Electrochemical determination of antioxidant capacity of fruit tea infusions

Phytochemical Composition and Antioxidant Activity of Various Extracts of Fibre Hemp (Cannabis sativa L.) Cultivated in Lithuania

The phytochemistry of fibre hemp (Cannabis sativa L., cv. Futura 75 and Felina 32) cultivated in Lithuania was investigated. The soil characteristics (conductivity, pH and major elements) of the cultivation field were determined. The chemical composition of hemp extracts and essential oils (EOs) from different plant parts was determined by the HPLC/DAD/TOF and GC/MS techniques. Among the major constituents, β-caryophyllene (≤46.64%) and its oxide (≤14.53%), α-pinene (≤20.25%) or α-humulene (≤11.48) were determined in EOs. Cannabidiol (CBD) was a predominant compound (≤64.56%) among the volatile constituents of the methanolic extracts of hemp leaves and inflorescences. Appreciable quantities of 2-monolinolein (11.31%), methyl eicosatetraenoate (9.70%) and γ-sitosterol (8.99%) were detected in hemp seed extracts. The octadecenyl ester of hexadecenoic acid (≤31.27%), friedelan-3-one (≤21.49%), dihydrobenzofuran (≤17.07%) and γ-sitosterol (14.03%) were major constituents of the methanolic extracts of hemp roots, collected during various growth stages. The CBD quantity was the highest in hemp flower extracts in pentane (32.73%). The amounts of cannabidiolic acid (CBDA) were up to 24.21% in hemp leaf extracts. The total content of tetrahydrocannabinol (THC) isomers was the highest in hemp flower pentane extracts (≤22.43%). The total phenolic content (TPC) varied from 187.9 to 924.7 (average means, mg/L of gallic acid equivalent (GAE)) in aqueous unshelled hemp seed and flower extracts, respectively. The TPC was determined to be up to 321.0 (mg/L GAE) in root extracts. The antioxidant activity (AA) of hemp extracts and Eos was tested by the spectrophotometric DPPH^● scavenging activity method. The highest AA was recorded for hemp leaf EOs (from 15.034 to 35.036 mmol/L, TROLOX equivalent). In the case of roots, the highest AA (1.556 mmol/L, TROLOX) was found in the extracts of roots collected at the seed maturation stage. The electrochemical (cyclic and square wave voltammetry) assays correlated with the TPC. The hydrogen-peroxide-scavenging activity of extracts was independent of the TPC.

Anti- and Pro-Oxidant Activity of Polyphenols Extracts of Syrah and Chardonnay Grapevine Pomaces on Melanoma Cancer Cells

The phenolic composition of Syrah and Chardonnay grape pomaces was studied to assess their antioxidant and prooxidant properties. Polyphenols were extracted by a "green" hydroalcoholic solvent (ethanol/water 1:1 v/v), and a detailed chemical and electrochemical characterization of the phenolic compounds was performed. The antioxidant and prooxidant capacity of the pomace was first studied by cyclic voltammetry (CV) and other reference analytical assays, then with biological tests on B16F10 metastatic melanoma cancer cells. Electrochemical data showed that, when a +0.5 V potential was applied, a low to moderate antioxidant capacity was observed. MTT test showed an increasing viability of melanoma cells, after treatments at low concentration (up to 100 μg/mL) and for a short time (6 h), but when cells were treated with higher doses of extract (≥250 μg/mL for 12/24 h), their viability decreased from 25 to 50% vs. control, depending on treatment time, dose, and extract origin. A stronger prooxidant activity resulted when 250 μg/mL of extract was combined with non-toxic doses of H₂O₂; this activity was correlated with the presence of copper in the extracts. This study shows the potential of winemaking by-products and suggests the opportunity to exploit them for the production of cosmeceuticals, or for combined therapies with approved anticancer drugs.

Detection of Synthetic Antioxidants: What Factors Affect the Efficiency in the Chromatographic Analysis and in the Electrochemical Analysis?

Antioxidants are food additives largely employed to inhibit oxidative reactions in foodstuffs rich in oils and fat lipids, extending the shelf life of foodstuffs and inhibiting alterations in color, flavor, smell, and loss of nutritional value. However, various research has demonstrated that the inadequate use of synthetic antioxidants results in environmental and health problems due to the fact that some of these compounds present toxicity, and their presence in the human body, in high concentrations, is related to the development of some cancer types and other diseases. Therefore, the development of analytical methods for identifying and quantifying synthetic antioxidants in foodstuffs is fundamental to quality control and in ensuring consumer food safety. This review describes the recent chromatographic and electrochemical techniques used in the detection of synthetic phenolic antioxidants in foodstuffs, highlighting the main characteristics, advantages and disadvantages of these methods, and specific typical features, which include extraction methods for sample preparation and materials used in the working electrode construction, considering chromatographic and voltammetric methods, since these specific features influence the efficiency in the analysis.

Physicochemical Analysis of Cold Brew and Hot Brew Peaberry Coffee

Peaberry coffee is the result of a natural mutation of coffee beans, and they make up only about 5–7% of coffee crops. A typical coffee cherry contains two seeds that are developed against each other, resulting in the distinctive half-rounded shape of coffee beans. However, failing to fertilize both ovules of one of the seeds or failure in endosperm development can cause only one of the seeds to develop, resulting in smaller, denser beans with a more domed shape. Peaberry coffees are said to be sweeter, lighter, and more flavorful since the peaberry beans receive all nutrients from the coffee cherry. Due to its exclusive nature, the chemical characteristic of peaberry coffee is not well understood. This study explores the acidities and antioxidant activity of peaberry coffee sourced from multiple regions. Total antioxidant capacity, total caffeoylquinic acid (CQA), total caffeine concentration, and pH levels were evaluated for peaberry coffee extracts prepared by cold and hot brewing methods. Little correlation between antioxidant activity and the concentrations of caffeine and CQA in peaberry beans was shown. Six methods were performed for the characterization of total antioxidant capacity including cyclic voltammetry, ABTS assay, and FRAP assay. Peaberry bean extract demonstrated higher average total caffeine concentrations compared to traditional coffee bean extracts.

Antioxidant Capacity of Herzegovinian Wildflowers Evaluated by UV–VIS and Cyclic Voltammetry Analysis

Considering the vast cultural and traditional heritage of the use of aromatic herbs and wildflowers for the treatment of light medical conditions in the Balkans, a comparison of the antioxidant capacity of wildflowers extracts from Herzegovina was studied using both cyclic voltammetry and spectrophotometry. The cyclic voltammograms taken in the potential range between 0 V and 800 mV and scan rate of 100 mV s−1 were used for the quantification of the electrochemical properties of polyphenols present in four aqueous plant extracts. Antioxidant capacity expressed as mmoL of gallic acid equivalents per gram of dried weight of the sample (mmoL GAE g−1 dw) was deduced from the area below the major anodic peaks (Q400 pH 6.0, Q500 pH 4.7, Q600 pH 3.6). The results of electrochemical measurements suggest that the major contributors of antioxidant properties of examined plants are polyphenolic compounds that contain ortho-dihydroxy-phenol or gallate groups. Using Ferric reducing-antioxidant power (FRAP) and 2,2′-azino-bis spectrophotometric methods (3-ethylbenzthiazoline-6-sulphonic acid) radical cation-scavenging activity (ABTS) additionally determined antioxidant capacity. The FRAP results ranged from 2.9702–9.9418 mmoL Fe/g dw, while the results for ABTS assays expressed as Trolox equivalents (TE) ranged from 14.1842–42.6217 mmoL TE/g dw. The Folin–Ciocalteu procedure was applied to determine the total phenolics content (TP). The TP content expressed as Gallic acid equivalents (GAE) ranged from 6.0343–9.472 mmoL GAE/g dw. The measurements of total flavonoid (TF) and total condensed tannin (TT) contents were also performed to obtain a broader polyphenolic profile of tested plant materials. Origanum vulgare L. scored the highest on each test, with the exception of TT content, followed by the Mentha × piperita L., Artemisia annua L., and Artemisia absinthium L., respectively. The highest TT content, expressed as mg of (−)catechin equivalents per gram of dried weight of sample (mg CE/g dw), was achieved with A. absinthium extract (119.230 mg CE/g dw) followed by O. vulgare (90.384 mg CE/g dw), A. annua (86.538 mg CE/g dw) and M. piperita (69.231 mg CE/g dw), respectively. In addition, a very good correlation between electrochemical and spectroscopic methods was achieved.

Intermolecular hydrogen bonds between catechin and theanine in tea: slow release of the antioxidant capacity by a synergetic effect

The health benefits of drinking tea stem from it being rich in polyphenols and other physiologically-active substances. Thus, exploring the synergistic effect between polyphenols and a variety of physiologically-active substances can contribute to our understanding of how tea benefits health. In this work, we have studied the interactions between catechin and theanine, exploring the synergetic antioxidant mechanism of the two molecules. Electrochemical characterization results showed that the oxidation peak current of catechin decreased gradually with the concentration of theanine, which is due to theanine spontaneously binding to catechin through intermolecular hydrogen bonds and forming molecular clusters via two hydrogen bonds. The binding constant is 4.75 at room temperature. The molecular clusters reduce the diffusion coefficient of catechin in solution, leading to the slow release of its antioxidant capacity (ability to effectively inhibit free radical oxidation reactions). Density functional theory calculations were also performed and verified the binding behavior. In identifying the synergistic effect between catechin and theanine on the antioxidant capacity of tea, this study adds to our understanding of the efficacy of tea polyphenols.

The health benefits of drinking tea stem from it being rich in polyphenols and other physiologically-active substances.

In Vitro Antioxidant and Prooxidant Activities of Red Raspberry (Rubus idaeus L.) Stem Extracts

Leaves and stems of red raspberry (Rubus idaeus) are used in Lithuanian folk medicine. Healing properties of raspberry are related to the content of bioactive compounds, mainly polyphenols. Extracts of raspberry leaves contained higher total phenolic content (TPC) (1290 mg/L, expressed in gallic acid equivalent) compared to that in extracts of stems or peeled bark (up to 420 mg/L and 598 mg/L, respectively). To find out whether the collection time of herbal material was critical for the properties of the extracts, the stems were collected at different times of the year. TPC in the extracts depended more on extraction conditions rather than on the sampling time. Antioxidant activity of raspberry stem and bark extracts tested by spectrophotometric (DPPH● scavenging) and electrochemical (cyclic and differential pulse voltammetry) assays correlated with TPC. DPPH radical scavenging activity values for stem, leaf, and bark extracts were as follows: ≤1.18 ± 0.07, 1.63 ± 0.10, and ≤1.90 ± 0.04 (mmol/L, TROLOX equivalent), respectively. Assessed electrochemically, hydrogen peroxide-scavenging activity of extracts was independent on TPC. The latter activity was related to the presence of some protein in the extract as revealed by gel electrophoresis. Prooxidant activity of raspberry stem extracts was dependent on solution pH and temperature.

Recent Advances in Analytical Methods for Determination of Polyphenols in Tea: A Comprehensive Review

Polyphenols, the most abundant components in tea, determine the quality and health function of tea. The analysis of polyphenols in tea is a topic of increasing interest. However, the complexity of the tea matrix, the wide variety of teas, and the difference in determination purposes puts forward higher requirements for the detection of tea polyphenols. Many efforts have been made to provide a highly sensitive and selective analytical method for the determination and characterization of tea polyphenols. In order to provide new insight for the further development of polyphenols in tea, in the present review we summarize the recent literature for the detection of tea polyphenols from the perspectives of determining total polyphenols and individual polyphenols in tea. There are a variety of methods for the analysis of total tea polyphenols, which range from the traditional titration method, to the widely used spectrophotometry based on the color reaction of Folin–Ciocalteu, and then to the current electrochemical sensor for rapid on-site detection. Additionally, the application of improved liquid chromatography (LC) and high-resolution mass spectrometry (HRMS) were emphasized for the simultaneous determination of multiple polyphenols and the identification of novel polyphenols. Finally, a brief outline of future development trends are discussed.

Camu-camu [Myrciaria dubia (HBK) McVaugh]: A review of properties and proposals of products for integral valorization of raw material

This review aims to evaluate the production and processing chain of camu-camu (Myrciaria dubia), giving suggestions to maximize the valorization of raw materials, demonstrating new product possibilities from processing to distribution and highlighting the suggested contributions. It is clear that despite the camu-camu pulp has important properties, a large part of its raw material, considered waste (around 50%) and formed by important bioactive compounds, can give rise to new products, such as bioactive extracts to be used by pharmaceutical, chemical and food industries, ingredients for bakery products, dairy and several others sectors, which constitutes opportunities, in addition to contributing to the reduction of agro-industrial waste and the preservation of the environment.

Electrochemical Methods for the Analysis of Milk

The milk and dairy industries are some of the most profitable sectors in many countries. This business requires close control of product quality and continuous testing to ensure the safety of the consumers. The potential risk of contaminants or degradation products and undesirable chemicals necessitates the use of fast, reliable detection tools to make immediate production decisions. This review covers studies on the application of electrochemical methods to milk (i.e., voltammetric and amperometric) to quantify different analytes, as reported over the last 10 to 15 years. The review covers a wide range of analytes, including allergens, antioxidants, organic compounds, nitrogen- and aldehyde containing compounds, biochemicals, heavy metals, hydrogen peroxide, nitrite, and endocrine disruptors. The review also examines pretreatment procedures applied to milk samples and the use of novel sensor materials. Final perspectives are provided on the future of cost-effective and easy-to-use electrochemical sensors and their advantages over conventional methods.

Red Wine Oxidation Characterization by Accelerated Ageing Tests and Cyclic Voltammetry

In order to obtain information on the oxidative behavior of red wines, oxygen consumption rates and electrochemical changes (cyclic voltammetry) were measured for nine red wines subject to three different accelerated ageing tests: chemical (with hydrogen peroxide), enzymatic (with laccase from Trametes versicolor), and temperature (at 60 °C). Oxidative behavior depended both on the wine sample and accelerated ageing test type. A good correlation was observed between electrochemical parameters of charges for reference/non-oxidized wines, in accordance with their antioxidant capacity, and the variation of charges after enzymatic and temperature tests, meaning that cyclic voltammetry could be used in order to predict these two oxidation tests and reflect the wine sensitivity towards respective oxidation targets. However, it was not possible to predict wine chemical oxidation test based on hydrogen peroxide from the electrochemical measurements.

Biochemical, antioxidant and sensory evaluation of Davidsonia pruriens and Davidsoina jerseyana fruit infusion

Davidsonia pruriens (DP) and Davidsonia jerseyana (DJ) are a gourmet bushfood with a sweet and sour taste. This study investigated the biochemical content, antioxidant activities, and sensory attributes of DP and DJ fruit infusions in comparison with commercial forest fruits (FF) infusion. Total phenolic and anthocyanin content was higher in FF infusion compared to DP or DJ fruit infusions (P < 0.05). An abundant amount of gallic acid was found in DP and DJ fruit infusions (P < 0.05). Quercetin, kaempferol-3-O-rutinoside, and peonidin-3-sambubioside was detected only in DP and DJ fruit infusions (P < 0.05). However, a high level of oxalic acid, minerals and soluble sugars were observed in FF infusions (P < 0.05). The antioxidant capacities and overall likeness score of DP or DJ infusion were comparable with the commercial FF infusion. Therefore, bioactive compounds, antioxidant activities and sensory properties suggested that DP and DJ fruit infusion have the potential to become a commercial health promoting drink.

Effects of Various Drying Methods on Some Physico-Chemical Properties and the Antioxidant Profile and ACE Inhibition Activity of Oyster Mushrooms (Pleurotus Ostreatus)

In food biotechnology, Pleurotus ostreatus is of great interest as a source of natural antioxidants and angiotensin-converting enzyme (ACE) inhibitors. However, research in this area has not yet been completed. The effect of various drying methods on the structural properties and the rehydration capacity of mushrooms was investigated in this paper. The content of secondary metabolites, the peptide profile, and the antioxidative effect and ACE inhibitory activity of dry mushrooms were investigated in vitro, simulating the process of gastrointestinal digestion. X-ray microtomography has confirmed that structure of lyophilic and sun-dried mushrooms is dominated by open pores, and in mushrooms dried with hot air and microwave, closed pores. Experiments have shown that the conditions of freeze drying and sun drying of Pleurotus ostreatus provide a higher rehydration capacity of dried mushrooms. The maximum activity of radical absorption of the oyster mushroom after microwave drying was observed. The iron restoring capacity of the mushrooms is maximally maintained with microwave drying and hot-air drying. The properties of the antioxidant product with an emphasis on the high activity of inhibiting lipid oxidation of the mushroom maximized after drying in the sun. Mushrooms dried lyophilically and in the sun showed the highest ACE inhibitory activity.

Increasing phenolic and aromatic compounds extraction and maximizing liking of lemon verbena (Aloysia triphylla) infusions through the optimization of steeping temperature and time

Herbal infusions are a new emerging trend among consumers, appearing in the market in many different forms. Due to intense competition, the commercial success of herbal infusions largely depends on flavour. The identification of the best combinations of steeping time and water temperature for the preparation of Aloysia triphylla infusions using a central composite design and response surface methodology was performed. The procedure aimed to maximize its antioxidant activity, phenolic and aromatic compounds, and consumers' liking of the infusions. The antioxidant activity and phenolic content were evaluated using the 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid radical cation) method and the Folin-Ciocalteu procedure. The analysis of aromatic compounds was performed based on the method of terpenic compounds. Sensory evaluation encompassed overall liking using a 9-point hedonic scale. Antioxidant activity and extraction of most phenolic compounds was higher for longer steeping times and higher temperatures, with some presenting a contrasting effect due to degradation at higher temperatures for longer steeping times. Results for terpenic compounds showed similar contrasting patterns. Based on the quadratic response surface, it was possible to predict the maximum overall liking for lemon verbena infusions prepared by brewing for 6 min at 96 ℃. Under such conditions, extraction of bioactive compounds was kept at a high level, close to the maximum attainable, while reducing the extraction of bitter compounds. These results are considered of great importance for the development of premium infusions from organic lemon verbena leaves.

A Nanoparticle-Based Label-Free Sensor for Screening the Relative Antioxidant Capacity of Hydrosoluble Plant Extracts

One of the most important aspects of the detection of antioxidant compounds is developing a fast screening method. The screening of the overall relative antioxidant capacity (RAC) of several Romanian hydrosoluble plant extracts is the focus of this work. This is important because of the presence of increasing levels of reactive oxygen species (such as H₂O₂) generates oxidative stress in the human body. The consequences are a large number of medical conditions that can be helped by a larger consumption of plant extracts as food supplements, which do not necessarily contain the specified antioxidant contents. By exploiting the catalytic properties of gold nanoparticles, a specific and sensitive nanoparticle-based label-free electrochemical sensor was developed, where the working parameters were optimized for RAC screening of hydrosoluble plant extracts. First, electrochemical measurements (cyclic voltammetry and amperometry) were used to characterize different nanoparticle-based sensors, revealing the best performance of gold nanoparticle-based sensors, obtaining a RAC of 98% for lavender extracts. The sensing principle is based on the quenching effect of antioxidants for H₂O₂ amperometric detection, where the decrease in electrical signal suggests an increasing antioxidant capacity. The obtained results were expressed in terms of ascorbic acid and Trolox equivalents in order to be able to correlate our results with classical methods like chemiluminescence and UV-Vis spectrophotometry, where a correlation coefficient of 0.907 was achieved, suggesting a good correlation between electrochemistry and spectrophotometry. Considering these results, the optimized gold nanoparticle-based label-free sensor can be used as a simple, rapid alternative towards classical methods for relative antioxidant capacity detection of hydrosoluble plant extracts.

Evaluation of total polyphenol content of wines by means of voltammetric techniques: Cyclic voltammetry vs differential pulse voltammetry

Taking advantage of the low oxidation potential of polyphenolic compounds, voltammetric techniques, such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV) are used rather indiscriminately. In this work, we report Total Polyphenols results (TPP) obtained by these two techniques from a set of nine samples of red and Tawny Port wine. The CV and DPV voltammograms display significant correlations with the physical-chemical parameters used to characterize red and Tawny Port wines, particularly with polyphenols. Although data obtained from CV and DPV for a single polyphenol are directly proportional, important deviations are found between voltammetric results from wines. Results from CV tend to be larger than those from DPV. This difference, that can reach 50% of the TPP value, was related to the presence of total sulphur dioxide. In view of the present study, the polyphenol quantification in wines should be performed by DPV to minimize the interference of SO₂.

A different approach for the analysis of grapes: Using the skin as sensing element

In this work, an alternative method to monitor the phenolic maturity of grapes was developed. In this approach, the skins of grapes were used to cover the surface of carbon paste electrodes and the voltammetric signals obtained with the skin-modified sensors were used to obtain information about the phenolic content of the skins. These sensors could easily detect differences in the phenolic composition of different Spanish varieties of grapes (Mencía, Prieto Picudo and Juan García). Moreover, sensors were able to monitor changes in the phenolic content throughout the ripening process from véraison until harvest. Using PLS-1 (Partial Least Squares), correlations were established between the voltammetric signals registered with the skin-modified sensors and the phenolic content measured by classical methods (Glories or Total Polyphenol Index). PLS-1 models provided additional information about Brix degree, density or sugar content, which usually used to establish the harvesting date. The quality of the correlations was influenced by the maturation process and the structural and mechanical skin properties. Thus the skin sensors fabricated with Juan García and Prieto Picudo grapes (that showed faster polyphenolic maturation and a higher amount of extractable polyphenols than Mencía), showed good correlations and therefore could be used to monitor the ripening.

Pro- and Antioxidant Activity of Three Selected Flavan Type Flavonoids: Catechin, Eriodictyol and Taxifolin

The flavanol (±)-catechin shows an OH group but no 4-keto group on ring C (C3), and no conjugation between ring A and B. The related flavanone (+)-eriodictyol has a keto group on C4 but no 3-OH group on ring C. (+)-Taxifolin, another flavanone, has an OH on C3 and a keto group on C4 of the C ring. Deoxyribose degradation assay systems, with hydrogen peroxide and ascorbic acid either added or omitted, were performed in variants in which Fe(III) was added in a complex with ethylenediaminetetraacetic acid (EDTA). In combination with differential pulse voltammetry (DVP), the specific redox-chemical contributions of the ring A m-dihydroxyl groups could be explored more specifically in addition to those of the traditionally investigated o-dihydroxyl groups of ring B.

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.

Substituent Inductive Effects on the Electrochemical Oxidation of Flavonoids Studied by Square Wave Voltammetry and Ab Initio Calculations

Flavonoids are natural products commonly found in the human diet that show antioxidant, anti-inflammatory and anti-hepatotoxic activities. These nutraceutical properties may relate to the electrochemical activity of flavonoids. To increase the understanding of structure–electrochemical activity relations and the inductive effects that OH substituents have on the redox potential of flavonoids, we carried out square-wave voltammetry experiments and ab initio calculations of eight flavonoids selected following a systematic variation in the number of hydroxyl substituents and their location on the flavan backbone: three flavonols, three anthocyanidins, one anthocyanin and the flavonoid backbone flavone. We compared the effect that the number of –OH groups in the ring B of flavan has on the oxidation potential of the flavonoids considered, finding linear correlations for both flavonols and anthocyanidins (R2=0.98). We analyzed the effects that position and number of –OH substituents have on electron density distributions via ab initio quantum chemical calculations. We present direct correlations between structural features and oxidation potentials that provide a deeper insight into the redox chemistry of these molecules.

Antioxidant Activity/Capacity Measurement. 1. Classification, Physicochemical Principles, Mechanisms, and Electron Transfer (ET)-Based Assays

Because there is no widely adopted "total antioxidant parameter" as a nutritional index for labeling food and biological fluids, it is desirable to establish and standardize methods that can measure the total antioxidant capacity (TAC) level directly from plant-based food extracts and biological fluids. In this review, we (i) present and classify the widely used analytical approaches (e.g., in vitro and in vivo, enzymatic and nonenzymatic, electron transfer (ET)- and hydrogen atom transfer (HAT)-based, direct and indirect assays) for evaluating antioxidant capacity/activity; (ii) discuss total antioxidant capacity/activity assays in terms of chemical kinetics and thermodynamics, reaction mechanisms, and analytical performance characteristics, together with advantages and drawbacks; and (iii) critically evaluate ET-based methods for analytical, food chemical, biomedical/clinical, and environmental scientific communities so that they can effectively use these assays in the correct places to meet their needs.

Development of a Novel, Low-Cost, Disposable Wooden Pencil Graphite Electrode for Use in the Determination of Antioxidants and Other Biological Compounds

The development of portable sensors that can be used outside the lab is an active area of research in the electroanalytical field. A major focus of such research is the development of low-cost electrodes for use in these sensors. Current electrodes, such as glassy-carbon electrodes (GCEs), are costly and require time-consuming preparation. Alternatives have been proposed, including mechanical pencil-lead electrodes (MPEs). However, MPEs themselves possess numerous drawbacks, particularly structural fragility. In this paper, we present a novel pencil-graphite electrode (PGE) fabricated from a regular HB#2 pencil. This PGE is a simple, disposable, extremely low-cost alternative to GCEs ($0.30 per PGE, vs. $190 + per GCE), and possesses the structural stability that MPEs lack. PGEs were characterized by square-wave voltammetry of ferricyanide, gallic acid, uric acid, dopamine, and several foodstuffs. In all cases, PGEs demonstrated sensitivities comparable or superior to those of the GCE and MPE (LOD = 5.62 × 10⁻⁴ M PGE, 4.80 × 10⁻⁴ M GCE, 2.93 × 10⁻⁴ M MPE). Signal areas and peak heights were typically four to ten times larger for the PGE relative to the GCE.

Antioxidants: Characterization, natural sources, extraction and analysis

Recently many review papers regarding antioxidants from different sources and different extraction and quantification procedures have been published. However none of them has all the information regarding antioxidants (chemistry, sources, extraction and quantification). This article tries to take a different perspective on antioxidants for the new researcher involved in this field. Antioxidants from fruit, vegetables and beverages play an important role in human health, for example preventing cancer and cardiovascular diseases, and lowering the incidence of different diseases. In this paper the main classes of antioxidants are presented: vitamins, carotenoids and polyphenols. Recently, many analytical methodologies involving diverse instrumental techniques have been developed for the extraction, separation, identification and quantification of these compounds. Antioxidants have been quantified by different researchers using one or more of these methods: in vivo, in vitro, electrochemical, chemiluminescent, electron spin resonance, chromatography, capillary electrophoresis, nuclear magnetic resonance, near infrared spectroscopy and mass spectrometry methods.

Electrochemical Methods for Total Antioxidant Capacity and its Main Contributors Determination: A review

Backround: The present review focuses on electrochemical methods for antioxidant capacity and its main contributors assessment. The main reactive oxygen species, responsible for low density lipoprotein oxidation, and their reactivity are reminded. The role of antioxidants in counteracting the factors leading to oxidative stress-related degenerative diseases occurence, is then discussed. Antioxidants can scavenge free radicals, can chelate pro-oxidative metal ions, or quench singlet oxygen. When endogenous factors (uric acid, bilirubin, albumin, metallothioneins, superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glutathione-S-transferase) cannot accomplish their protective role against reactive oxygen species, the intervention of exogenous antioxidants (vitamin C, tocopherols, flavonoids, carotenoids etc) is required, as intake from food, as nutritional supplements or as pharmaceutical products.

Literature study: The main advantages of electrochemical methods with respect to traditional, more laborious instrumental techniques are described: sensitivity, rapidity, simplicity of the applied analytical procedure which does not require complicated sample pre-treatment etc.

The paper reviews minutiously the voltammetric, amperometric, biamperometric, potentiometric and coulometric methods for total antioxidant capacity estimation. For each method presented, the electroactivity and the mechanism of electro-oxidation of antioxidant molecules at various electrodes, as well as the influences on the electroactive properties are discussed. The characteristics of the developed methods are viewed from the perspective of the antioxidant molecule structure influence, as well as from the importance of electrode material and/or surface groups standpoint.

The antioxidant molecule-electrode surface interaction, the detection system chosen, the use of modifiers, as well as the nature of the analysed matrix are the factors discussed, which influence the performances of the studied electrochemical techniques.

Conclusions: The electrochemical methods reviewed in this paper allow the successful determination of the total antioxidant capacity and of its main contributors in various media: foodstuffs and beverages, biological fluids, pharmaceuticals. The advantages and disadvantages of the electrochemical methods applied to antioxidant content and antioxidant activity assay are treated and interpreted, in the case of various analysed matrixes. Combining advanced materials with classical electrode construction, provides viable results and can constitute an alternative for the future.