Interaction between β-lactoglobulin and chlorogenic acid and its effect on antioxidant activity and thermal stability

Interaction of pepper numbing substances with myofibrillar proteins and numbness perception under thermal conditions: A structural mechanism analysis

This study examined the interaction between myofibrillar proteins (MPs) and the numbing substance hydroxy-α-sanshool (α-SOH) in a thermal environment, and provided an explanation of the numbness perception mechanism through muti-spectroscopic and molecular dynamics simulation methodology. Results showed that addition of α-SOH could reduce the particle size and molecular weight of MPs, accompanied by changes in the tertiary and secondary structure, causing the α-helix of MPs transitioned to β-sheet and β-turn due to the reorganization of hydrogen bonds. After a moderate heating (60 or 70 °C), MPs could form the stable complexes with α-SOH that were associated with attachment sites and protein wrapping. The thermal process might convert a portion of α-SOH' into hydroxy-β-sanshool' (β-SOH'). When docking with the sensory receptor TRPV1, the RMSD, RMSF and binding free energy all showed that β-SOH' demonstrated a low affinity, thereby reducing the numbing perception. These findings can provide a theoretical foundation for the advanced processing of numbing meat products.

Protein-Chlorogenic Acid Interactions: Mechanisms, Characteristics, and Potential Food Applications

The interactions between proteins and chlorogenic acid (CGA) have gained significant attention in recent years, not only as a promising approach to modify the structural and techno-functional properties of proteins but also to enhance their bioactive potential in food systems. These interactions can be divided into covalent (chemical or irreversible) and non-covalent (physical or reversible) linkages. Mechanistically, CGA forms covalent bonds with nucleophilic amino acid residues of proteins by alkaline, free radical, and enzymatic approaches, leading to changes in protein structure and functionality, such as solubility, emulsification properties, and antioxidant activity. In addition, the protein-CGA complexes can be obtained by hydrogen bonds, hydrophobic and electrostatic interactions, and van der Waals forces, each offering unique advantages and outcomes. This review highlights the mechanism of these interactions and their importance in modifying the structural, functional, nutritional, and physiological attributes of animal- and plant-based proteins. Moreover, the potential applications of these protein-CGA conjugates/complexes are explored in various food systems, such as beverages, films and coatings, emulsion-based delivery systems, and so on. Overall, this literature review provides an in-depth overview of protein-CGA interactions, offering valuable insights for future research to develop novel protein-based food and non-food products with improved nutritional and functional characteristics.

Formation mechanism of quinoa protein hydrolysate-EGCG complexes at different pH conditions and its effect on the protein hydrolysate-lipid co-oxidation in emulsions

This study aimed to investigate the interaction, structure, antioxidant, and emulsification properties of quinoa protein hydrolysate (QPH) complexes formed with (-)-epigallocatechin gallate (EGCG) at pH 3.0 and 7.0. Additionally, the effect of pH conditions and EGCG complexation on protein hydrolysate-lipid co-oxidation in QPH emulsions was explored. The results indicated that QPH primarily interacted with EGCG through hydrophobic interactions and hydrogen bonds. This interaction led to alterations in the secondary structure of QPH, as well as a decrease in surface hydrophobicity and free SH content. Notably, the binding affinity between QPH and EGCG was observed to be higher at pH 7.0 compared to pH 3.0. Consequently, QPH-EGCG complexes exhibited more significant enhancement in antioxidant and emulsification properties at pH 7.0 than pH 3.0. The pH level also influenced the droplet size, ζ-potential, and interfacial composition of emulsions formed by QPH and QPH-EGCG complexes. Compared to QPH stabilized emulsions, QPH-EGCG stabilized emulsions were more capable of mitigating destabilization during storage and displayed fewer lipid oxidation products, carbonyl generation, and sulfhydryl groups and fluorescence loss, which implied better oxidative stability of the emulsions. Furthermore, the QPH-EGCG complexes formed at pH 7.0 exhibited better inhibition of protein hydrolysate-lipid co-oxidation. Overall, these findings provide valuable insights into the potential application of QPH and its complexes with EGCG in food processing systems.

Covalent polyphenols-proteins interactions in food processing: formation mechanisms, quantification methods, bioactive effects, and applications

Proteins and polyphenols are abundant in the daily diet of humans and their interactions influence, among other things, the texture, flavor, and bioaccessibility of food. There are two types of interactions between them: non-covalent interactions and covalent interactions, the latter being irreversible and more powerful. In this review, we systematically summarized advances in the investigation of possible mechanism underlying covalent polyphenols-proteins interaction in food processing, effect of different processing methods on covalent interaction, methods for characterizing covalent complexes, and impacts of covalent interactions on protein structure, function and nutritional value, as well as potential bioavailability of polyphenols. In terms of health promotion of the prepared covalent complexes, health effects such as antioxidant, hypoglycemic, regulation of intestinal microbiota and regulation of allergic reactions have been summarized. Also, the possible applications in food industry, especially as foaming agents, emulsifiers and nanomaterials have also been discussed. In order to offer directions for novel research on their interactions in food systems, nutritional value, and health properties in vivo, we considered the present challenges and future perspectives of the topic.

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

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

Development and characterization of an active starch-based film as a chlorogenic acid delivery system

Given its health benefits for the human body, chlorogenic acid (CA) offers promising applications in the food industry. However, the instability and low bioavailability of CA remain to be solved. In this paper, a starch-based film prepared by the homogenization and solution-casting method was used as an effective carrier to alleviate these problems. Homogenization (10-50 MPa) reduced the starch paste viscosity and its particle sizes from 21.64 to 7.68 μm, which promoted the starch recrystallization and induced chemical cross-links between starch-CA, as confirmed by the FTIR result with an appearance of a new CO peak at about 1716 cm-1. Accordingly, the rapidly digestible starch content of the film was reduced to 27.83 % and the CA encapsulation efficiency was increased to 99.08 % (from 65.88 %). As a result, the film system extended CA's release time beyond 4 h and significantly increased the heat-treated CA's antioxidant activity. Besides, the tensile strength and elastic modulus of the film were also improved to 6.29 MPa (from 1.63 MPa) and 160.98 MPa (from 12.02 MPa), respectively, by homogenization. In conclusion, the developed active starch-based film could be used as an edible film for the production of functional food or active food packaging.

Optimization of the Green Extraction of Red Araçá (Psidium catteyanum Sabine) and Application in Alginate Membranes for Use as Dressings

In this research, the aim was to introduce innovation to the pharmaceutical field through the exploration of an underutilized plant matrix, the red araçá, along with the utilization of sodium alginate for the development of membranes designed for active topical dressings. Within this context, optimal extraction conditions were investigated using the central composite rotational statistical design (CCRD) to obtain a red araçá epicarp extract (RAEE) rich in bioactive compounds utilizing the maceration technique. The extract acquired under the optimized conditions (temperature of 66 °C and a hydroalcoholic solvent concentration of 32%) was incorporated into a sodium alginate matrix for the production of active membranes using a casting method. Characterization of the membranes revealed that the addition of the extract did not significantly alter its morphology. Furthermore, satisfactory results were observed regarding mechanical and barrier properties, as well as the controlled release of phenolic compounds in an environment simulating wound exudate. Based on these findings, the material produced from renewable matrices demonstrates the promising potential for application as a topical dressing within the pharmaceutical industry.

Molecular Mechanisms and Applications of Polyphenol-Protein Complexes with Antioxidant Properties: A Review

Proteins have been extensively studied for their outstanding functional properties, while polyphenols have been shown to possess biological activities such as antioxidant properties. There is increasing clarity about the enhanced functional properties as well as the potential application prospects for the polyphenol-protein complexes with antioxidant properties. It is both a means of protein modification to provide enhanced antioxidant capacity and a way to deliver or protect polyphenols from degradation. This review shows that polyphenol-protein complexes could be formed via non-covalent or covalent interactions. The methods to assess the complex's antioxidant capacity, including scavenging free radicals and preventing lipid peroxidation, are summarized. The combination mode, the type of protein or polyphenol, and the external conditions will be the factors affecting the antioxidant properties of the complexes. There are several food systems that can benefit from the enhanced antioxidant properties of polyphenol-protein complexes, including emulsions, gels, packaging films, and bioactive substance delivery systems. Further validation of the cellular and in vivo safety of the complexes and further expansion of the types and sources of proteins and polyphenols for forming complexes are urgently needed to be addressed. The review will provide effective information for expanding applications of proteins and polyphenols in the food industry.

From polyphenol to o-quinone: Occurrence, significance, and intervention strategies in foods and health implications

Polyphenol oxidation is a chemical process impairing food freshness and other desirable qualities, which has become a serious problem in fruit and vegetable processing industry. It is crucial to understand the mechanisms involved in these detrimental alterations. o-Quinones are primarily generated by polyphenols with di/tri-phenolic groups through enzymatic oxidation and/or auto-oxidation. They are highly reactive species, which not only readily suffer the attack by nucleophiles but also powerfully oxidize other molecules presenting lower redox potentials via electron transfer reactions. These reactions and subsequent complicated reactions are capable of initiating quality losses in foods, such as browning, aroma loss, and nutritional decline. To attenuate these adverse influences, a variety of technologies have emerged to restrain polyphenol oxidation via governing different factors, especially polyphenol oxidases and oxygen. Despite tremendous efforts devoted, to date, the loss of food quality caused by quinones has remained a great challenge in the food processing industry. Furthermore, o-quinones are responsible for the chemopreventive effects and/or toxicity of the parent catechols on human health, the mechanisms by which are quite complex. Herein, this review focuses on the generation and reactivity of o-quinones, attempting to clarify mechanisms involved in the quality deterioration of foods and health implications for humans. Potential innovative inhibitors and technologies are also presented to intervene in o-quinone formation and subsequent reactions. In future, the feasibility of these inhibitory strategies should be evaluated, and further exploration on biological targets of o-quinones is of great necessity.

Understanding the pH-dependent interaction of anthocyanin with two food-derived transferrins

The potential binding of cyanidin-3-O-glucoside (C3G) to bovine lactoferrin (BLF) and ovotransferrin (OTF) at pH 3, 5, and 7 was investigated for the first time. Multiple spectroscopic techniques demonstrated pH-dependent alterations in the conformational characteristics of BLF and OTF upon complexation with C3G. Fluorescence quenching assays showed that their highest binding affinity was at pH 7. Hydrophobic interactions and hydrogen bonds were found to be crucial in molecular dynamics simulations but with significantly lower probabilities of formation at pH 3 (p < 0.05). At pH 7, electrostatic attraction can occur for the negatively charged forms of C3G, and the well-maintained native structures of BLF and OTF may be favorable for stabilizing the C3G binding sites. This study sheds light on the stronger interaction of C3G with BLF/OTF at pH 7, which may have implications for future applications such as anthocyanin stabilization or the development of functional food ingredients.

A model study on the site-specificity of (-)-epicatechin-induced reactions in β-lactoglobulin by high-resolution mass spectrometry in combination with bioinformatics

Polyphenol-protein reactions in model solutions of β-lactoglobulin (β-LG) incubated with (-)-epicatechin at 37 °C and 60 °C were monitored by microLC-timsTOF Pro-MS/MS combined with bioinformatics strategies. The addition of (-)-epicatechin to the model solutions resulted in changes in tryptic peptide profiles. Covalent bond formation between (-)-epicatechin o-quinones and β-LG was identified for the residues S27, S30, K60, C66, K69, and C160, with C160 being the predominant binding site. Furthermore, the incubation of β-LG with (-)-epicatechin significantly promoted oxidation, especially for the residues M7 and M24. The reaction of monomeric (-)-epicatechino-quinone at C160 was also identified in the milk chocolate sample. The adaptation of this study by extending the scope of the reaction products offers significant potential for comprehensive food profiling strategies.

Calorimetric, volumetric and structural studies of the interaction between chlorogenic acid and dipalmitoylphosphatidylcholine bilayers

Chlorogenic acid (CGA) is the main component of coffee and an antioxidant. CGA has been reported to bear various good health effects. At the same time, it has been found that the addition of CGA induces an undesirable deformation of red blood cells. This fact suggests that CGA may bind to the proteins or/and membrane lipids of red blood cells. This study aimed to examine how CGA binds the bilayers of phosphatidylcholine (PC), one of red blood cells' primary lipids. To this end, we investigated the effect of CGA on the phase behavior and the structure of dipalmitoyl-PC (DPPC) bilayers in the form of multi-lamellar vesicles. Calorimetry and dilatometry measurements showed that the DPPC chain melting transition cooperativity decreases as increasing CGA concentrations. In addition, X-ray diffraction results showed that the lamellar repeat periodicity becomes disordered, and the periodicity disappears completely at high CGA concentrations. Together with these findings, it can be inferred that the CGA molecules do not penetrate inside the DPPC bilayers but bind to their surface in a negatively charged form.

Modification of hyaluronic acid to enable click chemistry photo-crosslinking of hydrogels with tailorable degradation profiles

Hyaluronic acid (HA) is a naturally occurring mucopolysaccharide that, due to its inherent bioactivity and extracellular matrix-like structure, has the potential to be utilised extensively in tissue engineering. However, this glycosaminoglycan lacks the properties required for cellular adhesion and photo-crosslinking by UV light, which significantly hinders this polymers applicability. This research presents a method for modifying hyaluronic acid via thiolation and methacrylation to generate a novel photo-crosslinkable polymer with improved physicochemical properties, biocompatibility and the potential to customize biodegradability according to the ratio of monomers used. A decrease in stiffness proportional to increasing thiol concentration was observed when testing the compressive strength of hydrogels. Conversely, it was noted that the storage moduli of hydrogels increased proportionally to thiol concentration indicating a greater degree of cross-linking with the addition of thiol. The addition of thiol to HA increased the biocompatibility of the material in both neuronal and glial cell lines and improved the degradability of methacrylated HA. Due to the enhanced physicochemical properties and biocompatibility imparted by the introduction of thiolated HA, this novel hydrogel system could have numerous bioengineering applications.

Effect of sodium alginate on the yogurt stability was dependent on the thickening effect and interaction between casein micelles and sodium alginate

The effect of sodium alginate (SA) on the yogurt stability and the related mechanisms were investigated. It was found that low-concentration SA (≤0.2 %) increased the yogurt stability, while high-concentration SA (≥0.3 %) decreased the yogurt stability. Sodium alginate increased the viscosity and viscoelasticity of yogurt and this effect was positively correlated with its concentration, suggesting that SA worked as the thickening agent in yogurt. However, addition of ≥0.3 % SA damaged the yogurt gel. These results suggested that interaction between milk protein and SA might play an important role in the yogurt stability besides the thickening effect. Addition of ≤0.2 % SA did not change the particle size of casein micelles. However, addition of ≥0.3 % SA induced aggregation of casein micelles and increased the size. And the aggregated casein micelles precipitated after 3 h storage. Isothermal titration calorimetry analysis showed that casein micelles and SA were thermodynamically incompatible. These results suggested that the interaction between casein micelles and SA induced aggregation and precipitation of casein micelles, which was critical in the destabilization of yogurt. In conclusion, the effect of SA on the yogurt stability was dependent on the thickening effect and the interaction between casein micelles and SA.

Effect of de-phenolization on protein-phenolic interactions of sunflower protein isolate

Proteins and phenolic compounds are significant components of foods that can interact, and this interaction can impact the functional properties of proteins and the bioactivity of phenolic compounds. Sunflower meal, which has a high potential to be an important alternative protein source, contains phenolic compounds mostly bonded with proteins. In this study, the interaction between proteins and phenolic compounds which naturally exist in sunflower and prone to oxidation during alkaline treatment (for protein isolation) was investigated. There was a significant decrease up to 96.21% in the content of total phenolics by methanol washing. Chlorogenic acid, cryptochlorogenic acid and caffeic acid were detected in the phenolic extract obtained from sunflower protein isolate, and they exhibited different levels of reduction after methanol washing. For the total antioxidant capacity analysis, a decrease by 50% was observed after 4hwashing with methanol solution, and there was no significant decrease afterwards. In addition, the fluorescence intensity of sunflower protein was diminished with reduced washing time, which was mostly attributed to the protein-phenolic interaction. According to hydrodynamic parameters, the main force of the sunflower protein-phenolic complex formation was assumed to be hydrophobic attraction. The Stern-Volmer plot indicated that the main quenching mechanism was only static at all temperature conditions.

Chemistry of Protein-Phenolic Interactions Toward the Microbiota and Microbial Infections

Along with health concerns, interest in plants as food and bioactive phytochemical sources has been increased in the last few decades. Phytochemicals as secondary plant metabolites have been the subject of many studies in different fields. Breakthrough for research interest on this topic is re-juvenilized with rising relevance in this global pandemics' era. The recent COVID-19 pandemic attracted the attention of people to viral infections and molecular mechanisms behind these infections. Thus, the core of the present review is the interaction of plant phytochemicals with proteins as these interactions can affect the functions of co-existing proteins, especially focusing on microbial proteins. To the best of our knowledge, there is no work covering the protein-phenolic interactions based on their effects on microbiota and microbial infections. The present review collects and defines the recent data, representing the interactions of phenolic compounds -primarily flavonoids and phenolic acids- with various proteins and explores how these molecular-level interactions account for the human health directly and/or indirectly, such as increased antioxidant properties and antimicrobial capabilities. Furthermore, it provides an insight about the further biological activities of interacted protein-phenolic structure from an antiviral activity perspective. The research on the protein-phenolic interaction mechanisms is of great value for guiding how to take advantage of synergistic effects of proteins and polyphenolics for future medical and nutritive approaches and related technologies.

Interaction Mechanism between OVA and Flavonoids with Different Hydroxyl Groups on B-Ring and Effect on Antioxidant Activity

Ovalbumin (OVA) is a common carrier with high efficiency to deliver flavonoids. The aim of this study was to investigate the interaction mechanism of OVA and four flavonoids (quercetin (Que), myricetin (Myri), isorhamnetin (Ish), and kaempferol (Kaem)) with similar structures by fluorescence spectra, SDS−PAGE, FT−IR, and molecular docking analysis, and the effect on the antioxidant abilities of flavonoids was also evaluated. Results indicated that the antioxidant activity of flavonoids was positively correlated to the number of phenolic hydroxyl groups of on the B-ring, and weakened when the C-3′ position was replaced by a methoxy group. The addition of OVA enhanced the antioxidant activity of Que/Kaem, while it masked the antioxidant activity of Myri. The formation of Que/Myri/Ish/Kaem−OVA complexes was a spontaneous exothermic process driven mainly by hydrogen bond and van der Waals force, which could result in the change in OVA conformation and induce the transformation of α-helix to β-sheet. Among these, Kaem exhibited the strongest binding ability with OVA, and showed the greatest impact on the secondary and conformational structure of OVA, followed by Que. The hydroxylation of C-3′ and methoxylation of C-5′ weaken the interaction of Kaem with OVA. Molecular docking analysis suggested that Que, Myri, Ish, and Kaem formed six, three, five, and four hydrogen bonds with OVA, and the number of hydrogen bonds was not positively correlated with their binding constants. Our findings can provide a theoretical basis for the application of OVA on improving the antioxidant activity of flavonoids, and may help to explain the delivery efficiency of OVA on different bioactive constituents.

The mechanism of molecular cross-linking against nonenzymatic degradation in the body wall of ready-to-eat sea cucumber

Ready-to-eat sea cucumbers (RSC) treated by high pressure steam were easily degraded during storage. Celery (Apium graveolens, AG) and chlorogenic acid (CA) were screened for enhancing the stability of RSC. After RSC cross-linked by AG or CA, the hardness was significantly increased by 108% or 254% at 30 d, and the relaxation time decrease by 31.90 or 39.89 ms, and the proportion of T₂₃ reduced by 0.40% or 1.15%. The crosslinked RSC exhibited smaller pore size with finer collagen fibrils. CA treatment caused the secondary structure changes in RSC. In addition, it also inhibited the break of peptide bonds in RSC collagen, observing the decrease of free hydroxyproline level from 46.63 to 34.53 μg/g, and the reduction of free ammonia nitrogen from 20.96 to 15.30 μmol/g. Therefore, AG and CA will have an important application in RSC processing industry.

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.

An Electrochemical Sensor for Quantitation of the Oral Health Care Agent Chlorogenic Acid Based on Bimetallic Nanowires with Functionalized Reduced Graphene Oxide Nanohybrids

Chlorogenic acid (CGA), a phenolic acid from coffee, has been regarded as a powerful ingredient against oxidative stress and inflammation. Meanwhile, its healing feature to interfere with periodontal disease (PD) makes it a promising drug candidate. However, the existing methods for chlorogenic acid detection limit its practical application in purification and further pharmacological study in stomatology due to their lack of accuracy and productivity. Therefore, it is crucial to find a forceful approach to precisely evaluate CGA for an in-depth anti-PD study. In this work, we reported a facile and controllable synthesis of Pt@Pd nanowires (NWs) in a non-compacted core-shell structure with high electrocatalytic activity. In addition, polyethylenimine (PEI)-capped reduced graphene oxide (rGO) nanoflakes provided large binding sites for a network structure composed of interweaved Pt@Pd nanowires and protected hemin from self-destruction, which empowered Pt@Pd NWs-Hemin-PEI-rGO nanohybrids to own a large electroactive surface area and great electrochemical property for CGA detection. The enzyme-free electrochemical sensor based on Pt@Pd NWs-Hemin-PEI-rGO displayed a favorable capacity for trace CGA detection with a detection limit of 7.8 nM and a wide linear range of 0.5 μM to 4 mM. The exceptional sensitivity and selectivity of the sensor made it accomplish the measurements of chlorogenic acid in soft drinks and coffee with high consistency of HPLC results. The satisfactory performance of the obtained sensor enables it to be used for quality control and study of drug metabolism in PD treatments.