Polyphenol Antioxidant Capacity Research Articles

The mechanism study of enhanced antioxidant capacity: Intermolecular hydrogen bonds between epigallocatechin gallate and theanine in tea

The interactions between various substances in foods have significant implications for their nutritional values. The antioxidant capacity of polyphenols in tea can also be modulated by interactions with other substances. In this study, the intermolecular hydrogen bonds between epigallocatechin gallate (EGCG) and theanine, as well as the antioxidant capacity, were both analyzed and demonstrated. The results showed that the antiradical activity against DPPH• increased by approximate 2.4 %, and the relative cellular activity of PC12 cells in hydrogen peroxide increased by approximate 3.4 %, when appropriate theanine was added to EGCG. This phenomenon could be interpreted by the intermolecular hydrogen bonds between EGCG and theanine, which activated the phenol hydroxyl group of EGCG, inducing the departure of proton and electron. Therefore, the antioxidant capacity was enhanced. The proposed mechanism was verified by electrochemical methods and density functional theoretical calculations. Electrochemical methods confirmed the interactions between EGCG and theanine, and exhibited the shift of the redox peaks before and after the formation of hydrogen bonds. The HOMO-LUMO energy gap of EGCG obtained by density functional theoretical calculation was reduced after hydrogen bonding with theanine.

Chia Oil Microencapsulation Using Tannic Acid and Soy Protein Isolate as Wall Materials.

The use of proteins to produce oil-containing microcapsules has been previously analyzed; however, their chemical modification, in order to improve their performance as wall materials, is a strategy that has not been widely developed yet. This study aimed to analyze the chemical modification of the proteins through cross-linking reactions with tannic acid and to evaluate their performance as wall materials to the microencapsulation of oils rich in polyunsaturated fatty acids. The cross-linking reaction of isolated soy protein and tannic acid was carried out at pH 10-11 and 60 °C. Subsequently, emulsions were made with a high-speed homogenizer and microcapsules were obtained by spray drying. Microcapsules were characterized by particle size, morphology (SEM), total pore area and % porosity (mercury intrusion methodology), superficial properties (contact angle), and size distribution of oil droplets (by laser diffraction). Additionally, encapsulation efficiency was determined as a function of total and surface oil. Oil chemical stability and quality were studied by Rancimat, hydroperoxide values, and fatty acid profiles. In addition, a storage test was performed for 180 days, and released oil and polyphenols were determined by in vitro gastric digestion. Moreover, the fatty acid composition of the oil and the total polyphenol content and antioxidant capacity of polyphenols were analyzed. The results showed that spray-dried microcapsules had an encapsulation efficiency between 54 and 78%. The oxidative stability exhibited a positive correlation between the amount of polyphenols used and the induction time, with a maximum of 27 h. The storage assay showed that the peroxide value was lower for those cross-linked microcapsules concerning control after 180 days. After the storage time, the omega-3 content was reduced by 49% for soy protein samples, while cross-linked microcapsules maintained the initial concentration. The in-vitro digestion assay showed a decrease in the amount of oil released from the cross-linked microcapsules and an increase in the amount of polyphenols and a higher antioxidant capacity for all samples (for example, 238.10 mgGAE/g and 554.22 mg TE/g for undigested microcapsules with TA 40% versus 322.09 mgGAE/g and 663.61 mg TE/g for digested samples). The microcapsules showed a high degree of protection of the encapsulated oil, providing a high content of polyunsaturated fatty acids (PUFAS) and polyphenols even in prolonged storage times.

Microencapsulation of organic coffee husk polyphenols: Effects on release, bioaccessibility, and antioxidant capacity of phenolics in a simulated gastrointestinal tract

Whey protein concentrate (WPC) and maltodextrin were used to microencapsulate polyphenols extract from organic coffee husks by spray drying. The microparticles were characterized and evaluated for their influence on the release, bioaccessibility, and antioxidant capacity of polyphenols in the simulated gastrointestinal tract. WPC as a single encapsulating agent promoted better yield (54.8%) of microparticles. The microparticles showed solubility above 92%, and lower hygroscopicity when encapsulated with maltodextrin alone (7.4%). Smaller diameter (6.78 µm), better encapsulation efficiency (89.1%) and retention of compounds (74.4%) were observed in microparticles with WPC in the composition. Polyphenols were completely released from the microparticles during simulated gastric digestion. The microparticles influenced the bioaccessibility of over 70% of the polyphenols in the intestinal phase. The microparticles showed rapid gastrointestinal release effect but favored the increase of bioaccessibility and preservation of the antioxidant capacity of polyphenols, especially those from the microparticles with WPC compared to the free extract.

Insights on the Role of Polyphenols in Combating Cancer Drug Resistance.

Chemotherapy resistance is still a serious problem in the treatment of most cancers. Many cellular and molecular mechanisms contribute to both inherent and acquired drug resistance. They include the use of unaffected growth-signaling pathways, changes in the tumor microenvironment, and the active transport of medicines out of the cell. The antioxidant capacity of polyphenols and their potential to inhibit the activation of procarcinogens, cancer cell proliferation, metastasis, and angiogenesis, as well as to promote the inhibition or downregulation of active drug efflux transporters, have been linked to a reduced risk of cancer in epidemiological studies. Polyphenols also have the ability to alter immunological responses and inflammatory cascades, as well as trigger apoptosis in cancer cells. The discovery of the relationship between abnormal growth signaling and metabolic dysfunction in cancer cells highlights the importance of further investigating the effects of dietary polyphenols, including their ability to boost the efficacy of chemotherapy and avoid multidrug resistance (MDR). Here, it is summarized what is known regarding the effectiveness of natural polyphenolic compounds in counteracting the resistance that might develop to cancer drugs as a result of a variety of different mechanisms.

Natural Polyphenols for the Preservation of Meat and Dairy Products.

Food spoilage makes foods undesirable and unacceptable for human use. The preservation of food is essential for human survival, and different techniques were initially used to limit the growth of spoiling microbes, e.g., drying, heating, salting, or fermentation. Water activity, temperature, redox potential, preservatives, and competitive microorganisms are the most important approaches used in the preservation of food products. Preservative agents are generally classified into antimicrobial, antioxidant, and anti-browning agents. On the other hand, artificial preservatives (sorbate, sulfite, or nitrite) may cause serious health hazards such as hypersensitivity, asthma, neurological damage, hyperactivity, and cancer. Thus, consumers prefer natural food preservatives to synthetic ones, as they are considered safer. Polyphenols have potential uses as biopreservatives in the food industry, because their antimicrobial and antioxidant activities can increase the storage life of food products. The antioxidant capacity of polyphenols is mainly due to the inhibition of free radical formation. Moreover, the antimicrobial activity of plants and herbs is mainly attributed to the presence of phenolic compounds. Thus, incorporation of botanical extracts rich in polyphenols in perishable foods can be considered since no pure polyphenolic compounds are authorized as food preservatives. However, individual polyphenols can be screened in this regard. In conclusion, this review highlights the use of phenolic compounds or botanical extracts rich in polyphenols as preservative agents with special reference to meat and dairy products.

Effect of In Vitro Gastrointestinal Digestion on Amino Acids, Polyphenols and Antioxidant Capacity of Tamarillo Yoghurts.

Laird’s Large tamarillo powder is high in protein (10%) essential amino acids (EAAs), gamma-aminobutyric acid (GABA) and polyphenols (0.6% phenolics plus anthocyanins) and fibre 25%. This study aimed to investigate, using a standardized static in vitro digestion model, the stability of amino acids and antioxidant capacity of polyphenols in yoghurt fortified with 5, 10 and 15% tamarillo powder either before (PRE) or after (POS) fermentation. Compared to plain yoghurt, the fruit polyphenols (rutinosides and glycosides) were retained and substantial increases in FEAAs (free essential amino acids), total phenolic content (TPC) and antioxidant activity were observed particularly at the end of intestinal phase of digestion. Together with SDS-PAGE results, peptides and proteins in tamarillo yoghurts were more easily digested and therefore may be better absorbed in the small intestine compared to the control. TPC and antioxidant activity of fortified yoghurts increased significantly after in vitro digestion. Relatively high bioaccessibilty of chlorogenic acid and kaempferol-3-rutinoside in digested PRE samples was observed. The results suggest that the yoghurt matrix might protect some compounds from degradation, increasing bioaccessibility and in the small intestine allow increased absorption and utilization possible. Fortification would deliver intact polyphenols and fibre to the large intestine and improve gut health. Further research of acceptability, shelf life, and then trials for health effects should be implemented.

Beta vulgaris rubra L. (Beetroot) Peel Methanol Extract Reduces Oxidative Stress and Stimulates Cell Proliferation via Increasing VEGF Expression in H2O2 Induced Oxidative Stressed Human Umbilical Vein Endothelial Cells.

The antioxidant capacity of polyphenols and flavonoids present in dietary agents aids in arresting the development of reactive oxygen species (ROS) and protecting endothelial smooth muscle cells from oxidative stress/induced necrosis. Beetroot (Beta vulgaris var. rubra L.; BVr) is a commonly consumed vegetable representing a rich source of antioxidants. Beetroot peel’s bioactive compounds and their role in human umbilical vein endothelial cells (HUVECs) are still under-researched. In the present study, beetroot peel methanol extract (BPME) was prepared, and its effect on the bio-efficacy, nuclear integrity, mitochondrial membrane potential and vascular cell growth, and immunoregulation-related gene expression levels in HUVECs with induced oxidative stress were analysed. Gas chromatography–mass spectroscopy (GC-MS) results confirmed that BPME contains 5-hydroxymethylfurfural (32.6%), methyl pyruvate (15.13%), furfural (9.98%), and 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-Pyran-4-one (12.4%). BPME extract effectively enhanced cell proliferation and was confirmed by MTT assay; the nuclear integrity was confirmed by propidium iodide (PI) staining assay; the mitochondrial membrane potential (Δψm) was confirmed by JC-1 staining assay. Annexin V assay confirmed that BPME-treated HUVECs showed 99% viable cells, but only 39.8% viability was shown in HUVECs treated with H2O2 alone. In addition, BPME treatment of HUVECs for 48 h reduced mRNA expression of lipid peroxide (LPO) and increased NOS-3, Nrf-2, GSK-3β, GPX, endothelial nitric oxide synthase (eNOS) and vascular cell growth factor (VEGF) mRNA expression levels. We found that BPME treatment decreased proinflammatory (nuclear factor-κβ (F-κβ), tissue necrosis factor-α (TNF-α), toll-like receptor-4 (TLR-4), interleukin-1β (IL-1β)) and vascular inflammation (intracellular adhesion molecule (ICAM), vascular cell adhesion molecule (VCAM), EDN1, IL-1β)-related mRNA expressions. In conclusion, beetroot peel treatment effectively increased vascular smooth cell growth factors and microtubule development, whereas it decreased vascular inflammatory regulators. BPME may be beneficial for vascular smooth cell regeneration, tissue repair and anti-ageing potential.

Noncovalent Interactions of Sea Buckthorn Polyphenols with Casein and Whey Proteins: Effect on the Stability, Antioxidant Potential, and Bioaccessibility of Polyphenols

In this work, effect of casein and whey protein interaction on the stability, antioxidant potential, and bioaccessibility of sea buckthorn polyphenols was investigated. The results revealed that casein–polyphenol and whey protein–polyphenol interaction both decreased the in vitro antioxidant capacity of polyphenols. On the other hand, the protein–polyphenol complexes increased the stability of sea buckthorn polyphenols during simulated in vitro digestion. Moreover, both the casein–polyphenol and whey protein–polyphenol complexes exhibited an increased bioaccessibility of polyphenols (60.97–64.97%) in comparison to that of free polyphenolic extract (40.01%). The main bonding force between sea buckthorn polyphenols and the proteins was found to be a hydrophobic interaction, as revealed by ATR-FTIR, UV–vis, and fluorescence spectroscopy. The particle size of casein–polyphenol and whey protein–polyphenol complexes was in the nanosize region (650–983 nm). The low span factors of polyphenol–protein complexes revealed the narrow range of particle size distribution and thus more homogeneity in the particle size. This finding highlights that the interaction between casein and whey proteins with sea buckthorn polyphenols could protect these bioactive compounds against the influence of simulated digestion.

Improved water solubility of quercetin by preparing complexation with cyclodextrins in binary solvent

The antioxidant capacity of polyphenols have been widely used in food and pharmaceutical industries. Quercetin (Quer) is a polyphenolic flavonoid that shows several biological effects such as antioxidant, antitumor, antibacterial and antiproliferative effects both in-vitro and in-vivo. However, the solubility of quercetin in water is poor. Thus, it is essential to improve solubility of quercetin in pharmaceuticals by making its complexation with other compounds. In this study, the synthesis of the 2-hydroxypropyl-β-cyclodextrin complex with quercetin (Quer-HPβCD) in the form of nanoparticles in water-ethanol solvents has been carried out. The results showed that the obtained yield of (Quer-HPβCD) complexation in binary solvent was greater than that in pure water. The highest Y value was 80% in a binary solvent with 20% v/v of ethanol. The composition, morphology, structural and thermodynamic properties of the nanoparticles Quer-HPβCD have been determined. This study demonstrated that using mixed water- ethanol solvent and lyophilization technique was able to produce quercetin nanoparticles with significantly smaller particle size. The nanoparticles have a spherical shape with an average size of about 40-60 nm. The results of the phase solubility diagram showed that in water the solubility of quercetin increased and linearly depended on the concentration of host’s molecule while Quer and HP-βCD obtained a 1:1 stoichiometric complex. The stability constant of (Quer-HPβCD) complex was found to be logK = 2.56. The Gibbs energy change of the complexation reaction was found to be -14.60 kJ/mol.

The antioxidant capacity and antioxidant system of Jerusalem artichoke (Helianthus tuberosus L.) tubers in relation to inulin during storage at different low temperatures

Jerusalem artichoke (Helianthus tuberosus L.) tubers are rich in inulin and have a much higher resistance to abiotic stress. Previous literatures have focused on changes of inulin in the tubers during postharvest storage, but little is known about the relationships between the antioxidant capacity, antioxidant system and inulin in Jerusalem artichoke tubers during storage. In this work, the inulin profiles and their in vitro radical scavenging abilities, phenolic content and its antioxidant capacity and the antioxidant systems-related enzymes activity in the tubers stored at 4, 0, −5, −12 and −18℃ were investigated to explore the correlations between the antioxidant capacity, antioxidant system and inulin in the tubers during storage. Compared with storage at relatively high temperature (4℃), the tubers stored at relatively low temperatures (−18 − 0℃) could effectively enhance the degree of polymerisation (DP), content and antioxidant capacity of inulin, the content and antioxidant capacity of polyphenols and the activity of catalases (CAT). The antioxidant capacity of the tubers stored at below 0℃ had no significant differences. Principle component analysis (PCA) was employed to examine the correlations between the antioxidant capacity, antioxidant system and inulin in the tubers during storage. These observations demonstrated the beneficial effects of the content and DP of inulin on antioxidant capacity and antioxidant system of Jerusalem artichoke tubers during storage and indicated that Jerusalem artichoke tubers stored at −5 to 0℃ should be considered as a suitable storage temperatures for different uses.

Artificial Intelligence (AI) to the Rescue: Deploying Machine Learning to Bridge the Biorelevance Gap in Antioxidant Assays.

Oxidative stress induced by excessive levels of reactive oxygen species (ROS) underlies several diseases. Therapeutic strategies to combat oxidative damage are, therefore, a subject of intense scientific investigation to prevent and treat such diseases, with the use of phytochemical antioxidants, especially polyphenols, being a major part. Polyphenols, however, exhibit structural diversity that determines different mechanisms of antioxidant action, such as hydrogen atom transfer (HAT) and single-electron transfer (SET). They also suffer from inadequate in vivo bioavailability, with their antioxidant bioactivity governed by permeability, gut-wall and first-pass metabolism, and HAT-based ROS trapping. Unfortunately, no current antioxidant assay captures these multiple dimensions to be sufficiently “biorelevant,” because the assays tend to be unidimensional, whereas biorelevance requires integration of several inputs. Finding a method to reliably evaluate the antioxidant capacity of these phytochemicals, therefore, remains an unmet need. To address this deficiency, we propose using artificial intelligence (AI)-based machine learning (ML) to relate a polyphenol’s antioxidant action as the output variable to molecular descriptors (factors governing in vivo antioxidant activity) as input variables, in the context of a biomarker selectively produced by lipid peroxidation (a consequence of oxidative stress), for example F2-isoprostanes. Support vector machines, artificial neural networks, and Bayesian probabilistic learning are some key algorithms that could be deployed. Such a model will represent a robust predictive tool in assessing biorelevant antioxidant capacity of polyphenols, and thus facilitate the identification or design of antioxidant molecules. The approach will also help to fulfill the principles of the 3Rs (replacement, reduction, and refinement) in using animals in biomedical research.

Colorimetric determination of polyphenols via agold nanoseeds-decorated polydopamine film.

A polystyrene ELISA plate (EP) modified with a thin film based on gold nanoseeds (AuSDs) assembled onto polydopamine (PDA) is proposed. The nanodecorated film (PDA@AuSD) allows to evaluate the polyphenols antioxidant capacity (AOC) through a colorimetric approach based on a seed-mediated growth strategy. Polyphenols, in the presence of the nanodecorated (PDA@AuSD) surfaces are able to drive an increase in size of the AuSDs according to their AOC; this produces an increase of the localized surface plasmon resonance (LSPR; maximum at λ ~ 550nm) that is taken as analytical signal. The PDA@AuSD EP manufacturing shows good intraplates repeatability (RSD ≤ 6.6%, n = 96 wells) and interplates reproducibility (RSD ≤ 7.4%, n = 748 wells), resulting stable for 1year. The AuSDs growth kinetic has been studied using 11 polyphenols belonging to different chemical classes and 4 different food samples. The PDA@AuSD film is able to return quantitative information on the AOC of food polyphenols. Good repeatability (RSD ≤ 5.7%, n = 12 EP wells) and reproducibility (RSD ≤ 8.1%, n = 12 EP wells) was achieved, with acceptable linear correlation coefficients (R2 ≥ 0.990) and useful limits of detection (LODs≤ 2.510-5molL-1). The samples analyzed with the PDA@AuSD device have been successfully ordered according to their AOC in agreement with conventional optical methods. The PDA@AuSD plate allows multiple measurements (96 wells per EP) with a one-step strategy, overcoming the limitations related to the use of colloidal nanoparticles; in addition, since absorbance is measured after washing, it is not affected by samplecolor or turbidity. Graphical abstract Schematic representation of ELISA plate (EP) modified with polydopamine (PDA) film decorated with gold nanoseeds (AuSD). The colorimetric assay, to evaluate the antioxidant capacity, is based on the AuSD growth mediated by polyphenols, resulting in absorbance increase at 550nm (ΔAbs550), which is employedas analytical signal.

Silver and gold nanoparticles based colorimetric assays for the determination of sugars and polyphenols in apples

In this work, the exploitability of rapid and easy to use methods for the evaluation of the antioxidant capacity (AOC) and sugars content (SC), through metal nanoparticles (MNPs) formation, has been proved and applied to apples. In particular, an AgNPs-based sugar quantification assays and an AuNPs-based polyphenols antioxidant capacity assay have been used as tools for the evaluation of apple extracts composition. Both assays are based on the ability of the analytes (sugars and polyphenols) to reduce the source of metal (Au3+ and Ag+), stabilizing, at the same time, the resulting MNPs colloidal suspensions. The AuNPs and AgNPs formation depends on the analyte structure and concentration, resulting in red (AuNPs) and yellow (AgNPs) colored suspensions. Both assays require an initial mixing step, followed by MNPs formation under mild conditions (10 min, room temperature or 45 °C), and the colorimetric response is easily acquired at a fixed wavelength (AgNPs: 430 nm and AuNPs: 540 nm). The analytical performance of both assays has been proven, obtaining good reproducibility (RSD ≤ 6%,), sensitivity (LODs ≤8.7 μmol L−1) and recoveries (91% −113.7%). The produced MNPs (AgNPs and AuNPs) have been characterized using UV–Vis spectroscopy and TEM, and the cross-reactivity between assays, as well as the possible endogenous interferents, studied. The assays have been tested on 42 apple samples, and the data obtained compared with those obtained by conventional methods (i.e. FC, ABTS, and ion chromatography). The proposed AgNPs-sugars assay gives results comparable (R = 0.915) to those determined by ion chromatography in terms of total sugars, and the AuNPs-polyphenols assay results able to assess the polyphenols antioxidant capacity, being correlated with those obtained by the ABTS method (R = 0.922). This MNPs-based approach demonstrated to be an excellent tool for rapid and facile analysis of sugars and polyphenols in apple samples.

Serum Albumin Modulates the Bioactivity of Rosmarinic Acid.

Rosmarinic acid (RA) is a phenolic compound with biological activity. The objective of the present study was to investigate whether this compound kept its biological activity in the presence of proteins. For this purpose, bovine serum albumin (BSA) was used as a model protein, and the capacity of the RA to inhibit acetylcholinesterase (AChE) and affect antioxidant activity was evaluated in the absence and presence of BSA. A mixture of phenolic compounds containing RA, obtained from a medicinal plant was added to this study. The AChE inhibitory activity of RA was reduced by ∼57% in the presence of BSA, while the antioxidant activity increased. These results lead to the investigation of the effect of RA on the BSA structure using Fourier transform infrared spectroscopy (FTIR). At 37°C and higher temperatures, RA caused a decrease in the temperature modifications on the protein structure. Furthermore, FTIR and native-gel analysis revealed that protein aggregation/precipitation, induced by temperature, was reduced in the presence of RA. The novelty of the present work resides in the study of the enzyme inhibitory activity and antioxidant capacity of polyphenols, such as RA, in the presence of a protein. The findings highlight the need to consider the presence of proteins when assessing biological activities of polyphenols in vitro and that enzyme inhibitory activity may be decreased, while the antioxidant capacity remains or even increases.

Antioxidant and anti-inflammatory effects of polyphenols extracted from Ilex latifolia Thunb.

To promote the rational and effective application of Ilex latifolia Thunb., a Chinese bitter tea widely consumed as a health beverage, polyphenols were extracted from its leaves and their cellular antioxidant activity (CAA) and anti-inflammatory effect against mouse macrophage RAW 264.7 cells were analyzed. Results showed that the antioxidant capacity of polyphenols was high, and their CAA values in PBS wash and no PBS wash protocols were 6871.42 ± 85.56 and 25161.61 ± 583.55 μmol QE (quercetin equivalents)/100 g phenolic extracts, respectively. In addition, polyphenols from I. latifolia displayed strong inhibition on LPS-induced NO-production in RAW 264.7 cells. Polyphenol treatment inhibited the release of pro-inflammatory cytokines (TNF-α, IL-1β and IL-6) induced by LPS in a dose-dependent manner by ELISA and mRNA expression analysis. Western blot results showed that the anti-inflammatory activity of polyphenols from I. latifolia might be exerted through inhibiting the activation of MAPKs (ERK and JNK) and NF-κB to decrease NO, COX-2 and pro-inflammatory cytokines production. Thus, the polyphenol enriched extracts from I. latifolia are a good source of natural antioxidants with a beneficial effect against inflammation, and they may be applied as a food supplement and/or functional ingredient.

Effect of Ultrasound on Polyphenols Extraction, Microstructure and Antioxidant Activity of Plum (Prunus salicina Lindl.)

The effects of ultrasonic treatment on the extraction and antioxidant capacity of polyphenols from plum fruit (<em>Prunus salicina</em> Lindl.) were evaluated. The microstructure of the extracted residue was observed by scanning electron microscope. The extraction efficiency of polyphenols increased gradually with the increase of ultrasonic power from 0 W to 420W and the extraction efficiency of total phenol at 420W of ultrasonic power was increased by 22.25% compared with that of without ultrasonic treatment. After ultrasonic treatment, the microstructure of the plum material had significant changed and there were more severe wrinkles of the cell wall and hollow structure in the microstructure of plum. Furthermore, ultrasound did not affect the DPPH scavenging capacity and hydroxyl radical scavenging capacity of plum fruit polyphenols. Therefore, ultrasound was suitable for the extraction of polyphenols from plum fruit.

The substituent effect on the antioxidant capacity of catechols and resorcinols

The antioxidant capacity of polyphenols is widely recognized; especially, the catechol moiety is considered a key piece in the structure of natural compounds with this characteristic. The resorcinol is also a dihydroxybenzene that is present in natural antioxidants; however, fewer experimental and theoretical studies have been addressed to this moiety. This work reports a comparative study of the substituent effect on properties related to the antioxidant capacity, as energy ionization (I), and O–H bond dissociation enthalpy (BDE), to analyze the electron transfer and hydrogen atom transfer (HAT) mechanisms, in derivatives of phenols, catechols and resorcinols. In the set of substituents tested \(({-}\hbox {CH}_3, {-}\hbox {CH}_2\hbox {CH}_3, {-}(\hbox {CH}_2)_2{-}\hbox {CH}_3, {-}\hbox {CH}{=}\hbox {CH}_2, {-}\hbox {CH}{=}\hbox {CHCOOH}, {-}\hbox {COOH}\) and \({-}\hbox {CO}(\hbox {CH}_2)_4{-}\hbox {CH}_3)\) electron-withdrawing and electron-donating groups, including alkyl chains, are considered. We found that electron-donating substituents reduce I and O–H BDE of resorcinols and catechols derivatives. In addition, the length of the alkyl chains is not relevant on resorcinols neither on catechols. With regard to the HAT process, a double bond in a substituent favors it, while the –COOH group shows a contrary effect. The combination of a double bond with a –COOH group, in the substituent, increases the BDE and reduces the electron donor capacity, and this result suggests that this combination induces a reduction in the antioxidant capacity in one polyphenol compound. In several reports, an intramolecular hydrogen bond has been proposed within to the most stable structure of catechol. However, by using arguments from the atoms in molecules approach and the electron localization function, we show that such an interaction is not relevant to stabilize this conformation and consequently and this is the reason that explains the unimportance of this interaction in the properties studied here and in previous studies.

Evaluation of polyphenols antioxidant capacity in the presence of complexants by FRAP assay

The influence of foreign substances on the results of spectrophotometric determination of polyphenol antioxidants by FRAP assay is investigated. The assay is based on the reduction of Fe 3+ ions by polyphenols in the presence of 2,2'-dipyridyl. Quercetin, rutin and gallic acid were used as model compounds. The absorbance at 520 nm is measured 60 minutes after mixing the reagents. The sensitivity of polyphenols determination decreases in the presence of fluorides, phosphates, citrates, tartrates and other substances not forming their own analytical signals but binding Fe 3+ ions in the stable complex compounds. This effect can be predicted by the calculation of complexation degree and taking into account the ligand concentration and pH value. The increase of the initial concentration of Fe(III) up to 10 -3 M decreases the effect of fluorides, but leads to side processes involving phosphates or salicylates. Binding of iron(III) leads to the systematic error when the total antioxidant capacity ( TAC ) is determined with a calibration curve (underestimation). The analysis of model mixtures with the additives method significantly reduces the impact of complexants and the abovementioned error. Foodstuffs which contain 10-4 M complexants or more have to be analyzed by the method of standard additives, which leads to higher TAC values than using of traditional TAC determination with calibration curve; the difference is about 20-50%. For the majority of examined foodstuffs the difference in the mean results for these analytical methods is statistically valid. The accuracy of the proposed method for some products (wine, beer, tea etc.) was confirmed with the added – found standard technique . Keywords: foodstuff, food analysis, polyphenols, complexants, FRAP assay, antioxidant activity DOI: http://dx.doi.org/10.15826/analitika.2016.20.3.004 N.S. Brilenok, V.I. Vershinin, M.V. Bakhareva Dostoevsky Omsk State University (OmGU) 55A Mira pr., Omsk, 644077,Russian Federation

Evaluating the antioxidant capacity of polyphenols with an off–on fluorescence probe and the mechanism study

A spin-labeled fluorescence probe (RNO˙) was employed to evaluate the antioxidant capacity of polyphenols. The hydrogen-transfer mechanism was proposed by kinetic studies using fluorescence spectroscopy, and the product was confirmed to be RNOH by HPLC-MS with little side products. The HPLC-UV/vis method devoted to the simultaneous monitoring of the RNO˙ and RNOH at 556 nm was developed, which can distinguish the antioxidant capacity of polyphenols with similar structure. The method has the potential to be used to screen antioxidants when modifying or optimizing natural antioxidants.

Phenol‐Based Antioxidants and the In Vitro Methods Used for Their Assessment

Abstract: In recent years, much interest has been observed in the field of phenol‐based antioxidants. As a result of this, many analytical methods have been developed for the purpose of the quantification of phenolic and polyphenolic antioxidant capacities in biological materials. Many of these methods have been altered for application toward the in vitro assessment of antioxidant activities in animal and human model systems as well as in vivo. Due to the varied applicability and usage, methods for the assessment of phenol antioxidant capacities have become so widespread that they are often misused. It is the intent of this work to review the chemistry behind the antioxidant activity of phenolics as well as summarize the many methods applicable for the measurement of in vitro phenolic antioxidant capacity.