Protein-polyphenol functional ingredients: The foaming properties of lactoferrin are enhanced by forming complexes with procyanidin

Interactions of different polyphenols with wheat germ albumin and globulin: Alterations in the conformation and emulsification properties of proteins

In this study, chlorogenic acid (CA), piceatannol (PIC), epigallocatechin-3-gallate (EGCG) and ferulic acid (FA) was selected to explore the influence of polyphenol on the structural properties of wheat germ albumin (WGA) and wheat germ globulin (WGG). The emulsifying properties of the emulsions prepared by WGA-EGCG complex were also evaluated. The results indicated that all polyphenols could significantly enhance the antioxidant capacity of WGA and WGG. In particular, EGCG increased the ratio of random coil in WGA and WGG, resulting in protein unfolding and shifting from an order to disorder structure. In addition, lipid oxidation and protein oxidation of the soybean oil emulsion was significantly slowed down by WGA-EGCG. The stability of the emulsions under various environmental stress and the storage time was significantly improved by WGA-EGCG. These findings can provide a reference for expanding the application of wheat germ protein in food industry.

Application of soy protein isolate-naringenin complexes as fat replacers in low-fat cream: Based on protein conformational changes, aggregation states and interfacial adsorption behavior

In this study, changes in the structural and functional properties of soybean protein isolate (SPI)-naringenin (NG) complexes under different amounts of naringenin treatments were explored, elucidating the effect of the complexes as fat replacers at the 15 % substitution level on the properties of low-fat cream. Finally, the correlation between the structure and function of the complex and the properties of low-fat cream was further analyzed. The addition of NG promotes the increase of SPI aggregation and particle size, and reduces the interfacial tension of the complex. Meanwhile, at the mass ratio of 48:3, NG and SPI formed a dendritic network structure suitable for stabilizing cream. The fat properties of cream indicate that low-fat creams stabilized by appropriate proportions of SPI-NG complexes displayed small and dense fat crystal network structures. In addition, low-fat cream stabilized by the SPI-NG complexes have improved whipping time, overrun, firmness, storage stability and rheological properties compared to natural SPI. It is worth noting that the overall quality of the cream stabilized by the SPI-NG complex with a mass ratio of 48:3 was almost close to that of full-fat cream. Therefore, this study promotes the potential applications of protein-polyphenol complexes as fat replacers in the food industry.

Modification mechanism of soybean protein isolate-soluble soy polysaccharide complex by EGCG through covalent and non-covalent interaction: Structural, interfacial, and functional properties

Soybean protein isolate was modified with polysaccharides and polyphenols to prepare a natural emulsifier with antioxidant capacity. Physicochemical, structural, interfacial, and functional properties of SPI-SSPS complex were investigated after covalent and non-covalent interacted with EGCG. SPI-SSPS-EGCG ternary complex with low EGCG concentrations (0.0625 and 0.125 mg/mL) showed a significant increase in absolute potential value and a decrease in turbidity. EGCG destroyed the original rigid structure of SPI-SSPS complex, and the covalent complexes had an ordered structure, while the non-covalent interaction resulted in disordered. The ternary complex with high EGCG concentrations (0.25 and 0.5 mg/mL) exhibited stronger EGCG binding capacity and lower surface hydrophobicity, which in turn affected its interfacial properties. The EAI and ESI of SPI-SSPS-EGCG covalent complex increased significantly, while the non-covalent complex had a significant change in EAI but no significant change in ESI with increasing EGCG concentration. The ternary complex showed significantly enhanced antioxidant capacity. The SPI-SSPS-EGCG ternary complex, with excellent antioxidant capacity and emulsifying property, making it suitable for emulsion delivery systems.

Complexation of bovine lactoferrin with selected phenolic acids via noncovalent interactions: Binding mechanism and altered functionality

Noncovalent interactions of 4 selected phenolic acids, including gallic acid (GA), caffeic acid (CA), chlorogenic acid (CGA), and rosmarinic acid (RA) with lactoferrin (LF) were investigated. Compound combined with LF in the binding constant of CA > GA > RA > CGA, driven by van der Waals and hydrogen bonding for GA, and hydrophobic forces for others. Conformation of LF was affected at secondary and ternary structure levels. Molecular docking indicated that GA and CA located in the same site near the iron of the C-lobe, whereas RA and CGA bound to the C2 and N-lobe, respectively. Significantly enhanced antioxidant activity of complexes was found compared with pure LF, as demonstrated by 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azinobis(2-ethylbenzothiazoline-6-sulfonate) (ABTS), and ferric reducing antioxidant power (FRAP) models. Caffeic acid, CGA, and RA significantly decreased the emulsifying stability index and improved foam ability of LF, and the effect of CA and RA was the most remarkable, respectively.

Non-covalent interactions between rice protein and three polyphenols and potential application in emulsions

Rice protein (RP) and polyphenols are often used in functional foods. This study investigated the non-covalent interactions between RP and three polyphenols (curcumin, CUR; quercetin, QUE; resveratrol, RES) and used the complexes as emulsifiers to create emulsions. Three polyphenols interacted with RP to varying extents, with QUE showing the greatest binding affinity and inducing the greatest alterations in its secondary structure. Molecular docking analysis elucidated the driving forces between them including hydrophobic interactions, hydrogen bonding, and van der Waals forces. Combination with QUE or RES induced structural changes of RP, increasing particle size of complexes. The synergistic effect of polyphenols and protein also enhanced radical scavenging capacity of complexes. Compared to pure protein, all complexes successfully created emulsions with smaller particle size (378-395 nm vs. 470 nm), higher absolute potential (37.43-38.26 mV vs. 35.62 mV), and greater lipid oxidation stability by altering protein conformation.

Hydroxyl group-induced enhancement of antioxidant activity of resveratrol over pterostilbene by binding to lactoferrin

The reduced antioxidant capacity of trans-resveratrol (Res) than the second generation of Res, namely pterostilbene (Pte), severely prohibits its in-depth intriguing radical-scavenging applications in food formulations. Herein, a unique chemical structure-dependent strategy was proposed to specifically enhance the radical scavenging activity of Res over Pte, relying on the two more hydroxyl groups on the A-benzene ring of Res, thus facilitating its binding with lactoferrin (LF) to form stable complexes through more hydrogen bonds. We prepared LF-Res and LF-Pte complexes, revealed their binding mechanisms by multispectral analysis and molecular docking/dynamics simulations, further evaluated their antioxidant properties via ABTS and DPPH assays and a model of inhibiting apple browning, eventually elucidated their structure-binding-property relationships. This contribution offers a new approach to restore the antioxidant capability of Res, also paves the way to precisely regulate the fascinating bioactivities of hydrophobic compounds by protein-binding in a chemical structure-, especially hydroxyl group-dependent manner.

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

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

Stability, Digestion, and Cellular Transport of Soy Isoflavones Nanoparticles Stabilized by Polymerized Goat Milk Whey Protein

Soy isoflavones (SIF) are bioactive compounds with low bioavailability due to their poor water solubility. In this study, we utilized polymerized goat milk whey protein (PGWP) as a carrier to encapsulate SIF with encapsulation efficiency of 89%, particle size of 135.53 nm, and zeta potential of -35.16 mV. The PGWP-SIF nanoparticles were evaluated for their stability and in vitro digestion properties, and their ability to transport SIF was assessed using a Caco-2 cell monolayer model. The nanoparticles were resistant to aggregation when subjected to pH changes (pH 2.0 to 8.0), sodium chloride addition (0-200 mM), temperature fluctuations (4 °C, 25 °C, and 37 °C), and long-term storage (4 °C, 25 °C, and 37 °C for 30 days), which was mainly attributed to the repulsion generated by steric hindrance effects. During gastric digestion, only 5.93% of encapsulated SIF was released, highlighting the nanoparticles' resistance to enzymatic digestion in the stomach. However, a significant increase in SIF release to 56.61% was observed during intestinal digestion, indicating the efficient transport of SIF into the small intestine for absorption. Cytotoxicity assessments via the MTT assay showed no adverse effects on Caco-2 cell lines after encapsulation. The PGWP-stabilized SIF nanoparticles improved the apparent permeability coefficient (Papp) of Caco-2 cells for SIF by 11.8-fold. The results indicated that using PGWP to encapsulate SIF was an effective approach for delivering SIF, while enhancing its bioavailability and transcellular transport.

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

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

Ultrasound and enzyme assisted preparation of novel lactoferrin-cereal phenolic acid conjugates: structural, physicochemical and functional properties

The effects of covalent binding of protocatechuic acid (PA) and gallic acid (GA) to lactoferrin (LF) on the structure, functional, and antioxidant properties of the protein conjugate were investigated. These protein-phenolic conjugates were produced by laccase cross-linking and ultrasound-assisted free radical grafting, which were characterized using turbidity, particle size, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analyses. Structural changes in conjugates were monitored by endogenous fluorescence spectroscopy, fourier transform infrared spectroscopy (FTIR), and circular dichroism (CD). The antioxidant capacities and pH stability were determined using DPPH, ABTS, FRAP, and potentiometric analysis. The enzymatic cross-linking and free radical grafting yielded LF-PA/GA conjugates with altered hydrodynamic diameter and zeta-potential. Spectroscopic and chromatographic analyses revealed that binding to PA/GA altered the molecular structure of LF, with a decrease in LF isoelectric point post binding to PA/GA, without affecting antioxidant activities. In conclusion, LF-PA/GA conjugates present potential applications in the food industry.

Interactions between humulinone derived from aged hops and protein Z enhance the foamability and foam stability

Foam is one of the important characteristics of beer, including foamability, foam stability and foam texture. Protein Z (PZ) is considered to be an important component of beer foam. In this study, the interaction between PZ and humulinone, a widespread compound in aged hops, and the effect on foam properties of PZ were investigated. The fluorescence spectra showed that the stoichiometric ratio of humulinone to PZ was 4.25 ± 0.48: 1, and the binding constant was (1.64 ± 0.17) × 105 M-1. MD and FTIR results showed that the main force of interaction between PZ and humulinone was hydrogen bond, and the possible sites were Asn-37, Ser-292, Lys-290 and Pro-395. Moreover, the addition of humulinone greatly reduced the surface tension of PZ solution, and changed the secondary structure of PZ, which is beneficial for the foam stability. Under the influence of humulinone, the foamability, foam stability and foam texture of PZ all increased.

Whey protein isolate-resveratrol complex as a radical scavenging foaming ingredient with increased ultraviolet stability

Functional foaming food ingredients play a vital role in preparing healthcare foods, however, the weak foamability and low photostability of ingredients severely limit their further development. Herein, whey protein isolate-resveratrol complexes (WPI-RES) were fabricated to address these challenges. Multi-spectral analysis and molecular simulation results revealed the key driving forces of hydrogen bonding and hydrophobic interactions to promote the formation of WPI-RES complexes, leading to the enhanced foamability and emulsifying properties of WPI after binding with RES. Importantly, the robust radical scavenging activity of RES within WPI was maintained under UV light irradiation compared to that of free RES as identified by DPPH assay, which was presumably due to inhibited photoisomerization of RES after binding to WPI. This work provides a promising foaming ingredient with increased ultraviolet stability and radical scavenging activity, paves the way to develop stable health-promoting foaming food products.

Investigation of peanut allergen-procyanidin non-covalent interactions: Impact on protein structure and in vitro allergenicity

Interactions between plant polyphenols and food allergens may be a new way to alleviate food allergies. The non-covalent interactions between the major allergen from peanut (Ara h 2) with procyanidin dimer (PA2) were therefore characterized using spectroscopic, thermodynamic, and molecular simulation analyses. The main interaction between the Ara h 2 and PA2 was hydrogen bonding. PA2 statically quenched the intrinsic fluorescence intensity and altered the conformation of the Ara h 2, leading to a more disordered polypeptide structure with a lower surface hydrophobicity. In addition, the in vitro allergenicity of the Ara h 2-PA2 complex was investigated using enzyme-linked immunosorbent assay (ELISA) kits. The immunoglobulin E (IgE) binding capacity of Ara h 2, as well as the release of allergenic cytokines, decreased after interacting with PA2. When the ratio of Ara h 2-to-PA2 was 1:50, the IgE binding capacity was reduced by around 43 %. This study provides valuable insights into the non-covalent interactions between Ara h 2 and PA2, as well as the potential mechanism of action of the anti-allergic reaction caused by binding of the polyphenols to the allergens.

Ellagic acid-loaded soy protein isolate self-assembled particles: Characterization, stability, and antioxidant activity

The limited water solubility and bioactivity of lipophilic phytochemicals may be enhanced by delivery systems. Ellagic acid (EA) has antioxidant and anti-inflammatory properties, but low solubility and instability limit its use in the food industry. In this study, the pH-shift method was applied to encapsulate EA with soy protein isolate (SPI). The interaction, encapsulation, and protective potential of the EA-loaded soy SPI complexes (SPI-EA) were investigated. The fluorescence spectra results suggest that the reaction between SPI and EA is spontaneous, with hydrophobic interactions predominating. Binding of EA molecules quenches the intrinsic fluorescence of SPI, mainly static quenching, with a binding site involved in the binding process. The ultraviolet (UV)-visible spectroscopy of the SPI-EA complexes included the characteristic absorption peaks of both SPI and EA, and the scanning electron microscopy images further indicated that the EA had been successfully embedded in SPI. Fourier transform infrared spectroscopy illustrates that EA has significantly changed the secondary structure of the SPI, primarily in the form of a decreased content of α-helix structures and an increased content of β-sheet and random coil structures. The encapsulation efficiency of EA was concentration-dependent, up to 81.08%. The addition of EA reduces the size of SPI particles (d < 155 nm). In addition, the SPI-EA complex showed up to 81.05% and 96.46% 1,1-diphenyl-2-picrylhydrazyl and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging activity. TGA showed that the degradation temperature of SPI-EA complex could be extended up to 300°C. And by encapsulation of EA, the loss of EA under the action of UV light, heat treatment, and high concentration of salt ion sensitive environment can be reduced. PRACTICAL APPLICATION: Ellagic acid (EA), a natural bioactive with low water solubility and stability, can be enhanced by forming an inclusion complex with soy protein isolate (SPI). SPI-EA complex has broad potential applications in the food, beverage, and pharmaceutical industries. Multiple spectral analyses have contributed to our understanding of the formation and interaction mechanisms of the SPI-EA complex under pH-driven conditions. Stability assays have also aided in the development of dietary resources for EA.

Comparing the interactions of nitrendipine with lysozyme or human serum albumin and the effects of vitamin C and naringin on these interactions by spectroscopy and molecular docking methods

The interactions between drugs and proteins play a pivotal role in determining the pharmacological effects and disposition of drugs within the human body. This study focuses on exploring the interaction between nitrendipine and lysozyme/human serum albumin. Spectroscopic analysis indicated a compound static quenching, indicative of the formation of stable complexes between the drug and proteins. The addition of vitamin C or naringin resulted in a decrease of the binding constant between nitrendipine and lysozyme/human serum albumin. The presence of these compounds may disrupt the interactions between the drug and proteins, potentially leading to an increased concentration of free nitrendipine in the bloodstream. Nitrendipine binds more easily to human serum albumin at 310 K, and human serum albumin has an average binding site ratio with nitrendipine approximately 0.1 higher than that with lysozyme. Vitamin C has a greater impact on the binding constant of nitrendipine to human serum albumin and lysozyme. Compared to the binary system of proteins with the drug, the ternary system with the addition of vitamin C at 310 K reduces the binding constants of lysozyme and human serum albumin by 85%. In conclusion, this study explores the significance of considering drug-protein interactions in understanding drug behavior and potential drug-food interactions.

Unveiling the flavone-solubilizing effects of α-glucosyl rutin and hesperidin: probing structural differences through NMR and SAXS analyses

Flavonoids often exhibit broad bioactivity but low solubility and bioavailability, limiting their practical applications. The transglycosylated materials α-glucosyl rutin (Rutin-G) and α-glucosyl hesperidin (Hsp-G) are known to enhance the dissolution of hydrophobic compounds, such as flavonoids and other polyphenols. In this study, the effects of these materials on flavone solubilization were investigated by probing their interactions with flavone in aqueous solutions. Rutin-G and Hsp-G prepared via solvent evaporation and spray-drying methods were evaluated for their ability to dissolve flavones. Rutin-G had a stronger flavone-solubilizing effect than Hsp-G in both types of composite particles. The origin of this difference in behavior was elucidated by small-angle X-ray scattering (SAXS) and nuclear magnetic resonance analyses. The different self-association structures of Rutin-G and Hsp-G were supported by SAXS analysis, which proved that Rutin-G formed polydisperse aggregates, whereas Hsp-G formed core-shell micelles. The observation of nuclear Overhauser effects (NOEs) between flavone and α-glucosyl materials suggested the existence of intermolecular hydrophobic interactions. However, flavone interacted with different regions of Rutin-G and Hsp-G. In particular, NOE correlations were observed between the protons of flavone and the α-glucosyl protons of Rutin-G. The different molecular association states of Rutin-G or Hsp-G could be responsible for their different effects on the solubility of flavone. A better understanding of the mechanism of flavone solubility enhancement via association with α-glucosyl materials would permit the application of α-glucosyl materials to the solubilization of other hydrophobic compounds including polyphenols such as flavonoids.

Noncovalent Interaction of Lactoferrin with Epicatechin and Epigallocatechin: Focus on Fluorescence Quenching and Antioxidant Properties

Lactoferrin (LF) from bovine milk possesses antioxidant activity, immune regulatory and other biological activities. However, the effects of epicatechin (EC) and epigallocatechin (EGC) interacting with LF on the antioxidant activity of LF have not been investigated. Therefore, this study aimed to explore their interaction mechanism and the antioxidant activity of LF. UV spectra revealed that EGC (100 μM) induced a higher blue shift of LF at the maximum absorption wavelength than that of EC (100 μM). Fluorescence spectra results suggested that LF fluorescence was quenched by EC and EGC in the static type, which changed the polarity of the microenvironment around LF. The quenching constants Ksv (5.91 × 103-9.20 × 103) of EC-LF complexes at different temperatures were all higher than that (1.35 × 103-1.75 × 103) of the EGC-LF complex. EC could bind to LF via hydrophobic interactions while hydrogen bonding and van der Waals forces drove the binding of EGC to LF. Both the EC-LF complex and EGC-LF complex could bind to LF with one site. EGC formed more hydrogen bonds with LF than that of EC. The antioxidant activity of LF was increased by the high addition level of EC and EGC. These findings would provide more references for developing LF-catechin complexes as functional antioxidants.

Pickering emulsions prepared using zein-sugarcane leaves polyphenol covalent crosslinking nanoparticles via ultrasonication: Capacities in storage stability, lipid oxidation, in vitro digestion and safety evaluation

This study firstly used sugarcane leaf polyphenols (SGLp) to modify zein to form covalent nanoparticles (SGLpZ) and used SGLpZ as an emulsifier to stabilize pickering emulsions (SZP) via ultrasonic method. The results showed that the addition of SGLp could alter the physicochemical properties of zein, including improving increasing the hydrophilicity of zein and the antioxidant properties of zein (three basic antioxidant activities test in vitro). SGLpZ could be able to form a dense film on the surface of the pickering emulsions which inhibited lipid oxidation as the concentration of SGLp increased at 4 ℃ for 20 days, thus stabilizing pickering emulsions (SZP). Further assessment of storage stability of pickering emulsions stabilized by SGLp was evaluated via measuring the free fatty acids (FFA) release in vitro gastrointestinal digestion. The results showed that the FFA release of SZP decreased from 20.61 ± 0.10% to 16.14 ± 0.69%. In addition, SGLp gave SZP a yellow color, which inspired that SZP could be used in the food industry to make yellow-colored functional foods. Finally, the safety of SZP initially assessed by in-vitro hemocompatibility and cytotoxicity (MTT) assays. In conclusion, our fingdings were beneficial for the further design and development of SGLp in food fields and enabled the development a new type in functional protein-plant polyphenols food pickering emulsions.

Covalent modification of (+)-catechin to improve the physicochemical, rheological, and oxidative stability properties of rice bran protein emulsion

The aim of this study is the effects of (+)-catechin (CC) covalent cross-linking (CCCI) (0.05-0.25 %, w/v) on the physicochemical properties, rheological properties, and oxidative stability of rice bran protein (RBP) emulsion. Analysis of particle size, ζ-potential, circular dichroism, fluorescence spectroscopy, surface hydrophobicity, and emulsifying properties demonstrated that a concentration of 0.15 % (w/v) CCCI facilitated protein structure unfolding, resulting in reduced particle size, enhanced electrostatic repulsion, and improved emulsion stability. Moreover, the covalent complexes of RBP-0.15 %CC (w/v) exhibited increased viscosity and shear stress, reflected by the highest G' and G″ values, ultimately enhancing the oxidative stability. Furthermore, analysis using atomic force microscopy and confocal laser scanning microscopy revealed that the RBP-0.15 %CC complexes exhibited the smallest particle size (164 nm) and displayed greater homogeneity. An increase in CC concentration to 0.25 % (w/v) resulted in a higher emulsion aggregation. The emulsions stabilized by CCCI exhibited superior rheological properties and enhanced oxidation stability compared to the control. In conclusion, an appropriate amount of CC can enhance the rheology and oxidation stability of the RBP emulsion, while CCCI treatment holds potential for expanding the utility of RBP in various applications.

Effects of different steam injection conditions on cappuccino's nutritional profile

The quality parameters of cappuccinos prepared with pasteurized milk or ultra-high-temperature milk steam-injected at different temperatures by a professional coffee machine have been assessed. In particular, the protein profile, the content of vitamins and lactose, the lipid peroxidation process, and the involvement of milk proteins in the foam formation were evaluated. The nutritional quality of milk seems not affected by the steam injection treatment carried out at a temperature of 60-65 °C, but at higher temperatures a decrement of lactoperoxidase, vitamin B6 and folic acid was observed. The milk used in cappuccino preparation is very important: pasteurized milk can form a more consistent and lasting foam with respect to ultra-high-temperature milk because of the presence of β-lactoglobulin and lactoferrin, both playing an important role in the foam formation and stability. This work would provide additional information to the coffee industry for the preparation of high nutritional and organoleptic quality cappuccinos.

Influence of hemin on structure and emulsifying properties of soybean protein isolate

Hemin has potential application value in plant-based meat analogues. However, mechanisms of interaction between hemin and plant protein are unclear. In this study, soy protein isolate (SPI) was applied to examine these interactions using multi-spectroscopic and molecular docking techniques. Additionally, the influence of hemin on emulsification of SPI was also explored. Fluorescence and UV-Vis spectra showed quenching of SPI by hemin was static, resulting in conformation changes on the surface amino acid residues, around which hydrophobicity was significantly reduced from 425.9 ± 16.2 to 108.9 ± 1.8 (p < 0.05). FTIR and CD spectra results suggested the protein secondary structure altered, and the content of α-helix and random coils increased by 1.13% and 1.43%, respectively. Furthermore, emulsifying properties of SPI were strengthened with increased hemin. This work improves our understanding of interactions between SPI and hemin and offer a theoretical basis for application of heme in plant-based meat analogues.

Investigation of bovine β-lactoglobulin-procyanidin complexes interactions and its utilization in O/W emulsion

Procyanidins are bioactive polyphenols that have a strong affinity to proteins. Beta-lactoglobulin (BLG) is widely used as an emulsifier in the food and other industries. This study evaluated the interaction between BLG and A-type procyanidin dimer (PA2) using the spectroscopic, thermodynamic, and molecular simulation. PA2 decreased the transmissivity and quenched the intrinsic fluorescence of BLG, suggesting that the two molecules formed a complex. The binding of PA2 reduced the surface hydrophobicity and altered the conformation of BLG with increasing the random coil regions. Thermodynamic and isothermal titration calorimetry analyses suggested that the main driving force of PA2-BLG interaction was hydrophobic attraction. Molecular docking simulations were used to identify the main interaction sites and forces in the BLG-PA2 complexes, which again indicated that hydrophobic interactions dominated. In addition, the influence of PA2 on the ability of BLG to form and stabilize O/W emulsions was analyzed. Emulsions formulated using BLG-PA2 complexes contained relatively small droplets (D_4,3 ≈ 0.7 μm) and high surface potentials (absolute value >50 mV). Compared to BLG alone, BLG-PA2 complexes improved the storage stability of the emulsions. This study provides valuable new insights into the formation, properties, and application of protein-polyphenol complexes as functional ingredients in foods.

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

Ultrasound treatment enhanced the functional properties of phycocyanin with phlorotannin from Ascophyllum nodosum

Introduction

Phycocyanin offers advantageous biological effects, including immune-regulatory, anticancer, antioxidant, and anti-inflammation capabilities. While PC, as a natural pigment molecule, is different from synthetic pigment, it can be easily degradable under high temperature and light conditions.

Methods

In this work, the impact of ultrasound treatment on the complex of PC and phlorotannin structural and functional characteristics was carefully investigated. The interaction between PC and phlorotannin after ultrasound treatment was studied by UV–Vis, fluorescence spectroscopy, circular dichroism (CD) spectroscopy, fourier transform infrared (FTIR) spectroscopy. Additionally, the antioxidant potential and in vitro digestibility of the complexes were assessed.

Results

The result was manifested as the UV–Vis spectrum reduction effect, fluorescence quenching effect and weak conformational change of the CD spectrum of PC. PC was identified as amorphous based on the X-ray diffraction (XRD) data and that phlorotannin was embedded into the PC matrix. The differential scanning calorimetry (DSC) results showed that ultrasound treatment and the addition of phlorotannin could improve the denaturation peak temperatures (Td) of PC to 78.7°C. In vitro digestion and free radical scavenging experiments showed that appropriate ultrasound treatment and the addition of phlorotannin were more resistant to simulated gastrointestinal conditions and could improve DPPH and ABTS+ free radical scavenging performance.

Discussion

Ultrasound treatment and the addition of phlorotannin changed the structural and functional properties of PC. These results demonstrated the feasibility of ultrasound-assisted phlorotannin from A. nodosum in improving the functional properties of PC and provided a possibility for the application of PC-polyphenol complexes as functional food ingredients or as bioactive materials.

Esterified Soy Proteins with Enhanced Antibacterial Properties for the Stabilization of Nano-Emulsions under Acidic Conditions

Soy protein isolate (SPI), including β-conglycinin (7S) and glycinin (11S), generally have low solubility under weakly acidic conditions due to the pH closed to their isoelectric points (pIs), which has limited their application in acidic emulsions. Changing protein pI through modification by esterification could be a feasible way to solve this problem. This study aimed to obtain stable nano-emulsion with antibacterial properties under weakly acidic conditions by changing the pI of soy protein emulsifiers. Herein, the esterified soy protein isolate (MSPI), esterified β-conglycinin (M7S), and esterified glycinin (M11S) proteins were prepared. Then, pI, turbidimetric titration, Fourier transform infrared (FTIR) spectra, intrinsic fluorescence spectra, and emulsifying capacity of esterified protein were discussed. The droplet size, the ζ-potential, the stability, and the antibacterial properties of the esterified protein nano-emulsion were analyzed. The results revealed that the esterified proteins MSPI, M7S, and M11S had pIs, which were measured by ζ-potentials, as pH 10.4, 10.3, and 9.0, respectively, as compared to native proteins. All esterified-protein nano-emulsion samples showed a small mean particle size and good stability under weakly acidic conditions (pH 5.0), which was near the original pI of the soy protein. Moreover, the antibacterial experiments showed that the esterified protein-based nano-emulsion had an inhibitory effect on bacteria at pH 5.0.

Fabrication of glycated yeast cell protein via Maillard reaction for delivery of curcumin: improved environmental stability, antioxidant activity, and bioaccessibility

BACKGROUND

The application of curcumin (CUR) in the food industry is limited by its instability, hydrophobicity and low bioavailability. Yeast cell protein (YCP) is a by-product of spent brewer's yeast, which has the potential to deliver bioactive substances. However, the environmental stresses such as pH, salt and heat treatment has restricted its application in the food industry. Maillard reaction as a non-enzymatic browning reaction can improve protein stability under environmental stress.

RESULTS

The CUR was successfully encapsulated into the hydrophobic core of YCP/glycated YCP (GYCP) and enhanced by hydrogen bonding, resulting in static fluorescence quenching of YCP/GYCP. The average diameter and dispersibility of GYPC-CUR nanocomplex were significantly improved after glucose glycation (121.40 nm versus 139.70 nm). Moreover, the encapsulation capacity of CUR was not influenced by glucose glycation. The oxidative stability and bioaccessibility of CUR in nanocomplexes were increased compared with free CUR, especially complexed with GYCP conjugates.

CONCLUSION

Steric hindrance provided by glucose conjugation improved the enviriomental stability, oxidative activity and bioaccessibility of CUR in nanocomplexes. Thus, glucose-glycated YCP has potential application as a delivery carrier for hydrophobic compounds in functional foods. © 2022 Society of Chemical Industry.

Novel Colloidal Food Ingredients: Protein Complexes and Conjugates

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

Interaction between Chinese quince fruit proanthocyanidins and bovine serum albumin: Antioxidant activity, thermal stability and heterocyclic amine inhibition

Heterocyclic amines (HCAs) are carcinogenic and mutagenic substances produced in fried meat. Adding natural antioxidants (e.g., proanthocyanidins (PAs)) is a common method to reduce HCAs; however, the interaction between the PAs and protein can affect the inhibitory efficacy of PAs on the formation of HCAs. In this study, two PAs (F1 and F2) with different degrees of polymerization (DP) were extracted from Chinese quince fruits. These were combined with bovine serum albumin (BSA). The thermal stability, antioxidant capacity and HCAs inhibition of all four (F1, F2, F1-BSA, F2-BSA) were compared. The results showed that F1 and F2 interact with BSA to form complexes. Circular dichroism spectra indicate that complexes had fewer α-helices and more β-sheets, β-turns and random coils than BSA. Molecular docking studies indicated that hydrogen bonds and hydrophobic interactions are the forces holding the complexes together. The thermal stabilities of F1 and, particularly, F2 were stronger than those of F1-BSA and F2-BSA. Interestingly, F1-BSA and F2-BSA showed increased antioxidant activity with increasing temperature. F1-BSA's and F2-BSA's HCAs inhibition was stronger than F1 and F2, reaching 72.06 % and 76.3 %, respectively, for norharman. This suggests that PAs can be used as natural antioxidants for reducing the HCAs in fried foods.

Protein-polysaccharides based nanoparticles for loading with Malus baccata polyphenols and their digestibility in vitro

The poor solubility, instability and low absorption rate obstruct the bioavailability of polyphenols isolated from Malus baccata (MBP) during gastrointestinal digestion. In order to solve the limitable problems, the food-grade nanoparticles were fabricated by mucin (MC) and Hohenbuehelia serotina polysaccharides (HSP) for delivery of MBP (MBP-NPs). The physicochemical properties and morphology of MBP-NPs prepared by different condition were respectively characterized. During gastrointestinal digestion in vitro, the release characteristic and variation in phenolic composition of MBP-NPs were evaluated. The results showed that MBP-NPs formed by hydrogen bonding and hydrophobic interaction possessed the regularly spherical shapes and smooth surfaces and semi-crystalline properties. Moreover, MBP-NPs presented the excellent physicochemical stability. During simulated gastrointestinal digestion in vitro, MBP-NPs exhibited the sustained release characteristics of phenolic compounds, which were confirmed by SDS-PAGE measurement. Compared with that of unencapsulated MBP, the significant variation was occurred in the phenolic composition of MBP-NPs, indicating that MBP-NPs could prevent the degradation and transformation of phenolic compounds. This study provides a novel strategy to improve the bioavailability of polyphenols.

Noncovalent interaction mechanism and functional properties of flavonoid glycoside-β-lactoglobulin complexes

The interaction of flavonoid glycosides with milk protein and effects on the functional properties of flavonoid glycoside-β-lactoglobulin complexes are still inexplicit. The noncovalent interactions between flavonoid glycosides including quercetin (QE), quercitrin (QI), and rutin (RU) with β-lactoglobulin (β-LG) were determined by computer molecular docking and multispectral technique analysis. The fluorescence quenching results indicated that the flavonoid glycosides formed stable complexes with β-LG by the static quenching mechanism. The computer molecular docking and thermodynamic parameters analysis conclude that the main interaction of β-LG-QE was via hydrogen bonding, while for β-LG-QI and β-LG-RU it is via hydrophobic forces. The order of binding affinity to β-LG was QE (37.76 × 10⁴ L mol^-1) > RU (16.80 × 10⁴ L mol^-1) > QI (11.17 × 10⁴ L mol^-1), which indicated that glycosylation adversely affected the colloidal complex binding capacity. In this study, the physicochemical properties of the protein-flavonoid colloidal complex were determined. The analysis by circular dichroism spectroscopy demonstrated that flavonoid glycosides made the protein structure looser by inducing the secondary structure of β-LG to transform from the α-helix and β-sheet to random coils. The hydrophobicity of β-LG decreased due to binding with flavonoid glycosides, while functional properties including foaming, emulsification, and antioxidant capacities of β-LG were improved due to the noncovalent interactions. This study presents a part of the insight and guidance on the interactive mechanism of flavonoid glycosides and proteins and is helpful for developing functional protein-based foods.

Complex plant protein prepared from rice protein and pea protein: Improve the thermal stability of betanin

Betanin (BN) is a kind of edible natural red pigment with a variety of biological activities, but the thermal instability of BN has critically restricted its application in food industry. In this study, complex plant protein (RP-PP) was constructed by rice protein (RP) and pea protein (PP) to study the thermal protection effect and protective mechanism on BN. Thermal degradation results indicated RP-PP significantly improved thermal protection effect, and the degradation rate of BN was decreased from 93.74 % to 56.48 % after heating at 80 ℃ for 60 min. The main interaction between RP-PP and BN was hydrophobic force based on the result of fluorescence spectroscopy, FTIR and molecular docking. In addition, a porous network structure of RP-PP was observed by SEM, and the pore structure gradually decreased at the presence of BN, which speculated BN was trapped in it. TEM observation showed that RP-PP gradually aggregated with the increasing BN concentration, leading to a significant increase in particle size and the formation of network structure. The BN acted as a bridge to the surrounding proteins in the aggregated complex and was encapsulated within it. The interaction and encapsulation may be the key reasons for the improved thermal stability of BN.

Impacts of Proanthocyanidin Binding on Conformational and Functional Properties of Decolorized Highland Barley Protein

The impacts of interaction between proanthocyanidin (PC) and decolorized highland barley protein (DHBP) at pH 7 and 9 on the functional and conformational changes in DHBP were investigated. It was shown that PC strongly quenched the intrinsic fluorescence of DHBP primarily through static quenching. PC and DHBP were mainly bound by hydrophobic interactions. Additionally, free sulfhydryl groups and surface hydrophobicity obviously decreased in DHBP after combining with PC. The zeta potential of DHBP-PC complexes at pH 7 increased significantly. A change in the structure of DHBP was caused by interactions with PC, resulting in an increase in the number of β-sheets, a decrease in the number of α-helixes, and a spectral shift in the amide Ⅱ band. Furthermore, the presence of PC enhanced the foaming properties and antioxidant activity of DHBP. Overall, this study suggests that DHBP-PC complexes at pH 7 could be designed as a stable additive, and illustrates the potential applications of DHBP-PC complexes in the food industry.

Inhibitory effects of ultrasonic and rosmarinic acid on lipid oxidation and lipoxygenase in large yellow croaker during cold storage

Lipid oxidation will lead to the deterioration of flavor, color and texture of aquatic products with high fatty acid content. The mechanism of ultrasound (US) combined with rosmarinic acid (RA) on lipid oxidation and endogenous enzyme activities of large yellow croaker during cold-storage (4 ℃) was investigated. The result showed that the US and RA have synergistic effects in delaying lipid oxidation and inhibiting endogenous lipase and lipoxygenase (LOX) activities related to oxidation. The inhibition of LOX activity by RA was dose-dependent, and US showed a negative effect on the inhibition of enzyme activity in the presence of low concentration RA. Moreover, RA changes the enzyme structure through static fluorescence quenching and interaction with enzyme molecules. Hydrogen bonding and hydrophobic interaction are the main interaction forces between RA and LOX. This study could provide basic mechanism of US treatment cooperating with polyphenols to inhibit lipid oxidation during food preservation.

The Interactional Characterization of Lentil Protein Isolate (LPI) with Cyanidin-3-O-Glucoside (C3G) and Their Effect on the Stability and Antioxidant Activity of C3G

The interaction between lentil protein isolate (LPI) and cyanidin-3-O-glucoside (C3G) was investigated via with UV−vis spectroscopy, circular dichroism, and fluorescence spectroscopy and the stability of anthocyanin was also evaluated. After LPI mixed with C3G, the turbidity and foaming capacity increased and the particle size and surface charge did not change significantly, while the surface hydrophobicity decreased significantly (p < 0.05). The fluorescence results indicated that C3G quenched the intrinsic of LPI by static quenching and LPI bound with C3G via hydrophobic effects with Ka of 3.24 × 106 M−1 at 298 K. The addition of LPI significantly (p < 0.05) slightly decreased the thermal and oxidation degradation of C3G by up to 90.23% and 54.20%, respectively, while their antioxidant activity was inhibited upon mixing. These alterations of physicochemical properties might be attributed to their structural changes during the interaction. The obtained results would be of help in stabilizing bioactive compounds and the development of functional foods.

Binding of Licochalcone A to Whey Protein Enhancing Its Antioxidant Activity and Maintaining Its Antibacterial Activity

Incorporating LA into whey protein by forming whey protein isolate-LA (WPI-LA) and polymerized whey protein-LA (PWP-LA) complexes is a good way to maintain its bioactivity and improve its functional performance within food matrices. Herein, we found that WPI and PWP were able to interact with LA as suggested by multi-spectroscopy, molecular docking, and molecular dynamics simulations. The interaction between whey protein and LA was a spontaneous non-covalent binding process, while PWP had a higher affinity for LA than WPI, resulting from its more negatively binding free energy with LA. Hydrogen bonds, van der Waals forces, and electrostatic interactions were responsible for WPI-LA interactions. Hydrophobic forces, van der Waals, and hydrogen bonds positively accounted for PWP-LA interactions. The antioxidant activity of LA was improved by complexation with whey proteins as identified by DPPH and ABTS. The antimicrobial efficiency of LA was partially screened by complexation with whey protein with MIC values increased by seven-fold compared to free LA but successfully recovered to its original efficiency upon isolating it from the complex. This work demonstrates the promising antioxidant and antibacterial activities of the whey protein-LA complex and provides a good candidate for developing a new class of natural functional ingredients for food systems.

Comparison of soy protein isolate-(-)-epigallocatechin gallate complexes prepared by mixing, chemical polymerization, and ultrasound treatment

The effects of the preparation method (mixing, chemical polymerization, or ultrasound treatment) on the structure and functional properties of soy protein isolate-(-)-epigallocatechin-3-gallate (SPI-EGCG) complexes were examined. The mixing treated SPI-EGCG samples (M-SE) were non-covalently linked, while the chemical polymerization and ultrasound treated SPI-EGCG samples (C-SE and U-SE, respectively) were bound covalently. The covalent binding of EGCG with protein improved the molecular weight and changed the structures of the SPI by decreasing the α-helix content. Moreover, U-SE samples had the lowest particle size (188.70 ± 33.40 nm), the highest zeta potential (-27.82 ± 0.53 mV), and the highest polyphenol binding rate (59.84 ± 2.34 %) compared with mixing and chemical polymerization-treated samples. Furthermore, adding EGCG enhanced the antioxidant activity of SPI and U-SE revealed the highest DPPH (84.84 ± 1.34 %) and ABTS (88.89 ± 1.23 %) values. In conclusion, the SPI-EGCG complexes prepared by ultrasound formed a more stable composite system with stronger antioxidant capacity, indicating that ultrasound technology may have potential applications in the preparation of protein-polyphenol complexes.

Boosting the Bioaccessibility of Dietary Bioactives by Delivery as Protein-Polyphenol Aggregate Particles

Protein-polyphenol aggregate particles concurrently fortify a functional food product with healthy dietary proteins and concentrated polyphenols. However, what impact does ingestion of aggregate particles have on ultimate health relevance of either the polyphenolic molecules in the matrix or the protein molecules? Because human health benefits are contingent on bioavailability after ingestion, the fate of these molecules during transit in the gastrointestinal tract (GIT) will dictate their utility as functional food ingredients. This brief review explores diverse applications of protein-polyphenol particles in the food industry and the bioaccessibility of both bioactive polyphenolic compounds and edible proteins. Evidence to date suggests that complexation of phytoactive polyphenolics effectively enhances their health-relevant impacts, specifically because the phytoactives are protected in the protein matrix during transit in the GIT, allowing intact, non-degraded molecules to reach the colon for catabolism at the gut microbiome level, a prerequisite to realize the health benefits of these active compounds.

Covalent and Noncovalent Complexation of Phosvitin and Gallic Acid: Effects on Protein Functionality and In Vitro Digestion Properties

To investigate the effects of different binding modes on the structure, function, and digestive properties of the phosvitin (Pv) and gallic acid (GA) complex, Pv was covalently and noncovalently combined with different concentrations of GA (0.5, 1.5, and 2.5 mM). The structural characterization of the two Pv-GA complexes was performed by Fourier transform infrared, circular dichroism, and LC-MS/MS to investigate the covalent and noncovalent binding of Pv and GA. In addition, the microstructure of the two Pv-GA complexes was investigated by super-resolution microscopy and transmission electron microscopy. The particle size and zeta potential results showed that the addition of GA increased the particle size and the absolute potential of Pv. The determination of protein digestibility, polyphenol content, SH and S-S group levels, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and antioxidant capacity of the digests indicated that noncovalent complexes had greater antioxidant and protective effects on polyphenols. Molecular docking revealed that GA was conjugated with Pv through hydrogen bond interactions.

Effects of selenium yeast and jujube powder dietary supplements on conformational and functional properties of post-mortem chicken myofibrillar protein

The aim of the study was to evaluate the effects of selenium yeast and jujube powder on the structure and functional properties of post-mortem myofibrillar protein (MP) in white feather broilers. Changes in the structure (surface hydrophobicity, secondary structure, and tertiary structure), functional properties (solubility, turbidity, emulsifying, and foaming characteristics), and gel properties (gel strength, springiness, and water-holding capacity) of the MPs of white feather broiler, which were fed with different concentrations of selenium yeast or/and jujube powder (selenium yeast: 0,0.3, and 0.6 mg/kg; jujube powder: 8% to replace corn) for 42 days, were determined at 0, 24, and 72 h post-mortem. The results showed that with increasing concentrations of selenium yeast and jujube powder in the diet, the α-helix content, solubility, emulsification, and foaming of post-mortem chicken MP increased significantly (P < 0.05). The gel strength, springiness, and water-holding capacity of MP also increased, but the differences between the treatment groups were not significant (P > 0.05). In addition, the β-folding content and turbidity of MP decreased significantly (P < 0.05). Both the increase in selenium yeast levels and the addition of jujube powder improved the structural integrity and functional properties of MP. The best improvement effect was found in the combination group of high-dose selenium yeast and jujube powder, and there were significant interactions between them in the indices of α-helix, β-folding, turbidity, emulsification, and foam stability of MP. In conclusion, supplementing diets with seleniumyeast and jujube powder could maintain the structural stability of MPs in post-mortem chicken breast, leading to good functional properties. The results of this study may provide new insights into the effects of pre-slaughter feeding on post-mortem muscle MP conformation control and quality improvement.

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.

Effect of Xanthan Gum, Kappa-Carrageenan, and Guar Gum on the Functional Characteristics of Egg White Liquid and Intermolecular Interaction Mechanism

This study evaluated the effects of three polysaccharides, xanthan gum (XG), kappa-carrageenan (CA), and guar gum (GG), on the foaming and emulsifying properties of egg white liquid (EWL) and explored the intermolecular interactions and aggregation states in the initial polysaccharide−EWL complex. The results showed that the addition of XG and GG significantly improved the foaming stability of EWL on the one hand, from 66% to 78% and 69%, respectively (p < 0.05). On the other hand, the addition of XG and GG significantly improved the foam uniformity and density, and the average foam area decreased from 0.127 to 0.052 and 0.022 mm2, respectively (p < 0.05). The addition of XG and CA significantly improved the emulsification activity index (from 13.32 to 14.58 and 14.36 m2/mg, respectively, p < 0.05) and the emulsion stability index (from 50.89 to 53.62 and 52.18 min, respectively, p < 0.05), as well as the interfacial protein adsorption at the oil−water interface; it also reduced the creaming index. However, GG negatively affected these indicators. Furthermore, the electrostatic and hydrophobic interactions among molecules in EWL due to XG and the electrostatic, hydrogen bonding, and hydrophobic interactions among molecules in EWL due to CA ultimately led to the irregular aggregation of egg white proteins. Hydrophobic interactions and disulfide bonds between molecules in EWL−containing GG formed filamentous aggregations of egg white proteins. This work reveals that molecules in the polysaccharide−egg white complexes aggregate by interaction forces, which in turn have different effects on the foaming and emulsifying properties of egg white proteins.

Pectin Stabilized Fish Gelatin Emulsions: Physical Stability, Rheological, and Interaction Properties

Pectin, a kind of natural polysaccharide, shows the attractive potential as a natural stabilizer for protein emulsion. The aim of this study is to investigate the effect of pectin on the physical stability, rheology, interface, and interaction properties of the fish gelatin (FG) emulsion, as pectin was utilized to improve the stability of FG, fish oil emulsion. During the study, when pH &lt; 6, the FG-pectin emulsion displayed better storage stability and salinity tolerance. Analyzing the result, pectin could avoid phase separation at the freeze-thaw process and prevent the liquid-gel transition of FG emulsions during storage. On the other hand, when pH ≥ 6, the emulsion displayed high viscosity due to the complex flocculation and stratified during long-term storage. Electrostatic interactions, hydrophobic interactions, and hydrogen bonding of the FG-pectin complexes in the emulsion were all reduced. Overall, pectin improved the stability of FG emulsions through electrostatic repulsion, hydrophobic interactions, and steric hindrance.