Tannins Extraction from Walnuts Residues

Tannins are natural water-soluble products, characterized by a phenolic structure and by the ability to bind and precipitate proteins. They are widely found in natural products, and their "historical" utilization was to convert animal hides into leather. Nowadays tannins are extensively used in food and beverage industry and in pharmaceutical and nutraceutical industry for their positive effects on human health. In conventional processes tannins are extracted from vegetable material by using water as solvent in a temperature range from 40 to 90 degrees C; other polyphenols are always extracted and are classified as non tannins. Scope of this work is to characterize residue (in particular the woody septum) of walnut core in terms of total extractable tannins. To this aim chemical analytic methods, reported in the literature, for the quantitative determination of these compounds in aqueous solution of unknown composition have been assessed. Total extractable tannins in woody septum have been determined by means of an experimental procedure developed in previous works focused on tannins extraction from chestnut wood. The evaluation of extractable tannins is very important to determine the feasibility of a process to extract tannins from this type of residue. Furthermore experimental data on equilibrium distribution of tannins between solid (woody septum) and liquid (water) at temperature of 80 degrees C have been collected. The obtained equilibrium data have been correlated by means of a linear adsorption isotherm.