An in-depth review on tannin sources, extraction methods, and industrial applications

Tannins are naturally occurring polyphenolic compounds that are widely distributed in a variety of plant parts, such as leaves, bark, fruits, and seeds. This review provides a comprehensive analysis of tannins, with a particular focus on their classification, historical context, chemical structure, extraction techniques, and diverse applications across industrial and biomedical fields. Tannins are typically categorized as either condensed or hydrolyzable, with each form exhibiting unique functional attributes and structural characteristics. The extraction of tannins has progressed from conventional water-based maceration and decoction to contemporary methods, including ultrasound-assisted, microwave-assisted, supercritical fluid, and enzyme-assisted extractions. Among these, nonthermal technologies such as ultrasound-assisted, enzyme-assisted and supercritical fluid extraction are particularly highlighted for their ability to preserve heat-sensitive tannin structures, reduce energy consumption…