Lab-on-valve combined with a kinetic-matching approach for fast evaluation of total antioxidant capacity in wines

Abstract

The ABTS˙⁺ assay, based on reduction of the 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulphonate) radical cation, has been automated using flow injection based methods, but biased results are often obtained because the scavenging reaction is not complete upon detection, providing underestimated antioxidant values for samples containing slow reacting compounds. In this work a mesofluidic lab-on-valve (LOV) system was developed to provide fast determination of total antioxidant capacity in a miniaturized fashion. The sample volume was downscaled to 1 μl, with consumption of 97 μl of ABTS (6.8 nmol) per assay. Total antioxidant capacity values for red wines were attained in <1 min by application of the kinetic matching approach, using tannic acid as standard. Calibration curves were linear between 2.5 and 12.5 μM of tannic acid, with a determination throughput of 36 h⁻¹. No statistical difference was found for Trolox equivalent antioxidant capacity (TEAC) values obtained using either an end-point batch-wise microplate method (reaction time of 300 min) or the proposed LOV method.