The Folin–Ciocalteu (FC) method of performing a total phenolics assay, originally developed for protein determination, has recently evolved as a total antioxidant capacity assay but was found to be ...incapable of measuring lipophilic antioxidants due to the high affinity of the FC chromophore, that is, multivalent-charged phospho-tungsto-molybdate(V), toward water. Thus, the FC method was modified and standardized so as to enable simultaneous measurement of lipophilic and hydrophilic antioxidants in NaOH-added isobutanol–water medium. Optimal conditions were as follows: dilution ratio of aqueous FC reagent with iso-BuOH (1:2, v/v), final NaOH concentration of 3.5 × 10–2 M, reaction time of 20 min, and maximum absorption wavelength of 665 nm. The modified procedure was successfully applied to the total antioxidant capacity assay of trolox, quercetin, ascorbic acid, gallic acid, catechin, caffeic acid, ferulic acid, rosmarinic acid, glutathione, and cysteine, as well as of lipophilic antioxidants such as α-tocopherol (vitamin E), butylated hydroxyanisole, butylated hydroxytoluene, tertiary butylhydroquinone, lauryl gallate, and β-carotene. The modified FC method reliably quantified ascorbic acid, whereas the conventional method could not. The modified method was reproducible and additive in terms of total antioxidant capacity values of constituents of complex mixtures such as olive oil extract and herbal tea infusion. The trolox equivalent antioxidant capacities of the tested antioxidant compounds correlated well with those found by the Cupric Reducing Antioxidant Capacity reference method.
It would be desirable to establish and standardize methods that can measure the total antioxidant capacity level directly from vegetable extracts containing phenolics. Antioxidant capacity assays may ...be broadly classified as electron transfer (ET)- and hydrogen atom transfer (HAT)-based assays. The majority of HAT assays are kinetics-based, and involve a competitive reaction scheme in which antioxidant and substrate compete for peroxyl radicals thermally generated through the decomposition of azo compounds. ET-based assays measure the capacity of an antioxidant in the reduction of an oxidant, which changes colour when reduced. ET assays include the ABTS/TEAC, CUPRAC, DPPH, Folin-Ciocalteu and FRAP methods, each using different chromogenic redox reagents with different standard potentials. This review intends to offer a critical evaluation of existing antioxidant assays applied to phenolics, and reports the development by our research group of a simple and low-cost antioxidant capacity assay for dietary polyphenols, vitamins C and E, and human serum antioxidants, utilizing the copper(II)-neocuproine reagent as the chromogenic oxidizing agent, which we haved named the CUPRAC (cupric ion reducing antioxidant capacity) method. This method offers distinct advantages over other ET-based assays, namely the selection of working pH at physiological pH (as opposed to the Folin and FRAP methods, which work at alkaline and acidic pHs, respectively), applicability to both hydrophilic and lipophilic antioxidants (unlike Folin and DPPH), completion of the redox reactions for most common flavonoids (unlike FRAP), selective oxidation of antioxidant compounds without affecting sugars and citric acid commonly contained in foodstuffs and the capability to assay -SH bearing antioxidants (unlike FRAP). Other similar ET-based antioxidant assays that we have developed or modified for phenolics are the Fe(III)- and Ce(IV)-reducing capacity methods.
Ferrozine (FZ) preferentially stabilizes Fe(II) over Fe(III) to raise the ferric reduction potential and oxidize antioxidants. The advantages of the ferric-ferrozine method over other iron-based ...total antioxidant capacity assays were: (i) higher molar absorptivity and enhanced sensitivity, (ii) lower interference from foreign ions, (iii) wide pH tolerance (iv) additivity of the absorbances for mixtures. Solid-phase extraction (SPE) could be combined with spectrophotometry, because the magenta-colored anionic Fe(II)-FZ complex was quantitatively sorbed on Sephadex QAE A-25 resin. The sensitivity enhancement using the resin enabled us to conduct total antioxidant capacity (TAC) measurements of antioxidant-poor samples. The apparent molar absorptivity, linear concentration range and trolox equivalent antioxidant capacities (TEAC) of certain antioxidants were found. The calibration curves (lines) of trolox, rutin, and rosmarinic acid individually and in herbal infusions—by using the method of standard additions—were parallel, confirming that the added antioxidants did not interact with herbal constituents to cause chemical deviations from Beer’s law.
Nanomaterials are preferred for scientific studies due to their spectral properties and perfect surface appearance. This study aims to introduce a novel, environmentally friendly, photocatalytic ...method for degrading methylene blue (MB) in aqueous solutions. With this purpose in mind, the study synthesizes nanoceria particles and coats them with zahter (Thymbra spicata; zahter-coated nanoceria, ZCNC) following the main outlines of green chemistry as characterized by SEM and FTIR analyses. The study proposes this new nanoparticle (with the aid of H.sub.2O.sub.2 and UV combinations) as an alternative to iron in Fenton-type reactions for enabling MB degradation. The maximum efficiency was observed through the ternary combination of zahter-coated nanoceria, UV light, and H.sub.2O.sub.2 at 63% concentration. The degradation of the MB solution was achieved by installing a small amount of ZCNC (0.1g), after which the absorbance values were measured at 664 nm. According to the possible reaction kinetics discussed within the study, the reaction rate was calculated at 1.49 * 10.sup.-2 min.sup.-1, thus enabling a faster reaction for a better evaluation of the reaction mechanism compared to other degradation processes that have been previously investigated.. Keywords: Hydroxyl radicals, nanoceria, Thymbra spicata, methylene blue, advanced oxidation process, photocatalytic degradation
Food colorants are an important class of food additives that give the first impression to consumers about the quality of food. Ce(IV)-reducing antioxidant capacity assay originally developed in our ...laboratories was adapted to the determination of synthetic food colorants for the first time. This method allowing for total antioxidant capacity assay of dietary polyphenols, flavonoids, and ascorbic acid in plant extracts is based on the room temperature oxidation of antioxidant compounds with Ce(IV) sulfate in dilute H
2
SO
4
solution and measurement of the absorbance of unreacted Ce(IV) at 320 nm. The results of the proposed method were correlated with high-performance liquid chromatography (HPLC) findings. Individual standard solutions, synthetic mixtures of synthetic colorants, and colorant extracts were identified and quantified with HPLC on a C
18
column equipped with a diode array detector, and slight modifications on the existing HPLC method were made to analyze synthetic colorant mixtures. This work proposes Ce(IV)-oxidative spectrophotometry as a complementary technique to HPLC in the analysis of food colorants.
Penicillin G, tetracycline and oxytetracycline are broad-spectrum antibiotics with considerably low side effects which are used in most of the poultries. Due to complex matrix effects, it is ...considerably difficult to isolate these compounds from other molecules (such as proteins and lipids) in order to analyze. In this study, a high performance liquid chromatography (HPLC) coupled with photodiode array (PDA) detector system was introduced for the determination of tetracycline, oxytetracycline and penicillin G residues in nine chicken breast samples. For the separation of tetracycline and oxytetracycline out of samples prior to the analysis, trichloroacetic acid (TCA) and McIlvaine buffer solutions were used while formic acid and phosphate buffer solutions were utilized for penicillin G using a solid phase extraction system. The peaks at the chromatograms were enlightened and recovery percentages were calculated using spiked samples (96.57% for penicillin G; 99.00% for oxytetracycline; 95.92% for tetracycline). LOD and LOQ values were calculated, respectively as 1.55 gL-1 and 5.20 gL-1 for tetracycline; 1.32 gL-1 and 4.39 gL-1 for oxytetracycline; 1.07 gL-1 and 3.60 gL-1 for penicillin G. With the proposed method, the determination of three antibiotic residues was performed in less than 15 minutes and applied successfully to real samples.
•Magnetic solid-phase extraction of Cr(VI) by melamine–formaldehyde resin was described.•An MSPE coupled with colorimetric assay has been presented for the detection of Cr(VI).•Colorimetric ...sensor(probe) has been based on Cit-polyvinyl alcohol-GNPs and p-amino hippuric acid.•After magnetic SPE, Cr(VI) can be detected with the naked eye or UV–vis spcrophotometry.•The coupled method (MSPE@GNP-based colorimetric probe) was suitable for field analysis.
A new method for magnetic solid-phase separation of trace-levels of Cr(VI) by using magnetic nanoparticles modified melamine–formaldehyde resin (Fe3O4@MFR) was described. Also, the selective and sensitive chemical optical probe was developed based on citrate-polyvinyl alcohol capped gold nanoparticle and modified with the reagent p-amino hippuric acid (PAH). Consequently, the optical probe was employed for the sensing of Cr(VI) ion in aqueous media. The sensing scheme is based on the complexation between PAH and reduced Cr(III). The linear calibration curve for Cr(VI) was calculated with preconcentration and was found in the range of 2.6–156 µg L−1 and the limits of detection for Cr(VI) were 10.4 µg L−1 and 2.0 µg L−1 with the naked eye and UV–vis spectroscopic detection, respectively. More importantly, both magnetic solid-phase extraction and colorimetric optical probe are selective for detection of the target analyte. The recoveries are between 96 and 99% when exercising 15 mg of the Fe3O4@MFR. The coupled approach was employed for the pre-concentration and quantification of Cr(VI) in two real water samples (tap water and mineral water) employing the standard addition protocol.
Cherry fruit is a natural food that has been consumed since ancient times due to its remarkable nutritional and therapeutic properties. In this study, total phenolic, total flavonoid, total monomeric ...anthocyanin contents, total antioxidant capacity and polyphenolic contents of fruit samples belonging to 14 (two of them endemic) different
Prunus
(cherry) taxa naturally distributed in Turkey were compared. Qualitative and quantitative determination of 23 individual phenolic compounds (fourteen phenolic acids, five flavonols, one flavan-3-ol, one flavone, one dihydrochalcone and one phytoalexin) was performed by LC–MS/MS (liquid chromatography technique coupled with tandem mass spectrometry). Antioxidant activities of fruit samples were determined using CERAC, CUPRAC and ABTS test methods. According to the results obtained, it was found that
Prunus mahaleb
var.
alpina
(107.57 mg cyanidin 3-glucoside/100 g FW) and
Prunus mahaleb
var.
mahaleb
(90.95 mg cyanidin 3-glucoside/100 g FW) had higher anthocyanin content compared to other fruit samples. It was determined that
Prunus incana
var.
velutina
, one of the endemic species, has a remarkable total phenolic content (10.76 mg gallic acid/g FW), individual phenolic content (641.58 mg/ 100 g, a total of individual phenolics with LC–MS/MS) and total antioxidant capacity (25.1 mg Trolox/100 g FW with CERAC assay). This article is the first study to report the comparative phytochemical content of different
Prunus
taxa in Turkey and the phytochemical properties of
Prunus incana
var.
velutina
. It has been concluded that endemic
Prunus incana
var.
velutina
has the potential to be used as an alternative to the taxa
Prunus mahaleb
,
Prunus avium
and
Prunus vulgaris
as a health-protective food and as a food additive due to its remarkable polyphenolic content, anthocyanin content and total antioxidant capacity.
Dietary antioxidants widely found in fruits and vegetables may serve the task of reducing oxidative damage in humans induced by free radicals and reactive oxygen species under ‘oxidative stress’ ...conditions. The aim of this work is to develop a simple, low-cost, sensitive, and diversely applicable indirect spectrophotometric method for the determination of total antioxidant capacity of several plants. The method is based on the oxidation of antioxidants with cerium(IV) sulfate in dilute sulfuric acid at room temperature. The Ce(IV) reducing capacity of the sample is measured under carefully adjusted conditions of oxidant concentration and pH such that only antioxidants and not other organic compounds would be oxidized. The spectrophotometric determination of the remaining Ce(IV) was performed after completion of reaction with antioxidants. Quercetin and gallic acid were used as standards for flavonoids and phenolic acids, respectively, and results of antioxidant measurements were reported as trolox equivalents. The developed procedure was successfully applied to the assay of total antioxidant capacity due to simple compounds such as trolox, quercetin, gallic acid, ascorbic acid, catechin, naringin, naringenin, caffeic acid, chlorogenic acid, ferulic acid, and
p-coumaric acid, and due to phenolic acids and flavonoids in the arieal parts of nettle (
Urtica Dioica L.). Blank correction of significantly absorbing plant extracts at 320
nm could be made with the aid of spectrophotometric titration. Plant selection was made in respect to high antioxidant content, and extraction was made with water. The proposed method was reproducible, and the trolox equivalent antioxidant capacities (TEAC coefficients) of the tested antioxidant compounds were correlated to those found by reference methods such as ABTS and CUPRAC. Since the TEAC coefficients found with the proposed method of naringin–naringenin and rutin–catechin pairs were close to each other, this Ce(IV)-based assay probably caused the simultaneous hydrolysis of flavonoid glycosides to the corresponding aglycones and their subsequent oxidation such that the hydrolysis products exhibed antioxidant capacities roughly proportional the number of –OH groups contained in a molecule.
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