Characterization of commercial enological tannins and its effect on human saliva diffusion

Abstract

Commercial oenological tannins (TECs) are widely used in the wine industry. TECs are rich in condensed tannins, hydrolyzable tannins or a mixture of both. Wine grapes are a important source of proanthocyanidins or condensed tannins while oak wood possess a high concentration of hydrolyzable tannins (Obreque-Slier et al., 2009). TECs contribute with the antioxidant capacity of wine, catalyze oxide-reduction reactions and participate in the removal of sulfur compounds and metals. One of the most important properties of TECs correspond to its contribution to the astringency (Zamora, 2003). Astringency, a sensation that is described as a puckering, rough, or drying mouth-feel, has been associated with interactions between some phenolic compounds (tannins) and salivary proteins (Bacon and Rhodes, 2000). A wide spectrum of enological tannins is now available on the market, classified mainly according to the enological properties. However, the tannins’ chemical nature is not always clearly defined. Furthermore, the effect of these on saliva is unknown. For that reason, the aim of this work was the chemical characterization of eleven commercial tannins sold for enological use. Likewise, we examined the effect of TECs on a physicochemical property of the salivary protein, namely, the mode of diffusion on cellulose membranes (Obreque-Slier et al., 2010). In this study, eleven enological tannins were characterized by classification into three groups according HPLC-DAD chromatography and spectroscopic analysis: enological products composed of proanthocyanidins, hydrolyzable, and the mixture of both types of tannins. Within each group, tannin composition varied greatly, mainly defined by the botanical origin of each commercial product. Similarly, when saliva was mixed with aliquots of increasing concentrations of TECs, we observed a progressive decrease in the blue-stained background of the distribution area of the salivary protein. The intensity of this restriction was in close relationship with the type of TECs. Finally, it was observed that certain TECs do not showed a effect on saliva diffusion on cellulose membranes.

References 1.- Bacon J., Rhodes M. 2000. Binding affinity of hydrolyzable tannins to parotid saliva and to proline-rich proteins derived from it. J Agric Food Chem 48, 838-843. 2.- Obreque-Slier E., Peña-Neira A., López-Solís R., Ramírez-Escudero C., Zamora-Marín F. 2009. Phenolic characterization of commercial enological tannins. Eur Food Res Technol 229, 859-866. 3.- Obreque-Slier E., Peña-Neira A., López-Solís, R. 2010. Quantitative determination of interactions between a tannin and a model protein using diffusion and precipitation assays on cellulose membranes. J Agric Food Chem 58, 8375-8379. 4.- Zamora, F. 2003. Elaboración y crianza del vino tinto: Aspectos científicos y prácticos. Madrid, España. Ediciones Mundi Prensa. 225p. Acknowledgments This study was supported by grant Fondecyt-Chile 1150240.