Relation between phenolic content, antioxidant capacity, oxygen consumption rate of diverse tannins

Abstract

The work was aimed at comparing some analytical methods used to characterize oenological tannins and the measure of oxygen consumption rate (OCR), in order to provide oenologists with a rapid method to test the antioxidant capacity of tannin based products and a tool to choose the best suited product for each purpose. Seven tannins with different botanical origin were studied by determining the polyphenolic content (Folin-Ciocalteau assay, GAE%; Total Polyphenols Index, TPI%; Phloroglucinolysis, CT%), antiradical activity (DPPH), reducing capacity (FRAP), redox properties (Linear Sweep Voltammetry, LSV). The OCR was measured with a noninvasive luminescence-based technology in an oxygen saturated model wine solution, containing transition metals and metabisulphite to better simulate the oxidative conditions. The results showed a high variability in polyphenolic content due to the botanical origin of tannins. The OCR determined over 21 days was described by quadratic equations, with coefficients varying with the dose and botanical origin of tannins and with SO2 concentration. The tannins ranked differently for antioxidant capacity, depending on the kind of test. The OCR was correlated with the LSV and FRAP indexes. The Factor Analysis of data distinguished three causes of variability between tannins (3 Factors) and the analytical parameters describing them: 1) the richness in polyphenols (First Factor, explaining the 34.02% of the total data variability), described by GAE%, TPI%, DPPH; 2) the tannin typology (Second Factor, 27.4%), described by LSV and CT%; 3) the oxygen consumption rate (Third Factor, 30.00%), described by OCR, LSV, FRAP.