RESUMO
The electrochemical behavior of Saccharomyces cerevisiae sp was studied using a glassy carbon electrode (GCE) modified with Nafion-dispersed oxidized multi-walled carbon nanotubes (OMWCNT). The morphology was studied using scanning electron microscopy (SEM), showing that the yeast sticks to the carbon nanotube surface instead of the glassy carbon surface. The redox couple Fe(CN)6 4-/Fe(CN)6 3- was used to determine the electroactive area and the heterogeneous transfer constant, which increased 80.5% and 108% respectively by the presence of nanotubes. The studies of the pH effect showed that the anodic potential decreases at alkaline pH and that the highest current intensity occurs at a pH value of 7.00. Studies of the scan rate effect have shown that yeast oxidation is an irreversible mixed control process in which two electrons participate. The relationship between yeast concentration and the anodic current density was studied using different electrochemical techniques obtaining the best analytical parameters through chronoamperometry. The linear range was between 3.36 and 6.52 g L-1, the limit of detection (LOD) and the limit of quantification (LOQ) were 0.98 g L-1 and 3.36 g L-1 respectively, and the sensibility obtained was 0.086 µA L g-1 mm-2. These results show that the multi-walled carbon nanotubes in water and Nafion® allow obtaining an anodic signal corresponding to the yeast, which facilitates its quantification through electrochemical methodologies, favoring the reduction of analysis times and costs compared with other techniques.
RESUMO
The antioxidant capacity in mango (pulp, peel, and seed) was measured using spectrophotometric and electrochemical methods in order to make traditional methods comparable with electrochemical ones, using reference standards Gallic Acid and Trolox. ABTS, DPPH, Total polyphenols, and electrochemical index were evaluated. In order to present the electrochemical results in a more comparable way, the voltammetric charge (using Differential pulse voltammetry) was used. Spectrophotometric methods allowed to determine the difference in contents of metabolites with antioxidant capacity, except in peel and seed, while the electrochemical method separated the three extracts and is not affected by interferences. Spectrophotometric methods present a good correlation with electrochemical methods, using the same reference standards, therefore, a better comparison between methods is possible.
Assuntos
Antioxidantes/química , Mangifera/química , Técnicas Eletroquímicas , Frutas/química , Frutas/metabolismo , Ácido Gálico/química , Mangifera/metabolismo , Extratos Vegetais/química , Polifenóis/química , Sementes/química , Sementes/metabolismo , EspectrofotometriaRESUMO
The growing interest in functional foods had led to the use of analytical techniques to quantify some properties, among which is the antioxidant capacity (AC). In order to identify and quantify this capacity, some techniques are used, based on synthetic radicals capture; and they are monitored by UV-vis spectrophotometry. Electrochemical techniques are emerging as alternatives, given some of the disadvantages faced by spectrophotometric methods such as the use of expensive reagent not environmentally friendly, undefined reaction time, long sample pretreatment, and low precision and sensitivity. This review focuses on the four most commonly used electrochemical techniques (cyclic voltammetry, differential pulse voltammetry, square wave voltammetry and chronoamperometry). Some of the applications to determine AC in foods and beverages are presented, as well as the correlation between both spectrophotometric and electrochemical techniques that have been reported.