Electrochemical quantification of the structure/antioxidant activity relationship of flavonoids

Argentinian Rose Petals as a Source of Antioxidant and Antimicrobial Compounds

The total phenolic, flavonoid, and anthocyanin contents were evaluated in 11 cultivars of Argentinian roses of different colors. HPLC-ESI-QTOF/MS was used to identify the components where ellagic and quinic acids, quercetin, and kaempferol glycosylated derivatives were found. The phenolic contents ranged from 78.8 ± 3.2 to 203.4 ± 3.1 mg GAE/g dw, the flavonoid content ranged from 19.1 ± 3.8 to 125.9 ± 6.5 mg QE/g dw, and the anthocyanin content ranged from less than 0.01 to 5.8 ± 0.1 mg CE/g dw. The dark red cultivars exhibited the greatest levels of the analyzed compounds and of the antioxidant activities, even higher than those of certain plants known for their high phenolic contents and antioxidant activity. Moreover, the addition of these extracts decreased the population of L. innocua and P. aeruginosa to undetectable levels 24 h after inoculation. Rose petal extracts, mainly those with a dark red color, can be used as natural additives in food, feed, and cosmetics, as they contain a high proportion of bioactive compounds with antioxidant and antimicrobial effects.

Rice Byproduct Compounds: From Green Extraction to Antioxidant Properties

Currently, rice (Oryza sativa L.) production and consumption is increasing worldwide, and many efforts to decrease the substantial impact of its byproducts are needed. In recent years, the interest in utilizing rice kernels, husk, bran, and germ for the recovery of different molecules, from catalysts (to produce biodiesel) to bioactive compounds, has grown. In fact, rice byproducts are rich in secondary metabolites (phenolic compounds, flavonoids, and tocopherols) with different types of bioactivity, mainly antioxidant, antimicrobial, antidiabetic, and anti-inflammatory, which make them useful as functional ingredients. In this review, we focus our attention on the recovery of antioxidant compounds from rice byproducts by using innovative green techniques that can overcome the limitations of traditional extraction processes, such as their environmental and economic impact. In addition, traditional assays and more innovative methodologies to evaluate the antioxidant activity are discussed. Finally, the possible molecular mechanisms of action of the rice byproduct antioxidant compounds (phenolic acids, flavonoids, γ-oryzanol, and vitamin E) are discussed as well. In the future, it is expected that rice byproduct antioxidants will be important food ingredients that reduce the risk of the development of several human disorders involving oxidative stress, such as metabolic diseases, inflammatory disorders, and cancer.

Identification of chemical components and rat serum metabolites in Danggui Buxue decoction based on UPLC-Q-TOF-MS, the UNIFI platform and molecular networks

Danggui Buxue Decoction (DBD), consisting of Astragalus membranaceus (Fisch.) Bge. var. mongholicus (Bge.) Hsiao (Huangqi, HQ) and Angelica sinensis (Oliv.) Diels (Danggui, DG), is a traditional Chinese medicine (TCM) formula with the function of tonifying Qi and promoting blood. In this study, ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) was used to comprehensively identify the chemical constituents in DBD and those entering into the rat serum after gastric perfusion. A combination of the UNIFI platform and Global Natural Product Social molecular networking (GNPS) was used to analyze the chemical composition of DBD. As a result, 207 compounds were unambiguously or tentatively identified including 60 flavonoids, 38 saponins, 35 organic acids, 26 phthalides, 12 phenylpropanoids, 11 amino acids and 25 others. Furthermore, a total of 80 compounds, including 29 prototype components and 51 exogenous metabolites, were detected in the serum of rats. Phase I reactions (oxidation, reduction, and hydration), phase II reactions (methylation, sulfation, and glucuronidation), and their combinations were the main metabolic pathways of DBD. The results provided fundamental information for further studying the pharmacological mechanisms of DBD, as well as its quality control research.

Chemical Characterization and Determination of the Antioxidant Properties of Phenolic Compounds in Three Scutellaria sp. Plants Grown in Colombia

Plants of the genus Scutellaria (Lamiaceae) have a wide variety of bioactive secondary metabolites with diverse biological properties, e.g., anti-inflammatory, antiallergenic, antioxidant, antiviral, and antitumor activities. The chemical composition of the hydroethanolic extracts, obtained from dried plants of S. incarnata, S. coccinea, and S. ventenatii × S. incarnata, was determined by UHPLC/ESI-Q-Orbitrap-MS. The flavones were found in a higher proportion. Baicalin and dihydrobaicalein-glucuronide were the major extract components in S. incarnata (287.127 ± 0.005 mg/g and 140.18 ± 0.07 mg/g), in S. coccinea (158.3 ± 0.34 mg/g and 51.20 ± 0.02 mg/g), and in S. ventenatii × S. incarnata (186.87 ± 0.01 mg/g and 44.89 ± 0.06 mg/g). The S. coccinea extract showed the highest antioxidant activity in the four complementary techniques employed to evaluate all extracts: ORAC (3828 ± 3.0 µmol Trolox^®/g extract), ABTS^+• (747 ± 1.8 µmol Trolox^®/g extract), online HPLC-ABTS^+• (910 ± 1.3 µmol Trolox^®/g extract), and β-carotene (74.3 ± 0.8 µmol Trolox^®/g extract).

Effects of Fisetin, a Plant-Derived Flavonoid, on Response to Oxidative Stress, Aging, and Age-Related Diseases in Caenorhabditis elegans

Fisetin (3,3',4',7-tetrahydroxyflavone), a flavonoid abundant in various fruits and vegetables, including apple, strawberry, and onion, shows several beneficial effects such as anti-oxidant, anti-inflammatory, and anti-tumor effects. The free radical theory of aging suggests that age-related accumulation of oxidative damage is the major cause of aging and that decreasing cellular oxidative stress can regulate aging. Here, we investigated the effects of dietary supplementation with fisetin on the stress response, aging, and age-related diseases. Fisetin reduced the cellular ROS levels and increased the resistance to oxidative stress. However, the response to UV irradiation was not affected by fisetin. Both the mean and maximum lifespans were significantly extended by fisetin; lifespan extension by fisetin was accompanied by reduced fertility as a trade-off. Age-related decline in motility was also delayed by supplementation with fisetin. Amyloid beta-induced toxicity was markedly decreased by fisetin, which required DAF-16 and SKN-1. Reduced motility induced by a high-glucose diet was completely recovered by supplementation with fisetin, which was dependent on SKN-1. Using a Parkinson's disease model, we showed that degeneration of dopaminergic neurons was significantly inhibited by treatment with fisetin. Genetic analysis revealed that lifespan extension by fisetin was mediated by DAF-16-induced stress response and autophagy. These findings support the free radical theory of aging and suggest that fisetin can be a strong candidate for use in novel anti-aging anti-oxidant nutraceuticals.

Phenolic compounds in Nordic berry species and their application as potential natural food preservatives

An increasing demand for natural food preservatives is raised by consumers. For Nordic berry species, abundance of phenolic compounds and potent activities of anti-oxidation and anti-bacteria enables a great potential as food preservatives. This review provides a systematic examination of current literature on phenolic profiles, anti-oxidative and anti-bacterial activities of various extracts of Nordic berry species, as well as the impact of various structure features of phenolics on the bioactivities. Special attention is placed on exploitation of leaves of berry species and pomaces after juice-pressing as side-streams of berry production and processing. The current progress and challenges in application of Nordic berry species as food preservatives are discussed. To fully explore the potential application of Nordic berry species in food industry and especially to valorize the side-streams of berry cultivation (leaves) and juice-pressing industry (pomaces), it is crucial to obtain extracts and fractions with targeted phenolic composition, which have high food preserving efficacy and minimal impact on sensory qualities of food products.

Combination of electrochemical unit and ESI-MS in fragmentation of flavonoids

INTRODUCTION

Predictive approaches on the activity of natural compounds based on the fragmentation by instrumental techniques are important for consideration of such molecules as drug candidates and defining new structures with promising properties. Since flavonoids are well-known antioxidants, their redox properties can be related to their pharmacological activity.

OBJECTIVES

In this work, the potential of electrochemical unit coupled to electrospray ionisation mass spectrometry (ESI-MS) was assessed for fragmentation activity relationships studies of selected flavonoids.

METHODOLOGY

Methodology of this research included electrochemical conversion of standards of flavonoids at different pH values and their further analysis with the use of ESI-MS. In addition, signals obtained from the blank samples were also identified and used for interpretation due to electrochemical nature of the ESI source. Half maximal inhibitory concentration (IC₅₀ ) values of flavonoids for 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) antioxidant activity assays were analysed for possible correlation with the structures of flavonoids and products of electrochemical conversion.

RESULTS

Fragmentation activity relationships were suggested using the proposed approach and for some of the flavonoids it was not specific enough to determine the input of a particular structural feature to the activity, but for others they were in agreement with those found in the literature. Obtained results showed potential of the proposed approach for application in plant sciences as a fast pre-screening tool for newly isolated bioactive compounds.

Isolation, Structure Elucidation and In Silico Prediction of Potential Drug-Like Flavonoids from Onosma chitralicum Targeted towards Functionally Important Proteins of Drug-Resistant Bad Bugs

Admittedly, the disastrous emergence of drug resistance in prokaryotic and eukaryotic human pathogens has created an urgent need to develop novel chemotherapeutic agents. Onosma chitralicum is a source of traditional medicine with cooling, laxative, and anthelmintic effects. The objective of the current research was to analyze the biological potential of Onosma chitralicum, and to isolate and characterize the chemical constituents of the plant. The crude extracts of the plant prepared with different solvents, such as aqueous, hexane, chloroform_, ethyl acetate, and butanol, were subjected to antimicrobial activities. Results corroborate that crude (methanol), EtoAc, and n-C₆H₁₄ fractions were more active against bacterial strains. Among these fractions, the EtoAc fraction was found more potent. The EtoAc fraction was the most active against the selected microbes, which was subjected to successive column chromatography, and the resultant compounds 1 to 7 were isolated. Different techniques, such as UV, IR, and NMR, were used to characterize the structures of the isolated compounds 1–7. All the isolated pure compounds (1–7) were tested for their antimicrobial potential. Compounds 1 (4′,8-dimethoxy-7-hydroxyisoflavone), 6 (5,3′,3-trihydroxy-7,4′-dimethoxyflavanone), and 7 (5′,7,8-trihydroxy-6,3′,4′-trimethoxyflavanone) were found to be more active against Staphylococcus aureus and Salmonella Typhi. Compound 1 inhibited S. typhi and S. aureus to 10 ± 0.21 mm and 10 ± 0.45 mm, whereas compound 6 showed inhibition to 10 ± 0.77 mm and 9 ± 0.20 mm, respectively. Compound 7 inhibited S. aureus to 6 ± 0.36 mm. Compounds 6 and 7 showed significant antibacterial potential, and the structure–activity relationship also justifies their binding to the bacterial enzymes, i.e., beta-hydroxyacyl dehydratase (HadAB complex) and tyrosyl-tRNA synthetase. Both bacterial enzymes are potential drug targets. Further, the isolated compounds were found to be active against the tested fungal strains. Whereas docking identified compound 7, the best binder to the lanosterol 14α-demethylase (an essential fungal cell membrane synthesizing enzyme), reported as an antifungal fluconazole binding enzyme. Based on our isolation-linked preliminary structure-activity relationship (SAR) data, we conclude that O. chitralicum can be a good source of natural compounds for drug development against some potential enzyme targets.

Electrochemical evaluation of the antioxidant capacity of natural compounds on glassy carbon electrode modified with guanine-, polythionine-, and nitrogen-doped graphene

An electrochemical sensor based on guanine-, polythionine-, and nitrogen-doped graphene modified glassy carbon electrode (G/PTH/NG/GCE) was fabricated and applied for antioxidant capacity evaluation of natural compounds and complexes in electrochemical method since natural sources of active compounds exhibited various antioxidant activities. When the antioxidants existed in the system, the generated hydroxyl radicals were scavenged and the damage to guanine immobilized on the electrode was reduced less resulting in the oxidation peak current increased in square wave voltammetry. After the modifications of polythionine- and nitrogen-doped graphene, the oxidation peak current was improved. The effects of pH, incubation time, and concentrations of guanine and Fe2+ ions on the performances of the electrode were investigated and optimized. The G/PTH/NG/GCE showed good linearity, reproducibility, and storage stability for antioxidant capacity evaluation of ascorbic acid at the optimum conditions. The antioxidant capacities of three flavonoids and three plant extracts were measured using the G/PTH/NG/GCE and DPPH methods. Myricetin showed the highest antioxidant capacity in both electrochemical and DPPH methods. The proposed G/PTH/NG/GCE exhibited easy fabrication procedure, rapid detection time, and low cost for the detection of antioxidant activity for various kinds of samples.

Estimation of the total antioxidant potential in the meat samples using thin-layer chromatography

There is limited literature on the antioxidative properties of food of animal origin. Measurements of antioxidative properties are usually performed using the reaction of reduction of colored 2,2-diphenyl-1-picrylhydrazyl (DPPH) radials. Changes of the DPPH color are tracked photometrically. These measurements are interfered by both, the tested samples and reduced DPPH. This study aims to demonstrate the ability to separate different forms of DPPH (DPPH• and DPPH-H) by thin-layer chromatography (TLC). Further, it has been practically applied in the study of the determination of antioxidative properties of the meat samples. It was found that TLC can be used for the separation of different forms of DPPH as well as for measurement of TAP (total antioxidant potential) values related to the DPPH•. The strongest antioxidant properties were observed for pork neck extracted in buffer pH 2 and for smoked salmon fish extracted in acetone, the lowest for veal and turkey fillet extracted in methanol.

Identification and characterization of chemical constituents in Dengzhan Shengmai Capsule and their metabolites in rat plasma by ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry

Dengzhan Shengmai Capsule (DZSMC) is a traditional Chinese medicine (TCM) formula with remarkable clinical effect in the treatment of stroke sequelae. Exploring the components of DZSMC and detecting the absorbed prototype constituents and metabolites in blood are of great significance to clarify the effective substances of this prescription. Here, a reliable method using ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-QTOF/MS) was established for the comprehensive analysis of chemical constituents of DZSMC and their metabolites in rat plasma after gastric perfusion. Two acquisition modes, including MS^E mode and Fast DDA mode, were performed for acquiring more precursor ions and cleaner precursor-product ions background during the study of constituents of DZSMC. As a result, a total of 125 constituents were unambiguously characterized or tentatively identified. For the first time, a total of 92 components, including 44 prototype components and 48 metabolites were unambiguously or tentatively identified in rat plasma. The metabolic pathways included phase I reactions (hydration, hydrogenation, oxidation, demethylation and hydroxylation) and phase II reactions (conjugation with glucuronide, sulfate and methyl). Furthermore, the metabolites from caffeic acid and scutellarin were characterized and validated by phase II metabolic reactions in vitro, which could be established as a simulated in vivo environment of metabolites identification and verification of TCM formula. It is the first systematic study on metabolism of DZSMC in vivo and could also provide a valid analytical strategy for characterization of the chemical compounds and metabolites of TCM formula.

Influence of Bovine Serum Albumin-Flavonoid Interaction on the Antioxidant Activity of Dietary Flavonoids: New Evidence from Electrochemical Quantification

Interaction between dietary flavonoids and albumins plays an important role in the bioavailability and bioactivity of flavonoids. Therefore, the influence of this interaction on the antioxidant activity of flavonoid has attracted much interest. In this study, a ceric reducing/antioxidant capacity assay (CRAC) was employed to investigate the effects of albumin-flavonoid interaction on the antioxidant activity of seven common flavonoids. The results obtained from the CRAC assay were also compared separately with the results from the spectrophotometric methods including 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assays. All the flavonoids show a decreasing in the antioxidant activity detected by CRAC assay, indicting a "masking effect" of bovine serum albumin (BSA)-flavonoid interaction. However, the results from DPPH and FRAP assays were conflicting, which may be attributed to the influence of solvent systems.

Glycosylation of 3-Hydroxyflavone, 3-Methoxyflavone, Quercetin and Baicalein in Fungal Cultures of the Genus Isaria

Flavonoids are plant secondary metabolites with a broad spectrum of biological activities. In nature, they occur mainly in the form of glycosides, but their extraction is often difficult and expensive, as is chemical synthesis. We have shown that biotransformations are an excellent method for obtaining flavonoid glycosides. We are the first team to describe the use of Isaria microorganisms in biotransformations of flavonoid compounds. In the present study as biocatalysts, we used one strain of Isaria fumosorosea KCH J2 isolated from a spider carcass in green areas of Wroclaw and two strains of I. farinosa (J1.4 and J1.6) isolated from insects found in already unused mines in Lower Silesia. The substrates were 3-hydroxyflavone, 3-methoxyflavone, quercetin (3,3',4',5,7-pentahydroxyflavone), and baicalein (5,6,7-trihydroxyflavone). For all the substrates that were used in this study, we obtained 4-O-methylglucopyranosides. In the case of substrates with a hydroxyl group in the third position, O-β-d-glucopyranosides were also formed. Isoquercetin that was obtained by biotransformation was used as a substrate to check the kinetics of the formation of flavonoid 4-O-methylglucopyranosides in I. fumosorosea KCH J2 culture. We did not observe the attachment of the methyl group to glucose unit in isoquercetin. Our finding suggest that the attachment of 4-O-methylglucopyranose occurs in one step.

Exploring optimal supplement strategy of medicinal herbs and tea extracts for bioelectricity generation in microbial fuel cells

This first-attempt study used extracts of appropriate antioxidant abundant Camellia and non-Camellia tea and medicinal herbs as model ESs to stably intensify bioelectricity generation performance in microbial fuel cells (MFCs). As electron shuttles (ESs) could stimulate electron transport phenomena by significant reduction of electron transfer resistance, the efficiency of power generation for energy extraction in microbial fuel cells (MFCs) could be appreciably augmented. Using environmentally friendly natural bioresource as green bioresource of ESs is the most promising to sustainable practicability. As comparison of power-density profiles indicated, supplement of Camellia tea extracts would be the most appropriate, then followed non-Camellia Chrysanthemum tea and medicinal herbs. Antioxidant activities, total phenolic contents and power stimulating activities were all electrochemically associated. In particular, the extract of unfermented Camellia tea (i.e., green tea) was the most promising ESs to augment bioenergy extraction compared to other refreshing medicinal herb extracts.

Evaluation of the antioxidant and gastroprotective activity and HPLC analysis of the hydroalcoholic extract of Tocoyena formosa leaves (Cham. & Schlecht) K. Schum

The peptic ulcer is a gastric disorder that affects millions of people and yet they cause many side effects. In this sense, natural products represent an important alternative to the discovery of compounds with gastroprotective activity. The present work has as its objective to evaluate the antioxidant and gastroprotective activity of the Hydroalcoholic Extract of Leaves from Tocoyena formosa (Cham. & Schlecht.) K. Schum (HELTF), this being much emphasized in traditional medicine for inflammatory morbidities and gastric symptoms. For the evaluation of the antioxidant activity, FRAP and DPPH tests were carried out, and for the evaluation of the gastroprotective activity, gastric lesion induction by ethanol, acidified ethanol, indomethacin and physical barrier tests were used. Antioxidant assay of HELTF revealed an EC50 of 558.66 μM FeSO4/g and IC50 of 189.78 μg/ml for FRAP and DPPH respectively. In gastroprotective, in ethanol model, all the doses presented significant activity in comparison to controls, however, in the gastric lesion induction test by acidified ethanol and indomethacin, only the dose of 200 mg/kg presented with significance. In the physical barrier test presented evidence that protection by the formation of a protective layer associated with mucus. Concluded, therefore, that HELTF possesses antioxidant and significate gastroprotective activity.

Structure-activity relationships and molecular docking of thirteen synthesized flavonoids as horseradish peroxidase inhibitors

For the first time, the structure-activity relationships of thirteen synthesized flavonoids have been investigated by evaluating their ability to modulate horseradish peroxidase (HRP) catalytic activity. Indeed, a modified spectrophotometrically method was carried out and optimized using 4-methylcatechol (4-MC) as peroxidase co-substrate. The results show that these flavonoids exhibit a great capacity to inhibit peroxidase with Ki values ranged from 0.14±0.01 to 65±0.04mM. Molecular docking has been achieved using Auto Dock Vina program to discuss the nature of interactions and the mechanism of inhibition. According to the docking results, all the flavonoids have shown great binding affinity to peroxidase. These molecular modeling studies suggested that pyran-4-one cycle acts as an inhibition key for peroxidase. Therefore, potent peroxidase inhibitors are flavonoids with these structural requirements: the presence of the hydroxyl (OH) group in 7, 5 and 4' positions and the absence of the methoxy (O-CH₃) group. Apigenin contributed better in HRP inhibitory activity. The present study has shown that the studied flavonoids could be promising HRP inhibitors, which can help in developing new molecules to control thyroid diseases.

Electrochemical methods as a tool for determining the antioxidant capacity of food and beverages: A review

The growing interest in functional foods had led to the use of analytical techniques to quantify some properties, among which is the antioxidant capacity (AC). In order to identify and quantify this capacity, some techniques are used, based on synthetic radicals capture; and they are monitored by UV-vis spectrophotometry. Electrochemical techniques are emerging as alternatives, given some of the disadvantages faced by spectrophotometric methods such as the use of expensive reagent not environmentally friendly, undefined reaction time, long sample pretreatment, and low precision and sensitivity. This review focuses on the four most commonly used electrochemical techniques (cyclic voltammetry, differential pulse voltammetry, square wave voltammetry and chronoamperometry). Some of the applications to determine AC in foods and beverages are presented, as well as the correlation between both spectrophotometric and electrochemical techniques that have been reported.