Characterization of tannin extracts derived from the bark of four tree species by HPLC and FTIR

The objective of this work was the extraction and quantification of tannins obtained from the bark of four tree species from the forests of Ixtlan de Juarez, Oaxaca, Mexico (Arbutus xalapensis Kunth., Prunus serotina Ehrh., Quercus crassifolia Humb. and Bonpl., and Quercus laurina Humb. and Bonpl.), In this extraction process, 90% ethanol was used as solvent at an extraction temperature of 70 degrees C for 2 h. The quantification of phenolic compounds, condensed tannins, and percentage of total extract, were obtained using the Stiasny number. The total extracts were 12.87, 16.38, 19.31, and 25.68% for P. serotina, Q. laurina, Q. crassifolia, and A. xalapensis, respectively. The condensed tannins were characterized by Fourier Transformed Infrared Spectroscopy (FTIR) where at 1626 cm(-1) is observed an isomerization that implies a rotation between the C and B rings that corresponding at elongation of bonds in benzene structure of catechin. The purity of the extracted tannins was analyzed by High Performance Liquid Chromatography (HPLC). The effectiveness of the extraction process was proven; the importance of knowing the amount of tannins will promote the utilization of the bark of these species. The results of the condensed tannin content place Quercus crasifolia (10.29%) and Arbutus xalapensis (13.12%) as potential sources of tannins.