Oxygen consumption by diferent oenological tanins in a model wine solution

Abstract

Oenological tannins are widely used in winemaking to improve some characteristics of wines [1] being the antioxidant properties probably one of the main reasons [2]. However, commercial tannins have different botanical sources and chemical composition [3] which probably determines different antioxidant potential. There are some few references about the antioxidant properties of commercial tannins [4] but none of them have really measured the direct oxygen consumption by them. The aim of this work was to measure the kinetics of oxygen consumption by different commercial tannins in order to determine their real capacities to protect wine against oxygen. MATERIAL AND METHODS: 4 different commercial tannins were used: T1: condensed tannin from grape seeds, T2: gallotannin from chinese gallnuts, T3: ellagitannin from oak and T4: tannin from quebracho containing condensed tannins and ellagitannins. All tannins were dissolved at different concentration in a model wine solution. The samples were placed in clear glass bottles into which a pill had been inserted (PreSens Precision Sensing GmbH) for the non-invasive measurement of dissolved oxygen by luminescence (NomasenseTM O2 Trace Oxigen Analyzer). The different solutions were saturated in oxygen by bubbling with air for 10 minutes. Once the bottles had been closed with a crown cap and bidule, oxygen was measured periodically [5]. RESULTS: The obtained results were used to develop a kinetic model in order to parameterize and compare the oxygen consumption rates of the different oenological tannins. Using this kinetic model it was possible to determine the average initial oxygen consumption rate (OCR) for the different commercial tannins. These results indicate that ellagitannins from oak (T3) are clearly the most effective as antioxidant with an OCR of 193.0 µg of O2/hour. Condensed tannins from grape seeds (T1) showed a OCR quite much lower (27.1 µg of O2/hour). In turn, tannins from quebracho (T4) showed an OCR intermediate between T3 and T1 (66.5 µg of O2/hour) which is quite logical since tannins from this botanical source contains ellagitannins and condensed tannins. Finally, gallotannins from chinese gallnuts (T2) showed the lowest OCR (6.9 µg of O2/hour). CONCLUSIONS: Ellagitannins have a capacity for oxygen consumption far greater than condensed tannins and especially than gallotannins. Consequently, ellagitannins are among the oenological tannins which are better able to protect the wine from oxidation.

REFERENCES: [1] Zamora F. (2003) Enólogos, 25, 26-30 [2] Versari, A., du Toit, W., Parpinello, G.P. (2013). Aust. J. Grape Wine Res., 19, 1-10. [3] Obreque-Slíer ; E., Peña-Neira, A., López-Solís , R., Ramírez-Escudero, C., Zamora, F. (2009) Eur Food Res Technol, 229, 859-866 [4] Magalhaes, L.M., Ramos, I.I., Reis, S., Segundo, M.A. (2014) Aust. J. Grape Wine Res., 20, 72-79. [5]Diéval, J.B., Vidal, S., Aagaard, O. (2011). Packag. Technol. Sci., 24, 375-385.