Analysis of binding interaction of genistein and kaempferol with bovine α-lactalbumin

Comparison of interactions between alpha-lactalbumin and three protopanaxadiol ginsenosides: Impacts on the structure and antitumor properties

In this research, interactions between α-lactalbumin (ALA) and three protopanaxadiol ginsenosides [20(S)-Rg3, 20(S)-Rh2, and 20(S)-PPD] were compared to explore the effects of similar ligand on structure and cytotoxicity of ALA. Multi-spectroscopy revealed the binding between ALA and ginsenoside changed the conformation of ALA, which related to different structures and solubility of ligands. Scanning electron microscope illustrated that all ALA-ginsenoside complexes exhibited denser structures via hydrophobic interactions. Additionally, the cytotoxic experiments confirmed that the cytotoxicity of ginsenoside was enhanced after binding with ALA. Molecular docking showed all three ginsenosides were bound to the sulcus depression region of ALA via hydrogen bonding and hydrophobic interaction. Furthermore, molecular dynamics simulation elucidated the precise binding sites and pertinent system properties. Among all three composite systems, 20(S)-Rh2 had optimal binding affinity. These findings enhanced understanding of the synergistic utilization of ALA and ginsenosides as functional ingredients in food, medicine, and cosmetics.

Phosphorylation modification of bovine bone collagen peptide enhanced its effect on mineralization of MC3T3-E1 cells via improving calcium-binding capacity

This study aimed to investigate the effect of phosphorylation modification of collagen peptide on its calcium-binding capacity and pro-mineralization activity. In this study, collagen peptide (Leu-Thr-Phe, LTF) and phosphorylated LTF (P-LTF) were synthesized and further chelated with calcium ions. The results showed that phosphorylation of LTF significantly enhanced its calcium-binding capacity. Spectra analysis revealed that the calcium-binding sites of P-LTF were mainly carbonyl, carboxyl, and phosphate groups. Molecular docking further demonstrated that the phosphate group introduced by phosphorylation enhanced the calcium-binding capacity of LTF by ionic bonds and coordination bonds. The stability analysis results suggested that intestinal fluid could repair the peptide-calcium complex destroyed by gastric fluid. The cell experiment displayed that P-LTF-Ca significantly improved the mineralization activity of MC3T3-E1 cells, and the order of effective influence was P-LTF-Ca > LTF-Ca > P-LTF > LTF. This study provided the theoretical basis for the potential application of phosphorylation modification in improving bone health.

The differential non-covalent binding of epicatechin and chlorogenic acid to ovotransferrin and the enhancing efficiency of immunomodulatory activity

Seeking safe and environmentally friendly natural immunomodulators is a pressing requirement of humanity. This study investigated the differential binding characteristics of two polar polyphenols (PP), namely epicatechin (EC) and chlorogenic acid (CA), to ovotransferrin (OVT), and explored the relationship between structural transformations and immunomodulatory activity of OVT-PP complexes. Results showed that CA exhibited a stronger affinity for OVT than EC, mainly driven by hydrogen bonds and van der Waals forces. Complexation-induced conformational variations in OVT, including static fluorescence quenching, increased microenvironment polarity surrounding tryptophan and tyrosine residues, and the transition from disordered α-helix to stable β-sheet. Furthermore, the structural conformation transformation of OVT-PP complexes facilitated the enhancement of immunomodulatory activity, with the OVT-CA (10:2) complex demonstrating the best immunomodulatory activity. Principal component analysis (PCA) and Pearson correlation analysis revealed the immunomodulatory activities of the OVT-PP complexes were influenced by surface hydrophobicity (negatively correlated), β-sheet percentage and polyphenol binding constants. It could be inferred that PP complexation increased the surface polarity of OVT, consequently enhancing its immunomodulatory activity by promoting cell membrane affinity and antigen recognition. This study provides valuable guidance for effectively utilizing polyphenol-protein complexes in enhancing immunomodulatory activity.

Myricetin and morin hydrate inhibit amyloid fibril formation of bovine α-lactalbumin (BLA)

Amyloid fibrils are self-assembled aggregates of proteins and peptides that can lead to a broad range of diseases called amyloidosis. So far, no definitive and approved treatment to target directly amyloid fibrils has been introduced. Nevertheless, the search for small molecules with ability to inhibit and suppress fibril formation is an active and promising area of the research. Herein, the binding interactions and inhibitory effects of myricetin and morin hydrate on the in vitro fibrillation of bovine α-lactalbumin (BLA) have been investigated. The intrinsic fluorescence of BLA was quenched by myricetin and morin hydrate through combination of the static and dynamic quenching along with non-radiative Förster energy transfer mechanisms. The binding of these two flavonoids to BLA were not accompanied by major alteration in the conformation of BLA as evidenced by CD studies. The results of the fluorescence quenching analyses indicated almost the same binding affinities of myricetin and morin hydrate toward BLA (Kb ~ 106 M-1). However, the results of thioflavin T (ThT) assays showed that myricetin is a stronger inhibitor against BLA fibrillation compared to morin hydrate.

Influence of pH and ionic strength on the physicochemical and structural properties of soybean β-conglycinin subunits in aqueous dispersions

Understanding the impact of pH and ionic strength on the physicochemical and structural properties of soy proteins at subunit level is essential for design and fabrication of many plant-based foods. In this study, soybean β-conglycinin and its subunit fractions αα' and β were dispersed in solutions with different pH values (3.7, 7.6, and 9.0) at low (5 mM NaCl) and high (400 mM NaCl) ionic strengths, respectively. The solubility, rheology, particle size, zeta potential, microstructure, secondary structure, and tertiary structure of the different dispersions were analyzed using a range of analytical methods. The β-conglycinin, αα'- and β-subunits aggregated near the isoelectric point (pH 3.7). Increasing the ionic strength led to the assembly of more homogeneous units. An increase in ionic strength at pH 7.6 and pH 9.0 led to electrostatic screening, which promoted dissociation of the aggregates. The β-subunit showed a greater sensitivity to pH and ionic strength than the αα'-subunits. Based on the evidence from a range of analytical methods, the highly hydrophilic extension region of the αα'-subunits played an important role in determining the stability of the β-conglycinin dispersions under different environmental conditions. Moreover, the N-linked glycans appeared to impact the conformation and aggregation state of the β-conglycinin.

Interaction mechanism of okra (Abelmoschus esculentus L.) seed protein and flavonoids: Fluorescent and 3D-QSAR studies

The binding capacity of 10 flavonoids with okra seed protein (OSP) was studied by fluorescence spectroscopy. The structure of flavonoids had an obvious impact on binding performance. The binding ability of flavanone was lower than that of flavone, isoflavone and dihydrochalcone. The binding capacity of flavonoid glycoside was superior to that of the corresponding flavonoid aglycone. The binding ability was positively correlated with the number of phenolic hydroxyl groups on the B ring. The steric field and electrostatic field model constructed by 3D-QSAR method could well explain the above interaction behavior. Thermodynamic analysis suggested that the quenching mechanism of OSP caused by flavonoids was static quenching, and the binding-site number was 1. In addition, hydrogen bonding and van der Waals force dominated this interaction. The 3D and synchronous fluorescence spectra showed that there was no significant change in the polarity of the environment around tryptophan and tyrosine residues during binding.

Inhibition of toll-like receptor 4 activation by apigenin and chrysin via competition for sites and conformational changes

The activation of toll-like receptor 4 (TLR4) signaling is crucial for initiating and coordinating the immune response against infections, and is proved as a vital target for inflammatory diseases. Herein, TLR4 with sufficient amount and functional activity was generated by heterologous expression and used to investigate the mechanism of apigenin (Api)/chrysin (Chr) inhibition of TLR4 activation. The results demonstrated that Api/Chr exhibited a strong fluorescence quenching effect through a static quenching and a high binding affinity (Ka > 105 L·mol-1) with TLR4, indicating the potential of Api/Chr as a TLR4 inhibitor. Additionally, the binding of Api/Chr induced a loose and unstable conformation of TLR4 with evidence like the decreased hydrophobicity of the tryptophan microenvironment, decreased α-helix content and increased free sulfhydryl content, resulting in reduced stability of the TLR4. The computer simulations revealed that Api/Chr occupied the myeloid differentiation factor 2 (MD-2) binding region, preventing MD-2 from binding to TLR4. Furthermore, the accuracy of the binding site between Api/Chr and TLR4 was confirmed through genetic mutations. Overall, the mechanism by which Api/Chr inhibited TLR4 activation was elucidated at the macroscopic and molecular levels, providing the worthful information concerning the future therapeutic application of Api/Chr as a natural TLR4 inhibitor.

Foaming properties are improved by interactions between brewer's spent grain proteins and carrageenans in aqueous solution

BACKGROUND

Foaming properties and macromolecular interactions in solution among brewer's spent grain proteins (CP) and iota and lambda carrageenans (i-CG and l-CG, respectively) as a function of aqueous medium pH (2-6) and protein-polysaccharide ratio, R_CP:CG (1:1, 2:1 and 4:1), were studied. At these conditions, the CP colloidal stability was favored by the formation of soluble electrostatic complexes with CG. Fluorescence (intrinsic and extrinsic) spectroscopy and dynamic light scattering techniques, including particle size and ζ-potential analysis, were applied to know the phase behavior of the biopolymer systems. The bubbling method was used to produce foams, and the foam expansion (%) and half-life time (t_1/2 ) were determined.

RESULTS

Both CG promoted an increased Trp fluorescence emission depending on the pH, suggesting conformational changes in CP. The CG in mixed systems produced a significant decrease in the extrinsic fluorescence intensity, mainly at low pH values, highlighting a reduction in CP surface hydrophobicity. At the examined pH range, the ζ-potential values for mixed-systems were negative, and their magnitudes were intermediate between CP and CG, revealing the associative electrostatic nature of biopolymer interactions, which were dependent on the R_CP:CG . The particle size analysis confirmed the formation of soluble electrostatic complexes in solution. Finally, using i-CG at pH 2 or 3 and 2:1 R_CP:CG , the best foaming properties for mixed systems were observed.

CONCLUSION

The formation of electrostatic complexes with a compact assembly among biopolymers, high negative net charge, and colloidal stability convert the CP-CG mixed solutions into promising biopolymer systems for food foams production. © 2022 Society of Chemical Industry.

Comparison of interaction, structure, and cell proliferation of α-lactalbumin-safflower yellow complex induced by microwave heating or conventional heating

BACKGROUND

The protein-polyphenol interaction mechanism has always been a research hotspot, but their interaction is affected by heat treatment, which is widely applied in food processing. Moreover, the effects of microwave or water-bath heating on the protein-polyphenol interaction mechanism have been not clarified. The pasteurization condition (65 °C, 30 min) was selected to compare the effects of microwave or water bath on binding behavior, structure, and cell proliferation between α-lactalbumin (α-LA) and safflower yellow (SY), thus providing a guide for the selection of functional dairy processing conditions.

RESULTS

Microwave heat treatment of α-LA-SY resulted in stronger fluorescence quenching than that of conventional heat treatment. Moreover, the binding constant K_a of all α-LA-SY samples was augmented significantly after microwave or water bath treatment, and microwave-heated α-LA-SY showed the maximum K_a . Fourier transform infrared spectroscopy showed that microwave heating resulted in more ordered structures of α-LA into its disordered structures than water bath heating. However, the ferric reducing antioxidant power and chroma value of α-LA-SY were more reduced by microwave heating than by water bath heating. Moreover, microwave heating facilitated the cell proliferation of α-LA-SY compared with water bath treatment.

CONCLUSION

It was demonstrated that microwave heating promoted interaction between α-LA and SY more than water bath heating did. Microwave heat treatment was a safe and effective way to enhance the binding affinity of α-LA to SY, being a potential application in food industry. © 2022 Society of Chemical Industry.

Insights into the interaction mechanism of acid phosphatase from Lateolabrax japonicus livers and rosmarinic acid using multispectroscopy and molecular docking

Acid phosphatase (ACP) is a key enzyme that hydrolyzes inosinic acid. The mechanisms underlying the interaction between rosmarinic acid (RA) and ACP and the inhibition of the enzyme were investigated using inhibition kinetics, UV-visible and fluorescence spectroscopy, circular dichroism, and molecular docking. The results showed that RA was a reversible inhibitor of ACP and that the inhibition mechanism was uncompetitive. The ACP fluorescence was quenched by RA, and the quenching mode was static. The interaction of ACP with RA was driven by H bonds and van der Waals forces. The addition of RA increased the α-helix content and decreased the β-sheet, β-turn, and random coil contents in ACP, thereby altering the secondary structure of the enzyme. This study enriched our understanding of inhibitory and interaction mechanisms involving ACP and RA.

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.

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

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

Investigation of binding interaction between bovine α-lactalbumin and procyanidin B2 by spectroscopic methods and molecular docking

The interactions between bovine α-lactalbumin and procyanidin B2 were fully investigated by spectroscopic methods and molecular docking. This study hypothesized that ALA could spontaneously interact with procyanidin B2 to form protein-based complex delivery carrier. Far UV CD and FTIR data demonstrated ALA's secondary structures were altered and intrinsic fluorescence quenching suggested ALA conformation was changed with procyanidin B2. Calorimetric technique illustrated ALA-procyanidin B2 complexation was a spontaneous and exothermic process with the number of binding site (n, 3.53) and the binding constant (K_b, 2.16 × 10⁴ M^-1). A stable nano-delivery system with ALA can be formed for encapsulating, stabilizing and delivering procyanidin B2. Molecular docking study further elucidated that hydrogen bonds dominated procyanidin B2 binding to ALA in a hydrophobic pocket. This study shows great potential in using ALA as protein-based nanocarriers for oral delivery of hydrophilic nutraceuticals, because procyanidin B2-loaded ALA complex delivery systems can be spontaneously formed.

Effects of Baicalein and Chrysin on the Structure and Functional Properties of β-Lactoglobulin

Two flavonoids with similar structures, baicalein (Bai) and chrysin (Chr), were selected to investigate the interactions with β-lactoglobulin (BLG) and the influences on the structure and functional properties of BLG by multispectral methods combined with molecular docking and dynamic (MD) simulation techniques. The results of fluorescence quenching suggested that both Bai and Chr interacted with BLG to form complexes with the binding constant of the magnitude of 10⁵ L·mol⁻¹. The binding affinity between BLG and Bai was stronger than that of Chr due to more hydrogen bond formation in Bai–BLG binding. The existence of Bai or Chr induced a looser conformation of BLG, but Chr had a greater effect on the secondary structure of BLG. The surface hydrophobicity and free sulfhydryl group content of BLG lessened due to the presence of the two flavonoids. Molecular docking was performed at the binding site of Bai or Chr located in the surface of BLG, and hydrophobic interaction and hydrogen bond actuated the formation of the Bai/Chr–BLG complex. Molecular dynamics simulation verified that the combination of Chr and BLG decreased the stability of BLG, while Bai had little effect on it. Moreover, the foaming properties of BLG got better in the presence of the two flavonoids compounds and Bai improved its emulsification stability of the protein, but Chr had the opposite effect. This work provides a new idea for the development of novel dietary supplements using functional proteins as flavonoid delivery vectors.

Lactoferrin-thymol complex for the disinfection of gram-positive Staphylococcus aureus and Gram-negative Escherichia coli

Seeking all-nature derived antibacterial agents with effective disinfection function, high human safety as well as environment-friendly characteristics are highly required in the food industry. Herein, we report the lactoferrin-thymol (LF-Thy) complex as an effective killing agent against Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus). The multi-spectroscopy results clearly demonstrate the combination of LF and Thy to form the LF-Thy complex, accompanied with LF conformation variations including the increase in the hydrophobicity of amino acid residues and changes in the types of secondary conformation distribution in LF. Molecular docking results show that LF exhibits three possible binding sites and five predicted stable binding modes for Thy with the help of hydrogen bonding and hydrophobic interactions. Moreover, LF-Thy demonstrated a significantly higher antibacterial ability compared to LF and displays effective disinfection function against E. coli and S. aureus. The minimum inhibitory concentration (MIC) of LF toward E. coli and S. aureus is >40 mg mL^-1 and 40 mg mL^-1, which decreases to 10 mg mL^-1 and 5 mg mL^-1 after combination with Thy, respectively. This work demonstrates the promising antibacterial activities of the LF-Thy complex and provides an alternative agent for combating bacterial infection in the food industry, which holds great potential for promoting the development of the all-natural healthcare food complex.

Interaction mechanism of flavonoids with whey protein isolate: A spectrofluorometric and theoretical investigation

The interaction mechanism between whey protein isolate (WPI) and flavonoids was investigated based on the spectrofluorometric and theoretical methods in this study. The binding capacities of 15 flavonoids with WPI were compared. Then, the 3D-QSAR model describing their binding behavior was established to illustrate the effect of flavonoid structure on binding. It was found that the flavonoids with electronegative group at C-3 or large substituent at C-3 and C-7 possessed high binding performance. The thermodynamic analysis further indicated the hydrophobic force was the main driving force for binding of WPI and flavonoids. Both synchronous and 3D fluorescence analysis suggested that the microenvironment around tryptophan residues had changed, which coincided with the result of molecular docking that tryptophan residue of α-lactalbumin contributed significantly to hydrogen bonding. Our results suggested that the combination of 3D-QSAR and molecular docking may prompt the interaction research between food-derived proteins and polyphenols.

Albumin-based dynamic double cross-linked hydrogel with self-healing property for antimicrobial application

Hydrogels as ideal material are widely used in biomedical field against bacterial infection. Hydrogels synthesized from natural protein possess better biocompatibility than that synthesized from synthetic polymers. In this work, we designed bovine serum albumin (BSA) based hydrogel via double dynamic crosslinking. The cleavage and rearrangement of disulfide bonds of BSA triggered by glutathione (GSH) forms a disulfide bridge network, and tetrakis (hydroxymethyl) phosphonium sulfate (THPS) grafts the amino groups of BSA by a Mannich-type reaction to form a second network. Integrating THPS into the BSA/GSH system enables gel formation and endows excellent antimicrobial properties. Rheological tests showed the hydrogel featuring elasticity, good mechanical strength and self-healing properties. Antibacterial and cytotoxicity tests proved the hydrogel excellent bacteriostatic ability and low cytotoxicity. This albumin-based hydrogel with low cost is expected to realize wide biomedical applications.

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.

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

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

The non-covalent interaction between two polyphenols and caseinate as affected by two types of enzymatic protein crosslinking

Caseinate was crosslinked by horseradish peroxidase (HRP) or microbial transglutaminase (TGase) and mixed with kaempferol and quercetin at 293-313 K (i.e. 20-40 °C), respectively. Generally, these two polyphenols dose-dependently induced fluorescent quenching in caseinate or its crosslinked products via a static mechanism, while enzymatic crosslinking endowed caseinate with higher affinity for the polyphenols with increased apparent binding constants [(9.94-168.77) × 10⁵versus (4.92-6.53) × 10⁵ L/mol], unchanged binding site number and slightly shortened binding distance. To form protein-polyphenol complexes, hydrophobic force was the main driving force for the HRP-crosslinked caseinate and unreacted caseinate, while hydrogen-bonds and van der Waals force were the main driving forces for the TGase-crosslinked caseinate. Overall, quercetin was more potent than kaempferol to bind to the proteins, while TGase-mediated caseinate crosslinking induced the highest affinity to the polyphenols with the largest ΔG decrease. Thus, two types of crosslinking impacted the driving forces, apparent binding constant and thermodynamic indices of caseinate-polyphenol interaction.

In vitro phenols bioaccessibility and antioxidant activity of goat milk yogurt fortified with Rhus coriaria leaf powder

Goat yogurt samples fortified with 20% (w/v) Rhus coriaria leaf powder were in vitro digested in order to evaluate the total phenolic content (TPC), antioxidant activity (AA), and bioaccessibility of phenolic compounds in the digestate. After digestion, TPC and AA values of the R. coriaria-fortified yogurts increased compared to the undigested yogurts (P < 0.001). In particular, TPC has increased about twice; whereas, AA values have increased about 10 and 6 times, for ABTS and FRAP assays, respectively. The bioaccessibility index was well above the 100% for all identified phenols; except for (-)-epicatechin (82.04%), rutin (51.51%), and gallic acid (5.42%). This different behavior highlighted that the bioaccessibility was modulated by both the yogurt-polyphenol complexes and phenol stability under digestion system. These findings can contribute to elucidate the influence of in vitro digestion on antioxidant capacity and polyphenols recovery infortified yogurts, and may help in the design of dairy products with better functional quality PRACTICAL APPLICATION: Rhus coriaria L. (Sumac) is a polyphenol-rich Mediterranean plant that may be used as functional ingredient to enrich fermented food such as yogurt. However, in fortified yogurts the evaluation of bioaccessibility, that is, the compounds released from the yogurt and stable in the digestive environment, thus able to exert their biological effects on the gastrointestinal system, is more important than the content of these compounds in the corresponding food. This study highlighted the phenolic content, antioxidant activity, and bioaccessibility of phenolic compounds in goat milk yogurt fortified with R. coriaria leaf powder after simulated gastro-pancreatic digestion.

Bovine alpha-lactalbumin assemblies with capsaicin: Formation, interactions, loading and physiochemical characterization

Numerous human conditions can benefit from diets rich in proteins and bioactives, such as capsaicin (CAP), yet their effective delivery is a sensorial, scientific and technological challenge. This study hypothesized that CAP can form various complexes with native bovine alpha-lactalbumin (holo-ALA) and decalcified-ALA (apo-ALA). Calorimetric and spectroscopic techniques reveals ALA-CAP molecular complexation is spontaneous, exothermic and accompanied by various conformational changes. ITC shows the interaction stoichiometry (n) and binding constant (K_b) for holo-ALA to be 0.87 ± 0.03, 1.54 ± 0.23 × 10⁵ M^-1 and for apo-ALA to be 0.64 ± 0.09, 9.41 ± 2.16 × 10⁴ M^-1. Molecular docking further elucidates that hydrogen bonds govern CAP binding to holo-ALA while hydrophobic interactions dominate binding to apo-ALA in a structural cleft. Finally, this work shows these interactions along with controlled aggregation can be utilized to form CAP-loaded colloids with encapsulation efficiency of 47.1 ± 1.0%. Thus, this study shows great promise in the prospective use of ALA as an edible delivery vehicle for CAP.

Characteristics of the interaction mechanisms of xylitol with β-lactoglobulin and β-casein: Amulti-spectral method and docking study

Proteins and functional polyols are essential food ingredients coexisting in the food matrix, and therefore, interactions between them inevitably occur. In this study, the interaction mechanisms of xylitol (XY) with bovine milk β-lactoglobulin (β-LG) and β-casein (β-CN) were studied using multispectral techniques and molecular docking. It was found that XY strongly quenched the intrinsic fluorescence of β-LG and β-CN by static quenching. The values of the binding constants were K_A(β-LG-XY) = 3.369 × 10⁴ L/mol and K_{A(β-CN- XY)} = 7.821 × 10⁴ L/mol, indicating that the binding affinity of XY to β-CN was higher than that for β-LG. Hydrogen bonding and van der Waals forces played a major role in the interactions of XY with β-LG and β-CN, and both interactions were exothermic. Simultaneous fluorescence, three-dimensional fluorescence, and circular dichroism spectroscopy showed that binding of XY did not change the secondary structure of β-LG. However, XY interaction with β-CN led to the conversion of α-helices to random coils and structural loosening. In addition, molecular docking predicted the most likely binding sites of XY in both proteins and the interaction forces involved in binding, confirming the spectroscopic results. This study improves the understanding of the interactions of XY with β-LG and β-CN in functional dairy products and provides a theoretical basis for the addition of XY in a functional milk base.

Investigating the calcium binding characteristics of black bean protein hydrolysate

The black bean protein has been widely utilized to prepare hydrolysates with different bioactive properties. Herein, we hydrolyzed the black bean protein to prepare hydrolysate with calcium binding activity and characterized its behavior. Our results showed that ficin was superior in obtaining hydrolysate with calcium binding capacity in comparison with trypsin, alcalase and bromelain. In particular, the optimal capacity of ficin hydrolysate reached 77.54 ± 1.61 μg mg-1, where the optimal hydrolysis conditions of ficin were a temperature of 70 °C, a pH value of 6.2, an enzyme concentration of 1.61% and a time of 3 h. This might be due to high proportions of aspartic acid and glutamic acid (35.59%). Further spectral analysis evidenced the formation of hydrolysate-calcium complexes, demonstrating that the interaction between hydrolysate and calcium ions primarily occur on carboxyl oxygen atoms and amino nitrogen atoms. These findings provide a possible utilization of black bean hydrolysate to serve as a calcium supplement nutraceutical to enhance the absorption and bioavailability.

Spectroscopic studies and molecular modelling of the aflatoxin M1-bovine α-lactalbumin complex formation

Since the high incidence of aflatoxin M1 (AFM1) in milk and dairy products poses a serious risk to human health, this work aimed to investigate the complex formation between bovine α-lactalbumin (α-La) and AFM1 using different spectroscopic methods coupled with molecular docking studies. Fluorescence spectroscopy measurements demonstrated the AFM1 addition considerably reduced the α-La fluorescence intensity through a static quenching mechanism. The results indicated on the endothermic character of the reaction, and the hydrophobic interaction played a major role in the binding between AFM1 and α-La. The binding site stoichiometric value (n = 1.32) and a binding constant of 2.12 × 10³ M^-1 were calculated according to the Stern-Volmer equation. The thermodynamic parameters ΔH, ΔS and ΔG_b were determined at 93.58 kJ mol^-1, 0.378 kJ mol^-1 K^-1 and -19.17 ± 0.96 kJ mol^-1, respectively. In addition, far-UV circular dichroism studies revealed alterations in the α-La secondary structures when the α-La-AFM1 complex was formed. An increased content of the α-helix structures (from 35 to 40%) and the β-sheets (from 16 to 19%) were observed. Furthermore, protein-ligand docking modelling demonstrated AFM1 could bind to the hydrophobic regions of α-La protein. Overall, the gathered results confirmed the α-La-AFM1 complex formation.

Binding mechanism and antioxidant capacity of selected phenolic acid - β-casein complexes

Phenolic acids are added to some dairy products as functional ingredients. The molecular interactions between the phenolic acids and milk proteins impacts their functional performance and product quality. In this study, the interactions between a milk protein (β-casein) and a number of phenolic acids was investigated: 3,4-dihydroxybenzoic acid (DA); gallic acid (GA); syringic acid (SA); caffeic acid (CaA); ferulic acid (FA); and, chlorogenic acid (ChA). The structural characteristics of the phenolic acids, such as type, hydroxylation, methylation, and steric hindrance, affected their binding affinity to β-casein. The strength of the binding constant decreased in the following order: CaA > ChA > FA > SA > GA > DA. Cinnamic acid derivatives (CaA, FA, and ChA) exhibited a stronger binding affinity with β-casein than benzoic acid derivatives (DA, GA, and SA). Hydrophobic forces and electrostatic interactions dominated the interactions of β-casein with benzoic acid and cinnamic acid derivatives, respectively. The number of hydroxyl groups on the phenolic acids enhanced their binding ability, while steric hindrance effects reduced their binding ability. The influence of methylation depended on phenolic acid type. After binding with phenolic acids, the conformation of the β-casein changed, with a loss of random coil structure, an increase in α-helix structure, and a decrease in surface hydrophobicity. Furthermore, the presence of β-casein decreased the in vitro antioxidant capacities of the phenolic acids, especially for gallic acid. These findings provide some useful insights into the structure-activity relationships of the interaction between β-casein and phenolic acids.