Feasibility Assessment of the Identification of the Source of Condensed Tannins in Leathers by FTIR Spectroscopy and Chemometrics

Abstract

This study aimed to investigate the feasibility of identifying the type of plant used in the tanning of leathers by cost-effective Fourier transform infrared (FTIR) spectroscopy. The investigation was performed on European horse-chestnut (fruit peel), mimosa, and quebracho and three specimens of mimosa-tanned leathers. Tannin extraction from plants was performed in an ultrasonic bath using acetone-water solvent (70%). Tannin extraction from leathers was carried out from the corium fibers using acetone-water solvent (1:1). After extraction, filtration, centrifugation, and solvent removal, the samples were subjected to FTIR spectroscopy. Principal Component Analysis (PCA) and hierarchical clustering were used to identify the source of tannins based on FTIR results. In addition to FTIR spectra, their first and second derivatives were also used in statistical analyses. The obtained FTIR spectra and their derivatives and the results of PCA and hierarchical clustering showed that rich plant sources of condensed tannins can be well differentiated by spectroscopy in the fingerprint region (700-1800cm-1). The PC1-PC2 plot in the analysis of FTIR spectra and the PC2-PC3 plot in the analysis of derivatives showed the best ability to differentiate and identify the extracts. Multivariate PCA and cluster analyses performed well in identifying the type of plant used in the tanning of the studied leathers, especially when applied to the derivatives of FTIR spectra.