Analysis of the interaction mechanism of Anthocyanins (Aronia melanocarpa Elliot) with β-casein

Study on the interaction mechanism between (-)-epigallocatechin-3-gallate and myoglobin: Multi-spectroscopies and molecular simulation

(-)-Epigallocatechin-3-gallate (EGCG) is remarkably efficacious in inhibiting the browning of red meat. We therefore propose a hypothesis that EGCG forms complexes with myoglobin, thereby stabilizing its structure and thus preventing browning. This study investigated the interaction mechanism between EGCG and myoglobin. EGCG induced static quenching of myoglobin. Noncovalent forces, including hydrogen bonds and van der Waals, primarily governing the interactions between myoglobin and EGCG. The interactions primarily disrupted myoglobin's secondary structure, thus significantly reducing surface hydrophobicity by 53% (P < 0.05). The modification augmented the solubility and thermal stability of myoglobin. The radius of gyration (Rg) value fluctuated between 1.47 and 1.54 nm, and the hydroxyl groups in EGCG formed an average of 2.93 hydrogen bonds with myoglobin. Our findings elucidated the formation of stable myoglobin-EGCG complexes and the myoglobin-EGCG interaction, thus confirming our initial hypothesis.

Antimicrobial activity, foaming properties, and interacting mechanism of rhamnolipids in presence of silk fibroin through spectroscopy, molecular docking, and microbiological experiments

As a type of biosurfactant, rhamnolipids (RLs) are multifunctional skin-care ingredients, and the molecular interaction of RLs with silk fibroin (SF) is a more complicated process than has long been believed. The interaction and functional properties of them, and their potential as fungicidal agents for agricultural products and as organic preservatives for cosmetics were assessed in this paper. The SF addition makes the RLs aggregation easier through the complexes formation, which decreases the applied concentration of surfactant. The results of spectroscopic analyses and molecular docking suggest that hydrogen bonding and van der Waals forces are significant contributed to the binding mechanism between the two substances. The addition of SF notably enhances the foaming capacity and stability of RLs. The certain antibacterial and antifungal properties of RLs are basically not affected by the SF addition, even the SF-RLS system demonstrates an unobvious synergistic inhibitory impact on Glomerella cingulate (GC). The results offer a theoretical framework for the utilization of RLs as natural fungicides and preservatives in presence of nutritional components, considering the properties of RLs as nontoxic, biodegradable, environmentally friendly, and good compatibility.

Enhancement of non-covalent interaction between soy protein isolate and quercetin by sodium alginate

Effects of sodium alginate (SA) on the non-covalent interaction between soybean protein isolate (SPI) and quercetin (Que) were investigated by multispectral technology, molecular docking and dynamics simulation technology. Structural alterations of the binary complexes were observed after SA addition, characterized by a red shift of maximum fluorescence emission wavelength. The introduction of 0.1% (w/v) SA led to a reduction of 12.3% in the α-helix and β-sheet structures, accompanied by 12.6% increase in the β-turn and random coil conformations. The binding of SA to SPI provided electrostatic interactions and facilitated the subsequent binding of SPI to Que. Molecular docking confirmed that hydrophobic interactions and electrostatic interactions were also the main driving force. Molecular dynamics simulation emphasized that the ternary complexes with SA exhibited greater stability compared to the binary ones. The foaming and emulsifying properties of SPI-Que complexes were enhanced by 33.76% and 68.28%, respectively, due to the addition of SA.

Study on the interaction mechanism of whey protein isolate with phosphatidylcholine: By multispectral methods and molecular docking

The elucidation of the interaction mechanism between phospholipids and milk proteins within emulsions is pivotal for comprehending the properties of infant formula fat globules. In this study, multispectral methods and molecular docking were employed to explore the relationship between phosphatidylcholine (PC) and whey protein isolate (WPI). Observations indicate that the binding constant, alongside thermodynamic parameters, diminishes as temperature ascends, hinting at a predominantly static quenching mechanism. Predominantly, van der Waals forces and hydrogen bonds constitute the core interactions between WPI and PC. This assertion is further substantiated by Fourier transform infrared spectroscopy, which verifies PC's influence on WPI's secondary structure. A detailed assessment of thermodynamic parameters coupled with molecular docking reveals that PC predominantly adheres to specific sites within α-lactalbumin, β-lactoglobulin, and bovine serum albumin, propelled by a synergy of hydrophobic interactions, hydrogen bonding, and van der Waals forces, with binding energies noted at -5.59, -6.71, and -7.85 kcal/mol, respectively. An increment in PC concentration is observed to amplify the emulsification properties of WPI whilst concurrently diminishing the zeta potential. This study establishes a theoretical foundation for applying the PC-WPI interaction mechanism in food.

Effect and mechanisms of thermal sterilization methods on the in vitro phenolic bioaccessibility of rose tea with milk

Rose polyphenols, key functional components in roses, require adequate bioaccessibility for their health benefits, subject to influence by food components and processing. Investigating the impact of various thermal sterilization methods on the bioaccessibility of rose polyphenols in rose tea with milk and the underlying mechanisms, our findings indicated a significant increase in bioaccessibility following treatment at 85 °C/30 min. Conversely, 121 °C/15 min treatment decreased bioaccessibility. Examining the interaction between β-casein in milk and rose polyphenols under different sterilization conditions, SEM and particle size analysis revealed binding, with fluorescence spectroscopy indicating non-covalent bonds. Binding forces followed the order 121 °C > 85 °C > 25 °C. Notably, at 85 °C, non-covalent binding improved polyphenol bioaccessibility, while the intensified binding at 121 °C decreased it. SDS-PAGE and amino acid analysis confirmed no covalent bond. This study establishes a theoretical basis for selecting thermal sterilization temperatures for milk-flower combinations, considering polyphenol bioaccessibility.

Exploring cheese and red wine pairing by an in vitro simulation of tasting

The cheese wine pairing is a beloved combination subject to a certain subjectivity due to sensorial, psychological, chemical, and cultural factors. This work represents a first attempt to explore the in vitro interactions between cheese, wine, and saliva to objectively measure the pairing. Two experimental red wines obtained from the same grape cultivar and four different cheeses were studied for their composition. Binding reactions between wine and cheese were carried out in three simulated tasting trials and, after precipitation, the wine phenolic content, Saliva Precipitation Index (SPI), and total proteins were evaluated. The optimal pairing (OP) was calculated considering the decrease in salivary and cheese proteins by wine, defined as the cleansing effect; the decrease in astringency due to the cheese, measured by the SPI, and the coating fat which would remain in mouth after eating a piece of cheese. Based on obtained results, the semi-hard cheese was identified as the best pairing option for the two experimental red wines. The differences in the phenolic content between the two wines were instead not enough to show a significant influence on the OP. The in vitro cheese wine pairing can contribute to understanding of wine tasting but it is only a part of the puzzle. However, this first contribution paves the way for additional studies on the molecular and chemical interactions involved in aroma and textural perception in simulated trials.

Comparison of pH-induced protein-polyphenol self-assembly methods: Binding mechanism, structure, and functional characteristics

Herein, we used pH-shifted and pH-driven methods to assemble kidney-bean protein isolate (KPI) and luteolin (Lut) into a nanocomplex and subsequently investigated their binding mechanism, structure, and functional properties. Results showed that the nanocomplex prepared by the pH-driven method exhibited a better encapsulation effect and controlled release of Lut. Fluorescence spectroscopy and molecular docking analysis showed that the binding affinities under alkaline conditions were higher than those under acidic and neutral conditions. Various spectral techniques were used to determine the structural changes in the KPI-Lut nanocomplex, including the transformation of α-helices and β-sheets and alteration of specific amino acid microenvironments, which were more pronounced in the pH-driven nanocomplex. The structural changes in the nanocomplex further affected their surface hydrophobicity and thermal stability. Additionally, the combination of KPI and Lut significantly improved the antioxidant activity and α-glucosidase inhibitory ability of the resultant nanocomplexes, particularly the one prepared by the pH-driven method.

Bovine milk β-casein: Structure, properties, isolation, and targeted application of isolated products

β-Casein, an important protein found in bovine milk, has significant potential for application in the food, pharmaceutical, and other related industries. This review first introduces the composition, structure, and functional properties of β-casein. It then reviews the techniques for isolating β-casein. Chemical and enzymatic isolation methods result in inactivity of β-casein and other components in the milk, and it is difficult to control the production conditions, limiting the utilization range of products. Physical technology not only achieves high product purity and activity but also effectively preserves the biological activity of the components. The isolated β-casein needs to be utilized effectively and efficiently for various purity products in order to achieve optimal targeted application. Bovine β-casein, which has a purity higher than or close to that of breast β-casein, can be used in infant formulas. This is achieved by modifying its structure through dephosphorylation, resulting in a formula that closely mimics the composition of breast milk. Bovine β-casein, which is lower in purity than breast β-casein, can be maximized for the preparation of functional peptides and for use as natural carriers. The remaining byproducts can be utilized as food ingredients, emulsifiers, and carriers for encapsulating and delivering active substances. Thus, realizing the intensive processing and utilization of bovine β-casein isolation. This review can promote the industrial production process of β-casein, which is beneficial for the sustainable development of β-casein as a food and material. It also provides valuable insights for the development of other active substances in milk.

Study on the interaction and functional properties of Dolichos lablab L. protein-tea polyphenols complexes

Tea polyphenols (TP) and plant proteins are significant materials in the food industry, the interactions between them are beneficial for their stability, functional properties, and biological activity. In this study, the mechanism and interaction between Dolichos lablab L. protein (DLP) obtained from nine treatments and three tea polyphenol monomers (EGCG, ECG, and EGC) were investigated. The results showed that the fluorescence of DLP was noticeably quenched and exhibited static quenching after the addition of polyphenols. DLP exhibited 1-2 binding sites for EGCG and ECG, but weakly binding to EGC (<1). The binding sites of DLP-TP were found to be in close proximity to the tyrosine residues, primarily interacting through hydrophobic interactions, van der Waals forces, and hydrogen bonds. The antioxidant capacity of DLP-TP compound was significantly improved after digestion. ECG showed a strong resistance to intestinal digestion. Compared with ECG (653.456 μg/mL), the content of free tea polyphenols of 20/40 kHz-ECG after digestion was 732.42 μg/mL. DLP-TP complexes significantly improved the storage stability, thermal stability, and bioaccessibility of tea polyphenols. The interaction between TP and DLP, as a protein-polyphenol complex, has great potential for application in preparing emulsion delivery systems due to their antioxidant activity and improved stability.

Protein and Peptide-Based Nanotechnology for Enhancing Stability, Bioactivity, and Delivery of Anthocyanins

Anthocyanin, a unique natural polyphenol, is abundant in plants and widely utilized in biomedicine, cosmetics, and the food industry due to its excellent antioxidant, anticancer, antiaging, antimicrobial, and anti-inflammatory properties. However, the degradation of anthocyanin in an extreme environment, such as alkali pH, high temperatures, and metal ions, limits its physiochemical stabilities and bioavailabilities. Encapsulation and combining anthocyanin with biomaterials could efficiently stabilize anthocyanin for protection. Promisingly, natural or artificially designed proteins and peptides with favorable stabilities, excellent biocapacity, and wide sources are potential candidates to stabilize anthocyanin. This review focuses on recent progress, strategies, and perspectives on protein and peptide for anthocyanin functionalization and delivery, i.e., formulation technologies, physicochemical stability enhancement, cellular uptake, bioavailabilities, and biological activities development. Interestingly, due to the simplicity and diversity of peptide structure, the interaction mechanisms between peptide and anthocyanin could be illustrated. This work sheds light on the mechanism of protein/peptide-anthocyanin nanoparticle construction and expands on potential applications of anthocyanin in nutrition and biomedicine.

Characterization of the interaction between allicin and soy protein isolate and functional properties of the adducts

BACKGROUND

Soybean meal, a by-product of the soybean oil production industry, has a high protein content but the compact globular structure of the protein from soybean meal limits its wide application in food processing. Allicin has been found to have numerous functional properties. In this study, allicin was interacted with soy protein isolate (SPI). The functional properties of the adducts were investigated.

RESULTS

Binding with allicin significantly quenched the fluorescence intensity of SPI. Static quenching was the main quenching mechanism. The stability of adducts decreased with increasing temperature. The greatest extent of binding between allicin and sulfhydryl groups (SH) of SPI was obtained at an allicin/SH molar ratio of 1:2. The amino groups of SPI did not bind with allicin covalently. Soy protein isolate was modified by allicin through covalent and non-covalent interactions. Compared with SPI, the emulsifying activity index and foaming capacity of adducts with a ratio of 3:1 were improved by 39.91% and 64.29%, respectively. Soy protein isolate-allicin adducts also exhibited obvious antibacterial effects. The minimum inhibitory concentrations (MICs) of SPI-allicin adducts on Escherichia coli and Staphylococcus aureus were 200 and 160 μg mL^-1 , respectively.

CONCLUSION

The interaction of allicin with SPI is beneficial for the functional properties of SPI. These adducts can be used in different food formulations as emulsifiers, foamers, and transport carriers. © 2023 Society of Chemical Industry.

First insights into the binding mechanism and colour effect of the interaction of grape seed 11S globulin with malvidin 3-O-glucoside by fluorescence spectroscopy, differential colorimetry and molecular modelling

Recently, the search for alternative proteins endogenous to grapes to be used as wine colour protecting agents became an important research trend. In this study, the molecular interaction between the grape seed 11S globulin from winemaking by-product and malvidin-3-O-glucoside was investigated by fluorescence, differential colorimetry and molecular modelling. Fluorescence studies revealed the formation of grape seed protein- pigment complex whose KS was 8.5 × 104 M-1 and binding sites, n = 1.3. Malvidin-3-O-glucoside showed darker and more vivid bluish colour of in the presence of 11S globulin, suggesting the flavylium cation protection in a hydrophobic region of the protein. Docking analysis and molecular dynamics simulation indicated that malvidin-3-O-glucoside interacts mainly with the acidic subunit (40 kDa) of the 11S globulin monomer (60 kDa). An average of two hydrogen bonds and Van der Wall forces were the main interaction forces found for the protein-pigment complex, whose stability was confirmed by root-means-square deviation.

Identification of binding sites for Tartary buckwheat protein-phenols covalent complex and alterations in protein structure and antioxidant properties

To investigate the effects of structure, multiple binding sites and antioxidant property of Tartary buckwheat protein-phenols covalent complex, protein was combined with different concentrations of phenolic extract. Four kinds of phenols were identified by UPLC-Q/TOF-MS, which were rutin, quercetin, kaempferol and myricetin. UV-vis absorption spectroscopy and X-ray diffraction showed that the phenols can successfully bind to BPI. Fourier-transform infrared, circular dichroism and fluorescence emission spectroscopy showed that the binding of phenol can change the secondary/tertiary structure of protein. The particle distribution indicated that the binding of phenols could reduce the particle size (from 304.70 to 205.55 nm), but cross-linking occurred (435.35 nm) when the bound phenol content was too high. Proteomics showed that only rutin, quercetin and myricetin can covalently bind to BPI. Meanwhile, 4 peptides covalently bound to phenols were identified. The DPPH· scavenging capacity of complexes were from 8.38 to 33.76 %, and the ABTS·⁺ binding activity of complexes were from 19.35 to 63.99 %. The antioxidant activity of the complex was significantly higher than that of the pure protein. These results indicated that protein-phenol covalent complexes had great potential as functional components in the food field.

A Comparative Study of Binding Interactions between Proteins and Flavonoids in Angelica Keiskei: Stability, α-Glucosidase Inhibition and Interaction Mechanisms

Flavonoids are easily destroyed and their activity lost during gastrointestinal digestion. Protein-based nanocomplexes, a delivery system that promotes nutrient stability and bioactivity, have received increasing attention in recent years. This study investigated the stability, inhibitory activity against α-glucosidase and interaction mechanisms of protein-based nanocomplexes combining whey protein isolate (WPI), soybean protein isolate (SPI) and bovine serum albumin (BSA) with flavonoids (F) from A. keiskei using spectrophotometry, fluorescence spectra and molecular docking approaches. The results show that the flavonoid content of WPI-F (23.17 ± 0.86 mg/g) was higher than those of SPI-F (19.41 ± 0.56 mg/g) and BSA-F (20.15 ± 0.62 mg/g) after simulated digestion in vitro. Furthermore, the inhibition rate of WPI-F (23.63 ± 0.02%) against α-glucosidase was also better than those of SPI-F (18.56 ± 0.02%) and BSA-F (21.62 ± 0.02%). The inhibition rate of WPI-F increased to nearly double that of F alone (12.43 ± 0.02%) (p < 0.05). Molecular docking results indicated that the protein-flavonoids (P-F) binding occurs primarily through hydrophobic forces, hydrogen bonds and ionic bonds. Thermodynamic analysis (ΔH > 0, ΔS > 0) indicated that the P-F interactions are predominantly hydrophobic forces. In addition, the absolute value of ΔG for WPI-F is greater (−30.22 ± 2.69 kJ mol−1), indicating that WPI-F releases more heat energy when synthesized and is more conducive to combination. This paper serves as a valuable reference for the stability and bioactivity of flavonoids from A. keiskei.

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.

Collagen hydrolysates improve the efficiency of sodium alginate-encapsulated tea polyphenols in beads and the storage stability after commercial sterilization

This study showed that sodium alginates (SA)-based beads reinforced with collagen hydrolysates (CHs) significantly increased an encapsulation rate of tea polyphenols (TP) from 34.54 % to 85.06 % when the mass ratio of SA: CHs increased from1.5:0 to 1.5:0.5. And after the 30-day storage at 37 °C, the retention rate of TP in beads with CHs at the solutions with pH = 4.0 or pH = 7.0 increased from 61.10 % to 80.21 %, or from 67.72 % to 80.47 % after sterilization at 98 °C or 121 °C for 30 min, respectively. Also, the addition of CHs at 0.5 % resulted in a greater retention of the polyphenolic compositions values of TP determined by UPLC-Orbitrap-MS system. Additionally, the DPPH and ABTS⁺ free-radical scavenging capacities and ferric-reducing antioxidant power of beads with CHs after sterilization at 98 °C or 121 °C for 30 min were significantly higher than which without CHs. Physical phenomena based on ζ-potential, particle size, fluorescence, UV spectroscopy and confocal laser scanning microscope showed that tightly non-covalent complexes of CHs in combination to TP could be uniformly and stably distributed in the network of SA solution for encapsulating TP in SA-based beads. These findings provided suggestions for the co-encapsulation design and development of hydrophilic nutritive compounds based on CHs in SA-based beads.

Protein-binding approaches for improving bioaccessibility and bioavailability of anthocyanins

Color is an important characteristic of food. Over the last 15 years, more attention has been paid to natural colorants because of the rising demand for clean-label food products. Anthocyanins, which are a group of phytochemicals responsible for the purple, blue or red hues of many plants, offer a market advantage. In addition, anthocyanin-rich foods are associated with protection against cardiovascular disease, thrombosis, diabetes, cancer, microbial-based disorders, neurological disorders, and vision ailments. However, the real health value of anthocyanins, whether as a natural colorant or a functional ingredient, is dependent on the ultimate bioaccessibility and bioavailability in the human body. Many animal and human clinical studies revealed that, after intake of anthocyanin-rich foods or anthocyanin extracts, only trace amounts (< 1% of ingested content) of anthocyanins or their predicted metabolites were detected in plasma after a standard blood draw, which was indicative of low bioavailability of anthocyanins. Protein binding to anthocyanins is a strategy that has recently been reported to enhance the ultimate bioactivity, bioaccessibility, and bioavailability of anthocyanins as compared to anthocyanins delivered without a protein carrier. Therefore, in this review, we address anthocyanin properties in food processing and digestion, anthocyanin-protein complexes used in food matrices, and changes in the bioaccessibility and bioavailability of anthocyanins when bound into anthocyanin-protein complexes in foods. Finally, we summarize the challenges and prospects of this delivery system for anthocyanin pigments.

Zein enhanced the digestive stability of five citrus flavonoids via different binding interaction

BACKGROUND

Zein is commonly used to construct food flavonoid delivery systems. This study investigated the effect and mechanism of zein on the digestive stability of five citrus flavonoids, namely hesperetin (HET), hesperidin (HED), neohesperidin (NHD), naringenin (NEN), and naringin (NIN).

RESULTS

Zein enhanced the digestive stability of the five citrus flavonoids, especially that of HET and NEN, during digestion in the stomach and small intestine. Fluorescence spectroscopy results suggested that citrus flavonoids spontaneously quenched the endogenous fluorescence of zein in static quenching mode. The binding of HET, HED and NHD to zein was driven respectively by electrostatic, hydrophobic and electrostatic interaction. However, Van der Waals' force and hydrogen (H)-bond interaction represented the primary driving force for binding NEN, and NIN to zein to form complexes. The binding of the five citrus flavonoids to zein also caused a diverse bathochromic shift in ultraviolet absorbance. Analysis using Fourier-transform infrared and Raman spectroscopy revealed that the binding behavior of the five citrus flavonoids had different effects on changes in the secondary structures, disulfide bonds, and tyrosine exposure of zein. The results were also partially verified by molecular dynamic simulation.

CONCLUSIONS

Zein enhanced the digestive stability of the five citrus flavonoids via different binding interactions that was due to the difference in molecular structure of citrus flavonoids. © 2022 Society of Chemical Industry.

Preventive Effect and Mechanism of Anthocyanins from Aronia Melanocarpa Elliot on Hepatic Fibrosis Through TGF-β/Smad Signaling Pathway

In order to explore the effect and mechanism of Aornia mealnocarpa Elliot anthocyanins (AMA) at the cellular level on hepatic fibrosis (HF), molecular docking, RT-PCR and Western Blotting were used to explore the molecular mechanism and the effects of different doses AMA on HSC-T6 cells by TGF-β1 induction. The results showed that the binding energy of anthocyanins on TGF-β1 (PDB ID: 3KFD) was in the range of -9.5 to 8.6 kcal/mol, with good low energy parameters and binding positions. AMA could effectively inhibit the expressions of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), and total serum bilirubin (TSB), and improved the expressions of total protein (TP) and albumin (ALB). RT-PCR and Western bloting results showed that AMA could inhibited the secretion of inflammatory cytokines IL-1, IL-6, TNF-α and COX-2, and inhibit the expression of TGF-β1, P-Smad2, α-SMA and Collagen I in TGF-β /Smad signaling pathway. This study revealed the AMA's inhibition effects and mechanism of malignant biological behavior of HSC-T6 cells, in order to provide theoretical basis for the prevention and treatment of HF by Aronia melanocarpa Elliot.

Study on the mechanism of non-covalent interaction between rose anthocyanin extracts and whey protein isolate under different pH conditions

The non-covalent interaction between anthocyanin and dietary protein had an impact on their physicochemical property. The purpose of this study was to study the non-covalent interaction mechanism between rose anthocyanin extract (RAEs) and whey protein isolate (WPI), and further compare the interaction mechanism with pure anthocyanin (PC) and WPI. At pH 3.0 and pH 7.0, RAEs and WPI had non-covalent interactions in the two systems with two types of unequal and mutually influencing binding sites, and the interaction forces were both hydrogen bonds and van der Waals forces. Interestingly, PC and WPI also had non-covalent interactions in both systems, the number of which binding sites was about one type, and the forces were hydrogen bonds and van der Waals forces. In addition, a variety of spectral combination techniques indicated that RAEs and PC caused similar changes in the secondary structure of WPI.

Dual aggregation in ground state and ground-excited state induced by high concentrations contributes to chlorophyll stability

Chlorophyll (Chl) has great application potential in food colouring and nutritional supplementation. Since Chl is easily degraded, stability protection is vital to its application. Herein, a dual aggregation mechanism induced by high concentrations to improve Chl stability was proposed. As a result, the Chl retention at high concentrations increased to 323.92% of that at low concentrations. To explain aggregation, the Chl dimer was observed by atomic force microscopy, and a stable structural model of the Chl a "sandwich" dimer was established. It was proven that Chl dimer stability was dominated by van der Waals (vdW) interactions, while monomer orientation during aggregation was dominated by electrostatic interactions. Charge transfer (CT) was also shown to be a key interaction in the dimer. Excitation at 393 nm was first proposed for CT identification. This research hopes to provide new ideas for the design of food ingredients in human health promotion.

Changes on the conformational and functional properties of soybean protein isolate induced by quercetin

The conformational changes and functional properties of SPI induced by quercetin was investigated via fourier transform infrared (FTIR) spectroscopy, fluorescence spectroscopy, circular dichroism (CD) spectroscopy and molecular docking. A decrease in the fluorescence intensity and a blue shift in the maximum wavelength were observed due to the binding process with fluorescent residues. The analysis of Stern-Volmer equation showed that the fluorescence quenching induced by quercetin took the form of static quenching, and the binding stoichiometry between SPI and quercetin was 1:1. The values of ΔH and ΔS were both positive illustrating that hydrophobic interaction was the primary binding force between quercetin and SPI. Results of FTIR and CD indicated that the binding with quercetin changed the secondary structure of SPI, resulting in a partially unfolded and more flexible structure. SDS-PAGE confirmed there was no covalent interaction between the two constituents. Molecular docking demonstrated that there were stable configurations and high matching degrees in both 11S and 7S proteins with quercetin via hydrogen bonds and hydrophobic interactions. Meanwhile, modification by quercetin enhanced the foaming and emulsifying capacities of SPI. These findings might provide theory reference for elucidation the mechanism of polyphenols-proteins interaction and development of related food additive products in future.

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

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

Interaction between secondary lipid oxidation products and hemoglobin with multi-spectroscopic techniques and docking studies

This study aimed to explore the effect of secondary lipid oxidation products (SLOPs) on hemoglobin (Hb) in chicken model. The fluorescence quenching technique and molecular docking were employed, and the apparent binding constants K_sv and the binding site numbers of SLOPs with Hb were calculated. The results revealed that three SLOPs (hexanal, benzaldehyde, and 2-pentanone) obviously promoted the oxidation of Hb, which is consistent with the change of Hb hydrophobicity, particle size, polydispersity index and zeta potential. The SLOPs strongly quenched the intrinsic fluorescence of Hb and triggered the alterations in the Hb structure. Hydrophobic interaction was the main force between SLOPs and Hb. Among the three SLOPs, hexanal demonstrated more stronger oxidation on Hb, which is closely related to its hydrophobic ability and structure characteristic, especially 10 μM hexanal is more prone to form an obvious unfolded structure and caused molecular aggregation than lower concentrations.

Interaction between Curcumin and β-Casein: Multi-Spectroscopic and Molecular Dynamics Simulation Methods

Effect of temperature and pH on the interaction of curcumin with β-casein was explored by fluorescence spectroscopy, ultraviolet-visible spectroscopy and molecular dynamics simulation. The spectroscopic results showed that curcumin could bind to β-casein to form a complex which was driven mainly by electrostatic interaction. The intrinsic fluorescence of β-casein was quenched by curcumin through static quenching mechanism. The binding constants of curcumin to β-casein were 6.48 × 10⁴ L/mol (298 K), 6.17 × 10⁴ L/mol (305 K) and 5.73 × 10⁴ L/mol (312 K) at pH 2.0, which was greater than that (3.98 × 10⁴ L/mol at 298 K, 3.90 × 10⁴ L/mol at 305 K and 3.41 × 10⁴ L/mol at 312 K) at pH 7.4. Molecular docking study showed that binding energy of β-casein-curcumin complex at pH 2.0 (−7.53 kcal/mol) was lower than that at pH 7.4 (−7.01 kcal/mol). The molecular dynamics simulation study showed that the binding energy (−131.07 kJ/mol) of β-casein-curcumin complex was relatively low at pH 2.0 and 298 K. α-Helix content in β-casein was decreased and random coil content was increased in the presence of curcumin. These results can promote a deep understanding of interaction between curcumin and β-casein and provide a reference for improving the bioavailability of curcumin.

Weak Binding of Epigallocatechin to α-Lactalbumin Greatly Improves Its Stability and Uptake by Caco-2 Cells

Improving the stability and bioavailability of catechins is of great importance. Epigallocatechin (EGC), the major catechin in green tea, is a potent antioxidant with numerous attributed health benefits. However, the low permeability and stability limit its enrichment in the diet for preventive medicine. In this study, we explored the interaction of EGC and α-lactalbumin by spectroscopic, thermodynamic, and crystallographic methods. The isothermal titration calorimetry experiments elucidated that α-lactalbumin binds to EGC at a ratio of 1:1 with a low affinity of (4.01 ± 0.11) × 10⁵ M^-1. A crystal structure solved at a high resolution (1.2 Å) provided direct evidence for the weak interaction between EGC and α-lactalbumin at an atomic level. The novel binding site was discovered at the exterior surface of α-lactalbumin for the first time, supporting a new binding behavior. Consequently, our results demonstrated that the binding of α-lactalbumin to EGC could protect EGC against light-induced, thermal-induced, and pH-induced damage. More importantly, the formed complex has better bioaccessibility than unbound EGC, which was approved by a cell absorption experiment. Such research is beneficial for designing protein-based nanocarriers for polyphenols.

Spectroscopic and docking studies of the interaction mechanisms of xylitol with α-casein and κ-casein

The molecular interactions of xylitol (XY) with α-casein (α-CN) and κ-casein (κ-CN) at pH 7.4 as a function of temperature (298, 308, and 318 K) were characterized by multispectral techniques and molecular docking. The fluorescence results showed that XY strongly quenched the intrinsic fluorescence of α- and κ-CN by static quenching, as well as the presence of a single binding site for XY on both proteins with a binding constant value of ∼10⁵ L/mol. The binding affinity of both proteins for XY decreased with increasing temperature, and Van der Waals forces, hydrogen bonding and protonation were the key forces in the interactions. The addition of XY altered the polarity of the microenvironment of proteins and changed their secondary structure from ordered to disordered. The molecular docking results showed that XY had different binding sites to α- and κ-CN, with several amino acids involved in the binding processes.

Enhanced physicochemical stabilities of cyanidin-3-O-glucoside via combination with silk fibroin peptide

Applications of cyanidin-3-O-glucoside (C3G) are limited due to the poor stabilities. In this work, we proposed using silk fibroin peptide (SFP) to bind with C3G and form nanocomposites (134.73 ± 4.51 nm) for stabilization. When interacted with C3G, the fluorescence of SFP contributed by tyrosine and phenylalanine amino acids was quenched, which was proved a static quenching with the β-sheet structure of SFP unchanged. With the further exploration of the physicochemical stabilities of C3G in the nanocomposites, we demonstrated that the tolerance of C3G to the alkaline environment and the retention ratio of C3G in various concentrations of metallic ion Cu²⁺ were significantly improved. In addition, the heat resistance of C3G in SFP at 80 °C was also enhanced with up to an increase of 2.5 times for the average half-life of C3G. Our results shed light on SFP could enhance physicochemical stabilities of C3G with maintaining its antioxidant activity.

Counter-Current Fractionation-Assisted Bioassay-Guided Separation of Active Compound from Blueberry and the Interaction between the Active Compound and α-Glucosidase

An efficient strategy for the selection of active compounds from blueberry based on counter-current fractionation and bioassay-guided separation was established in this study. Blueberry extract showed potential α-glucosidase inhibitory activity. After extraction by different solvents, the active components were enriched in water. The water extract was divided into six fractions via high-speed counter-current chromatography to further track the active components. Results indicated that the α-glucosidase inhibition rate of F4 was remarkable higher than the others. Cyanidin-3-glucoside (C3G) with a purity of 94.16% was successfully separated from F4 through column chromatography, and its structure was identified by ultraviolet spectral, Fourier-transformed infrared spectroscopy, high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry, ¹H nuclear magnetic resonance (NMR), and ¹³C NMR. The interaction mechanism between C3G and α-glucosidase was clearly characterized and described by spectroscopic methods, including fluorescence and circular dichroism (CD) in combination with molecular docking techniques. C3G could spontaneously bind with α-glucosidase to form complexes by hydrogen bonds. The secondary structure of α-glucosidase changed in varying degrees after complexation with C3G. The α-helical and β-turn contents of α-glucosidase decreased, whereas the β-sheet content and the irregular coil structures increased. Molecular docking speculated that C3G could form hydrogen bonds with α-glucosidase by binding to the active sit (Leu 313, Ser 157, Tyr 158, Phe 314, Arg 315, and two Asp 307). These findings may be useful for the development of functional foods to tackle type 2 diabetes.