Table 3.

Summary of the case studies documenting the AC values and other parameters calculated by using the electrochemical techniques.

Studied Extract	Extract Type	Conventional Techniques	Electrochemical Techniques	Electrodes	Parameter Identified	Remarks	Ref.
Zespri® Sweet Green kiwifruit (Actinidia chinensis x Actinidia deliciosa)	Flesh and skin extract of the kiwi fruit	For phenolic contents: TPC analysis TFC analysis TAC analysis ABTS assay DPPH assay FRAP assay	CV coupled with the HPLC	Reference Electrode: Ag/AgCl electrode Working Electrode: Glassy carbon electrode	Identification of phenolic contents by comparing them with the phenolic standards. Identified phenolic components: Catechin Gallic acid Protocatechuic acid Vanillic acid Caffeic acid Syringic acid Epicatechin Epigallocatechin gallate p-Coumaric acid Rutin Ferulic acid Epicatechin gallate Quercetin trans-Cinnamic acid The reducing potential and AOC of these compounds were studied by using the parameters of Epa, Ipa and Q500.	Among the fourteen identified phenolic components, CV was able to identify the nine antioxidant molecules present in the extract. Moreover, CV was identified to be the better technique in comparison to the spectroscopic and antioxidants assays as it records the total AOC values in comparison to the particular mechanism (scavenging, ability to reduce metal, or lipid peroxidation inhibition. One drawback that was observed in case of CV technique was that the ascorbic acid could not be studied through this, while other techniques detected it in the phytochemical profiling.	[50]
Zespri® SunGold Kiwifruit (Actinidia chinensis)
Hayward commercial fruit
Vitis vinifera L. (Grape pomace)	Grape pomace (seed, skin and stem extract)	TPC analysis TBARS assay	CV	Three-electrode system Reference system: Ag/AgCl electrodeWorking electrode: Glassy carbon electrode Auxiliary electrode: Platinum wire	Identification of electrochemical phenolic compounds: (3′, 4′-dihydroxyl moiety of phenolic compounds). The Q500 parameter was used to identify the total phenolic content of the extract. The Ipc, Ipa, Epa, Epc, and Emid parameters are utilized to investigate the following observables: Total AOC of the extracts Byproducts after the antioxidant reaction Concentration of antioxidantsElectrochemical mechanism	Individual phenols are not detected. Correlation between the TBARS and CV was studied by Pearson’s correlation.	[80]
Greigia Sphacelata	Fruit	ORAC test	DPV	Three-electrode system Reference system: Ag/AgCl electrodeWorking electrode: Glassy carbon electrode Auxiliary electrode: Platinum wire	Current, potential and area under the current-potential curve are the main Electrochemical parameters utilized to investigate the AOC potential of the sample.	Despite differences in the operating mechanism of the utilized assays of ORAC assay (fluorescent method) and DPV (an electrochemical method), Pearson’s correlation test revealed that both methods exhibited a correlation value of 0.969 with each other. The authors also reported that the understudy sample has very low antioxidant activity values.	[88]
Solanum nigrum	Black nightshade fruit	TPC analysis TFC analysis TAC analysis DPPH assay FRAP assay	CV	Three-electrode system Reference system: Hg/Hg2Cl2 electrode Working electrode: Glassy carbon electrode Auxiliary electrode: Platinum wire	Epa and Ipa values were used to estimate the AOC values of the fruit extract. The higher Ipa values were co-related with, the higher antioxidant activity. The shape of the voltammogram (i.e., absence of the cathodic peak) was used to obtain information regarding the irreversibility of the phenolic components present in the extract.	Superoxide radical scavenging assay was utilized as a means to study the AOC values by using the CV technique, indicating that CV can be used to investigate the ability of the extract to quench the superoxide radical. Ethyl acetate extract of fruit expressed better AOC and scavenging results in comparison to chloroform and n-butanol extract of the fruit.	[89]
Phoenix dactylifera. L.	Date palm fruit	TPC analysis TFC analysis DPPH assay FRAP assay	CV	Three-electrode system Reference system: Hg/Hg2Cl2 electrode Working electrode: Glassy carbon electrode Auxiliary electrode: Platinum wire	Reduction in the Ipa values associated with the superoxide radical was used as a representation tool indicating the decrease in the concentration of radical owing to the presence of phytochemicals in the extract. The shape of voltammogram is used for studying the irreversibility of the phytochemicals involved.	Authors observed that spectrophotometer suffers from the drawback that phytochemicals exhibit the peaks in the same range and, consequently, are not properly identified by spectroscopic techniques. The electrochemical method removes this problem.	[62]
Bunchosia glandulifera	Seed, bark, leaf and root extract	TPC analysis β-Carotene test Ascorbic acid test DPPH assay FRAP assay ABTS assay	CV DPV	Three-electrode system Reference system: Ag/AgCl electrode Working electrode: Glassy carbon electrode Auxiliary electrode: Platinum wire	Current, potential and area under the current-potential curve are the main electrochemical parameters utilized to investigate the AOC potential of the sample	The solvent of DMSO is noxious and its use as a solvent should not be encouraged. However, the study presented an excellent comparison between electrochemical methodologies and revealed that the CV showed better linearity in the case of the DPV. Furthermore, the authors found the AOC value of the seed extract presented the best results among all other extracts.	[90]
Punica granatum L.	Pomegranate peels	TPC analysis TFC analysis TCT analysis DPPH assay FRAP assay	CV	Three-electrode system Reference system: Ag/AgCl electrode Working electrode: Glassy carbon electrode Auxiliary electrode:Platinum wire	Anodic current, anodic potential and area under the current-potential curve are the main electrochemical parameters utilized to investigate the AOC potential of the sample.	The extraction of the phenolic components was performed by using the response surface methodology (RSM). The authors identified that the AOC potential of the five medicinal plants exhibited almost 36 times lower efficacy in comparison to the ascorbic acid-based test, indicating that the CV is not suitable for measuring the AOC value for the extracts containing the high molecular weight antioxidants.	[91]
Argania spinosa L.	Argan hull
Corrigiola telephiifolia Pourr.	Serghina
Prunus dulcis	Almond
Rubia tinctorum L.	Madder root

Abbreviations: Total Phenolic Content (TPC), Total Flavonoid Content (TFC), Total Flavanol Content (TAC), 2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)-diammonium salt (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric reducing ability of plasma (FRAP), High-Performance Liquid Chromatography (HPLC), Cyclic voltammetry (CV), silver/silver chloride (Ag/AgCl), Oxygen radical absorption capacity (ORAC), Dimethyl sulfoxide (DMSO).