Analytical Approaches for the Identification and Characterization of Tannins in Natural Matrices. A Comprehensive Review

Tannins are structurally diverse plant-derived polyphenols with growing relevance across food, pharmaceutical, materials, environmental, and cultural heritage applications, yet their complex chemistry continues to challenge routine analysis. This review critically evaluates analytical strategies for identifying and characterizing tannins in natural matrices and proposes a stepwise pathway tailored to analytical goals. The workflow progresses from rapid qualitative screening to advanced structure-oriented methods, integrating complementary techniques rather than treating them in isolation. Qualitative methods, including spot tests and microscopy, confirm the presence and distribution of tannins. Semi-quantitative approaches, such as direct UV-Vis spectroscopy, FTIR/NIR, and selected thermal methods, estimate tannin levels or profiles when full quantification is unnecessary. Quantitative methods comprise (a) UV-Vis colorimetric assays for global parameters (e.g., total tannins or phenolics) and (b) chromatographic techniques, particularly HPLC coupled with diode-array detection or mass spectrometry, for accurate determination of individual components down to trace levels. Structural elucidation relies on gel permeation chromatography, advanced MS, and NMR, complemented by thermal analysis to assess thermal stability and performance in various materials. Throughout, the review compares principles, sample preparation requirements, cost, speed, sensitivity, selectivity, reproducibility, and typical analysis times, emphasizing integrated, chemometrics-assisted workflows rather than single-method solutions. Correctly combining techniques is essential to support sustainable industrial applications, green chemistry, regulatory compliance, and conservation science, particularly when minimally invasive analysis is required.