Characterization of binding interactions of anthraquinones and bovine β-lactoglobulin

Interactions between β-lactoglobulin and polyphenols: Mechanisms, properties, characterization, and applications

β-lactoglobulins (βLGs) have a wide range of applications in food because of their ability to emulsify, foam, and gel. This makes them good functional additives. However, their performance depends on temperature, pH, and mineral levels, so their functional qualities are limited in particular applications. How polyphenols (PPs) interact with βLG is crucial for the functional characteristics and quality of dietary compounds. In most food systems, a spontaneous interaction between proteins and PPs results in a "protein-PP conjugate," which is known to affect the sensory, functional, and nutraceutical qualities of food products. The βLG-PP conjugates can be used to enhance the quality of food. This article emphasizes analytical techniques for describing the characteristics of βLG-PP complexes/conjugates. It also goes over the functions of βLG-PP conjugates, including their solubility, thermal stability, emulsifying, and antioxidant qualities. The majority of βLG-PPs interactions is due to non-covalent (H-bonding, electrostatic interactions) or covalent bonds that are mostly caused by βLG or PP oxidation through enzymatic or non-enzymatic mechanisms. Furthermore, the conformation or type of proteins and PPs, as well as environmental factors like pH and temperature, have a significant impact on proteins-PPs interactions. Higher thermal stability, antioxidant activities, and superior emulsifying capabilities of the βLG-PP conjugates make them useful as innovative additives to enhance the quality and functions of food products.

Probing the interactions of genistein with HMGB1 through multi-spectroscopic and in-silico approaches

Functional regulation of proteins by ligand-protein interactions plays a crucial role in understanding biological processes and identifying potential drugs. High mobility group box 1 (HMGB1) plays a pivotal role in sterile inflammation as a key immunomodulatory protein. Genistein, a well-known isoflavone compound, has been shown to have neuroprotective effects. In this study, we investigated the genistein-HMGB1 interactions using experimental and computational approaches. Our results revealed that genistein binds to HMGB1 with a KD value of 6.06 × 10-5 M. The addition of genistein significantly quenched the fluorescence of HMGB1. Thermodynamic analyses demonstrated that hydrogen bonds and hydrophobic forces are the primary forces during the binding process. Furthermore, the interaction between genistein and HMGB1 led to changes in the microenvironment of protein chromogenic amino acids and subtle alterations in the protein secondary structure. Molecular modeling results indicate that Pro95, Pro98, and Lys154 are the major amino acid residues for genistein binding to HMGB1. Meanwhile, at the cellular level, an inhibitory effect of genistein on HMGB1-induced NO release from microglia was observed, demonstrating an inhibition rate of 42.1 %. Our studies demonstrated that genistein could be applied in treating neurological diseases through its interaction with HMGB1.

Albumin as an Effective Auxiliary Agent for the Enriched Extraction of Anthraquinones and Curcumin from Plant Matrices

Nowadays, several processes to enrich desired bioactive compounds in plant extracts have been developed. The objective of the present study was to assess the performance of bovine serum albumin in increasing the extractive yields of anthraquinones and diarylheptanoids from their respective raw plant powder extracts. Aloe emodin, rhein, emodin, and chrysophanol, from Polygonum cuspidatum, Senna alexandrina, Rhamnus frangula, and Rheum palmatum, and curcumin from Curcuma longa were analyzed in parent dry extracts, solubilized either with water, ethanol, or hydro-alcoholic mixtures, and in ones treated with aqueous solutions of bovine serum albumin by HPLC with UV/Vis detection. The different ratios between the volumes of solvents, powdered plant extracts, and bovine serum albumin were tested. The addition of albumin provided an increase in the yields of aloe emodin in the range 7.8-50.4-fold; of rhein in the range 6.1-14.1-fold; of emodin in the range 19.7-39.7-fold; of chrysophanol in the range 15.1-28.7-fold; and, finally, of curcumin of 32.1-fold. The addition of bovine serum albumin in the processing of plant extracts has been shown to be a novel and a valid alternative, comparing favourably to already reported methodologies. The easy-to-handle procedures, readily accessible facilities, and the employment of cheap substrates and reagents represent the most evident advantages of the methodology described herein.

Covalent conjugation with polyphenol reduced the sensitization of walnut and ameliorated allergy by enhancing intestinal epithelial barrier in mice

In order to reduce the sensitization of walnut protein (WP), the effects of the interaction between WP and (-)-Epigallocatechin gallate (EGCG), quercetin, trans-ferulic acid, and resveratrol were investigated. Covalent and non-covalent conjugations were compared. The results suggested that covalent conjugation reduced the free amino acid content, sulfhydryl content, and surface hydrophobicity. When compared to non-covalent conjugation, covalent modification showed a lower IgE binding capacity, accompanied by changes in protein conformation. Moreover, animal experiments revealed that there were up-regulation of transforming growth factor-β, T-box expressed in t cells, and forkhead transcription factor Foxp3 mRNA expression, and down-regulation of IL-4, IL-17, GATA binding protein 3 and retinoid-related orphan nuclear receptor γt mRNA expression in the conjugate groups. These results suggested that covalent conjugation of polyphenols, especially EGCG, likely ameliorated allergy by promoting Th1/Th2 and Treg/Th17 balance and alleviating allergy-induced intestinal barrier damage, which might be a support in reducing the allergenicity of WP.

Modular preparation of biphenyl triazoles via click chemistry as non-competitive hyaluronidase inhibitors

Hyaluronidase is a promising target in drug discovery, given its overexpression in a range of physiological and pathological processes, including tumor migration, skin aging, sagging, and wrinkling, as well as inflammation and bacterial infections. In this study, to identify novel hyaluronidase inhibitors, we applied click chemistry for the modular synthesis of 370 triazoles in 96-well plates, starting with biphenyl azide. Utilizing an optimized turbidimetric screening assay in microplates, we identified Fmoc-containing triazoles 5 and 6, as well as quinoline-containing triazoles 15 and 16, as highly effective hyaluronidase inhibitors. Subsequent research indicated that these triazoles potentially interact with a novel binding site of hyaluronidase. Notably, these inhibitors displayed minimal cytotoxicity and showed promising anti-inflammatory effects in LPS-stimulated macrophages. Remarkably, compound 6 significantly reduced NO release by 74 % at a concentration of 20 μM.

Possible NLO response and electrical/charge transfer capabilities of natural anthraquinones as p-type organic semiconductors: a DFT approach

CONTEXT

Organic semiconductors (OSCs) have attracted a great deal of interest in recent days. There are various types of OSCs, among which small molecules have various inherent benefits. Further research is needed to advance this new kind of material because the field is still developing, and the current focus is on creating small molecules that exist naturally for OSCs. OSCs with nonlinear optical (NLO) characteristics offer a significant advantage over others. Thus, this study theoretically investigates naturally occurring anthraquinones such as chrysophanol and rhein as potential OSCs, as well as their NLO properties. The calculated properties include the ionization potential (IP), electron affinity (EA), and bandgap (Eg). The FMO energy levels together with the Eg, IP (8.17-8.53 eV), and EA (1.87-2.44 eV) suggest the semiconductor nature of the studied compounds. The calculated values of reorganization energy (λ) and transfer integrals (V) suggest the p-type character of both molecules. Rhein has the lowest λh (0.19 eV) and Eg (3.28 eV) and the highest Vh, predominantly because of its better p-type character. The polarizability increases due to the presence of an electron-withdrawing substituent, leading to better NLO performance for Rhein, which is supported by its lower LUMO and Eg values.

METHODS

The studied molecules were optimized with the DFT/B3LYP-GD3/6-31+G(d,p) method using Gaussian 16 software. The crystal structure was simulated with Materials Studio 7.0, and the V values were calculated with the ADF package. The CDD and DOS plots were obtained with the Multiwfn 3.8 program.

A Review on Bioactive Anthraquinone and Derivatives as the Regulators for ROS

Anthraquinones are bioactive natural products, which are often found in medicinal herbs. These compounds exert antioxidant-related pharmacological actions including neuroprotective effects, anti-inflammation, anticancer, hepatoprotective effects and anti-aging, etc. Considering the benefits from their pharmacological use, recently, there was an upsurge in the development and utilization of anthraquinones as reactive oxygen species (ROS) regulators. In this review, a deep discussion was carried out on their antioxidant activities and the structure-activity relationships. The antioxidant mechanisms and the chemistry behind the antioxidant activities of both natural and synthesized compounds were furtherly explored and demonstrated. Due to the specific chemical activity of ROS, antioxidants are essential for human health. Therefore, the development of reagents that regulate the imbalance between ROS formation and elimination should be more extensive and rational, and the exploration of antioxidant mechanisms of anthraquinones may provide new therapeutic tools and ideas for various diseases mediated by ROS.

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.

Insights into the interaction of cyclooxygenase and lipoxygenase with natural compound 3,4',5,7-Tetrahydroxyflavone based on multi-spectroscopic and metabolomics

Hypoxia induce right ventricular dysfunction in human heart, but the molecular mechanism remains limited. As known, cyclooxygenases (COX) and lipoxygenases (LOX) play a key role in the cardiovascular system under hypoxia. 3,4',5,7-Tetrahydroxyflavone (THF), which widely exists in a variety of plants and vegetables, is famous for good ability to relieve cardiac injury, but the mechanism remains to be further understood. In this study, we firstly estimated the preventive role of THF against hypoxia-induced right ventricular dysfunction. Metabolomics analysis showed there were differential metabolites involved in above process, which helped us to screen the crucial regulated enzymes of these metabolites. Molecular docking and multi-spectroscopic revealed the molecular mechanism of interaction between THF and COX/LOX. Results suggested that THF bound to COX/LOX through static quenching and these bindings were driven by hydrogen bonds. After binding with THF, the secondary structure of COX/LOX was changed. In general, this study indicated that THF inhibited COX/LOX by spontaneously forming complexes with them.

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.

Inhibitory Effects of Myriocin on Non-Enzymatic Glycation of Bovine Serum Albumin

Advanced glycation end products (AGEs) are the compounds produced by non-enzymatic glycation of proteins, which are involved in diabetic-related complications. To investigate the potential anti-glycation activity of Myriocin (Myr), a fungal metabolite of Cordyceps, the effect of Myr on the formation of AGEs resulted from the glycation of bovine serum albumin (BSA) and the interaction between Myr and BSA were studied by multiple spectroscopic techniques and computational simulations. We found that Myr inhibited the formation of AGEs at the end stage of glycation reaction and exhibited strong anti-fibrillation activity. Spectroscopic analysis revealed that Myr quenched the fluorescence of BSA in a static process, with the possible formation of a complex (approximate molar ratio of 1:1). The binding between BSA and Myr mainly depended on van der Waals interaction, hydrophobic interactions and hydrogen bond. The synchronous fluorescence and UV-visible (UV-vis) spectra results indicated that the conformation of BSA altered in the presence of Myr. The fluorescent probe displacement experiments and molecular docking suggested that Myr primarily bound to binding site 1 (subdomain IIA) of BSA. These findings demonstrate that Myr is a potential anti-glycation agent and provide a theoretical basis for the further functional research of Myr in the prevention and treatment of AGEs-related diseases.

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

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

DeepBindBC: a practical deep learning method for identifying native-like protein-ligand complexes in virtual screening

Identifying native-like protein-ligand complexes (PLCs) from an abundance of docking decoys is critical for large-scale virtual drug screening in early-stage drug discovery lead searching efforts. Providing reliable prediction is still a challenge for most current affinity predicting models because of a lack of non-binding data during model training, lost critical physical-chemical features, and difficulties in learning abstract information with limited neural layers. In this work, we proposed a deep learning model, DeepBindBC, for classifying putative ligands as binding or non-binding. Our model incorporates information on non-binding interactions, making it more suitable for real applications. ResNet model architecture and more detailed atom type representation guarantee implicit features can be learned more accurately. Here, we show that DeepBindBC outperforms Autodock Vina, Pafnucy, and DLSCORE for three DUD.E testing sets. Moreover, DeepBindBC identified a novel human pancreatic α-amylase binder validated by a fluorescence spectral experiment (K_a= 1.0×10⁵ M). Furthermore, DeepBindBC can be used as a core component of a hybrid virtual screening pipeline that incorporating many other complementary methods, such as DFCNN, Autodock Vina docking, and pocket molecular dynamics simulation. Additionally, an online web server based on the model is available at http://cbblab.siat.ac.cn/DeepBindBC/index.php for the user's convenience. Our model and the web server provide alternative tools in the early steps of drug discovery by providing accurate identification of native-like PLCs.

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.

New ligand-binding sites identified in the crystal structures of β-lactoglobulin complexes with desipramine

The homodimeric β-lactoglobulin belongs to the lipocalin family of proteins that transport a wide range of hydrophobic molecules and can be modified by mutagenesis to develop specificity for novel groups of ligands. In this work, new lactoglobulin variants, FAF (I56F/L39A/M107F) and FAW (I56F/L39A/M107W), were produced and their interactions with the tricyclic drug desipramine (DSM) were studied using X-ray crystallography, calorimetry (ITC) and circular dichroism (CD). The ITC and CD data showed micromolar affinity of the mutants for DSM and interactions according to the classical one-site binding model. However, the crystal structures unambiguously showed that the FAF and FAW dimers are capable of binding DSM not only inside the β-barrel as expected, but also at the dimer interface and at the entrance to the binding pocket. The presented high-resolution crystal structures therefore provide important evidence of the existence of alternative ligand-binding sites in the β-lactoglobulin molecule. Analysis of the crystal structures highlighted the importance of shape complementarity for ligand recognition and selectivity. The binding sites identified in the crystal structures of the FAF-DSM and FAW-DSM complexes together with data from the existing literature are used to establish a systematic classification of the ligand-binding sites in the β-lactoglobulin molecule.

Antioxidant activity, stability, in vitro digestion and cytotoxicity of two dietary polyphenols co-loaded by β-lactoglobulin

The combination of multiple dietary polyphenols may have synergistic beneficial effects. And the beneficial effects can be further improved by the encapsulation of proteins. The interactions of procyanidin B2 (PB2) and/or dihydromyricetin (DMY) with β-lactoglobulin (β-LG) were investigated using multi-spectroscopic techniques and molecular docking. The structural change of β-LG in the presence of PB2 and/or DMY was demonstrated by dynamic light scattering, Fourier transform infrared spectroscopy and circular dichroism spectroscopy. Response surface analysis was used to optimize the synergistic antioxidant activity between PB2 and DMY. Besides, the antioxidant activity, stability, in vitro digestion and cytotoxicity of PB2 and DMY in the binary and ternary systems were investigated. These studies will elucidate the interaction mechanism of PB2 and/or DMY with β-LG. The research results can provide theoretical support for the development of functional foods and beverages with synergistic activity, improved stability and bioaccessibility, thereby promoting human health and preventing diseases.

Interactions between puerarin/daidzein and micellar casein

Puerarin (PUE) and daidzein (DAI) are polyphenols with extensive biological activities. In the present study, the interactions between PUE/DAI and micellar casein (MC) were investigated, and the physicochemical properties of their complexes were analyzed. The results of fluorescence spectrum analysis and molecular docking revealed that the main interactions between DAI and MC were hydrophobic forces, while that between PUE and MC was hydrogen bonding. The FTIR and XRD analyses confirmed the formation of complexes between MC and PUE/DAI. After binding to PUE/DAI, the size of MC increased. The weight loss rate of MC decreased after complexing with PUE/DAI, but its morphology was not extensively modified. The DPPH radical scavenging capacities of PUE-MC and DAI-MC complexes were higher than those of free PUE/DAI in both water and ethanol. In vitro release experiments showed that the release rate of PUE/DAI was inhibited by MC under simulated intestinal conditions. PRACTICAL APPLICATIONS: The low water solubility and poor bioavailability of PUE and DAI limit their application. Micellar casein has high affinity for PUE and DAI. After encapsulated by micellar casein, the release rates of PUE and DAI were prolonged during simulated intestinal digestion. The results would provide useful information for improving the solubility and bioavailability of PUE and DAI, and broadening the use of them in the food and pharmaceutical industry.

Binding of Chloroquine to Whey Protein Relieves Its Cytotoxicity while Enhancing Its Uptake by Cells

Chloroquine (CQ) is a famous medicine for treatment of diseases including malaria and pneumonia caused by COVID-19, but gastrointestinal disorder caused by its oral administration is a great concern. Milk is usually recommended to be taken with CQ to reduce such effect. However, the mechanism underlying this phenomenon remains unknown. Here, we found that β-lactoglobulin (β-LG), α-lactalbumin (α-LA), bovine serum albumin (BSA), and lactoferrin (LF) in whey proteins were able to interact with CQ to form complexes as suggested by fluorescence resonance energy transfer (FRET) and molecular docking. Indeed, the crystal structure revealed that β-LG is bound to CQ through hydrophobic interactions and hydrogen bonding with a ratio of 1:1. Consequently, the formation of these protein-CQ complexes not only reduced the cytotoxicity of chloroquine to the stomach and gut cells but also facilitated its uptake by cells. This work gave an example to understand the relationship between food and drug.

Casein Micelles as an Emerging Delivery System for Bioactive Food Components

Bioactive food components have potential health benefits but are highly susceptible for degradation under adverse conditions such as light, pH, temperature and oxygen. Furthermore, they are known to have poor solubilities, low stabilities and low bioavailabilities in the gastrointestinal tract. Hence, technologies that can retain, protect and enable their targeted delivery are significant to the food industry. Amongst these, microencapsulation of bioactives has emerged as a promising technology. The present review evaluates the potential use of casein micelles (CMs) as a bioactive delivery system. The review discusses in depth how physicochemical and techno-functional properties of CMs can be modified by secondary processing parameters in making them a choice for the delivery of food bioactives in functional foods. CMs are an assembly of four types of caseins, (α_s1, α_s2, β and κ casein) with calcium phosphate. They possess hydrophobic and hydrophilic properties that make them ideal for encapsulation of food bioactives. In addition, CMs have a self-assembling nature to incorporate bioactives, remarkable surface activity to stabilise emulsions and the ability to bind hydrophobic components when heated. Moreover, CMs can act as natural hydrogels to encapsulate minerals, bind with polymers to form nano capsules and possess pH swelling behaviour for targeted and controlled release of bioactives in the GI tract. Although numerous novel advancements of employing CMs as an effective delivery have been reported in recent years, more comprehensive studies are required to increase the understanding of how variation in structural properties of CMs be utilised to deliver bioactives with different physical, chemical and structural properties.

Activity of Anthracenediones and Flavoring Phenols in Hydromethanolic Extracts of Rubia tinctorum against Grapevine Phytopathogenic Fungi

In this work, the chemical composition of Rubia tinctorum root hydromethanolic extract was analyzed by GC-MS, and over 50 constituents were identified. The main phytochemicals were alizarin-related anthraquinones and flavoring phenol compounds. The antifungal activity of this extract, alone and in combination with chitosan oligomers (COS) or with stevioside, was evaluated against the pathogenic taxa Diplodia seriata, Dothiorella viticola and Neofusicoccum parvum, responsible for the so-called Botryosphaeria dieback of grapevine. In vitro mycelial growth inhibition tests showed remarkable activity for the pure extract, with EC50 and EC90 values as low as 66 and 88 μg·mL-1, respectively. Nonetheless, enhanced activity was attained upon the formation of conjugate complexes with COS or with stevioside, with synergy factors of up to 5.4 and 3.3, respectively, resulting in EC50 and EC90 values as low as 22 and 56 μg·mL-1, respectively. The conjugate with the best performance (COS-R. tinctorum extract) was then assayed ex situ on autoclaved grapevine wood against D. seriata, confirming its antifungal behavior on this plant material. Finally, the same conjugate was evaluated in greenhouse assays on grafted grapevine plants artificially inoculated with the three aforementioned fungal species, resulting in a significant reduction in the infection rate in all cases. This natural antifungal compound represents a promising alternative for developing sustainable control methods against grapevine trunk diseases.

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.

Characterization of a novel lipase from Bacillus licheniformis NCU CS-5 for applications in detergent industry and biodegradation of 2,4-D butyl ester

Enzymatic degradation has become the most promising approach to degrading organic ester compounds. In this study, Bacillus licheniformis NCU CS-5 was isolated from the spoilage of Cinnamomum camphora seed kernel, and its extracellular lipase was purified, with a specific activity of 192.98 U/mg. The lipase was found to be a trimeric protein as it showed a single band of 27 kDa in SDS-PAGE and 81 kDa in Native-PAGE. It was active in a wide range of temperatures (5-55 °C) and pH values (6.0-9.0), and the optimal temperature and pH value were 40 °C and 8.0, respectively. The enzyme was active in the presence of various organic solvents, metal ions, inhibitors and surfactants. Both crude and purified lipase retained more than 80% activity after 5 h in the presence of commercial detergents, suggesting its great application potential in detergent industry. The highest activity was found to be towards medium- and long-chain fatty acids (C₆-C₁₈). Peptide mass spectrometric analysis of the purified lipase showed similarity to the lipase family of B. licheniformis. Furthermore, it degraded more than 90% 2,4-D butyl ester to its hydrolysate 2,4-D within 24 h, indicating that the novel lipase may be applied to degrade organic ester pesticides.

Interaction between caffeic acid/caffeic acid phenethyl ester and micellar casein

Caffeic acid (CA) and caffeic acid phenethyl ester (CAPE) are bioactive molecules with poor solubility. We investigated the interaction between CA/CAPE and micellar casein (MC), and the physico-chemical and antioxidant properties of the complexes. Fluorescence spectroscopy analysis showed that both CA and CAPE formed complexes with MC via hydrophobic interactions. The binding constant was higher for CAPE than for CA at each temperature. The complexes were confirmed by FTIR and XRD. The secondary structure of MC was not affected by CAPE, but its morphology changed. CA/CAPE did not induce the dissociation of casein micelles. CA and CAPE increased and decreased, respectively, the bulk and tapped densities of MC. The complexes had higher thermal stability and DPPH radical scavenging capacity than free MC or CA/CAPE.

Spectroscopic, molecular docking and molecular dynamic simulation studies on the complexes of β-lactoglobulin, safranal and oleuropein

Herbal bioactive compounds have captured pronounced attention considering their health-promoting effects as well as their functional properties. In this study, the binding mechanism between milk protein bovine β-lactoglobulin (β-LG), oleuropein (OLE) and safranal (SAF) found in olive leaf extract and saffron, respectively via spectroscopic and in silico studies. Fluorescence quenching information exhibited that interactions with both ligands were spontaneous and hydrophobic interactions were dominant. Also, the CD spectroscopy results demonstrated the increase in β-sheet structure and decrease in the α-helix content for both ligands. Size of β-LG-OLE complex was higher than β-LG-SAF due to the conformation and larger molecular size. Molecular docking and simulation studies revealed that SAF and OLE bind in the central calyx of β-LG and the surface of β-LG next to hydrophobic residues. Lastly, OLE formed a more stabilized complex compared to SAF based on the molecular dynamic simulation results.

Interaction of vitamin B12 with β-lactoglobulin: a computational study

The β-Lactoglobulin (βLG) is a major whey protein that has the potential to bind various ligands; hence it is used as a model protein in protein-ligand interaction studies. Vitamin B12 is an essential nutrient for the human body, which helps in the synthesis of DNA, proteins, and the production of red blood cells. Binding interaction of vitamin B12 with βLG will help to understand the potency of βLG as a transporter for vitamin B12. Our experimental findings already showed that βLG binds with vitamin B12 successfully (Swain et al., 2020). Nevertheless, to further support our experimental results firmly, here, we have employed computational tools such as molecular docking and molecular dynamics (MD) simulation. The molecular docking technique was used to elucidate the probable binding sites and binding affinity of vitamin B12 on βLG. The docked complex of vitamin B12 with βLG was subjected to MD simulation to investigate its stability and other interaction properties over a time frame. The study revealed that the compound is stable, and vitamin B12 imposes no change to the secondary structure of the βLG. The computational results agree reasonably well with our experimental study.

Kinetic interactions of nanocomplexes between astaxanthin esters with different molecular structures and β-lactoglobulin

The influence of different fatty acid carbon chains on the kinetic interactions of nanocomplexes between esterified astaxanthin (E-Asta) and β-lactoglobulin (β-Lg) were investigated by multi-spectroscopy and molecular modeling techniques. We synthesized ten different E-Asta bound to β-Lg and formed nanocomplexes (< 300 nm). Fluorescence spectroscopy showed moderate affinities (binding constants Ka = 10³-10⁴ M^-1). Docosahexaenoic acid astaxanthin monoester (Asta-C22:6) had the strongest binding affinity towards β-Lg (Ka = 3.77 × 10⁴ M^-1). The fluorescence quenching of β-Lg upon binding of E-Asta displayed a static mechanism, with binding sites (n) equal to 1. Fourier transform infrared spectroscopy and ultraviolet-visible absorption spectroscopy revealed that E-Asta might enter the β-Lg hydrophobic cavity, leading to unfolding of the peptide chain skeleton. In summary, β-Lg and E-Asta can form stable nanocomplex emulsions to achieve an effective delivery process for E-Asta.

Covalent conjugation with (-)-epigallo-catechin 3-gallate and chlorogenic acid changes allergenicity and functional properties of Ara h1 from peanut

Ara h1 is a major allergen from peanut. We investigated the effect of covalent conjugation of Ara h1 and dietary polyphenols on allergenicity and functional properties of Ara h1. Enzyme-linked immunosorbent assay revealed that the covalent conjugation of dietary polyphenols significantly reduced the IgE binding capacity of Ara h1. Covalent binding of dietary polyphenols with Ara h1 reduced histamine release by 40% in basophils. The decreased IgE binding capacity of Ara h1 could be ascribed to changes in protein conformation. The IgE epitope of Ara h1 might be blocked by polyphenols at the binding site. Analysis of pepsin digestion of Ara h1-polyphenol conjugates indicated that the covalent binding increased pepsin digestibility and reduced IgE binding capacity. Furthermore, covalent conjugation of Ara h1 with polyphenols decreased denaturation temperature and increased antioxidant activity. Ara h1 conjugated with polyphenols may be a promising approach for reducing the allergenicity of Ara h1.

Therapeutic Emergence of Rhein as a Potential Anticancer Drug: A Review of Its Molecular Targets and Anticancer Properties

According to the World Health Organization (WHO), cancer is the second-highest cause of mortality in the world, and it kills nearly 9.6 million people annually. Besides the fatality of the disease, poor prognosis, cost of conventional therapies, and associated side-effects add more burden to patients, post-diagnosis. Therefore, the search for alternatives for the treatment of cancer that are safe, multi-targeted, effective, and cost-effective has compelled us to go back to ancient systems of medicine. Natural herbs and plant formulations are laden with a variety of phytochemicals. One such compound is rhein, which is an anthraquinone derived from the roots of Rheum spp. and Polygonum multiflorum. In ethnomedicine, these plants are used for the treatment of inflammation, osteoarthritis, diabetes, and bacterial and helminthic infections. Increasing evidence suggests that this compound can suppress breast cancer, cervical cancer, colon cancer, lung cancer, ovarian cancer, etc. in both in vitro and in vivo settings. Recent studies have reported that this compound modulates different signaling cascades in cancer cells and can prevent angiogenesis and progression of different types of cancers. The present review highlights the cancer-preventing and therapeutic properties of rhein based on the available literature, which will help to extend further research to establish the chemoprotective and therapeutic roles of rhein compared to other conventional drugs. Future pharmacokinetic and toxicological studies could support this compound as an effective anticancer agent.

Characterization of binding interaction of triclosan and trypsin

Triclosan (TCS), a broad-spectrum antibacterial agent, exhibits a high exposure in the environment. However, the residual TCS in the environment poses a potential risk to human health. In this study, spectroscopic methods, molecular docking and animal experiment were conducted to completely understand the interaction between trypsin and TCS. The formation of the TCS-trypsin complex was spontaneously achieved through hydrogen bonds and Van der Waals forces with a binding constant (K_a) between 10³ and 10⁴ L mol^-1. In addition, the trypsin activity in fish intestine was inhibited by TCS exposure, revealing the potentially negative effects of TCS on metabolism. The results might be explained by changes in the conformation of the trypsin, inducing the content of unordered coil increasing significantly (from 36.2% to over 80%). This work provides useful information for assessing the toxicity of TCS at the molecular level.

Effect of ultrasound on binding interaction between emodin and micellar casein and its microencapsulation at various temperatures

Emodin is a bioactive compound with strong anti-inflammatory and antioxidant properties. Micellar casein is casein concentrates close to the native state of casein micelles. The interaction of emodin and micellar casein under heat treatment in the absence and presence of ultrasound was investigated, and the properties of microencapsulated emodin in micellar casein were compared. Fluorescence experiments proved that the major interaction between emodin and micellar casein was through hydrophobic forces under heat treatment in the absence and presence of ultrasound. However, ΔH, ΔS and ΔG of emodin-casein complexation without sonication were higher than those with sonication, in contradiction to binding constants. The particle sizes of emodin-casein complexes in the presence of ultrasound were smaller than those without sonication, while the specific surface area showed an opposite trend. As to encapsulation, emodin-casein capsules under heat-sonication treatment showed higher antioxidant properties than those of heat treatment alone under similar experimental conditions. Interestingly, micellar casein-emodin encapsulation in the presence of ultrasound showed a lower release rate of emodin in gastrointestinal conditions than that without ultrasound at the emdoin concentration of 10 μmol per gram casein. Ultrasound has been shown to be a potential processing technology for customizing the release kinetics of bioactive compounds.

Separation of Protein-Binding Anthraquinones from Semen Cassiae Using Two-Stage Foam Fractionation

Anthraquinones are compounds of high medicinal value in many plants. Based on their good protein binding affinity, foam fractionation was attempted to separate them using proteins in the aqueous extract of Semen Cassiae as collectors. Firstly, the interaction between anthraquinones and Semen Cassiae proteins has been analyzed by the Stem–Volmer equation with physcion as a standard. The results show that physcion had good interaction with the proteins via hydrophobic forces. More importantly, the proteins effectively assisted the foam fractionation of several anthraquinones including aurantio-obtusifolin, aloe-emodin, rhein, emodin, chrysophanol, and physcion. On this basis, a two-stage foam fractionation technology was developed for process intensification using a foam fractionation with vertical sieve trays (VSTs). VSTs, initial feed concentration of total anthraquinones, temperature, volumetric air flow rate and pore diameter of gas distributor had significant effects on enrichment ratio and recovery yield of anthraquinones. Under suitable conditions, the enrichment ratio of total anthraquinones reached 47.0 ± 4.5 with a concentration of 939 ± 94 mg/L in the foamate while their total recovery percentage reached more than 47.7%. In addition, foam fractionation also increased the purity and hydroxyl radical scavenging activity of total anthraquinones. The results had significant implications for the separation of anthraquinones from Semen Cassiae.

A novel non-enzymatic sensing platform for determination of 5'-guanosine monophosphate in meat

Graphitic carbon nitride (g-C₃N₄) doped carboxylated MWCNTs nanocomposite was synthesized using a simple method. The composite films containing 45 wt%, 50 wt%, 56 wt%, 67 wt% fraction of the carboxylated MWCNTs doped into g-C₃N₄ were fabricated and characterized. An electrochemical non-enzymatic sensor for determination of 5'-guanosine monophosphate (GMP) based on the nanocomposite was developed. The results indicate that the g-C₃N₄-carboxylated MWCNTs nanocomposite has highly electrocatalytic activity, good conductivity and biocompatibility, which plays an essential role in the determination of GMP. Under the optimum conditions, the linear fitting equation was I (µA) = -0.0022c (μg·mL^-1) + 0.3560 (R² = 0.9982). The linear range was from 0.5 to 100 μg·mL^-1 and the detection limit (LOD, S/N = 3) was 0.109 μg·mL^-1. This non-enzymatic sensor can offer a better alternative to other methods for the analysis of GMP because of cheap cost, low detection limit and good anti-jamming capability in meat quality evaluation.