Research background. The objective of this paper is to introduce an instrumentally simple analytical tool for determination of cocoa solids content in chocolates. This electroanalytical method is based on amperometric oxidation of all present antioxidants in chocolates at boron-doped diamond electrode (BDDE) that is integrated in a flow injection analysis (FIA) wall-jet electrode system. Experimental approach. As part of optimisation, thirteen commonly occurring antioxidants were investigated using cyclic voltammetry at BDDE in 0.1 mol/L phosphate buffer with different methanol (MEOH) content. Working parameters, such as of MeOH content, flow rate, and detection potential, were optimised. Principally, the height of the oxidation peak (current response) representing the oxidation of the sum of antioxidants (Total Antioxidant Content; TAC) was expressed as Trolox content. Results and conclusions. For analytical purpose, a linear range from 5.0 to 100 mg/L Trolox described by regression equation and characterized by correlation of determination 0.9994 was found. Obtained high positive correlation between determined values of Trolox equivalent antioxidant capacity (TEAC) and cocoa contents characterised by correlation coefficient of 0.9187 for eight randomly selected samples (one white, two milk, and five dark chocolates) confirmed the fact that cocoa solids represent the main source of antioxidants (reducing agents). Novelty and scientific contribution. The research demonstrates that TEAC values could be probably considered as additional marker of cocoa content in the chocolate analysis to commonly used theobromine (authenticity of food products). The developed FIA method could therefore serve as simple analytical tools in the food quality control.

This review highlights the progress made in recent years on biosensors aimed at detecting relevant analytes/markers of food peroxidation. Starting from the basic definition of biosensors and the chemical features of peroxidation, here we describe the different approaches that can be used to obtain information about the progress of peroxidation and the efficacy of antioxidants. Aptamers, metal–organic frameworks, nanomaterials, and supported enzymes, in conjunction with electrochemical methods, can provide fast and cost-effective detection of analytes related to peroxidation, like peroxides, aldehydes, and metals. The determination of (poly)phenols concentrations by biosensors, which can be easily obtained by using immobilized enzymes (like laccase), provides an indirect measure of peroxidation. The rationale for developing new biosensors, with a special focus on food applications, is also discussed.

The electrochemical responses of chlorophenols can be effectively enhanced by using the surfactant cetyltrimethylammonium bromide (CTAB) in combination with a carbon paste electrode (CPE). The influence of CTAB on the electrochemical behavior of hydroquinone, phenol, 2-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, p-chloro-m-cresol and pentachlorophenol at the CPE was investigated in the phosphate buffer solution (pH 7). The concentration of CTAB affecting the electrochemical reaction of phenols was examined and the optimal concentration was 0.2 mM. In this research we have applied electrochemical methods, such as cyclic voltammetry and differential pulse voltammetry (DPV). The CPE modified with CTAB in DPV increased signal intensity for chlorophenols by around 5 to 13 times and was successfully applied to determination of chlorophenols in soil samples.

An Erratum to this paper has been published: https://doi.org/10.1134/S1061934821340013