Characterization of 37 enological tannins using a multiple technique approach: Linear sweep voltammetry as a rapid method both for classification and determination of antioxidant properties

Abstract

In this work, 37 enological tannins of different classes were studied to investigate whether linear sweep voltammetry (LSV) could be a method to determine the family of a sample and its antioxidant capacity. A "wholistic" approach was used, combining LSV data with nuclear magnetic resonance (NMR), polyphenol quantification (Folin-Ciocalteu method and gravimetric analysis), antiradical activity (DPPH assay), and reducing capacity (FRAP assay). Voltammetric data were processed with statistical techniques and the results show the clustering of tannins in three different classes: ellagitannins, gallotannins, and condensed tannins. These findings were confirmed by NMR data treated with the same procedure. Finally, ellagitannins showed a high reducing capacity and gallotannins showed a high antiradical capacity. Importantly, LSV indices were shown to be significantly correlated with DPPH and FRAP parameters. Therefore, the hypothesis of LSV as a potentially useful technique to choose the most suitable tannin for a determined antioxidant purpose was successfully proved.

Keywords: Antioxidant capacity; Linear sweep voltammetry; Nuclear magnetic resonance; Principal component analysis; Tannin.