o-Quinones formed in plant extracts. Their reactions with amino acids and peptides

NDGA enhances the physicochemical and anti-biodegradation performance of dentin collagen

OBJECTIVES

Collagen fibrils from carious dentin matrix are prone to enzymatic degradation. This study investigates the feasibility and mechanism of nordihydroguaiaretic acid (NDGA), as a collagen crosslinker, to bio-modify the demineralized dentin matrix.

METHODS

The physicochemical properties of the crosslinked dentin matrix were characterized by swelling ratio, ninhydrin assay, Fourier Transform Infrared spectroscopy, and atomic force microscopy. The collagenase degradation resistance was evaluated by measuring loss of dry mass, hydroproline release, loss of elasticity, and micro-nano structure integrity. The cytotoxicity of NDGA-crosslinked dentin collagen was evaluated by flow cytometry.

RESULTS

NDGA crosslinked dentin matrix without destroying the integrity of collagen. Mechanistically, NDGA formed bisquinone bond between two adjacent o-quinone groups, resulting in NDGA polymeric matrix in which collagen fibrils were embedded. NDGA modification could significantly enhance the stiffness of dentin matrix at macro-nano scale. The NDGA-crosslinked dentin matrix exhibited remarkably low collagen degradation and sustained bulk elasticity after collagenase challenge, which were attributed to decreased water content, physical masking of collagenase bind sites on collagen, and improved stiffness of collagen fibrils. Notably, NDGA-crosslinked dentin matrix exhibited excellent biocompatibility.

CONCLUSION

NDGA, as a biocompatible collagen crosslinker, improves the mechanical properties and biodegradation resistance of demineralized dentin matrix.

Polyphenols Can Improve Resin-Dentin Bond Durability by Promoting Amorphous Calcium Phosphate Nanoparticles to Backfill the Dentin Matrix

Objective

To investigate the effects of proanthocyanidins (PA), myricetin, resveratrol, and kaempferol on the modification of dentin collagen and the inhibition of matrix metalloproteinase (MMP) activity, and to evaluate their contributions to the biomimetic remineralization and resin-dentin bonding performance.

Methods

Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and in situ zymography were applied to verify the collagen modification and MMP activity inhibition induced by these four polyphenols. Scanning electron microscopy/energy dispersive spectrometer (SEM/EDS) analysis, X-ray diffraction (XRD), ATR-FTIR, Vickers hardness numbers (VHN), and micro-computed tomography (micro-CT) were performed to characterize the remineralized dentin. Microtensile bond strength (μTBS) and nanoleakage were investigated to evaluate the effects of the four polyphenols on resin-dentin bonding durability.

Results

ATR-FTIR and in situ zymography confirmed that these four polyphenols could modify dentin collagen and inhibit MMP activity, respectively. Chemoanalytic characterization exhibited the efficacies of the four polyphenols in promoting dentin biomimetic remineralization. The surface hardness of PA-pretreated dentin was the greatest. Micro-CT results demonstrated that the PAs group possessed the highest amount of dentin surface minerals and the lowest amount of deep-layer minerals. The surface and deep-layer mineral contents of the Myr group were higher than Res and Kae groups. Treatment with these four polyphenols significantly increased the initial μTBS compared with the control group without primer conditioning. μTBS decreased significantly during aging, and the decrease was more severe in the PAs and Kae groups than in the Myr and Res groups. With or without aging, the polyphenol groups exhibited relatively less fluorescence. However, the Myr and Res groups showed less serious nanoleakage after aging.

Conclusion

PA, myricetin, resveratrol, and kaempferol can modify dentin collagen, inhibit MMP activity, promote biomimetic remineralization, and improve resin-dentin bond durability. Compared with PA and kaempferol, myricetin and resveratrol are more effective in improving resin-dentin bonding.

Temperature affects the kinetics but not the products of the reaction between 4-methylbenzoquinone and lysine

Quinones are electrophilic compounds that can undergo Michael addition or Schiff base reaction with nucleophilic amines, but the effect of temperature has not been systematically studied. The aim of this study was to characterize how temperature affects the reaction mechanism and kinetics of 4-methylbenzoquinone (4MBQ) with lysine (Lys), N^α-acetyl Lys or N^ε-acetyl Lys. The products were identified and characterized by LC-MS/MS, which revealed formation of Michael addition products, Schiff base, and a di-adduct in Lys and N^α-acetyl Lys-containing reaction mixtures. The product profiles were not affected by temperature in the range of 15-100 °C. NMR analysis proved that Michael addition of N^α-acetyl Lys occurred on the C5 position of 4MBQ. Rate constants for the reactions studied by stopped-flow UV-vis spectrophotometry under pseudo-first-order conditions where the amines were present in excess in the range 15 °C to 45 °C showed the α-amino groups of Lys are more reactive than the ε-groups. The kinetics results revealed that the temperature dependence of reaction rates followed the Arrhenius law, with activation energies in the order: Lys < N^ε-acetyl Lys < N^α-acetyl Lys. Our results provide detailed knowledge about the temperature dependence of the reaction between Lys residues and quinones under conditions relevant for storage of foods.

Food polyphenols and Maillard reaction: regulation effect and chemical mechanism

Maillard reaction is a non-enzymatic thermal reaction during food processing and storage. It massively contributes to the flavor, color, health benefits and safety of foods and could be briefly segmented into initial, intermediate and final stages with the development of a cascade of chemical reactions. During thermal reaction of food ingredients, sugar, protein and amino acids are usually the main substrates, and polyphenols co-existed in food could also participate in the Maillard reaction as a modulator. Polyphenols including flavan-3-ols, hydroxycinnamic acids, flavonoids, and tannins have shown various effects throughout the process of Maillard reaction, including conjugating amino acids/sugars, trapping α-dicarbonyls, capturing Amadori rearrangement products (ARPs), as well as decreasing acrylamide and 5-hydroxymethylfurfural (5-HMF) levels. These effects significantly influenced the flavor, taste and color of processed foods, and also decreased the hazard products' level. The chemical mechanism of polyphenols-Maillard products involved the scavenging of radicals, as well as nucleophilic addition and substitution reactions. In the present review, we concluded and discussed the interaction of polyphenols and Maillard reaction, and proposed some perspectives for future studies.

Synthesis, Structure and Catechol Oxidase Activity of Mono Nuclear Cu(II) Complex with Phenol-Based Chelating Agent with N, N, O Donor Sites

A square-planar Cu(II) complex [Cu(L)Cl], 1, with sterically constrained tridentate phenol-based ligand (HL= N,N,N′-trimethyl-N′-(2-hydroxy-3,5-di-tert-butylbenzyl)-ethylenediamine) with N, N, O donor sites has been synthesized. The complex is characterized by single crystal X-ray diffraction study as well as other spectroscopic techniques. The reported complex crystallizes in monoclinic space group C2/c with a = 30.248(6), b = 13.750(3) and c = 11.410(2) Å with β = 110.232(2)°. The Cu(II) ion adopts a square planar environment in this complex. Electrochemical study of the complex 1 gives quasi-reversible reductive response at E1/2 ≈ −0.5 V due to the reduction of the Cu(II) center along with a reversible oxidation peak at E1/2 ≈ 0.75 V. The oxidation peak arises due to the ligand-based oxidation of phenolate group to phenoxyl radical in the complex. The Cu(II) complex exhibits catechol oxidase activity in methanol as observed by the UV–vis spectroscopy of the aerial oxidation of 3,5-DTBC to 3,5-DTBQ and the reaction proceeds via the formation of ligand phenoxyl radical. The turnover number for complex 1 is 2560 h−1.

Benzothiazines as Major Intermediates in Enzymatic Browning Reactions of Catechin and Cysteine

The course of melanin formation is yet not thoroughly resolved on a mechanistic level. With the present study, incubations of catechin (CA)- and cysteine-derived dihydro-1,4-benzothiazine carboxylic acid derivatives were investigated for colored products during enzymatic browning. Analyses by high-performance liquid chromatography (HPLC)-mass spectrometry revealed the formation of two novel decarboxylated dihydro-1,4-benzothiazine derivatives [8-(3,5,7-trihydroxy-3,4-dihydro-2H-chromen-2-yl)-5-hydroxy-3,4-dihydro-2H-benzothiazine and 7-(3,5,7-trihydroxy-3,4-dihydro-2H-chromen-2-yl)-5-hydroxy-3,4-dihydro-2H-benzothiazine] preferentially under acidic conditions. Furthermore, in model reactions under neutral pH, a colored phenazine dimer intermediate was isolated by high-performance countercurrent chromatography and preparative HPLC when conducting the incubations in the presence of o-phenylenediamine (OPD). Mass spectrometry and nuclear magnetic resonance spectroscopy unequivocally verified the structure as (12E)-5,5'-dioxo-11a,11a'-bis(3,5,7-trihydroxy-3,4-dihydro-2H-chromen-2-yl)-3,3',4,4',5a,5a',6,6',11,11',11a,11a'-dodecahydro-2H,2'H,5H,5'H-12,12'-bi[1,4]thiazino[2,3-b]phenazine-3,3'-dicarboxylic acid. Enzymatically catalyzed incubations under aeration starting from the initial CA-cysteine adducts and their follow-up dihydro-1,4-benzothiazine carboxylic acids, respectively, proved that the unstable colored compound was a trichochrome-like reaction intermediate of the browning reaction cascade which can be trapped by postincubation with OPD, thus verifying their direct mechanistic relationship.

Biorefinery of Green Biomass─How to Extract and Evaluate High Quality Leaf Protein for Food?

There is a growing need for protein for both feed and food in order to meet future demands. It is imperative to explore and utilize novel protein sources such as protein from leafy plant material, which contains high amounts of the enzyme ribulose-1,5-biphosphate carboxylase/oxygenase (RuBisCo). Leafy crops such as grasses and legumes can in humid climate produce high protein yields in a sustainable way when compared with many traditional seed protein crops. Despite this, very little RuBisCo is utilized for foods because proteins in the leaf material has a low accessibility to monogastrics. In order to utilize the leaf protein for food purposes, the protein needs to be extracted from the fiber rich leaf matrix. This conversion of green biomass to valuable products has been labeled green biorefinery. The green biorefinery may be tailored to produce different products, but in this Review, the focus is on production of food-grade protein. The existing knowledge on the extraction, purification, and concentration of protein from green biomass is reviewed. Additionally, the quality and potential application of the leaf protein in food products and side streams from the green biorefinery will be discussed along with possible uses of side streams from the protein production.

Interactions between Phenolic Acids, Proteins, and Carbohydrates-Influence on Dough and Bread Properties

The understanding of interactions between proteins, carbohydrates, and phenolic compounds is becoming increasingly important in food science, as these interactions might significantly affect the functionality of foods. So far, research has focused predominantly on protein-phenolic or carbohydrate-phenolic interactions, separately, but these components might also form other combinations. In plant-based foods, all three components are highly abundant; phenolic acids are the most important phenolic compound subclass. However, their interactions and influences are not yet fully understood. Especially in cereal products, such as bread, being a nutritional basic in human nutrition, interactions of the mentioned compounds are possible and their characterization seems to be a worthwhile target, as the functionality of each of the components might be affected. This review presents the basics of such interactions, with special emphasis on ferulic acid, as the most abundant phenolic acid in nature, and tries to illustrate the possibility of ternary interactions with regard to dough and bread properties. One of the phenomena assigned to such interactions is so-called dry-baking, which is very often observed in rye bread.

Galla Chinensis, a Traditional Chinese Medicine: Comprehensive review of botany, traditional uses, chemical composition, pharmacology and toxicology

ETHNOPHARMACOLOGICAL RELEVANCE

Galla chinensis (GC), a traditional Chinese medicine (TCM), has a wide range of pharmacological properties which have been widely used for more than 1400 years. Based on shape, GC is divided into two groups: jiaobei and dubei. It is a bitter, sour, cold and astringent substance which is usually used for treating diarrhea, constipation, bleeding, cough, vomiting, sweating, hemorrhoids, and anal and uterine prolapse. It is distributed in Japan, North Korea, and all parts of China.

AIM OF STUDY

This study was aimed at carrying out a comprehensive overview of the current status of research on Galla chinensis (GC) for better understanding of it characteristics, while providing a clear direction for future studies. It has aroused the interest of researchers, leading to development of medicinal value, expansion of its application, and provision of wider and more effective drug choices. This study was focused on the traditional uses, botany, chemical composition, pharmacology and toxicology of GC. Finally, the study focused on possible future research directions for GC.

MATERIALS AND METHODS

A comprehensive analysis was done based on academic papers, pharmaceutical monographs, ancient medicinal works, and drug standards of China. This review used Galla and Galla chinensis as keywords for retrieval of information on GC from online databases such as PubMed, Elsevier, CNKI, Web of Science, Google Scholar, SCI hub, and Baidu academic.

RESULTS

It was found that the chemical constituents of GC included tannins, phenolic acid, amino acids and fatty acid, with polyphenol compounds (especially tannins and gallic acid) as the distinct components. In vitro and in vivo studies revealed that GC exerted numerous biological effects such as anti-caries, antibacterial, antiviral, anticancer, and antioxidant effects. The therapeutic effect of GC was attributed mainly to the biological properties of its bioactive components.

CONCLUSIONS

GC is an important TCM which has potential benefit in the treatment of a variety of diseases. However, the relationship amongst the structure and biological activity of GC and its components, mechanism of action, toxicity, pharmacokinetics and target organs need to be further studied. Quality control and quality assurance programs for GC need to be further developed. There is need to study the dynamics associated with the accumulation of chemical compounds in GC as well as the original plants and aphid that form GC.

Rational Development of Stable PYY3-36 Peptide Y2 Receptor Agonists

PURPOSE

The anorectic effect of PYY_3-36 makes it a potential pharmacological weight loss treatment. Modifications of the endogenous peptide to obtain commercially attractive pharmacological and biophysical stability properties are examined.

METHODS

Half-life extended PYY_3-36 analogues were prepared and examined regarding Y₂-receptor potency as well as biophysical and stability properties.

RESULTS

Deamidation of asparagine in position 18 and 29 was observed upon incubation at 37°C. Asparagine in position 18 - but not position 29 - could be substituted to glutamine without detrimental effects on Y₂-receptor potency. Covalent dimers were formed via the phenol impurity benzoquinone reacting with two N-terminal residues (Isoleucine-Lysine). Both residues had to be modified to suppress dimerization, which could be done without negatively affecting Y₂-receptor potency or other stability/biophysical properties. Introduction of half-life extending modifications in position 30 and 35 eliminated aggregation at 37°C without negatively affecting other stability properties. Placement of a protracting moiety (fatty acid) in the receptor-binding C-terminal region reduced Y₂-receptor potency substantially, whereas only minor effects of protractor position were observed on structural, biophysical or stability properties. Lipidated PYY_3-36 analogues formed oligomers of various sizes depending on primary structure and solution conditions.

CONCLUSIONS

By rational design, a chemically and physically stable Y₂-receptor selective, half-life extended PYY_3-36 peptide has been developed.

Effect of TiF4 varnish after pre-treatment with proanthocyanidin or chlorhexidine on the progression of erosive dentin loss in the presence or absence of the demineralized organic matrix

This study evaluated the protective effect of TiF₄ varnish, after pre-treatment with proantocyanidin or chlorhexidine, on the progression of erosive dentin loss (EDL), under the presence or absence of the demineralized organic matrix (DOM). Bovine root dentin samples were eroded for 30 min (0.1% citric acid, pH 2.5) and the loss was measured by profilometry. Half of them were subjected to the DOM removal using collagenase for 4 days, while the other half remained immersed in water. The removal of DOM was checked by profilometry. Samples were divided into 24 groups (n = 15) according to the factors: 1- With or without DOM; 2- Pre-treatment with 0.012% chlorhexidine gel, 10% proanthocyanidin gel or untreated for 1 min; 3-Final Treatment with TiF₄ varnish, NaF varnish, placebo varnish or untreated for 6 h. The samples were submitted to a pH cycling for 5 days: 0.1% citric acid (4 × 90s/day) and artificial saliva between the challenges. The final profile was obtained for the calculation of EDL (μm, three-way ANOVA/Tukey test). When DOM was preserved, the EDL was lower compared to the condition without DOM (7.08 ± 4.03 μm and 9.80 ± 3.79 μm, p < 0.001, respectively), regardless of the treatments. The pre-treatment had no influence on the progression of EDL (p = 0.637), while the final treatment (TiF₄ varnish only, 6.77 ± 4.08 μm) was effective in reducing the progression of EDL (NaF varnish: 9.52 ± 4.02 μm; Placebo varnish: 8.64 ± 4.06 μm and no treatment: 8.80 ± 3.95 μm). It can be concluded that DOM has important protective effect on the progression of EDL. TiF₄ was the unique treatment capable of reducing EDL progression, regardless of the pre-treatment of DOM.

Oxidative Fragmentation of Aspalathin Leads to the Formation of Dihydrocaffeic Acid and the Related Lysine Amide Adduct

In the present study, the degradation of C-glucosidic dihydrochalcone aspalathin as the major phenolic compound in rooibos (Aspalathus linearis) was investigated. Analyses by gas chromatography-mass spectrometry of aqueous aspalathin-lysine incubations after silylation showed the formation of dihydrocaffeic acid [3-(3,4-dihydroxyphenyl)-propionic acid] under oxidative conditions as a novel degradation product up to 10 mol %. High-performance liquid chromatography analyses revealed the concurrent formation of the dihydrocaffeic acid lysine amide at about 30-fold lower concentrations, which was unequivocally verified by synthesis of an authentic reference standard. The amide was also verified in aspalathin-protein incubations after enzymatic hydrolysis by high-performance liquid chromatography-tandem mass spectrometry analyses. Thus, the covalent interaction of phenolic plant compounds with proteins under mild conditions (ambient temperatures and neutral pH) was confirmed for the first time. Acid and free amide were also quantitated in rooibos teas with significantly higher values in fermented varieties. The mechanism of formation was clarified to be initiated by singlet oxygen and to include a rearrangement-fragmentation mechanism with 1,2,3,5-tetrahydroxybenzene as the counterpart.

A simple Cu(II) complex of phenolic oxime: synthesis, crystal structure, supramolecular interactions, DFT calculation and catecholase activity study

A copper (II) complex [Cu(4-MeO-salox)₂](1) based on saloxime ligand was synthesized and characterized using single crystal X-ray diffraction studies. The geometry was further emphasized by DFT optimization. The complex was found to be pseudo-macrocyclic mononuclear having square planer geometry. The complex 1 shows two types of supramolecular hydrogen bonding interactions and forms the multi-dimensional framework with the help of CH∙∙∙O, OH∙∙∙O and π∙∙∙π(chelate) interactions. The complex 1 performs as efficient catalyst in catecholase activiy having good turnover number (TON), k_cat = 22.97 h⁻¹ where TON is the number of catechol molecules converted into quinone by catalyst molecule i.e 1 in a unit time.

Influence of proanthocyanidins combined with ethanol-wet bonding on the bonding quality of fibre posts to root dentine

This study evaluated the influence of a bonding approach using proanthocyanidins (PAs) combined with ethanol-wet bonding (EWB) and a hydrophobic adhesive on the bonding quality of fibre posts. After endodontic treatment and post-space preparation, 72 single-rooted extracted human teeth were etched, thoroughly rinsed, and then treated using the following procedures (n = 24 teeth per group): group 1, no pretreatment; group 2, pretreatment with absolute ethanol three times, for 30 s each time; or group 3, pretreatment with absolute ethanol solution containing 5% PAs three times, for 30 s each time. Six teeth per group were dried according to a dry and a wet drying protocol and then observed using field emission-scanning electron microscopy. The remaining 18 teeth in each group were cemented with fibre posts: All-Bond 3 and Duo-Link cement were used for group 1; and hydrophobic adhesive and Duo-Link cement were used for groups 2 and 3. Push-out bond strength, failure mode, and nanoleakage were evaluated immediately and after collagenase treatment. Higher push-out bond strength and less nanoleakage were observed in the two ethanol-pretreatment groups, regardless of storage conditions. Teeth pretreated with PAs + ethanol exhibited significantly higher push-out bond strength after collagenase treatment than did teeth pretreated with ethanol alone. Within the limits of this study, the bonding approach of PAs combined with EWB and a hydrophobic adhesive synergistically improved the durability of fibre post bonds.

Detection and Characterization of Catechol Quinone-Derived Protein Adducts Using Biomolecular Mass Spectrometry

The catechol quinone (CQ) motif is present in many biologically relevant molecules throughout endogenous metabolic products, foods, drugs, and environmental pollutants. The CQ derivatives may undergo Michael addition, and has been shown to yield covalent bonds with nucleophilic sites of cysteine, lysine, or histidine residue of proteins. The CQ-adducted proteins may exhibit cytotoxicity or biological functions different from their un-adducted forms. Identification, characterization, and quantification of relevant protein targets are essential but challenging goals. Mass spectrometry (MS) is well-suited for the analysis of proteins and protein modifications. Technical development of bottom-up proteomics has greatly advanced the field of biomolecular MS, including protein adductomics. This mini-review focuses on the use of biomolecular MS in (1) structural and functional characterization of CQ adduction on standards of proteins, (2) identification of endogenous adduction targets, and (3) quantification of adducted blood proteins as exposure index. The reactivity and outcome of CQ adduction are discussed with emphases on endogenous species, such as dopamine and catechol estrogens. Limitations and advancements in sample preparation, MS instrumentation, and software to facilitate protein adductomics are also discussed.

The Oxidative Pathway to Dopamine-Protein Conjugates and Their Pro-Oxidant Activities: Implications for the Neurodegeneration of Parkinson's Disease

Neuromelanin (NM) is a dark brown pigment found in dopaminergic neurons of the substantia nigra (SN) and in norepinephrinergic neurons of the locus coeruleus (LC). Although NM is thought to be involved in the etiology of Parkinson's disease (PD) because its content decreases in neurodegenerative diseases such as PD, details are still unknown. In this study, we characterized the biosynthetic pathway of the oxidation of dopamine (DA) by tyrosinase in the presence of thiol peptides and proteins using spectroscopic and high-performance liquid chromatography (HPLC) methods and we assessed the binding of DA via cysteine residues in proteins by oxidation catalyzed by redox-active metal ions. To examine whether the protein-bound DA conjugates exhibit pro-oxidant activities, we measured the depletion of glutathione (GSH) with the concomitant production of hydrogen peroxide. The results suggest that the fate of protein-bound DA conjugates depends on the structural features of the proteins and that DA-protein conjugates produced in the brain possess pro-oxidant activities, which may cause neurodegeneration due to the generation of reactive oxygen species (ROS) and the depletion of antioxidants.

Influence of Nucleophilic Amino Acids on Enzymatic Browning Systems

In the present study the enzymatic oxidation of gallic acid and catechin catalyzed by nashi pear polyphenol oxidase (PPO) in the presence of the amino acids lysine, arginine, or cysteine was investigated for polyphenol-amino acid adducts. HPLC analyses revealed the formation of two novel dihydrobenzothiazine carboxylic acid derivatives (8-(3',4'-dihydro-2 H-chromene-3',5',7'-triol)-3,4-dihydro-5-hydroxy-2 H-benzothiazine-3-carboxylic acid and 7-(3',4'-dihydro-2 H-chromene-3',5',7'-triol)-3,4-dihydro-5-hydroxy-2 H-benzothiazine-3-carboxylic acid) from 2'-cysteinyl catechin and 5'-cysteinyl catechin in cysteine incubations, respectively. In contrast, arginine and lysine did not lead to any amino acid adducts. Target compounds were separated by high-performance countercurrent chromatography and preparative HPLC and unequivocally characterized by mass spectrometry and nuclear magnetic resonance spectroscopy. Mechanistic incubations starting from the catechin-cysteine adducts showed that both catechin and PPO are crucial components in the formation of the dihydrobenzothiazines. The cysteine incubations showed a red-brown coloration, which coincided with formation and degradation of the dihydrobenzothiazines finally leading to the formation of high-polymeric melanins. Therefore, these compounds might be the key intermediates to understand development of color during cysteine-driven enzymatic browning reactions.

Exploration of catecholase-like activity of a series of magnetically coupled transition metal complexes of Mn, Co and Ni: new insights into the solution state behavior of Mn complexes

Oxidation state dependent catecholase activity has been explored with Mn-Schiff-base complex which transform oxidation state from +ii to +iii in solution with time by combined experimental and theoretical investigations.

Polyphenol uses in biomaterials engineering

Polyphenols are micronutrients obtained from diet that have been suggested to play an important role in health. The health benefits of polyphenols and their protective effects in food systems as antioxidant compounds are well known and have been extensively investigated. However, their functional roles as a "processing cofactor" in tissue engineering applications are less widely known. This review focuses on the functionality of polyphenols and their application in biomaterials. Polyphenols have been used to stabilize collagen and to improve its resistance to degradation in biological systems. Therefore, they have been proposed to improve the performance of biomedical devices used in cardiovascular systems by improving the mechanical properties of grafted heart valves, enhancing microcirculation through the relaxation of the arterial walls and improving the capillary blood flow and pressure resistance. Polyphenols have been found to stimulate bone formation, mineralization, as well as the proliferation, differentiation, and the survival of osteoblasts. These effects are brought about by the stimulatory effect of polyphenols on osteoblast cells and their protective effect against oxidative stress and inflammatory cytokines. In addition, polyphenols inhibit the differentiation of the osteoclast cells. Collectively, these actions lead to promote bone formation and to reduce bone resorption, respectively. Moreover, polyphenols can increase the cross-linking of dentine and hence its mechanical stability. Overall, polyphenols provide interesting properties that will stimulate further research in the bioengineering field.

Dual function of proanthocyanidins as both MMP inhibitor and crosslinker in dentin biomodification: A literature review

Proanthocyanidin, a natural phytochemical bioactive agent, simultaneously can silence the activity of dentinal proteases and crosslink the collagen matrix; both of these phenomena would be the fundamentals for bio-stability of resin-dentin interface which is essential for a promising adhesive dentistry. This review provides an overview of the data developed by different groups of researchers and highlighted topics are proanthocyanidin chemistry, natural resources and the unique interactions between proanthocyanidincollagen and proanthocyanidin-MMPs in dentin. Besides, clinical applications of proanthocyanidin in the form of proanthocyanidin-containing adhesives, preconditioners and etchants have been reviewed. One hundred and twelve studies have been published in peer-reviewed journals from 1981 to 2017, all were comprised in this review, some of them have been actually proven to be promising from clinical point of view and others need further assessment before their adoption as clinically practicable protocols.

Comparative evaluation of grape seed and cranberry extracts in preventing enamel erosion: An optical emission spectrometric analysis

Introduction:

Dental erosion is defined as the loss of tooth structure due to chemical process that does not involve bacteria. The management of such a condition calls for a comprehensive approach to identifying the cause and treating it.

Aim:

The aim of this study is to comparatively evaluate the role of grape seed extract (GSE) and cranberry extract (CE) in preventing dental erosion using optical emission spectrometry.

Materials and Methods:

Prepared enamel specimens were subjected to the erosive challenge using HCl for 10 s, followed by immersion in experimental natural groups and control fluoride group for 30 s and artificial saliva for 60 min. This cycle was repeated three times. The amounts of calcium and phosphorous present in the acid solution after 1^st, 2^nd, and 3^rd erosive challenges were determined for each group using induced coupled plasma-optical emission spectrometry.

Results:

The cumulative calcium and phosphorous release after the 1^st, 2^nd, and 3^rd erosive challenges were found to be the least in SnF2 group, followed by GSE group and then in CE group.

Conclusion:

The protective of GSE and CE was inferior to the gold standard control group of stannous fluoride role, against enamel erosion. GSE showed better remineralizing effect; however, there was no statistically significant difference between the two groups.

Green Tea Polyphenols Decrease Strecker Aldehydes and Bind to Proteins in Lactose-Hydrolyzed UHT Milk

The effect of epigallocatechin gallate enriched green tea extract (GTE) on flavor, Maillard reactions and protein modifications in lactose-hydrolyzed (LH) ultrahigh temperature (UHT) processed milk was examined during storage at 40 °C for up to 42 days. Addition of GTE inhibited the formation of Strecker aldehydes by up to 95% compared to control milk, and the effect was similar when GTE was added either before or after UHT treatment. Release of free amino acids, caused by proteolysis, during storage was also decreased in GTE-added milk either before or after UHT treatment compared to control milk. Binding of polyphenols to milk proteins was observed in both fresh and stored milk samples. The inhibition of Strecker aldehyde formation by GTE may be explained by two different mechanisms; inhibition of proteolysis during storage by GTE or binding of amino acids and proteins to the GTE polyphenols.

Control of Maillard Reactions in Foods: Strategies and Chemical Mechanisms

Maillard reactions lead to changes in food color, organoleptic properties, protein functionality, and protein digestibility. Numerous different strategies for controlling Maillard reactions in foods have been attempted during the past decades. In this paper, recent advances in strategies for controlling the Maillard reaction and subsequent downstream reaction products in food systems are critically reviewed. The underlying mechanisms at play are presented, strengths and weaknesses of each strategy are discussed, and reasonable reaction mechanisms are proposed to reinforce the evaluations. The review includes strategies involving addition of functional ingredients, such as plant polyphenols and vitamins, as well as enzymes. The resulting trapping or modification of Maillard targets, reactive intermediates, and advanced glycation endproducts (AGEs) are presented with their potential unwanted side effects. Finally, recent advances in processing for control of Maillard reactions are discussed.

The Oxidative Activity of Ellagitannins Dictates Their Tendency To Form Highly Stabilized Complexes with Bovine Serum Albumin at Increased pH

Many food and forage plants contain tannins, high molecular weight polyphenols that characteristically interact strongly with protein, forming complexes that affect taste, nutritional quality, and the health of the consumer. In the present study, the interaction between bovine serum albumin (BSA) and each of seven hydrolyzable tannins or epigallocatechin gallate was examined. The objective was to define the effect of tannin oxidation, measured as oxidative activity (browning) or as oxidizability (degradation monitored by HPLC), on the formation on highly stabilized tannin-protein complexes and to determine how the reaction depended on the pH conditions. Gel electrophoresis and MALDI-TOF-MS were used to assess the formation of tannin-protein complexes. The results showed that tannin oxidizability was directly correlated with the tendency of the tannins to form highly stabilized complexes with BSA at increased pH (7.6). However, at slightly lower pH (6.7), other tannin features, such as the size and flexibility of the tannin, appeared to dictate the formation of highly stabilized tannin-protein complexes.

Effects of Peach Cultivar on Enzymatic Browning Following Cell Damage from High-Pressure Processing

Peach cultivars contribute to unique product characteristics and may affect the degree of browning after high-pressure processing (HPP). Nine peach cultivars were subjected to HPP at 0, 100, and 400 MPa for 10 min. Proton nuclear magnetic resonance (¹H NMR) relaxometry, light microscopy, color, polyphenol oxidase (PPO) activity, and total phenols were evaluated. The development of enzymatic browning during refrigerated storage occurred because of damage during HPP that triggered loss of cell integrity, allowing substrates to interact with enzymes. Increasing pressure levels resulted in greater damage, as determined by shifts in transverse relaxation time (T₂) and by light micrographs. Discoloration was triggered by membrane decompartmentalization but limited by PPO activity, which was found to correlate to cultivar harvest time (early, mid, and late season). Outcomes from the microstructure, ¹H NMR ,and PPO activity evaluation were an effective means of determining membrane decompartmentalization and allowed for prediction of browning scenarios.

The Impact of Maturity Stage on Cell Membrane Integrity and Enzymatic Browning Reactions in High Pressure Processed Peaches (Prunus persica)

Fruit maturity is an important factor associated with final product quality, and it may have an effect on the level of browning in peaches that are high pressure processed (HPP). Peaches from three different maturities, as determined by firmness (M1 = 50-55 N, M2 = 35-40 N, and M3 = 15-20 N), were subjected to pressure levels at 0.1, 200, and 400 MPa for 10 min. The damage from HPP treatment results in loss of fruit integrity and the development of browning during storage. Increasing pressure levels of HPP treatment resulted in greater damage, particularly in the more mature peaches, as determined by shifts in transverse relaxation time (T2) of the vacuolar component and by light microscopy. The discoloration of peach slices of different maturities processed at the same pressure was comparable, indicating that the effect of pressure level is greater than that of maturity in the development of browning.

Quinone-induced protein modifications: Kinetic preference for reaction of 1,2-benzoquinones with thiol groups in proteins

Oxidation of polyphenols to quinones serves as an antioxidative mechanism, but the resulting quinones may induce damage to proteins as they react through a Michael addition with nucleophilic groups, such as thiols and amines to give protein adducts. In this study, rate constants for the reaction of 4-methylbenzoquinone (4MBQ) with proteins, thiol and amine compounds were determined under pseudo first-order conditions by UV-vis stopped-flow spectrophotometry. The chemical structures of the adducts were identified by LC-ESI-MS/MS. Proteins with free thiols were rapidly modified by 4MBQ with apparent second order rate constants, k2 of (3.1±0.2)×10(4)M(-1)s(-1) for bovine serum albumin (BSA) and (4.8±0.2)×10(3)M(-1)s(-1) for human serum albumin at pH 7.0. These values are at least 12-fold greater than that for α-lactalbumin (4.0±0.2)×10(2)M(-1)s(-1), which does not contain any free thiols. Reaction of Cys-34 of BSA with N-ethylmaleimide reduced the thiol concentration by ~59%, which resulted in a decrease in k2 by a similar percentage, consistent with rapid adduction at Cys-34. Reaction of 4MBQ with amines (Gly, Nα-acetyl-l-Lys, Nε-acetyl-l-Lys and l-Lys) and the guanidine group of Nα-acetyl-l-Arg was at least 5×10(5) slower than with low-molecular-mass thiols (l-Cys, Nα-acetyl-l-Cys, glutathione). The thiol-quinone interactions formed colorless thiol-phenol products via an intermediate adduct, while the amine-quinone interactions generated colored amine-quinone products that require oxygen involvement. These data provide strong evidence for rapid modification of protein thiols by quinone species which may be of considerable significance for biological and food systems.

Evidence for the Formation of Benzacridine Derivatives in Alkaline-Treated Sunflower Meal and Model Solutions

Sunflower extraction meal (SEM) is an economically interesting protein source. During alkaline extraction of proteins, the presence of chlorogenic acid (CQA) in the meal gives rise to the formation of o-quinones. Reactions with nucleophiles present in proteins can lead to green discoloration. Although such reactions have been known for a long time, there is a lack of information on the chemical nature of the reaction products. SEM and model systems consisting of amino acids and CQA were subjected to alkaline treatment and, for comparison, to oxidation of CQA by polyphenoloxidase (PPO). Several green trihydroxy benzacridine (TBA) derivatives were tentatively identified in all samples by UHPLC-DAD-MS/MS. Surprisingly, in alkaline-treated samples of particular amino acids as well as in SEM, the same six TBA isomers were detected. In contrast, the enzymatically oxidized samples resulted in only three TBA derivatives. Contrary to previous findings, neither peptide nor amino acid residues were attached to the resultant benzacridine core. The results indicate that the formation of TBA derivatives is caused by the reaction between CQA quinones and free NH₂ groups. Further research is necessary to elucidate the structure of the addition products for a comprehensive evaluation of food and feed safety aspects.

Exploration of biological activities of alkyne arms containing Cu(ii) and Ni(ii) complexes: syntheses, crystal structures and DFT calculations

Several mononuclear Cu(ii) and Ni(ii) Schiff base (N,O-donor) complexes were synthesized and characterized. The binding ability with DNA and BSA and catecholase activity of the complexes were investigated.