Complex Coulometric Evaluation of the Antioxidant Properties of Beer

Abstract

The reactivity of coulometric titrants (bromine, iodine, and hexacyanoferrate(III) ions) with respect to the antioxidants (AOs) of beer is evaluated. It is shown that electrogenerated iodine interacts with ascorbic acid and sulfur-containing compounds, but does not oxidize phenolic AOs. The stoichiometric coefficients of reactions of phenolic AOs with electrogenerated bromine and hexacyanoferrate(III) ions are found. A comprehensive assessment of the antioxidant properties of beer is carried out through overall antioxidant parameters (total antioxidant capacity (TAC) according to the reaction with electrogenerated bromine, ferric reducing power (FRP) according to the reaction with electrogenerated hexacyanoferrate(III) ions, and oxidation by). Sixteen samples, differing in the type of fermentation, variety, and style, are considered. A statistically significant difference between the parameters for individual samples is shown. The TAC and FRP of beer correlate with the total concentration of phenolic compounds and antioxidant activity (r = 0.7175–0.8703 at rcrit = 0.4973), which confirms the correctness of the results obtained using coulometric titration. Differences in the overall antioxidant parameters of the top-fermented and bottom-fermented beers, as well as filtered and unfiltered light and dark beers, are statistically insignificant (p = 0.10–0.82). The change in the overall antioxidant parameters of beer during storage in air is evaluated.