Assessment of the Antioxidant Activity of Catechin in Nutraceuticals: Comparison between a Newly Developed Electrochemical Method and Spectrophotometric Methods

Abstract

The analysis of antioxidants in different foodstuffs has become an active area of research, which has led to many recently developed antioxidant assays. Many antioxidants exhibit inherent electroactivity, and, therefore, the use of electrochemical methods could be a viable approach for evaluating the overall antioxidant activity of a matrix of nutraceuticals without the need for adding reactive species. Green tea is believed to be a healthy beverage due to a number of therapeutic benefits. Catechin, one of its constituents, is an important antioxidant and possesses free radical scavenging abilities. The present paper describes the electrochemical properties of three screen-printed electrodes (SPEs), the first one based on carbon nanotubes (CNTs), the second one based on gold nanoparticles (GNPs) and the third one based on carbon nanotubes and gold nanoparticles (CNTs-GNPs). All three electrodes were modified with the laccase (Lac) enzyme, using glutaraldehyde as a cross-linking agent between the amino groups on the laccase and aldehyde groups of the reticulation agent. As this enzyme is a thermostable catalyst, the performance of the biosensors has been greatly improved. Electro-oxidative properties of catechin were investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV), and these demonstrated that the association of CNTs with GNPs significantly improved the sensitivity and selectivity of the biosensor. The corresponding limit of detection (LOD) was estimated to be 5.6 × 10−8 M catechin at the CNT-Lac/SPE, 1.3 × 10−7 M at the GNP-Lac/SPE and 4.9 × 10−8 M at the CNT-GNP-Lac/SPE. The biosensors were subjected to nutraceutical formulations containing green tea in order to study their catechin content, using CNT-GNP-Lac/SPE, through DPV. Using a paired t-test, the catechin content estimated was in agreement with the manufacturer’s specification. In addition, the relationship between the CNT-GNP-Lac/SPE response at a specific potential and the antioxidant activity of nutraceuticals, as determined by conventional spectrophotometric methods (DPPH, galvinoxyl and ABTS), is discussed in the context of developing a fast biosensor for the relative antioxidant activity quantification.

Sensitive Detection of Hydroxytyrosol in Extra Virgin Olive Oils with a Novel Biosensor Based on Single-Walled Carbon Nanotubes and Tyrosinase

“…Galvinoxyl is reduced by scavenging hydrogen donor free radicals as shown in reaction (3) [ 78 ]: G· + IH → GH + I· where G· is galvinoxyl; GH is reduced galvinoxyl; IH is a hydrogen donor free radical scavenger, in this case, HT; and I· is the corresponding radical of IH.…”

Extraction and Purification of Catechins from Tea Leaves: An Overview of Methods, Advantages, and Disadvantages

“…One commonly used technique, because of its cost-effectiveness and simplicity, is solvent extraction, where the plant material or tea leaves are immersed in a suitable solvent that can form hydrogen bonds with catechins, such as ethanol or water, to dissolve them. Afterward, the solvent is evaporated, leaving a concentrated extract containing catechins, which can then undergo further purification steps [23,24].…”

Chemical Composition, Antioxidant Potential, and Nutritional Evaluation of Cultivated Sorghum Grains: A Combined Experimental, Theoretical, and Multivariate Analysis

“…The ABTS assay is a widely used spectrophotometric method for the evaluation of antioxidant capacity, based on the quenching of a stable-colored radical (ABTS •+ ), indicating the radical scavenging ability of antioxidants. The ABTS assay was performed using the method described by Munteanu and Apetrei, with slight modifications [ 34 ]. Briefly, the ABTS •+ reagent was prepared by mixing equal volumes of 5 mM ABTS and 2.45 mM K 2 S 2 O 8 solution.…”