Tannins from Different Parts of the Chestnut Trunk (Castanea Sativa Mill.): a Green and Effective Extraction Method and Their Profiling by High-Performance Liquid Chromatography-Diode Array Detector-Mass Spectrometry

Chestnut wood is a rich source of hydrolyzable tannins, which include gallotannins and ellagitannins, such as castalin, vescalin, castalagin, and vescalagin. The study was aimed to improve knowledge on hydrolyzable tannins from chestnut wood, evaluating the extraction process, the curing time of wood, and the composition of the dry tannin extracts. Different extraction conditions (e.g., wood-chips/solvent ratio and temperature) were evaluated, and more than 50 ellagitannins and gallotannins were tentatively identified by HPLC-MS. The highest yields in tannins on dried matter were obtained for the samples with the higher curing time by the extraction carried out at 100 °C (maximum applied temperature). The extracts of different chestnut samples extracted at 100 °C showed a high content of total tannins, with values determined by HPLC-DAD ranging between 19.6 and 25.6% of the dry extract. The values of total tannin content determined using both the HPLC-DAD and the Folin-Ciocalteu methods, both expressed as gallic acid, were compared and correlated, and a multiplication factor of 3.25 was proposed. The use of this factor is a simple way to convert nonhomogeneous quantitative results on tannin concentration in chestnut wood present so far in the literature.