental test and theoretical prediction. Compared with the control BLF, the secondary structure of BLF in the non-covalent complex was rearranged and unfolded to provide more active sites, the tertiary structure of the covalent conjugate was changed, and the amino group of the protein participated in the covalent reaction. After adding CA, the covalent conjugates have better functional activity. These lactoferrin-polyphenol couplings can carry various bioactive compounds to create milk-based delivery systems for encapsulation.

Fabrication and characterization of electrospun catechins-loaded nanofibres for fortification of milk

Catechins in their free form are bitter in taste, and undergo deterioration and oxidation during processing and storage that limit their use as nutraceuticals in foods. Therefore, catechins were electrospun using zein as encapsulating polymer into nanofibres at 15, 18 and 21% w/w concentrations, 16, 20 and 24 kV applied voltage and 0.5 and 1.0 mL/h feed rate. The electrospinning conditions were optimized using Taguchi L18 (21 × 32) design. Encapsulation efficiency as high as 92.8% and mean fibre diameter as low as 95.2 nm were obtained at 18% concentration of zein, 0.5 mL/h feed rate and 20 kV applied voltage. Scanning electron and atomic force micrographs revealed that the nanofibres produced at zein concentration of 18% and above were clean and beadfree, with cylindrical morphology and non-porous topography. The hydrodynamic diameter, zeta potential and polydispersity index of catechins-loaded nanofibres at optimized conditions were 172.3 nm, -26.3 mV and 0.15. FTIR spectroscopy and X-ray diffractometry confirmed that catechins were encapsulated within the nanofibres. The catechins got released from loaded nanofibres in a controlled and sustained manner, while their antioxidant property was retained. The physico-chemical and sensory qualities of milk were not affected after fortification with catechins-loaded nanofibres.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05891-0.

Interactions between proteins and phenolics: effects of food processing on the content and digestibility of phenolic compounds

Phenolic compounds have recently become one of the most interesting topics in different research areas, especially in food science and nutrition due to their health-promoting effects. Phenolic compounds are found together with macronutrients and micronutrients in foods and within several food systems. The coexistence of phenolics and other food components can lead to their interaction resulting in complex formation. This review article aims to cover the effects of thermal and non-thermal processing techniques on the protein-phenolic interaction especially focusing on the content and digestibility of phenolics by discussing recently published research articles. It is clear that the processing conditions and individual properties of phenolics and proteins are the most effective factors in the final content and intestinal fates of phenolic compounds. Besides, thermal and non-thermal treatments, such as high-pressure processing, pulsed electric field, cold plasma, ultrasonication, and fermentation may induce alterations  in those interactions. Still, new investigations are required for different food processing treatments by using a wide range of food products to enlighten new functional and healthier food product design, to provide the optimized processing conditions of foods for obtaining better quality, higher nutritional properties, and health benefits. © 2024 Society of Chemical Industry.

Interfacing β-casein - Phenolic compound interactions via molecular dynamics simulations with diffusion kinetics in delivery vehicles

The effect that protein-bioactive interactions may have on diffusion kinetics in foods and nutraceuticals was investigated by examining the diffusion kinetics of phenolic compounds (ferulic acid and epicatechin) of varying size, in the presence and absence of bovine β-casein. In the presence of the protein, the diffusion rate for ferulic acid and epicatechin was shown to decrease from 2.76 × 10-11 and 1.33 × 10-11 to 8.51 × 10-12 and 1.00 × 10-12 m2/s, respectively. The magnitude of the decrease in diffusion rate appears to be governed by interaction strength, with pulling simulations and umbrella sampling determining binding energies of -4.6 and -6.7 kcal mol-1 for protein-ferulic acid and protein-epicatechin interactions. This outcome indicates that dissociation of the bioactive from the delivery matrix may be the rate limiting process for diffusion in low solid systems. This work offers valuable insights for the use of pulling/umbrella simulations in understanding the impact of interactions on diffusion in foods and nutraceuticals.

Bioaccessibility and antioxidant capacity of kefir-based smoothies fortified with kale and spinach after in vitro gastrointestinal digestion

The kefir-based smoothies with kale and spinach were designed as a ready-to-drink and innovative functional snack. Microbiological, physicochemical, as well as pre- and postgastrointestinal total antioxidant capacity (TAC; CUPRAC, DPPH, and FRAP) analyses were conducted. It was determined that the kefir-based smoothies with vegetables had higher ash, carbohydrate, and dietary fiber values. Fructose and glucose contents of smoothy with kale were high, while smoothy with spinach included high sucrose and maltose. The microbiology results revealed that kefir-based vegetable smoothies had minimum Lactobacillaceae viability (>log 7 cfu g-1) for the required functional effect after 14-day storage. Moreover, the addition of kale significantly increased (p < .01) the level of initial TAC (CUPRAC, DPPH, and FRAP) and total phenolic content (TPC) values. After in vitro gastric digestion analysis, smoothie with spinach demonstrated higher TAC and TPC values and the control sample had higher TAC and TPC values compared with a predigestion step. It was found that in vitro intestinal DPPH values were higher for the sample with spinach samples, while the sample with kale had the highest FRAP values. It was also found that the bioaccessibility indexes of plain kefir were determined to be the highest in both in vitro gastric and intestinal procedures. The present study provided novel insights into the in vitro digestion properties of kefir fortified with vegetables. Nevertheless, further studies are needed to identify the functional properties of the milk and plant matrices mixture using in vitro and in vivo trials.

Production of Acid and Rennet-Coagulated Cheese Enriched by Olive (Olea europaea L.) Leaf Extract-Determining the Optimal Point of Supplementation and Its Effects on Curd Characteristics

This study investigated the potential of olive leaf extract (OLE), as a functional ingredient, to improve cheese properties, because it is rich in phenols. Milk and dairy products are poor in phenolic compounds. The main objective was to determine the most effective coagulation method and timing of OLE supplementation to maximize retention in the cheese matrix. Experimental cheeses were produced using the rennet and acid coagulation methods, with OLE added either directly to the cheese milk or to the curd phase. Three OLE effective concentrations corresponding to 25%, 50%, and 75% inhibition of DPPH reagent (EFC25, EFC50, and EFC75, respectively) were added, i.e., 11.5 mg GAE L-1, 16.6 mg GAE L-1, and 26.3 mg GAE L-1, respectively. The results showed that OLE significantly increased the concentration of total phenols, total flavonoids, and antioxidant activity in all cheese samples and in the residual whey, especially at higher effective concentrations (EFC 50 and EFC 75). Rennet-coagulated cheese to which OLE was added prior to coagulation (EM 25, EM 50, EM 75) exhibited higher hardness, gumminess, and chewiness but lower elasticity, suggesting alterations in the paracasein matrix. OLE did not adversely affect acidity, water activity, or cheese yield. However, higher EFC resulted in significant colour changes (∆E* > 3.0). In conclusion, the enrichment of cheesemaking milk with OLE and the application of the rennet coagulation method are the most suitable to optimise the production of OLE-enriched cheese. This research shows the potential to improve the nutritional value of cheese while maintaining its desired characteristics.

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.

Freeze-dried persimmon peel: A potential ingredient for functional ice cream

The peels are considered part of waste products, which are generally discarded. The use of persimmon peel is associated with its phenolic content, dietary fibers, minerals, and pectins. The main objective of this study was to evaluate changes in antioxidant activity, total phenolic contents (TPC), and color parameters of persimmon peels after freeze drying (-85 °C for 24h), vacuum oven drying (45 °C for 12h), oven drying (50 °C for 12h) and microwave oven drying treatment (900W for 10s). In the next step, the functional ice cream was prepared and studied by adding dried persimmon peel powder (DPPP). Various properties of the resulting ice cream at 4 levels of DPPP addition were investigated. The results showed that the highest value of L*,a*,and b* parameters were in the freeze-dried sample. There was a significant difference in the TPC of samples that dried by different methods (p < 0.05). The highest amount of TPC was observed in the freeze-dried sample (673 ± 2.0 mgGAE/100g) and the lowest one was observed in the oven-dried sample (352 ± 0.5 mgGAE/100g). The highest value for IC50 (concentration of the antioxidant compound that is necessary for the DPPH radical concentration to reach 50 % of the initial value) was in the sample dried in the oven, following the vacuum oven, microwave, and the lowest value was in the freeze-dried sample. DPPP produced by the freeze-drying method was applied in ice cream formulation at different levels (0-3 %wt.). By increasing the amount of DPPP from 0 to 3 %, the overrun and L* decreased and a*, b*, hardness, and melting resistance of ice cream increased significantly (p < 0.05). Based on our findings, DPPP has the potential to be applied as an added-value ingredient in the ice cream industry to improve the functional characteristics of its products.

Bioactive Dairy-Fermented Products and Phenolic Compounds: Together or Apart

Fermented dairy products (e.g., yogurt, kefir, and buttermilk) are significant in the dairy industry. They are less immunoreactive than the raw materials from which they are derived. The attractiveness of these products is based on their bioactivity and properties that induce immune or anti-inflammatory processes. In the search for new solutions, plant raw materials with beneficial effects have been combined to multiply their effects or obtain new properties. Polyphenols (e.g., flavonoids, phenolic acids, lignans, and stilbenes) are present in fruit and vegetables, but also in coffee, tea, or wine. They reduce the risk of chronic diseases, such as cancer, diabetes, or inflammation. Hence, it is becoming valuable to combine dairy proteins with polyphenols, of which epigallocatechin-3-gallate (EGCG) and chlorogenic acid (CGA) show a particular predisposition to bind to milk proteins (e.g., α-lactalbumin β-lactoglobulin, αs1-casein, and κ-casein). Reducing the allergenicity of milk proteins by combining them with polyphenols is an essential issue. As potential 'metabolic prebiotics', they also contribute to stimulating the growth of beneficial bacteria and inhibiting pathogenic bacteria in the human gastrointestinal tract. In silico methods, mainly docking, assess the new structures of conjugates and the consequences of the interactions that are formed between proteins and polyphenols, as well as to predict their action in the body.

Molecular insight into binding behavior of caffeine with lactoferrin: Spectroscopic, molecular docking, and simulation study

The majority of bioactive substances in the human diet come from polyphenols. Here, we use spectroscopy, molecular docking, molecular dynamics simulations, and in vitro digestion to look at the relationship between caffeine (CAF) and bovine lactoferrin (BLF). The correlation analysis of the CAF-BLF fluorescence quenching process revealed that the reaction was spontaneous and that the CAF-BLF fluorescence quenching process may have been static. The predominant intrinsic binding forces were hydrogen bonds and van der Waals forces, which were also supported by molecular docking and molecular dynamics simulations. Through Fourier infrared and circular dichroism spectroscopy experiments, it was found that CAF changed the secondary structure of BLF and might bind to the hydrophobic amino acids of BLF. Compared with BLF, CAF-BLF showed inhibitory effects on digestion in simulated in vitro digestion. It will be helpful to better understand the interaction between CAF and BLF and provide the basis for the development of innovative dairy products.

Regulation Mechanism of Phenolic Hydroxyl Number on Self-Assembly and Interaction between Edible Dock Protein and Hydrophobic Flavonoids

In this study, galangin (Gal), kaempferol (Kae), quercetin (Que), and myricetin (Myr) were chosen as the representative flavonoids with different phenolic hydroxyl numbers in the B-ring. The edible dock protein (EDP) was chosen as the new plant protein. Based on this, the regulation mechanism of the phenolic hydroxyl number on the self-assembly behavior and molecular interaction between EDP and flavonoid components were investigated. Results indicated that the loading capacity order of flavonoids within the EDP nanomicelles was Myr (10.92%) > Que (9.56%) > Kae (6.63%) > Gal (5.55%). Moreover, this order was consistent with the order of the hydroxyl number in the flavonoid's B ring: Myr (3) > Que (2) > Kae (1) > Gal (0). The micro morphology exhibited that four flavonoid-EDP nanomicelles had a core-shell structure. In the meantime, the EDP encapsulation remarkably improved the flavonoids' water solubility, storage stability, and sustained release characteristics. During the interaction of EDP and flavonoids, the noncovalent interactions including van der Waals forces, hydrophobic interaction, and hydrogen bonding were the main binding forces. All of the results demonstrated that the hydroxyl number of bioactive compounds is a critical factor for developing a delivery system with high loading ability and stability.

Molecular dynamics simulation and in vitro digestion to examine the impact of theaflavin on the digestibility and structural properties of myosin

In this study, the interaction mechanism between theaflavin and myosin was explored to confirm the potential application of theaflavin in the meat protein system. A series of theaflavin and myosin solutions were prepared for spectroscopic studies. Spectroscopy results showed that theaflavins formed complexes with myosin and affected the microenvironment of myosin. And that addition of theaflavin cause static quenching of the myosin solution. Theaflavin and bovine myosin combined through hydrophobic interaction to form a complex, and gradually increasing the temperature was conducive to the binding of theaflavin and bovine myosin. This interaction results in a decrease in the α -helix content of myosin. Molecular dynamics simulation results confirmed that hydrophobic interactions and hydrogen bonds made the protein structure more compact and stable. And the in vitro digestion process was simulated. The results showed that the addition of theaflavin could significantly reduce the digestibility of myosin.

Interaction between Bovine Serum Albumin in Fresh Milk Cream and Encapsulated and Non-Encapsulated Polyphenols of Tamarillo

The fortification of dairy products with polyphenols is known to deliver additional health benefits. However, interactions between polyphenols may form complexes and cause a loss of functionality overall. This study aimed to investigate potential interactions between polyphenols, in encapsulated and non-encapsulated forms, extracted from tamarillo fruit and bovine serum albumin (BSA) from fresh milk cream. Fortification with tamarillo extract was made at 1, 2 and 3% (w/w), and the resultant changes in physicochemical, rheological and functional properties were studied. With an increase in fortification, the absorbance of protein-ligand in the protein-polyphenol complex was decreased by up to 55% and 67% in UV and fluorescent intensities, respectively. Chlorogenic acid and kaempferol-3-rutinoside were more affected than delphinidin-3-rutinoside and pelargonidin-3-rutinoside. Static quenching was the main mechanism in the fluorescence spectra. Tryptophan and tyrosine residues were the two major aromatic amino acids responsible for the interactions with BSA. There were at least three binding sites near the tryptophan residue on BSA. The rheological property remained unaffected after the addition of non-encapsulated tamarillo extracts. Antioxidant capacity was significantly decreased (p < 0.05) after the addition of encapsulated extracts. This may be explained by using a low concentration of maltodextrin (10% w/w) as an encapsulating agent and its high binding affinity to milk proteins.

Evaluation of in vitro whey protein digestibility in a protein-catechins model system mimicking milk chocolate: Interaction with flavonoids does not hinder protein bioaccessibility

Flavonoids are largely present in plant food such as cocoa and derived products. These compounds can interact with proteins inherently contained in the food matrix and/or the proteolytic enzymes involved in gastrointestinal digestion. The flavonoid/protein interaction might hamper protein bioaccessibility and digestibility, affecting the nutritional quality. However, information on the digestion fate of proteins in food matrices containing both proteins and flavonoids is limited. The aim of this work was to evaluate the interaction between proteins and flavonoids and verify the potential effects of this interaction on protein digestibility. Taking milk chocolate as model, first a simple whey proteins/catechins mixed system was evaluated, and then the effects on digestibility were also verified in a real sample of commercial milk chocolate. The effects of the catechins/whey proteins interaction in the model system were evaluated by optical and chiro-optical spectroscopy, outlining a slight protein structure modification upon interaction with catechins. The digestibility of the protein fraction both in the model system, with and without catechins, and also in milk chocolate, was then determined by the application of INFOGEST in vitro digestion method: the bioaccessibility was evaluated in terms of protein hydrolysis and protein solubilisation, and major peptides generated by the digestion were also determined by LC/HR-MS. Despite the slight interaction with proteins, flavonoids were found to not hinder nor modify protein solubilization, protein hydrolysis and peptide profile by digestive enzymes. Also protein digestibility in milk chocolate, evaluated by SDS-PAGE, was found to be complete. The present data clearly indicate that the interaction of the proteins with the flavonoids present in the cocoa matrix does not to affect protein bioaccessibility during digestion.

Interactions between tea polyphenols and nutrients in food

Tea polyphenols (TPs) are important secondary metabolites in tea and are active in the food and drug industry because of their rich biological activities. In diet and food production, TPs are often in contact with other food nutrients, affecting their respective physicochemical properties and functional activity. Therefore, the interaction between TPs and food nutrients is a very important topic. In this review, we describe the interactions between TPs and food nutrients such as proteins, polysaccharides, and lipids, highlight the forms of their interactions, and discuss the changes in structure, function, and activity resulting from their interactions.

Pulsed electric field improves the EGCG binding ability of pea protein isolate unraveled by multi-spectroscopy and computer simulation

Understanding molecular mechanisms during protein modification is critical for expanding the application of plant proteins. This study investigated the conformational change and molecular mechanism of pea protein isolate (PPI) under pulsed electric field (PEF)-assisted (-)-Epigallocatechin-Gallate (EGCG) modification. The flexibility of PPI was significantly enhanced after PEF treatment (10 kV/cm) with decrease (23.25 %) in α-helix and increase (117.25 %) in random coil. The binding constant and sites of PEF-treated PPI with EGCG were increased by 2.35 times and 10.00 % (308 K), respectively. Molecular docking verified that PEF-treated PPI had more binding sites with EGCG (from 4 to 10). The number of amino acid residues involved in hydrophobic interactions in PEF-treated PPI-EGCG increased from 5 to 13. PEF-treated PPI-EGCG showed a significantly increased antioxidant activity compared to non-PEF-treated group. This work revealed the molecular level of PEF-assisted EGCG modification of PPI, which will be significant for the application of PPI in food industry.

Mango (Mangifera indica L.) young leaf extract as brine additive to improve the functional properties of mozzarella cheese

Mango (Mangifera indica L.) has been an important plant in traditional medicine for over 4000 years, probably because of its remarkable antioxidant activity. In this study, an aqueous extract from mango red leaves (M-RLE) was evaluated for its polyphenol profile and antioxidant activity. The extract was used as brine replacement (at 5%, 10% and 20% v/v) in fresh mozzarella cheese for improving its functional properties. During storage (12 d at 4 ± °C), compositional analysis performed on mozzarella has shown a progressive increase of iriflophenone 3-C-glucoside and mangiferin, the compounds most present in the extract, with a noticeable preference for the benzophenone. At the same time, the antioxidant activity of mozzarella peaked at 12 d of storage, suggesting a binding action of that matrix for the M-RLE bioactive compounds. Moreover, the use of the M-RLE has not negatively influenced the Lactobacillus spp. population of mozzarella, even at the highest concentration.

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.

Cocoa polyphenols and milk proteins: covalent and non-covalent interactions, chocolate process and effects on potential polyphenol bioaccesibility

In this study, we discussed covalent and non-covalent reactions between cocoa polyphenols and proteins (milk and cocoa) and the possible effects of these reactions on their bioaccessibility, considering environmental and processing conditions. Better insight into these interactions is crucial for understanding the biological effects of polyphenols, developing nutritional strategies, and improving food processing and storage. Protein-polyphenol reactions affect the properties of the final product and can lead to the formation of various precursors at various stages in the manufacturing process, such as fermentation, roasting, alkalization, and conching. Due to the complex composition of the chocolate and the various technological processes, comprehensive food profiling strategies should be applied to analyze protein-polyphenol covalent reactions covering a wide range of potential reaction products. This will help to identify potential effects on the bioaccessibility of bioactive compounds such as low-molecular-weight peptides and polyphenols. To achieve this, databases of potential reaction products and their binding sites can be generated, and the effects of various process conditions on related parameters can be investigated. This would then allow to a deeper insight into mechanisms behind protein-polyphenol interactions in chocolate, and develop strategies to optimize chocolate production for improved nutritional and sensory properties.

Improvement of the emulsifying properties of mixed emulsifiers by optimizing ultrasonic-assisted processing

Optimizing ultrasound (ULD)-assisted flavonoid modification is an important component of enhancing its application potential. In this work, diverse flavonoids, such as quercetin (Que), apigenin (Api), and morin (Mor), were used to modify protein in myofibrillar protein (MP)/cellulose nanocrystal (CN) complexes using ULD-assisted method. Compared with the MP/CNs group, the triiodide contents of MP-Que/CNs, MP-Api/CNs, and MP-Mor/CNs increased by 1175.84%, 479.05%, and 2281.50% respectively. The findings revealed that the actual intensity of ULD was drastically reduced by the molecular weight decrease of these flavonoids. For olive oil emulsions prepared with mixed emulsifiers, the low interfacial diffusion rates (0.03 mN·m·s-1/2) and weak emulsifying activity (8.33 m2/g) of the MP/CN complexes were significantly improved by the flavonoids after ULD-assisted treatment. Notably, the emulsions prepared using MP-Api/CNs contained smaller oil droplets and exhibited better emulsifying properties, compared to emulsions prepared with MP-Mor/CNs or MP-Que/CNs. This study is essential for ULD-assisted treatment since the processing impact may be increased by choosing the most suitable flavonoid.

Assessment of Various Food Proteins as Structural Materials for Delivery of Hydrophobic Polyphenols Using a Novel Co-Precipitation Method

In this study, sodium caseinate (NaCas), soy protein isolate (SPI), and whey protein isolate (WPI) were used as structural materials for the delivery of rutin, naringenin, curcumin, hesperidin, and catechin. For each polyphenol, the protein solution was brought to alkaline pH, and then the polyphenol and trehalose (as a cryo-protectant) were added. The mixtures were later acidified, and the co-precipitated products were lyophilized. Regardless of the type of protein used, the co-precipitation method exhibited relatively high entrapment efficiency and loading capacity for all five polyphenols. Several structural changes were seen in the scanning electron micrographs of all polyphenol-protein co-precipitates. This included a significant decrease in the crystallinity of the polyphenols, which was confirmed by X-ray diffraction analysis, where amorphous structures of rutin, naringenin, curcumin, hesperidin, and catechin were revealed after the treatment. Both the dispersibility and solubility of the lyophilized powders in water were improved dramatically (in some cases, >10-fold) after the treatment, with further improvements observed in these properties for the powders containing trehalose. Depending on the chemical structure and hydrophobicity of the tested polyphenols, there were differences observed in the degree and extent of the effect of the protein on different properties of the polyphenols. Overall, the findings of this study demonstrated that NaCas, WPI, and SPI can be used for the development of an efficient delivery system for hydrophobic polyphenols, which in turn can be incorporated into various functional foods or used as supplements in the nutraceutical industry.

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.

Application of encapsulated Indigofera tinctoria extract as a natural antioxidant and colorant in ice cream

In this study, Indigofera tinctoria extract (ITLE) along with maltodextrin in different concentrations was encapsulated using a freeze dryer, and some physicochemical properties were measured. Powder containing 30% maltodextrin was selected as the optimal powder for use in ice-cream production in four levels (0%-1.8%), and some quality parameters were examined. The results showed that with increasing the carrier concentration, moisture content, aw, solubility, a*, and b* of the powders decreased; bulk density, tapped density, and L* did not change significantly; total phenolic content and antioxidant activity of powders also increased significantly (p < .05). Addition of encapsulated ITLE to the ice cream caused a significant decrease in L*, b*, and melting rate, a significant increase in a*, overrun, and hardness of the samples and no change in the viscosity of the ice-cream mix (p < .05). Ice cream containing 1.2% encapsulated ITLE had higher sensory acceptance than other levels following control ice cream. The results of this study showed that ITLE can be used as a desirable additive in the production as a natural antioxidant and color agent.

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.

Phenolic compounds in walnut pellicle improve walnut (Juglans regia L.) protein solubility under pH-shifting condition

This study focused on the interaction of walnut protein with phenolic extracts of walnut pellicle (PEWP) under alkaline condition, leading to enhancement of protein solubility under neutral condition. First, the change of PEWP under alkaline condition was determined by RP-HPLC and mass spectrometry, and the results showed that most ellagitannins in PEWP could be retained under alkaline condition within 3 h. Interaction between PEWP and walnut protein under pH-shifting condition resulted in the remarkable increase of protein solubility (above 90%) at neutral pH. The results from SDS-PAGE and SEC showed that the improved solubility lied in the formation of large and soluble protein aggregates due to the covalent interaction among walnut protein and polyphenols. A significant change in tertiary structure of protein-phenolic complex was witnessed by fluorescence spectrum and near-UV circular dichroism. Meanwhile, walnut protein-polyphenol interaction led to a slight increase in β-turn while a slight decrease in β-sheet. Combined with amino acid composition, it could be illustrated that the covalent bonding for walnut protein with polyphenol mainly occurred at Lysine residues.

Current Research on the Extraction, Functional Properties, Interaction with Polyphenols, and Application Evaluation in Delivery Systems of Aquatic-Based Proteins

Globally, aquatic processing industries pay great attention to the production of aquatic proteins for the fulfillment of the nutritive requirements of human beings. Aquatic protein can replace terrestrial animal protein due to its high protein content, complete amino acids, unique flavor, high quality and nutritional value, and requirements of religious preferences. Due to the superior functional properties, an aquatic protein based delivery system has been proposed as a novel candidate for improving the absorption and bioavailability of bioactive substances, which might have potential applications in the food industry. This review outlines the extraction techniques for and functional properties of aquatic proteins, summarizes the potential modification technologies for interaction with polyphenols, and focuses on the application of aquatic-derived protein in delivery systems as well as their interaction with the gastrointestinal tract (GIT). The extraction techniques for aquatic proteins include water, salt, alkali/acid, enzyme, organic solvent, and ultrasound-assisted extraction. The quality and functionality of the aquatic proteins could be improved after modification with polyphenols via covalent or noncovalent interactions. Furthermore, some aquatic protein based delivery systems, such as emulsions, gels, films, and microcapsules, have been reported to enhance the absorption and bioavailability of bioactive substances by in vitro GIT, cell, and in vivo animal models. By promoting comprehensive understanding, this review is expected to provide a real-time reference for developing functional foods and potential food delivery systems based on aquatic-derived proteins.

Ultrasound-Assisted Encapsulation of Anthraquinones Extracted from Aloe-Vera Plant into Casein Micelles

Aloe-vera extracted anthraquinones (aloin, aloe-emodin, rhein) possess a wide range of biological activities, have poor solubility and are sensitive to processing conditions. This work investigated the ultrasound-assisted encapsulation of these extracted anthraquinones (AQ) into casein micelles (CM). The particle size and zeta potential of casein micelles loaded with aloin (CMA), aloe-emodin (CMAE), rhein (CMR) and anthraquinone powder (CMAQ) ranged between 171–179 nm and −23 to −17 mV. The AQ powder had the maximum encapsulation efficiency (EE%) (aloin 99%, aloe-emodin 98% and rhein 100%) and encapsulation yield, while the whole leaf Aloe vera gel (WLAG) had the least encapsulation efficiency. Spray-dried powder (SDP) and freeze-dried powder (FDP) of Aloe vera showed a significant increase in size and zeta potential related to superficial coating instead of encapsulation. The significant variability in size, zeta potential and EE% were related to anthraquinone type, its binding affinity, and its ratio to CM. FTIR spectra confirmed that the structure of the casein micelle remained unchanged with the binding of anthraquinones except in casein micelles loaded with whole-leaf aloe vera gel (CMWLAG), where the structure was deformed. Based on our findings, Aloe vera extracted anthraquinones powder (AQ) possessed the best encapsulation efficiency within casein micelles without affecting its structure. Overall, this study provides new insights into developing new product formulations through better utilization of exceptional properties of casein micelles.

Explore the Interaction between Ellagic Acid and Zein Using Multi-Spectroscopy Analysis and Molecular Docking

With the increasing interest in value-added maize products, the interaction of zein with bioactive molecules to become more nutritional and beneficial to human health has gained a lot of attention. To broaden the application of ellagic acid (EA) in maize flour products, we investigated the interaction between zein and EA. The fluorescence quenching type of zein interacting with EA was mainly static quenching through hydrophobic interaction, as demonstrated by quenching behavior modeling, and ultraviolet-visible spectroscopy confirmed the formation of zein–EA complexes. Synchronous fluorescence spectroscopy showed that EA reduced the polarity of zein around tyrosine residues, which were exposed to a more hydrophobic microenvironment. Meanwhile, circular dichroism suggested that EA noticeably changed the secondary structure of zein, which was mainly reflected in the increase of α-helix and β-sheet content and the decrease of random coil content. Finally, the molecular docking simulation found that zein could have five active sites binding to EA and there was hydrogen bond interaction besides hydrophobic interaction. The findings of this study provided a basis for a theory for the interaction mechanism between zein and EA, which could be essential for developing value-added plant-derived protein products using EA as a functional component.

Compositional Changes in the Extra Virgin Olive Oil Used as a Medium for Cheese Preservation

The influence of semi-hard (C1), hard (C2), and soft whey cheese (C3) immersed in extra virgin olive oil (EVOO) on its oxidative and hydrolytic parameters, fatty acids, and phenolic composition during two months of simultaneous storage was investigated. Accelerated hydrolytic and oxidative degradation was noted in EVOO stored with the immersed cheese compared to control oil. Oxidation indicator (K232), myristic (C 14:0), and trans-oleic fatty acid (C18:1t) exceeded the prescribed limit for the EVOO category in oils stored with immersed C1 and C2, which indicated that standard analytical parameters are ineffective as tools to examine the declared quality and authenticity of such topping oils. The noted changes in fatty acid profile were primarily prescribed to the migration of fats. C1 and C2 influenced a comparable reduction in EVOO total identified phenolic content (−92.1% and −93.5%, respectively), despite having a different content of total proteins and moisture, whereas C3 influenced a slightly lower reduction (−85.0%). Besides the protein profile, other cheese compounds (e.g., moisture, carbohydrates) have been shown to have a considerable role in the development of the EVOO phenolic profile. Finally, compositional changes in EVOO used as a medium for cheese preservation are under significant influence of the cheese’s chemical composition.

Impact of non-covalent bound polyphenols on conformational, functional properties and in vitro digestibility of pea protein

This study investigated the effects of the non-covalent interaction of pea protein isolate (PPI) with epigallocatechin-3-gallate (EGCG), chlorogenic acid (CA) and resveratrol (RES) on the structural and functional properties of proteins. The conformational changes of the protein structure with EGCG, CA and RES were analyzed using fourier transform infrared spectroscopy. Polyphenols strongly quenched the intrinsic fluorescence of PPI mainly through static quenching. The main interaction force was hydrogen bonding and van der Waals forces for PPI-EGCG, the main interaction force of PPI-CA complex was electrostatic interaction, while RES and PPI were bound by hydrophobic interaction. Free sulfhydryl groups and surface hydrophobicity significantly decreased in PPI after binding with phenolic compounds. The presence of EGCG, CA and RES enhanced the emulsification, foaming and in vitro digestibility of PPI. These results illustrate the potential applications of PPI-polyphenol complexes in food formulations.

Seaweed Phenolics as Natural Antioxidants, Aquafeed Additives, Veterinary Treatments and Cross-Linkers for Microencapsulation

Driven by consumer demand and government policies, synthetic additives in aquafeed require substitution with sustainable and natural alternatives. Seaweeds have been shown to be a sustainable marine source of novel bioactive phenolic compounds that can be used in food, animal and aqua feeds, or microencapsulation applications. For example, phlorotannins are a structurally unique polymeric phenolic group exclusively found in brown seaweed that act through multiple antioxidant mechanisms. Seaweed phenolics show high affinities for binding proteins via covalent and non-covalent bonds and can have specific bioactivities due to their structures and associated physicochemical properties. Their ability to act as protein cross-linkers means they can be used to enhance the rheological and mechanical properties of food-grade delivery systems, such as microencapsulation, which is a new area of investigation illustrating the versatility of seaweed phenolics. Here we review how seaweed phenolics can be used in a range of applications, with reference to their bioactivity and structural properties.