Equilibrium and extraction kinetics of tannins from chestnut tree wood in water solutions

Tannins are natural water-soluble products, characterized by a phenolic structure and the ability to bind and precipitate proteins. They are widely found in natural products, and their 'historical' utilization was in tanning animal hides into leather. Nowadays, tannins are extensively used in the food and beverage industry and in pharmaceutical and nutraceutical industries for their positive effects on human health. In conventional processes, tannins are extracted from vegetable material by using water as a solvent in a temperature range of 40-90 degrees C; other polyphenols are always extracted and classified as nontannins. The scope of this work is to characterize chestnut tree wood in terms of the total extractable tannins. To this aim, analytic methods, reported in the literature, for the quantitative determination of these compounds in aqueous solution of unknown composition have been assessed. Experimental data on equilibrium distribution of tannins between solid (wood) and liquid (water) at a temperature of 80 degrees C are presented. The obtained results have been correlated by means of the Freundlich isotherm. Experimental data are also reported on the extraction kinetics of tannins from the solid phase. Experimental extraction curves were simulated by a plug flow model, and an overall mass transfer coefficient was evaluated. (C) 2010 Curtin University of Technology and John Wiley & Sons, Ltd.