Azino-bis(3-ethylbenzothiazoline)-6-sulfonate Research Articles

Mechanism investigation on the formation of high valent iron intermediate in Fe(VI) oxidation using ABTS as a probe: Effect of excess Fe(VI)

This work investigated the reaction of 2,2′-azino-bis(3-ethylbenzothiazoline)-6-sulfonate (ABTS) with Fe(VI) in phosphate buffer, in a wide concentration range of Fe(VI), to ascertain the potential influence of Fe(VI) on the type and fate of the high valent iron intermediate. The reaction of ABTS with equimolar amounts of Fe(VI) stopped at the formation of ABTS+, accompanied by the complete reduction of Fe(VI) to produce Fe(V) as the only high valent iron intermediate, thereby providing a model system involving Fe(V) alone. Even in the presence of the target compound (propranolol, methyl phenyl sulfoxide and carbamazepine), Fe(VI) was also completely transformed to Fe(V) rather than to oxidize the target compound. Thus, the observed degradation of the target compound was caused by Fe(V) alone, confirming the feasibility of the reaction as a model system involving Fe(V) only. Comparatively, the formation of ABTS+ (Stage I) and its further oxidation by Fe(VI) (Stage II) was found in the reaction of ABTS with excess Fe(VI). Stage II produced one-electron transfer product (i.e., ABTS2+) only in the case of pH ≤ 5 (k = 2.55 × 105 M−1s−1, pH = 4) while proceeded oxidative degradation rather than one-electron transfer in the pH range of 6–8 (k = 2.33 × 103 M−1s−1, pH = 7). Based on the distribution of the speciation of Fe(VI) species, H2FeO4 was confirmed to be the active species for one-electron transfer path while HFeO4- species was responsible for the oxidative degradation. Correspondingly, Fe(VI) was transformed to Fe(V) or Fe(IV), which did not react with other intermediates (i.e., ABTS+ and ABTS2+).

Differential antioxidant activity of glucuronoxylooligosaccharides (UXOS) and arabinoxylooligosaccharides (AXOS) produced by two novel xylanases

XOS are particularly interesting bioactive molecules. Bacillus safensis CBLMA18, a xylanolytic bacterium has been isolated and two of its xylanases have been identified and fully characterized. Xyn11A is an extracellular 22.5-kDa GH11 xylanase while a second xylanase, Xyn10B, corresponds to an intracellular 48-kDa GH10 enzyme. Both unimodular xylanases showed activity only on xylan substrates with important differences in their catalytic pattern. Xyn11A displays higher activity on glucuronoxylans, with an optimum at pH 8 and 50 °C, and a Vmax of 5281 U/mg on beechwood xylan, meanwhile Xyn10B prefers arabinoxylans, with an optimum of pH 7 and 60 °C, and a Vmax of 50.29 U/mg on rye arabinoxylan. The antioxidant activity of xylanase-generated XOS obtained from glucuronoxylans (UXOS) and arabinoxylans (AXOS) was tested with the ABTS (2, 2′-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)) method. UXOS showed higher antioxidant activity than AXOS (>80% of antioxidant capacity). Thin layer chromatography and MALDI-TOF MS analysis showed that UXOS comprise neutral and acidic XOS with methylglucuronic acid (MeGlcA) ramifications, while AXOS contain only neutral molecules with arabinose decorations. The MeGlcA ramifications seem to have an important role in the antioxidant capacity of oligosaccharides. Besides, the increase of UXOS size correlates with an increase in their activity.

Electrostatic Interaction-Induced Formation of Enzyme-on-MOF as Chemo-Biocatalyst for Cascade Reaction with Unexpectedly Acid-Stable Catalytic Performance.

Combining biocatalytic and chemocatalytic reactions in a one-pot reaction not only avoids the tedious isolation of intermediates during the reactions but also provides a desirable alternative to extend the range of catalytic reactions. Here, we report a facile strategy to immobilize an enzyme, glucose oxidase (GOx), on PCN-222(Fe) induced by electrostatic interaction in which PCN-222(Fe) serves as both a support and chemocatalyst. The immobilization was confirmed through ζ potential measurement, confocal laser scanning microscopy, Fourier transform infrared spectrometry, and UV-vis spectroscopy. This chemo-biocatalyst was applied to a cascade reaction to catalyze glucose oxidation and ABTS (ABTS = 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (or pyrogallol) oxidation. The catalytic kinetics studies show that these chemo-biocatalytic cascade reactions obey the Michaelis-Menten equation, which indicates that the cascade reactions follow the typical enzymatic dynamic regulation process. Interestingly, GOx/PCN-222(Fe) exhibits an exceptional acid-stable catalytic performance as evidenced by circular dichroism spectroscopy where no significant structure change was observed toward acidic solutions with different pH values. GOx/PCN-222(Fe) also displays desirable recyclability since no significant loss of conversion rates was found after six repeated reactions. This work presents a convenient strategy to construct metal-organic framework based chemo-biocatalysts, which may find potential applications in sensing and nanomachines.

Schistocerca piceifrons piceifrons (Orthoptera: Acrididae) as a Source of Compounds of Biotechnological and Nutritional Interest.

The Central American locust, Schistocerca piceifrons piceifrons (Walker) is a major agricultural pest in Mexico and Central America. Control measures against this pest have generated much environmental damage and substantial financial costs because chemical insecticides are used. Yet various Orthoptera species also appear to be a potential source of nutrients and a source of bioactive metabolites. Here, we studied the presence of secondary metabolites in the adult stage of S. p. piceifrons by applying different colorimetric techniques. Adults were collected from the southern region of Tamaulipas, Mexico, during September–December 2017. These samples were subjected to sequential processes of eviscerating, drying, pulverizing, extracting, and detecting of metabolites. Extractions were carried out in water, 50% ethanol, and absolute ethanol. The presence of phenolic compounds, alkaloids, tannins, saponins, flavonoids, and quantity of antioxidants against the DPPH (2, 2-diphenyl-1-picrylhydrazyl) and ABTS (2, 2′-azino-bis, 3-ethylbenzothiazoline-6-sulfonic acid) radicals were determined and reported. Proximate analysis showed that S. p. piceifrons has a high protein content (80.26%), low fat content (6.21%), and fiber content (12.56%) similar to other Orthoptera species. Chitin and chitosan contents of S. p. piceifrons were 11.88 and 9.11%, respectively; the recovery percentage of chitosan from chitin was 76.71%. Among the Orthoptera, the protein content of this pest is among the highest while its contents of chitin and chitosan are similar to those of other insect species (e.g., Bombix mori Linnaeus [Lepidoptera: Bombycidae]). Our results suggest this pest species is a potential source of bioactive compounds of biotechnological interest for use by pharmaceutical and food industries.

Enhanced transformation of sulfonamide antibiotics by manganese(IV) oxide in the presence of model humic constituents

In this study, a manganese(IV) oxide-mediator (MnO2-mediator) system for the abatement of sulfonamide antibiotics was evaluated. Two simple model humic constituents, syringaldehyde (SA) and acetosyringone (AS), could promote the transformation of sulfonamides at pH 5–8. Two additional potential mediators, tannic acid and 2,2′-azino-bis(3-ethylbenzothiazoline)-6-sulfonate (ABTS), had negligible enhancement on the transformation of sulfonamides by MnO2. The enhancing effect was attributed to the reaction of the oxidized mediator (i.e., phenoxy radical or benzoquinone-like compounds) produced from the oxidation of the mediators by MnO2 with SMX. Thereby cross-coupling products from sulfamethoxazole (SMX) with oxidized SA were formed in the MnO2-SA system, which was confirmed by liquid chromatography/electrospray ionization-triple quadrupole mass spectrometry. Coexisting metal ions (i.e., Ca(II), Mg(II) and Mn(II)) showed inhibitory effects in the order of Mn(II)> Ca(II)> Mg(II). For repetitive runs of the MnO2-SA-SMX system, MnO2 lost its oxidative capacity due to the sorption of Mn(II) on the reactive sites of the MnO2 surface. A full regeneration of partially deactivated MnO2 by oxidation of the sorbed Mn(II) with Mn(VII) could be achieved.

Anti-inflammatory and antioxidant properties of leaf extracts of eleven South African medicinal plants used traditionally to treat inflammation

Ethnopharmacological relevanceInflammation is a complex mechanism employed by the body to promote healing and restoration to normal function in the event of injury. Eleven plant species were selected in this study based on their use in traditional medicine against inflammation in South Africa. MethodsHexane, acetone, ethanol, methanol and water extracts of the powdered plants were prepared and a total of fifty-five extracts were tested for their anti-inflammatory and antioxidant activities. The anti-inflammatory activity of extracts was evaluated via the 15-lipoxygenase (15-LOX) inhibitory and the nitric oxide (NO) inhibition assays using lipopolysaccharide (LPS)-activated RAW 264.7 murine macrophages. Total flavonoid and total phenolic contents were determined. The antioxidant activity of the extracts was performed using radical scavenging DPPH (2, 2-diphenyl-1-picrylhydrazyl) and electron reducing ABTS (2, 2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) assays. ResultsThe hexane extract of Typha capensis (TC) had good lipoxygenase inhibitory activity with IC50 of 4.65 µg/mL, significantly (p < 0.05) higher than that of the positive control quercetin (IC50 = 24.60). The same extract also had good nitric oxide inhibitory activity with 86% NO inhibition and cell viability of 97% at 50 µg/mL. The TC acetone extract had the best antioxidant activity with IC50 of 7.11 and 1.91 µg/mL respectively in the DPPH and ABTS assays. Following fractionation of the TC plant material, the ethyl acetate fraction had interesting antioxidant activity and the methanol/water (35%) and hexane fractions had good 15-LOX inhibitory activity. The antioxidant and anti-inflammatory activities therefore resided in both polar and more non-polar fractions. ConclusionThe acetone extract of Typha capensis and its fractions had good anti-inflammatory and antioxidant activities, supporting the medicinal use of this species against inflammation. Other species including Ficus elastica, Carpobrotus edulis, Cotyledon orbiculata and Senna italica also had good activity worthy of further investigation.

Potential of Trametes maxima IIPLC-32 derived laccase for the detoxification of phenolic inhibitors in lignocellulosic biomass prehydrolysate

Lignin derived inhibitors have a detrimental effect on biomass hydrolysis making the use of lignocellulosic biomass irrelevant at industrial scale. Laccase mediated removal of inhibitors has generated significant interest owing to its wide range of substrate specificity, low cost and environment-friendly nature making it an appropriate choice for the biotechnology industry. In the present work, a white rot fungal strain isolated from decaying wood samples was characterized for laccase production using a dual screening approach with ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate)) and methylene blue as substrates. Extracellular laccase was purified from this strain using anion exchange chromatography and observed to have molecular mass of 70 kDA. The UV–vis spectra of the purified enzyme confirmed blue type laccase. The enzyme exhibited stability in the pH range 2–5 and temperature of 50–70 °C with ABTS. The enzyme also displayed elevated level of tolerance to inhibitors like sodium azide and dithiothreitol. Purified laccase showed Km and Kcat value of 59.73 μM and 1168 sec−1 respectively with ABTS and 16.29 μM, 84.3 sec−1 using syringaldazine as substrate respectively. The 0.1U/ml of Trametes maxima IIPLC-32 laccase removed 66% of lignin-derived soluble phenolic inhibitors from sugarcane bagasse within half hour at 5.5 pH. These properties indicate a high potential of Trametes maxima IIPLC-32 laccase for industrial applications.

Antioxidant activity of xylooligosaccharides produced from glucuronoxylan by Xyn10A and Xyn30D xylanases and eucalyptus autohydrolysates

Antioxidant activity of xylooligosaccharides (XOS) released from beechwood and birchwood glucuronoxylans by two different xylanases, one from family GH10 (Xyn10A) and another from family GH30 (Xyn30D) was examined. The ABTS (2, 2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) method was used, since it resulted more accurate for the antioxidant activity determination of XOS. Thin layer chromatography and MALDI-TOF MS analysis showed that Xyn10A produced a mixture of neutral and acidic XOS whereas the XOS produced by Xyn30D were all acidic, containing a methylglucuronic acid (MeGlcA) ramification. These acidic XOS, MeGlcA substituted, showed a strongly higher antioxidant activity than the XOS produced by Xyn10A (80% vs. 10% respectively, at 200 μg mL−1). Moreover, the antioxidant activity increased with the degree of polymerization of XOS, and depended on the xylan substrate used. The antioxidant capacity of eucalyptus autohydrolysates after xylanase treatment was also analysed, showing a decrease of their antioxidant activity simultaneous with the decrease in XOS length.

Physicochemical properties and structural characteristics of soluble dietary fibers from yellow and purple fleshed potatoes by-product

ABSTRACTWe extracted soluble dietary fiber from yellow (YSDF) and purple (PSDF) fleshed potatoes by-product to compare their physicochemical properties and structural characteristics. YSDF and PSDF showed similar monosaccharide compositions. YSDF gave a higher oil-holding capacity and swelling capacity (15.6 ± 1.1 g/g, 18.7 ± 0.8 mL/g) than PSDF (12.5 ± 0.9 g/g, 13.5 ± 1.0 mL/g). Emulsifying activity and emulsion stability of YSDF (33.8 ± 1.4 mL/100 mL and 31.5 ± 0.3 mL/100 mL, respectively) were significantly higher than those of PSDF (24.8 ± 1.1 mL/100 mL and 19.6 ± 1.8 mL/100 mL, respectively). Although PSDF showed a stronger DPPH (1,1-Diphenyl-2-picrylhydrazyl radical 2,2-Diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl) and ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate)) free radical-scavenging activities (0.18 ± 0.01 and 2.39 ± 0.20 mg Trolox/g SDF), FRAP (ferric-reducing antioxidant power) free radical-scavenging activity was similar to that of YSDF. Furthermore, molecular weight of YSDF (3967.3 Da) was lower than that of PSDF (4462.8 Da). Thermal property was different between YSDF and PSDF, and YSDF presented more rough, irregular, and porous surface. It can be concluded that SDFs from yellow fleshed potatoes are more suitable to use as fiber-rich functional ingredients.

Isolation, Synthesis, and Radical-Scavenging Activity of Rhodomelin A, a Ureidobromophenol from the Marine Red Alga Rhodomela confervoides.

A novel ureidobromophenol, rhodomelin A (1), was characterized from Rhodomela confervoides. Its structure was elucidated by spectroscopic analysis. Both enantiomers of 1 were synthesized using a convergent strategy starting from d/l-pyroglutamic acids, respectively, allowing assignment of the R-configuration for the naturally occurring isomer by chiral HPLC analysis. Rhodomelin A represents the first example of a naturally occurring ureidopyrrolidone alkaloid incorporating a γ-aminobutyric acid unit. The scavenging activity of 1 toward DPPH (1,1-diphenyl-2-picrylhydrazyl) and ABTS (2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate)) radicals was assayed.

Antioxidant, Anti-urease Activities and Genotoxic Effects of Terfezia claveryi Methanol Extracts on Human Lymphocytes

Objective: Terfezia claveryi is a dark brown color truffle and has been used extensively in human diet in Turkey. Therefore; it is an important issue to determine their biological activities and toxicity. This study aims to investigate the antioxidant and anti-urease effects of T. claveryi methanol extracts and to evaluate the genotoxicity of each extract. Methods: The antioxidant activities of methanol extracts were examined by 2,2-diphenyl-1-picryl-hydrazyl (DPPH), 2,2’-azino-bis(3-ethylbenzothiazoline-6- sulfonate (ABTS) and ferric reducing/antioxidant power (FRAP) methods. The amount of total phenolic compounds contained in the extracts was determined using the Folin-Ciocalteu reagent (FCR) method. Anti-urease activities of methanol extracts were evaluated by indophenol method. In addition, potential DNA damaging effects of T. claveryi extracts on human lymphocytes were determined by the alkaline comet assay. Results: UM extract exhibited higher DPPH radical scavenging activity than MM extract [the concentration of the substance which provides the inhibition of 50% of the radical (IC 50 ):0.77±0.01 mg/mL, 1.17±0.02 mg/mL, respectively, p <0.0001] however, lower activity than standard ( p <0.0001). Both extracts in different concentrations of T. claveryi caused DNA damage ( p <0.0001) compared with solvent control DMSO. Also, total comet scores was higher in cells which had been incubated with MM extract ( p <0.05). UM extract exhibited higher ferric reducing and anti-urease activity than MM extract but not found statistically different; also activities of both extract were found lower than positive controls of each methods ( p <0.0001). Conclusion: T. claveryi methanol extracts induced genotoxicity on lymphocytes and showed very low antioxidant activity compared to standards. This preliminary study should be confirmed with further studies and in diferent cell lines.

Sonication Effect on Bioactive Compounds of Cashew Apple Bagasse

This study describes some effects of high-power ultrasound on cashew apple bagasse. The main objective was to develop an optimized process for sonication of cashew apple bagasse, evaluating the effect of ultrasound on antioxidant compounds. To define the best conditions for sonication, a 23 factorial central composite design was used changing the independent variables: bagasse/water ratio, ultrasonic power intensity (W/cm2), and processing time (min). Antioxidant compounds such as vitamin C, β-carotene, and total phenolic compounds were determined. The total antioxidant capacity (ABTS(2,2 AZINO BIS (3-ethylbenzo thiazoline 6 sulfonic acid) diammoninum salt and DPPH (2,2-Diphenyl-1-picryl-hidrazil)) was also evaluated. A thermal treatment was carried at the highest temperature reached after sonication (51 °C) to evaluate the heat effect due to a temperature increase during processing. Sonication changed the bagasse aspect from a fibrous residue to a pleasant yellow puree. The maximal concentration of vitamin C, phenolics, and β-carotene was obtained when the processing conditions were as follows: bagasse/water ratio of 1:4 (w/w), ultrasound power intensity of 226 W/cm2, and 6 min of processing. The high total phenolic content (2186 mg of gallic acid/100 g DW), vitamin C (148 mg/100 g DW), and β-carotene (12 mg/100 g) obtained proved the sonication efficiency. The antioxidant activity determined by the DPPH and ABTS assays confirmed the suitability of ultrasound for the preparation of antioxidant-rich cashew apple bagasse puree.

Automatic evaluation of peroxidase activity using different substrates under a micro sequential injection analysis/lab-on-valve (μSIA-LOV) format

In the present work, an automatic methodology, allowing the evaluation of peroxidase activity, and the comparison of the effect of two substrates in this activity, was developed. Automation was carried out using a miniaturized micro-sequential injection analysis system, usually called μSIA-LOV (Lab-on-valve). This kind of system allows downscaling of current flow injection and sequential injection systems. For the automatic evaluation of peroxidase activity it was selected two different reactions using different substrates - 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate (ABTS) and a mixture of 4-aminoantipyrine and phenol, that were implemented in a μSIA-LOV manifold. The experimental parameters such as reagent ratios and volumes, pH, temperature and reaction time, were optimized and kept constant for the two reactions. The use of these two reactions allowed the applicability of the system in two different ranges of concentrations (up to 0.20U mL−1 when it was used ABTS and up to 0.80U mL−1 for the reaction with 4-AAP and phenol) with different sensitivities and detection limits of 1.9×10−4U mL−1 and 9.2×10−3U mL−1 (using ABTS and 4-AAP with phenol, respectively). Horseradish, ginger and avocado samples were analyzed proving that the developed methodology constitutes a robust, versatile, rapid and simple alternative for the evaluation of peroxidase activity, adapted to the actual demands of reagents economy and reduced residue production, being in good agreement with the actual recommendations of green chemistry.

Comparative study on the phenolic content, antioxidant properties and HPLC fingerprinting of the leaf extracts of Clerodendrum volubile P. Beauv

The present study aimed to investigate the phenolic contents and antioxidant properties of the various leaf extracts (methanol, ethanol, ethyl acetate) of Clerodendrum volubile. In vitro scavenging activities of the extracts were assessed against 1,1-diphenyl-2 picrylhydrazyl (DPPH), 2,2- azinobis (3-ethylbenzo-thiazoline- 6-sulfonate (ABTS) radical scavenging ability (ABTS) radicals. The reducing power ability and high-performance liquid chromatography-diode-array detector (HPLCDAD) of the extracts was also determined. The methanol extract had the highest reducing power, DPPH and ABTS radicals scavenging activities, followed by ethanol and ethyl acetate extracts. The HPLC-DAD results revealed the presence of both phenolic acids (caffeic acid, gallic acid) and flavonoids (catechin, quercetin, rutin, quercitrin, kaempferol, luteolin, apigenin) as its major bioactive polyphenolics. The difference in scavenging potential of the extracts may be due to variation in the phytoconstituents extracted using various solvents. The result suggests that the methanol leaf extract of Clerodendrum volubile could serve as a potential source of antioxidants and can be explored as a therapeutic agent in free radical induced diseases.

Proteinease inhibition, membrane stabilization, antioxidant and phytochemical evaluations of leaves, seeds and calyces of four selected edible medicinal plants

AbstractThe aqueous extracts of the edible parts of four common medicinal plants (Hibiscus sabdariffa, Telfairia occidentalis, Moringa oleifera and Ocimum gratissimum) readily consumed as food or supplements in many African settings are examined for some of their acclaimed pharmacological activities and possible potential associated risks. The classes of phytochemicals present are examined qualitatively and quantitatively, while the antioxidant activities were determined using three assays which include 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonate (ABTS) and hydrogen peroxide (H2O2) assays. The anti-inflammatory activities were also examined using proteinase inhibitory assays and red blood cell membrane stabilisation assays. Both the antioxidant and anti-inflammatory activities of the plants indicated that the plants have potentials for applications in foods and nutraceuticals that can be used for the management of various ailments and diseases. However, the consu...

Optimization of laccase production from Aspergillus flavus by design of experiment technique: Partial purification and characterization.

The present study describes isolation of laccase producing fungal strain and optimization of the process parameters by design of experiment (DOE) technique to achieve the maximum production of extracellular laccases by Aspergillus flavus obtained from natural habitat. Bromophenol blue dye and ABTS (2,2′-azinobis 3-ethyl-benzothiazoline-6-sulfonate) were used as substrates for the screening of laccase activity. Design expert 8.0.7.1 software was used to optimize culture conditions such as carbon source, nitrogen source, temperature and pH. Subsequently, optimization for inoculums size was also carried out. The optimization studies revealed that the laccase yield was highest when operated at the following conditions: carbon source – cellulose (8%), nitrogen source – peptone (2%), temperature – 35 °C, pH – 7 and inoculum of size 1.5 cm.

Structure-Functional Study of Tyrosine and Methionine Dipeptides: An Approach to Antioxidant Activity Prediction.

Quantum chemical methods allow screening and prediction of peptide antioxidant activity on the basis of known experimental data. It can be used to design the selective proteolysis of protein sources in order to obtain products with antioxidant activity. Molecular geometry and electronic descriptors of redox-active amino acids, as well as tyrosine and methionine-containing dipeptides, were studied by Density Functional Theory method. The calculated data was used to reveal several descriptors responsible for the antioxidant capacities of the model compounds based on their experimentally obtained antioxidant capacities against ABTS (2,2′-Azino-bis-(3-ethyl-benzothiazoline-6-sulfonate)) and peroxyl radical. A formula to predict antioxidant activity of peptides was proposed.

Yield potential and antioxidant activity of potatoes with coloured flesh

In the experiment yield potential and antioxidant activity (AOA) of 13 potato cultivars with different flesh colour (purple (p); red (r); yellow (y) and white (w)) were evaluated at two localities with different environmental condi tions in three years 2009–2011. Yield potential was evaluated at harvest time in physiological maturity of crop stand. The results confirm that total yield and yield of tubers > 40 mm of coloured potatoes cvs. Red Emmalie/r (68.98 t/ha), Blaue Elise/p (59.96 t/ha), Valfi/p (53.72 t/ha) were comparable with control cvs. Agria/y, Lady Balfour/w and Russet Burbank/w. Some cultivars with lower yield had share of tubers above 40 mm comparable with control cultivars (94.45% and 93.48% in case of cvs. Valfi/p and Blue Congo/p), respectively. Antioxidant activity was determined as ascorbic acid equivalent by ABTS (2,2´-azinobis (3-ethylbenzothiazoline-6-sulfonate) method. The lowest antioxidant activity was observed in the control cvs. Lady Balfour/w (ascorbic acid equivalent (AAE) 74.1 mg/kg fresh mattter (FM)), Agria/y (AAE 84.4 mg/kg FM) and Russet Burbank (AAE 93.9 mg/kg FM). In the group of cultivars with red flesh AOA was 3.2 to 5.1 times higher and in a group of purple-fleshed cultivars it was from 3.7 to 7.0 times higher.

ABTS as an Electron Shuttle to Enhance the Oxidation Kinetics of Substituted Phenols by Aqueous Permanganate.

In this study, it was, interestingly, found that 2,2'-azino-bis(3-ethylbenzothiazoline)-6-sulfonate (ABTS), a widely used electron shuttle, could greatly accelerate the oxidation of substituted phenols by potassium permanganate (Mn(VII)) in aqueous solutions at pH 5-9. This was attributed to the fact that these substituted phenols could be readily oxidized by the stable radical cation (ABTS(•+)), which was quickly produced from the oxidation of ABTS by Mn(VII). The reaction of Mn(VII) with ABTS exhibited second-order kinetics, with stoichiometries of ∼5:1 at pH 5-6 and ∼3:1 at pH 7-9, and the rate constants varied negligibly from pH 5 to 9 (k = (9.44 ± 0.21) × 10(4) M(-1) s(-1)). Comparatively, the reaction of ABTS(•+) with phenol showed biphasic kinetics. The second-order rate constants for the reactions of ABTS(•+) with substituted phenols obtained in the initial phase were strongly affected by pH, and they were several orders of magnitude higher than those for the reactions of Mn(VII) with substituted phenols at each pH. Good Hammett-type correlations were found for the reactions of ABTS(•+) with undissociated (log(k) = 2.82-4.31σ) and dissociated phenols (log(k) = 7.29-5.90σ). The stoichiometries of (2.2 ± 0.06):1 (ABTS(•+) in excess) and (1.38 ± 0.18):1 (phenol in excess) were achieved in the reaction of ABTS(•+) with phenol, but they exhibited no pH dependency.

A comparative study of the capsaicinoid and phenolic contents and in vitro antioxidant activities of the peppers of the genus Capsicum: an application of chemometrics

This paper presents a comparison of the contents of capsaicin, dihydrocapsaicin and total phenolics as well as of the antioxidant activities of six types of peppers of the genus Capsicum. The varieties were analyzed in terms of their in vitro antioxidant activity using ferric reducing antioxidant powder (FRAP), 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2'-azinobis 3-ethylbenzothiazoline 6-sulfonate (ABTS(●+)) assays. The contents of phenolics and capsainoids as well as the antioxidant activities were higher in seeds than in pulps. The correlations (ρ < 0.01) between the phenolic composition and the capsaicinoids levels were high (r = 0.98). Similarly high were also the correlations between the antioxidant activities and the contents of total phenolics and capsaicinoids. Data were analyzed using principal component analysis (PCA), hierarchical cluster analysis (HCA) and multiple linear regression (MLR). PCA explained 97.77% of the total variance of the data, and their separation into three groups in a scatter plot was divised. Using HCA, three clusters were suggested. Cluster one, formed by pulps (bell pepper, orange habanero, cayenne, dedo de moça and red habanero), showed the lowest levels of the compounds quantified. Most seed samples were grouped in cluster two (bell pepper, cayenne, dedo de moça and malagueta) together with malagueta pulp. Cluster three was formed by orange and red habanero seeds, which showed the highest levels of all compounds analyzed. The MRL revealed that the values of capsaicinoids and total phenols are more adequate to predict the antioxidant activity measured by the FRAP assay.