Automated electrochemical determination of beer total antioxidant capacity employing microdialysis online-coupled with amperometry

Abstract

Electrochemical techniques are rarely applied for the evaluation of total antioxidant capacity of beers due to severe electrode inactivation (fouling) by adsorbed oxidation products of the species present in the samples. In this work, we show that microdialysis online-coupled with amperometry is suitable for beer analysis, permitting also an assay automation. The working electrode of the amperometric detector employs a carbon fiber microelectrode that is regenerated between the analyses by short (1 sec) rapid (50 Hz) sinusoidal potential cycling between 0 and 2.9 Vvs Ag/AgCl. This step, along with the sample cleanup by microdialysis effectively removes electrode fouling. The suitability of this approach for beer analysis was studied using eight different beers produced by international manufacturers. The results were compared with standard Kaneda diphenylpicrylhydrazil (DPPH) assay. Steady state currents, obtained at 600 mV vs Ag/AgCl correlate well with the results obtained with Kaneda method and thus can be used for quantification of beers' antioxidant capacities. HPLC-ED of microdialysates with and without DPPH treatment were employed to get an insight into DPPH reactivity with beer components.