1,721,064 research outputs found
A deeper insight into the oxidative mechanism of caffeine and related xanthines: may caffeine be considered as an antioxidant?
No full textCaffeine (CAF) is present in many consumer products as coffee, tea, chocolate, soft and energy drinks, resulting the most widely consumed psychoactive substance in human dietary. Many of its physiological effects are well known. Recently, antioxidant properties have been suggested for CAF that seems showing protective effects against oxidative stress (OS).Inert to hydrogen (H)/electron (E) scavengers as ABTS·+ and DPPH, CAF has been proposed as an excellent HO· scavenger.
The oxidative path of CAF in aqueous medium has been widely studied since 70s4, but until today the mechanism through which CAF and related xanthines might exert their antioxidant activity is not fully understood.
The electrochemical oxidation of CAF, theobromine (TBr) and theophylline (TPh) was studied in aprotic medium by ciclyc voltammetry and controlled potential electrolysis carried out in UV cell modified for spectroelectrochemistry, to investigate on the radical intermediates involved in the primary oxidative process and their possible fate. The chemical oxidation of the same xanthines was carried out with PbO2, superoxide radical anion and galvinoxyl free radical and reactions were monitored via UV spectrophotometry, to investigate on the reactivity towards reactive oxygen species (ROS).
Antioxidant activity based on electron transfer (ET) and/or H-atom transfer (HT) mechanisms was evaluated
Recovery of natural antioxidants from spent coffee grounds
No full textSpent coffee grounds (SCG) were extracted with an environmentally friendly procedure and analyzed to evaluate the recovery of relevant natural antioxidants for use as nutritional supplements, foods, or cosmetic additives. SCG were characterized in terms of their total phenolic content by the Folin-Ciocalteu procedure and antioxidant activity by the DPPH scavenging assay. Flavonoid content was also determined by a colorimetric assay. The total phenolic content was strongly correlated with the DPPH scavenging activity, suggesting that phenolic compounds are mainly responsible for the antioxidant activity of SCG. An UHPLC-PDA-TOF-MS system was used to separate, identify, and quantify phenolic and nonphenolic compounds in the SCG extracts. Important amounts of chlorogenic acids (CGA) and related compounds as well as caffeine (CAF) evidenced the high potential of SCG, a waste material that is widely available in the world, as a source of natural phenolic antioxidants. © 2013 American Chemical Society
Evaluation of the antioxidant activity of Flavonoids by "Ferric Reducing Antioxidant Power" assay and cyclic voltammetry.
No full textFlavonoids, naturally occurring phenolic compounds, have recently been studied extensively for their antioxidant properties. The structure–antioxidant activity relationships (SAR) of flavonoids have been evaluated against different free radicals, but bferric reducing antioxidant powerQ (FRAP) assay, which determines directly the reducing capacity of a compound, has not been used for this purpose. In this study, the antioxidant activities of 18 structurally different flavonoids were evaluated by FRAP assay modified to be used in 96-well microplates. Furthermore, their oxidation potentials were also measured, which were in the range of +0.3 V (myricetin) to +1.2 V (5- hydroxy flavone) and were in good agreement with FRAP assay results. Quercetin, fisetin and myricetin had the lowest oxidation potentials and appeared the most active compounds in FRAP assay and were 3.02, 2.52 and 2.28 times more active than Trolox, respectively. Indications were found that the o-dihydroxy structure in the B ring and the 3-hydroxy group and 2,3-double bond in the C ring give the highest contribution to the antioxidant activity
Determination of caffeine @ gold nanoparticles modified gold (Au) electrode: a preliminary study
No full textCaffeine is a natural alkaloid exerting many physiological effects,
such as stimulation of the central nervous system, diuresis and
gastric acid secretion. It is widely distributed in plant products and
beverages and its quantification is mainly of pharmaceutical and
alimentary concern. In this paper, we describe an electrochemical
study based on the modification of a gold electrode (Au) surface by
deposition of functionalized gold nanoparticles by Cyclic Voltammetry
(CV). The oxidation system is characterized by an anodic peak in the
positive-going step and by the absence of any cathodic peak on the
reverse scan, indicating that the oxidation is irreversible. At the
modified electrode, the voltammetric peak height increases vs. that
@ the bare one, depending on the nanoparticles functionalization.
The best performances were observed @ Au electrode modified with
colloidal gold nanoparticles (AuNPs) stabilized into a chitosan matrix.
In order to optimize the influence of different electrolytes on the
sensor response, different electrolytic solutions (nitric acid, sulfuric
acid, phosphoric acid and hydrochloric acid) were used. The
electrochemical behavior of caffeine was also studied in aprotic
medium with the aim to clear up the different mechanisms the
oxidative process occurs through in aqueous and in aprotic medium
Cyclic Voltammetry, spectroelectrochemistry and electron spin resonance as combined tools to study thymoquinone in aprotic medium
No full textIs coffee silverskin actually a suitable source of either food supplements or additives? UPLC-PDA-ESI-TOF/MS metabolic profiling of aqueous extracts: natural antioxidants vs phytotoxins
No full textIn the last decades coffee has been widely recognized as an important source of antioxidants and radical scavengers, with increasing evidence supporting its health-promoting potential. Many of these benefits are ascribed to chlorogenic acids (CGAs) contained in coffee beans. A growing interest in the valorization of coffee wastes like spent coffee grounds and by-products like Silverskin (SS) is justified by their richness in polyphenols. As a consequence of the increasing consumption of Green Coffee (GC) as antioxidant-rich dietary supplement, concern has been expressed about its use as food additive or supplement. In fact, atractyligenin and its derivatives, compounds structurally related to the phytotoxin atractyloside, have been recently extracted from raw coffee and their phytotoxic activity has been evaluated. A deeper knowledge about the presence of such compounds also in SS, is supported by the recent interest in the use of SS as a source of food additives or dietary supplements. In this contribution, the UPLC-PDA-ESI-TOF/MS metabolic profiles of SS aqueous extracts of different coffee varieties have been determined and compared to that of GC. Atractyligenin, carboxyatractyligenin and five glucosyde derivatives were identified. In contrast to GC, where only atractyligenin glucopyranosyl derivatives were detected, in all SS also the aglycones were identified and their content was higher in Arabica than in Robusta. Compared to GC, GPCA reaches higher concentration in Arabica and comparable concentration in Robusta SS. Interestingly, the content of CGA in aqueous extracts of SS is reversed compared to atractyligenin derivatives. Moreover, an atractyligenin derivative not previously detected in GC, has been detected in GC. Concluding, the use of SS as food or dietary supplements needs careful evaluation and further and adequate controls on SS raw material are necessary in order to assess its suitability as functional ingredient for food or nutraceutical products
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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