Rapid assessment of endpoint antioxidant capacity of red wines through microchemical methods using a kinetic matching approach.

Antioxidant capacity of food samples is usually assessed by different analytical methods, however the results attained even for the same method are strongly dependent on the selected reaction time and also on the standard compound used. To tackle this problem, we propose here a kinetic matching approach, associated to the conversion of results into equivalents of a common standard compound, as a universal way for expression of results. The methodology proposed was applied to methods based on different chemistries (Folin-Ciocalteu (F-C), CUPRAC, DPPH(•) and ABTS(•+) assays) and red wines (n=40) were chosen as a model of complex food sample. For implementation of the kinetic matching approach, the standard phenolic mixture (caffeic acid, (+)-catechin, hesperetin, morin and (-)-epigallocatechin gallate) was chosen for calibration in F-C, CUPRAC and DPPH(•) assays, while tannic acid was suitable for ABTS(•+) assay. Results showed that, for all methods, there was no statistical difference between results attained by the kinetic matching approach (after <10 min of reaction) and that at endpoint conditions (after 60 to 300 min). The repeatability and the reproducibility of the kinetic matching approach was <4.5%, for all antioxidant assays. The sample throughput increases from <18 (endpoint measurements) to >108 h(-1) using the proposed kinetic approach. Moreover, we have established here a way of converting results to equivalents of a common standard, providing values independent of its kinetic profile, by using the ratio between calibration sensitivities performed at endpoint conditions.