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 and support eco-friendly processing. Tannins are utilized in leather tanning, food preservation, medicine, water treatment, corrosion inhibition, and the development of innovative materials, such as bio-based adhesives and packaging films. Condensed tannins show industrial promise due to antioxidant and antibacterial properties, while hydrolyzable tannins offer medicinal benefits such as anti-inflammatory and anticancer effects. However, challenges remain in standardizing extraction, characterizing structures, and mitigating the anti-nutritional impacts. The review highlights future directions, including the biotechnological enhancement of tannin-producing plants, the development of eco-friendly extraction methods, and the integration into sustainable product systems that align with circular economy models. Through the integration of multidisciplinary research and collaboration with industry, tannins can be further utilized as a versatile and sustainable resource that holds significant scientific and commercial importance.