Characterization of Commercial Hydrolyzable and Condensed Tannins by Fourier Transform Infrared Spectroscopy

Abstract

This study uses Fourier transform infrared spectroscopy to characterize and differentiate four major commercial tannin extracts (quebracho colorado, mimosa, tara, and chestnut) to establish a robust quality control framework for their industrial utilization in bio-based materials and green chemistry applications. While all tannins exhibited common O–H and aromatic C=C–C stretching bands, specific spectral regions allowed for clear discrimination without time-consuming wet-chemical assays. Condensed tannins (quebracho and mimosa) showed an intense C–O ether linkage peak (1240-1285 cm⁻¹), absent in hydrolyzable extracts. Conversely, hydrolyzable tannins (tara and chestnut) were distinctly identified by a prominent ester carbonyl C=O band (1705–1735 cm⁻¹). Further differentiation revealed gallotannin-specific markers in tara (e.g., 1090, 870, 755 cm⁻¹) that were notably weak or absent in chestnut, corroborating chestnut's predominant composition of ellagitannins. This systematically indexed FTIR database provides a rapid, non-destructive, and reliable screening tool for the classification, authentication, and standardization of diverse commercial tannin sources, streamlining their selection and processing as high-value technological inputs in sustainable formulations.