Antioxidant Determination with the Use of Carbon-Based ...

1.Cyclic voltammetry;
Chronoamperometry;
Square-wave
voltammetry;-poly(gallic acid)/multiwalled carbon nanotube modified glassy carbon electrode;-supporting electrolyte 0.2 M H3PO4;
-cyclic voltammetric scan rate 50 mV/s;
-catalytic rate constant of 2.75 × 104 mol L&#;1 s&#;1, in chronoamperometry;
-voltammetric oxidation peak for gallic acid at 0.53 V vs Ag/AgCl, in CV and SWV;
-linear range of 4.975 × 10&#;6 to 3.381 × 10&#;5 M (SWV);
-LOD 3.22 × 10&#;6 M gallic acid (SWV);
-the SWVs of a fresh pomegranate juice sample shows three anodic peaks at 0.60, 0.70 and 1.0 V; signals can be attributed to the oxidation of different polyphenolic compounds, including gallic acid and catechin;
-determination of total phenolic content in pomegranate juice, as gallic acid equivalent;
-lack of interference of ascorbic acid, fructose, potassium nitrate and barbituric acid;[173]2.Cyclic voltammetry;
Differential pulse voltammetry;-nanocarbon-nanosilver hybrid electrode;-supporting electrolyte: Phosphate buffer solution, pH 7.0;
-CV studies confirmed that silver nanoparticles were efficiently immobilized on the Printex carbon surface; anodic and cathodic peak potentials noticed, were assigned to the redox pair Ag0/Ag+, whose presence was confirmed in the nanocomposite&#;s structure;
-DPV peak of gallic acid at 0.091 V vs. Ag/AgCl;
-sensitivity 0.254 μA/mol L&#;1 in DPV;
-LOD 0. μM in DPV;
-linear range 5.0 × 10&#;7&#;8.5 × 10&#;6 in DPV;
-estimation of antioxidant activity in wine;[174]3.Cyclic voltammetry;
Amperometry;-single-walled carbon nanotubes electrode, covalently functionalized with polytyrosine;-supporting electrolyte 0.050 M phosphate buffer solution, pH 7.40;
-CVs recorded between &#;0.200 V and 0.800 V (vs. Ag/AgCl) at a scan rate of 0.100 V s&#;1;
-cyclic voltammetric oxidation peak potential for gallic acid at 0.2 V;
-amperometric working potential 0.200 V;
-amperometric sensitivity 163.2 mA/mol L&#;1;
-amperometric LOD 8.8 × 10&#;9 M;
-quantification of polyphenols in tea extracts: Green-Patagonia, red-Patagonia, classic-Green Hill and herbal (Taragüí);[175]4.Differential pulse
Voltammetry;-TiO2 nanoparticles/ multiwalled carbon nanotubes-modified glassy carbon electrode;
-guanine biosensor based on TiO2 nanoparticles and multiwalled carbon nanotubes, immobilized on glassy carbon electrode;-supporting electrolyte:
phosphate buffer solution, pH 7.4;
-oxidation DPV peak at 0.80 V (vs. SCE) corresponding to the electro-oxidation of guanine at the developed biosensor;
-the peak intensity value of guanine oxidation increased linearly with increasing metabisulfite (employed as OH radical scavenger) concentration from 1 to 30 mmol L&#;1;
-LOD 0.54 mmol L&#;1 for the guanine biosensor;
-quantification of the antioxidant capacity in drug samples (adrenaline hydrochloride injection);[176]5.Cyclic voltammetry;
Differential pulse
Voltammetry;-carbon paste electrode;-supporting electrolyte: 0.1 M phosphate buffer, pH 5.0;
-a cyclic voltammetric anodic peak at 0.33 V, with a corresponding cathodic peak at 0.28 V, vs Ag/AgCl, for 1% coffee sample in 0.1 M phosphate buffer pH 5.0;
-two further anodic peaks at 0.55 V and 0.78 V were observed in DPVs of 0.5% coffee sample, in the same electrolyte;
-good correlation with DPPH photometry and HPLC;
-evaluation of the antioxidant activity of roasted coffee samples;
-determination of electrochemical index of roasted coffee samples on the basis of the sum of the ratios of anodic peak currents to anodic peak potentials noticed on DPVs;[177]6.Cyclic voltammetry;
Square-wave voltammetry;
Chronoamperometry-nanocomposite-graphene/poly (3,4-ethylenedioxythiophene): Poly (styrenesulfonate) modified screen-printed carbon electrode;-supporting electrolyte: Ethanolic phosphate buffer solution based on 60% ethanol and 0.1 M phosphate buffer saline, pH 7.0;
-method relied on DPPH reduction by antioxidants;
-the presence of Trolox yielded a well&#;countoured anodic peak at around 0.9 V and a small cathodic peak at 0.3 V.
-cathodic cyclic voltammetric peak potentials of catechin and caffeic acid were present at &#;0.03 V and&#;0.025 V vs. Ag/AgCl;
-square voltammetric peak of DPPH at 0.25 V;
-chronoamperometric DPPH detection at 0.2 V vs. Ag/AgCl; the linear calibration between the difference of cathodic DPPH currents (in the presence and absence of standard Trolox solution) and Trolox concentration in a range of 5&#;30 μM;
-LOD 0.59 μM and LOQ 1.97 μM (chronoamperometry);
-RSD of reproducibility is 2.13% (chronoamperometry);
-RSD of repeatability 2.78% (chronoamperometry);
-evaluation of the antioxidant activity in Thai herb and herbal beverage, expressed as mg of Trolox/g of sample;[178]7.Differential pulse voltammetry;-multi-walled carbon nanotubes-modified glassy carbon electrode;-supporting electrolyte: 0.1 M phosphate buffer (pH 4.0&#;7.0);
-three DPV oxidation peaks observed at 0.39, 0.61 and 0.83 V for red dry wine and at 0.39, 0.80 and 1.18 V vs. Ag/AgCl for white dry wine, in phosphate buffer pH 4.0;
-RSD% (as gallic acid equivalents) comprised between 1.0 and 6.9, as function of the wine sample;
-evaluation of red and white dry wine antioxidant capacity, as gallic acid equivalents per 1 L of wine;[179]8.Differential pulse voltammetry;-carbon paste electrode;
-laccase-based modified carbon paste biosensor for the determination of phenolic content;-supporting electrolyte: 0.1 mol L&#;1 phosphate buffer, pH 6.0;
-biosensor was characterized by enhanced activity in mild acid medium and the response time (corresponding to the time required for enzyme oxidation of phenolic compounds), was lower than 30 s, but gradually increased up to 240 s, when a plateau was reached;
-honey samples presented 2 to 3 anodic DPV peaks, the first at about 0.2 V, the second at about 0.5 V and the third nearby 0.8 V vs. Ag/AgCl;
-electrochemical index determination, based on the sum of ratios of peak currents to peak potentials;
-determination of phenolic content in honey samples;[180]9.Cyclic voltammetry;
Differential pulse voltammetry;-carbon black nanoparticles press imprinted films;-supporting electrolyte: Phosphate buffer pH 7.40;
-scan rate of 50 mV s&#;1 in the potential range of -0.20 V to +1.0 V vs. Ag/AgCl (CV);
-pulse amplitude 50 mV/s, scan rate 10 m Vs&#;1 (DPV);
-anodic peaks of o-diphenols and m-phenols present in olive oil extract, noticed in the range 0.120&#;0.160 V and 0.590&#;0.610 V (vs. Ag/AgCl), respectively; consistency with results obtained for the standards (DPV);
-good repeatability for o-phenols;
-RSD < 6% (o-phenols), RSD < 15% (m-phenols) in CV;
-stable and reproducible voltammetric response of carbon black nanoparticles-based electrode;
-determination of phenolic content and electrochemical indexes in olive oil extracts, using hydroxytyrosol and tyrosol as standards;[181]10.
Cyclic voltammetry;
Differential pulse voltammetry;-glassy carbon electrode;-supporting electrolyte: Dimethylsulfoxide, with tetrabutylammonium hexafluorophosphate 0.1 mol L&#;1;
-the CVs were obtained at a scan rate of 100 mV s&#;1;
-DPV pulse width = 5 mV, pulse amplitude = 60 mV and scan rate = 20 V s&#;1;
-oxidation of ascorbic acid at 0.90 V in cyclic voltammetry and around 0.75 V vs. Ag/AgCl in differential pulse voltammetry;
-in the CVs of the bark extract, a very well contoured peak was observed at 1.3 V, corresponding to meta-diphenols and isolated phenols;
-in the CVs of the root and leaf extracts, an additional peak at 0.9 V indicates the presence of phenolics with ortho- or para-diphenol groups, in low amounts;
-determination of the antioxidant capacity of

Bunchosia glandulifera

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(Jacq.) Kunth (Malpighiaceae) extracts, using ascorbic acid as standard;[182]11.Chrono-amperometry;
Differential pulse voltammetry;-glassy carbon electrode modified with multi-walled carbon nanotubes;
-glassy carbon polyquercetin-modified electrode;-supporting electrolyte: Phosphate buffer pH 7.0;
-antioxidant capacity using gallic acid as reference;
-DPVs recorded from 0 to 0.8 V (pulse amplitude 50 mV, pulse time 50 ms and potential scan rate 10 mV/s);
-DPVs of tea on the polyquercetin-modified electrode exhibited oxidation peaks at 0.080 and 0.19 V depending on the type of tea and a less configured oxidation step between 0.55 and 0.62 V vs Ag/AgCl;
-chronoamperograms recorded at a constant potential of 0.2 V, potential corresponding to oxidation of tea antioxidants;
-RSD = 0.5&#;20%, as function of the tea type (chronoamperometry);
-determination of the antioxidant capacity of tea, highest content for Green Sencha;[183]12.Cyclic voltammetry;-glassy carbon electrode;-supporting electrolyte: Phosphate buffer pH = 7.0;
-cyclic voltammetric scans performed between 0.0 and 0.5 V vs Ag/AgCl at a scanning rate of 5 mV/s;
-anodic peak at 244 mV for pomace and its parts (skins and stems), and 252 mV for seeds;
-analyse of winemaking by-products (pomace, skins, seeds and stems separated from pomace);[184]13.Cyclic voltammetry;-glassy carbon electrode;-supporting electrolyte: 0.1 M sodium acetate&#;acetic acid buffer at pH 3.6;
-all the grapes revealed peak I at 0.26&#;0.31 V, peak II between 0.42 and 0.55 V, and peak III at approximately 0.66 V vs Ag/AgCl;
-correlations of anodic peak area with phenolic content and antioxidant activity were assessed;
-determination of phenolic contents and antioxidant capacity in 12 grape cultivars;[185]14.Cyclic voltammetry;
Square-wave
voltammetry;
Differential pulse voltammetry-glassy carbon electrode;
-laccase-modified carbon paste electrode;-supporting electrolyte: 0.1 M phosphate buffer solution, pH 6.0, using Ag/AgCl reference;
-CV: Scan rate of 100 mV s&#;1 within the range 0&#;1.4 V;
-SWV: Pulse amplitude 50 mV, frequency 50 Hz and a potential increment of 2 mV, scan rate of 100 mV s&#;1;
-first peak present between 100 and 400 mV, second between 0.55 and 0.7, and third at around 1 V, in CV/SWV;
-solutions of the extracts yielded highest DPV peaks at 0.2 V, alongside peaks present at 0.6 and 0.9 V;
-electrochemical indexes were calculated based on the sum of ratios of peak currents to peak potentials in DPV;
-antioxidant activity evaluation of dried herbal extracts;
-highest electrochemical indexes obtained for

Gingko biloba

and

Hypericum perforatum

, consistent with the results obtained by spectrophotometry;[186]15.Cyclic voltammetry;
Differential pulse voltammetry;-glassy carbon electrode;-supporting electrolyte 0.1 M KCl;
-CV scan from 0 to + mV at a scan rate of 100 mV s&#;1;
-DPV scan from 0 to + mV at a scan rate of 100 mV s&#;1;
-the first peak of mature-phase milk occurred at around 400 mV; colostrum, had oxidation peaks at very high potential, around 800 mV (DPV) vs Ag/AgCl;
-mature-phase milk yielded a peak at around 400 mV; pasteurized milk had a peak at around 500 mV (CV);
-areas below oxidation peaks proportional to the amount of antioxidant compounds;
-free radical scavenging activity was highest for fresh breast milk and lowest for pasteurized breast milk, confirming the results obtained in DPPH assay;
-correlation between DPV and CV (r = 0.602,

p

< 0.001); correlation between DPV and DPPH method (r = 0.339,

p

= 0.003); correlation between CV and DPPH method (r = 0.468

p

< 0.000);[187]16.Cyclic voltammetry;
Differential pulse voltammetry;-screen-printed carbon electrodes;-supporting electrolyte 0.1 M HCl;
-in CV, the potential recorded between 0.0 V and +1.2 V, at 100 mV s&#;1 scan rate, using silver pseudo-reference electrode;
-optimum DPV parameters: 100 mV modulation amplitude, 10 mV step potential, 0.05 s modulation time and 0.5 s interval time;
-ortho-diphenols (oleuropein, hydroxytyrosol and caffeic acid) show one anodic peak between 0.5 and 0.6 V, and one cathodic peak between 0.4 and 0.6 V (CV); same compounds present an anodic peak at +0.5 V, in standard and real sample (DPV);
-ferulic acid gave an oxidation peak at higher potential (0.7 V), in the standard solution, whereas this signal was almost negligible in the real sample (DPV);
-tyrosol is oxidized at +0.93 V, alongside other mono-phenols (such as vanillic acid) that suffer oxidation around this potential value, in standard and real sample (DPV);
-LOD of 0.022 mg L&#;1 for caffeic acid and tyrosol, in DPV;
-determination of hydrophilic phenols in olive oil;[188]17.Cyclic voltammetry;
Differential pulse voltammetry;
Square-wave voltammetry;-electroactivated pencil graphite electrode;-supporting electrolyte: 0.05 mol L&#;1 potassium hydrogen phthalate;
-naringenin is irreversibly oxidized, giving rise to two pH-dependent peaks due to mixed (diffusion- and adsorption-controlled) electrode processes involving two electrons and one proton;
-LOD = 3.06 × 10&#;8 mol L&#;1, and LOQ = 1.02 × 10&#;7 mol L&#;1 for DPV, expressed as naringenin;
-LOD = 4.40 × 10&#;8 mol L&#;1, and LOQ = 1.11 × 10&#;7 mol L&#;1 for SWV, expressed as naringenin;
-application to determination of polyphenol content in citrus juice;[189]18.Amperometry;
Cyclic voltammetry;-disposable polyester screen-printed graphitic macroelectrodes;-supporting electrolyte: 1:1 (v/v) methanol: Ethanol mixture containing 0.05 mol/L&#;1 LiCl;
-CV scans between &#;0.3 and +1.0 V, scan rate 50 mV s&#;1, for DPPH 1 mmol/L&#;1 (in 50 mmol L&#;1 LiCl prepared in methanol:ethanol) and for DPPH in the presence of antioxidants;
-chlorogenic acid, caffeic acid, catechin and quercetin were oxidized between +0.7 and +0.9 V (CV);
-oxidation processes of tocopherol and BHT occurred at more positive potentials, around +1.0 V (CV);
-amperometric detection of DPPH remaining after reaction with antioxidants, at +0.1 V (vs. pseudo AgCl).
-analysis of edible oils;[190]19.Cyclic voltammetry;
Differential pulse voltammetry;
Linear sweep
voltammetry;-multi-walled carbon nanotube paste electrode;-supporting electrolyte: 0.02 M acetate-acetic acid buffer/4% methanol (pH 4.5);
-CV scan between 0 and 1.5 V, at 100 mV s&#;1;
-DPV pulse amplitude 50 mV and scan rate 100 mV s&#;1
-CV oxidation potential at 1.12 V;
-DPV oxidation potential at 1.19 V;
-the average Tafel slopes of mushroom extract was found to be 1.258 mV per decade, in LSV;
-assay of

Morchella esculenta

L. as ethnomedicinal food;
-obtained net electrochemical antioxidant power as 2.7 ± 0.12 mg per gram, using ascorbic acid as reference;[191]20.Cyclic voltammetry;-carbon paste electrode incorporating 2,2-diphenyl-1-picrylhydrazyl;-supporting electrolyte: Phosphate buffer solution 0.1 M, pH 7.0;
-potential ranges investigated: 0.00 V to &#;1.00 V; 0.60 V to &#;0.20 V and 0.45 V to 1.10 V, vs. Ag/AgCl;
-a peak potential of &#;833 mV, due to the irreversible reduction of the nitro functions on the phenyl group, present in the structure of DPPH;
-for tea extract analyzed, signals recorded in the potential window 0.4 V&#;1.1 V;
-tea extracts presented an anodic peak at about 0.8 V and a cathodic one at around 0.75 V;[192]21.Cyclic voltammetry;
Amperometry;-single walled carbon nanotubes-, graphene- and gold nanoparticles-based screen-printed electrodes;-supporting electrolyte: Sodium phosphate buffer solution 0.1 M, pH 7.0;
-assessment of the quenching capacity of plant extracts (

Hippophae fructus

and

Lavandula Flowers

) in the presence of H2O2 (chosen as model reactive oxygenated species);
-cyclic voltammograms reveal anodic peaks below 0.45 V vs Ag/AgCl, in the presence of extract;
-a marked cyclic voltammetric anodic peak at 0.09 V, and a small cathodic peak at 0.35 V noticed for lavender extracts;
-amperometric assay based on sensor&#;s sensitivity to H2O2 in the absence / presence of the extract;
-best sensitivity obtained at the gold nanoparticles-modified sensor: 6.43 ± 0.2 µA cm&#;2 mM&#;1;
-amperometric determinations at constant potential of 0.55 V, with linearity of 2 to 30 mM hydrogen peroxide:
-antioxidant capacity determination of hydrosoluble plant extracts;[17]22.Cyclic voltammetry;-glassy carbon electrode;-supporting electrolyte: Tetrabutylammonium perchlorate, in dimethyl sulfoxide 99%;
-scan rate 25 mV/s in CV;
-the voltammograms of the figs and almond extracts presented redox signals at positive potentials, the anodic oxidation being noticed at 1.175 V and 1.218 V, respectively, vs saturated calomel reference;
-determination of antioxidant activity of dry fruits (almond, apricot, cashew, figs, peanut, pistachio, raisins, and walnut);[193]23.Cyclic voltammetry;-glassy carbon electrode;-supporting electrolyte: Sodium acetate-acetic acid buffer (0.1 mol L&#;1, pH = 4.5) in acidified 80% methanol;
-analytical cyclic voltammetric signals for all target phenolic compounds present between 0 mV and 800 mV, at a scan rate of 100 mV s&#;1;
-cyclic voltamogramms of berry fruits presented anodic peaks between 310 mV (quercetin) and 0.756 mV (coumaric acid) vs. Ag/AgCl
-antioxidant capacity quantification relied on the area underneath the anodic peak, corresponding to the charge up to a potential value of 500 mV (Q500);
-evaluation of antioxidant activity of 15 berry samples (strawberries, blackberries, blueberries and red raspberries);[194]24.Amperometry;-glassy carbon electrode integrated in a flow injection system with sequential diode array and amperometric detection;-supporting electrolyte: Ethanol 12% v/v and tartaric acid 2 g/L, pH 3.6;
-amperometric determinations at 800 mV vs. Ag/AgCl;
-calibration curve over the range 0&#;0.19 mM gallic acid equivalents;
-determination of total polyphenol content and antioxidant activity of white, red wines and oenological tannins;
-total wine phenolic content between 1.08 and 15.4 mM gallic acid;
-concentration range 0.07&#;0.34 mM gallic acid obtained for tannin solutions;[195]25.Cyclic voltammetry;
Differential pulse voltammetry;-glassy carbon electrode;-supporting electrolyte: Sodium acetate 0.1 mol L&#;1;
-two CV oxidation waves at potentials of 0.45 V and 0.84 V vs Ag/AgCl, pointing towards the presence in the extract of minimum two kinds of reducing species, or a single reducing species that can be oxidized by two stable intermediates;
-extracts showed no voltammetric waves in the range of reduction potentials, suggesting that the reducing species in the extract of

Mimosa albida

leaves can exhibit antioxidant potential;
-two oxidation waves noticed on DPVs, indicating the existence of two antioxidant compounds: One species with greater antioxidant capacity with oxidation potential at 0.34 V, and the other one with lower antioxidant power, at 0.79 V;
-oxidation signal for

Mimosa albida

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-modified silver nanoparticles at +0. V (CV);
-analysis of aqueous leaf extract of

Mimosa albida

and assay of antioxidant capacity of

Mimosa albida

-modified silver nanoparticles;[196]26.Differential pulse voltammetry;-glassy carbon electrode;-supporting electrolyte: Sodium phosphate buffer solution 0.1 M, pH 7.4;
-scan rate 50 mV/s; pulse period 35 ms; potential step 10 mV;
-at increasing amounts of added extract, DPV oxidation peaks were noticed, at approximately 0.270 V, 0.430V, and 0.880 V vs. Ag/AgCl;
-determination of the antioxidant capacity of the

Greigia Sphacelata

fruit;[197]27.Cyclic voltammetry;
Differential pulse voltammetry;-glassy carbon electrodes modified with carbon nanotubes and chitosan;-supporting electrolyte: Britton-Robinson electrolyte buffer, at pH 3.0;
-chicoric acid anodic peak at 0.610 ± 0.060 V and cathodic peak at 435 ± 0.055 V vs Ag/AgCl, at 300 mV s&#;1 scan rate;
-the intensities of oxidation and reduction currents linearly vary with the square root of the scanning speed, in cyclic voltammetry;
-DPVs showed oxidation peaks for caftaric acid at 0.505 ± 0.002 V, and for chicoric acid at 0.515 ± 0.001 V vs Ag/AgCl, which are consistent with the results obtained at the assay of pharmaceutical forms;
-determination of total polyphenol content and antioxidant activity of

Echinacea purpurea

extracts in 3 different pharmaceutical forms (capsules, tablets and tincture);[198]28.Staircase voltammetry;glassy carbon electrode;-supporting electrolyte-100 mM KNO3;
-staircase voltammograms recorded successively for 4 cycles between +1.0 and &#;1.2 V vs Ag/AgCl;
-scan rate 50 mV/s, starting and ending in +1.0 V;
-the half-wave potential (E1/2), or the potential corresponding to half the anodic peak current (Ipa) was considered; lower E1/2 values are correlated to higher antioxidant potential;
-the peak intensity or, more accurately the surface area under the oxidation peak, provided quantitative informations: Antioxidant concentration/antioxidant capacity;
-analytical peaks present between &#;0.6 and 0 V, and around 0.5 V;
-evaluation of antioxidant activity for teas, wines and (superfood) juices;
-antioxidant index calculated relying on the maximum charge of oxidation (Qmax), the standard potential of the oxygen evolution reaction (vs. Ag/AgCl) and the standard potential of hydrogen evolution reaction (vs. Ag/AgCl);[199]29.Cyclic voltammetry;-glassy carbon electrode;-supporting electrolyte &#;0.1 M H2SO4 solution;
-scan rate investigated in the range of 20&#;160 mV s&#;1;
-dependence of charge under the anodic peak, on the concentration of tested red corn pigments, quantified in the region &#;0.2&#;1.2 V;
-CV for dark red corn seeds extract (1 mg mL&#;1) presents two anodic peaks at about 0.4 V and 0.65 V; a cathodic peak at the reverse scan, at about 0.2 V vs saturated calomel reference;
-evaluation of total phenolic and flavonoid contents in red corn;[200]30.Voltammetry;-carbon fiber ultramicroelectrodes;-linear relationship between anodic peak current and caffeic acid (reference antioxidant) concentration from 3.0 to 500 μmol L&#;1;
-repeatability illustrated by a RSD of 2.7%;
-sensitivity 12 μA L mol&#;1;
-Ag/AgCl electrode used as reference;
-LOD 0.41 μmol L&#;1;
-LOQ 1.26 μmol L&#;1;
-estimation of antioxidant capacity in three different wines, and in green and red grape samples;[201]31Cyclic voltammetry;
Square-wave voltammetry;-carbon electrode modified with guanine-, polythionine-, and nitrogen-doped graphene;-determinations performed in PBS pH = 1.5;
-1.0&#;mg/mL&#;1 guanine solution as optimum for modification of the electrode;
-a pair of redox peaks found between 0 and 0.3&#;V in CV; peak currents increased with increasing scan times; a thin blue membrane formed on the surface of electrode, showed that thionine was successfully polymerized;
-oxidation peak for ascorbic acid at about 1.1 V (SWV);
-linear range for ascorbic acid (standard antioxidant) analytical response ranged from 0.5 to 3.0 mg L&#;1 in SWV;
-LOD 0.21 mg L&#;1 (SWV);
-RSD 3.1% (SWV);
-determination of antioxidant capacity of fruit juices (grape juice, guava juice, and orange juice) and jute leaves extract, ramie leaves extract, and hemp leaves extract;[202]32Differential pulse stripping voltammetry (DPSV);
Cyclic voltammetry;-glassy carbon electrode modified with polyglycine;-supporting electrolyte: Britton-Robinson electrolyte buffer, pH 3.0;
-well-configured oxidation peak of quercetin (model antioxidant) occurs at around +460 mV, a corresponding cathodic peak being visible at 420 mV vs Ag/AgCl;
-peaks shifted towards less positive potentials when the scan rates increased from 20 to 400 mV/s in CV;
-oxidation peak current assigned to phenolic compounds of yam, at 430 mV, consistent to the peak potential of quercetin, on differential pulse stripping voltammograms;
-DPSV-pulse amplitude of 50 mV, pulse width of 500 ms;
-LOD 0.39 µg L&#;1 (DPSV);
-LOQ 1.39 µg L&#;1 (DPSV);
-electrode modification resulted in 3.15-fold increase of sensitivity, when compared to the bare glassy carbon;
-total antioxidant capacity of 0.1 kg of yam, obtained as 96.15 +/&#; 0.85 µg/L of equivalents quercetin at 95% confidence level;
-relative standard deviation of 0.88%;[203]33Cyclic voltammetry;
Chronoamperometry;-biosensor based on laccase immobilized onto a gold nanoparticles/graphene nanoplatelets-modified screen-printed carbon electrode;-supporting electrolyte: Sodium phosphate buffer solution 0.1M, pH 7.0;
-potential range from &#;0.6 V to 1.2 V with a scan rate of 0.05 V/s and a step potential of 2.0 mV (CV);
-anodic and cathodic CV peaks of hydroquinone at 0.2 V vs Ag/AgCl and 0 V, respectively, at a scan rate of 0.05 V s&#;1;
-excellent electrocatalytic activity towards oxidation of hydroquinone at a potential of &#;0.05 V in hydrodynamic amperometry;
-linear range 4&#;130 µM (chronoamperometry);
-LOD 1.5 µM chronoamperometry)
-LOQ 5 µM (chronoamperometry);
-determination of phenolic antioxidant capacity in wine and blueberry syrup;[204]34.Cyclic voltammetry;-glassy carbon electrode;-supporting electrolyte: 0.1 M sodium acetate/acetic acid bufer solution, pH 3.6;
-potential scans performed from &#;0.4 V to 1 V vs Ag/AgCl at a scan rate of 25 mV s&#;1;
-total antioxidant capacity expressed as ascorbic acid equivalents;
-crude medicinal plant extracts exhibited an oxidation peak around 750 mV on cyclic voltammograms;
-medicinal plant extracts have less than 36 times smaller total antioxidant capacity, when compared to ascorbic acid;
-it was concluded that cyclic voltammetry and FRAP are recommended for flavonoid quantitation; [205]

1. Introduction

Increasing body immunity and maintaining health through antioxidant preparations has become a new concern after the COVID-19 pandemic. Antioxidants are chemical substances that interrupt the cascade of free radical reactions within the human body. Free radicals are generated as byproducts of metabolic and physiological processes and are an essential part of the immune system of aerobic organisms, including humans. According to sources [ 1 2 ], radicals have one or more unpaired electrons, rendering them unstable and able to damage other atoms by losing electrons in order to become stable. These substances are called reactive oxygen/nitrogen species (ROS/RNS), and include hydroxyl, hydrogen peroxide, superoxide, nitric oxide, and peroxynitrite [ 3 4 ]. There are two types of antioxidants: endogenous antioxidants, produced by our bodies [ 5 ], and exogenous antioxidants, which are provided by food or nutritional supplements; one example of the latter are polyphenolic compounds [ 6 7 ]. The high content of phenolic components in the samples results in high levels of antioxidant activity [ 8 ].

11,12,13,

In some diets, spices, herbs, fruits, and vegetables can provide additional natural antioxidants to support antioxidant defenses [ 9 ]. Antioxidants sourced from food, beverages, and herbal medicines must be controlled for their quality so that the antioxidants consumed can optimally counteract free radicals in the body in order to help prevent disease. Several research studies have indicated that medical conditions, including inflammation, osteoporosis, hepatopathy, diabetes, cancer, and neuro-degenerative diseases, are frequently linked with elevated levels of oxidative stress [ 10 14 ]. There are significant differences between RNS and ROS and the ways in which antioxidants protect the body against them. Enhancing cellular defenses through antioxidants can effectively neutralize oxidative stress [ 15 16 ].

Spices and herbs are known to have high antioxidant activity and beneficial effects on human health in certain spices. Antioxidants derived from spices include bioactive compounds consisting of flavonoids, phenolic compounds, and compounds containing sulfur, tannins, alkaloids, diterpenes, and vitamins [ 15 ]. The compounds exhibit variations in their antioxidant efficacy. For instance, flavonoids can eliminate free radicals and establish associations with catalytic metal ions, rendering them reactive. Numerous academic studies have shown that spices and herbs, including, but not limited to, rosemary, sage, and oregano, possess high levels of phenolic compounds and antioxidants. Antioxidants can safeguard oils against oxidative degradation. When incorporated into food, antioxidants can impede the formation of harmful oxidation byproducts, preserve the nutritional tributes, and prolong the duration of product storage. Spices contain inherent antioxidants that aid in the mitigation of oxidative stress. Oxidative stress is a biological state that results from heightened concentrations of unpaired electrons, known as free radicals, within cellular and tissue environments. Various detrimental factors, including gamma radiation, UV and X-rays, psychological stress, contaminated food, unfavorable environmental circumstances, strenuous physical exertion, tobacco use, and alcohol addiction, can trigger this condition [ 17 18 ].

According to previous studies, the process of inhibiting free radicals by antioxidants can be achieved by donating an electron to oxidant compounds, thereby impeding their activity. The efficacy of antioxidants in mitigating the effects of free radicals can be classified into two distinct groups. The initial classification, namely primary, pertains to antioxidants that undergo chain termination to impede the generation of free radicals. In this process, antioxidants donate hydrogen from their active hydroxyl groups to produce more radicals [ 19 ]. The second category pertains to the deactivation of free radicals by transferring single electrons to form more stable substances, accomplished by antioxidants [ 20 ]. Antioxidants are compounds that have many benefits, including use in beauty and cosmetic products [ 21 ], health care [ 22 ], food ingredients and preservatives [ 23 ], the production of silver nanoparticles [ 24 ], and others.

30,

Antioxidant detection can be achieved using spectrophotometry [ 25 ], colorimetry [ 26 ], chromatography [ 27 ], spectroscopy, and electrochemical methods [ 28 ]. The utilization of the chromatographic technique comes with a higher cost due to the expense of the equipment involved. While the method can differentiate between distinct antioxidant constituents in various food items, it only furnishes data regarding their concentration. The spectroscopic technique relies on the spectral characteristics of a reference material because of its determinant principle, which leads to unavoidable errors in the measurement results, including determining the actual color of the sample, such as orange juice, etc. For this reason, it is necessary to pay attention to and develop simple, sensitive, and fast methods for analysis, such as the electrochemical method. In general, the conventional method is sensitive and efficient. Still, the work is usually carried out in a centralized laboratory, requires resources and experts in the field, and comes at a high costs and takes a long time. The electrochemical approach offers numerous benefits, including rapid detection time, minimal sample volume requirement, exceptional precision, and heightened sensitivity. By circumventing the need for laborious pre-treatment of samples, interference from colored samples can be minimized [ 29 31 ]. One method utilized to evaluate antioxidant capacity is the electrochemical approach, which is preferred for its accuracy, affordability, simplicity, rapid response, and high sensitivity [ 32 ]. A multitude of electrochemical methodologies, including square wave voltammetry (SWV), cyclic voltammetry (CV), and differential pulse voltammetry (DPV), have been extensively utilized in various research endeavors to explore redox systems and produce results [ 33 34 ].

The information literature review was collected from scientific journals, Wiley Online Library, Scopus, Google Scholar, and Science Direct. The keyword is biosensor antioxidant and electrochemical method. The articles obtained are filtered by title, abstract, and full text.

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