Automatic flow system for sequential determination of ABTS*+ scavenging capacity and Folin-Ciocalteu index: a comparative study in food products.

In the present work, an automatic flow procedure for the sequential spectrophotometric determination of Folin-Ciocalteu reducing capacity (FC assay) and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS*+) scavenging capacity expressed as the trolox equivalent (TEAC assay) is proposed for a comparative study of antioxidant properties in food products. Exploiting the flexibility of flow management associated to the computer control offered by multisyringe flow injection analysis, both methodologies were carried out in the same manifold using gallic acid and trolox as standard compounds. The proposed system configuration allowed the performance of each method separately or in tandem, providing 24 determinations per hour, which accounts for its application in routine analysis. The present methodology was applied to a large number of beverages (n=72), namely red and white wines, herbal and tea infusions, juices and beers. The results obtained showed that FC reducing capacity and TEAC values of red wines were significantly different from those obtained for the other beverages, while tea infusions provided significantly higher TEAC values when compared to white wines, herbal infusions, juices and beers. A good correlation was found between TEAC and FC reducing capacity (R>0.9) for red wines, herbal and tea infusions, and beers. For these beverages, similar slope values were found (106-140 mg L(-1) of gallic acid per mM of Trolox), except for beers that showed a higher response for FC assay. These results provided evidence that the correlation between these assays vary according to the type of sample, reinforcing the idea that more than one method should be used for evaluation of antioxidant capacity.