From structural complexity to circular applications: a comparative review of the enzymatic degradation of polydopamine, tannins, lignins, and melanins

Abstract

Polydopamine, tannins, lignins, and melanins are diverse natural and bio-inspired polyphenolic materials known for their structural complexity, functional versatility, and growing technological importance. Their widespread presence in biological systems and emerging applications in coatings, packaging, biomedicine, and sustainable materials call for a deeper understanding of their biodegradation. This review presents a comparative analysis of their enzymatic breakdown, highlighting the roles of oxidoreductases, including laccases, peroxidases, and tyrosinases, in facilitating polymer depolymerization, structural modifications, and downstream valorization. Unique structural features such as catechol units in polydopamine, galloyl groups in tannins, phenylpropanoid backbones in lignins, and indole-quinone frameworks in melanins dictate their degradation rates and enzyme accessibility, presenting specific challenges and opportunities. Beyond biodegradation, this review situates these processes within the framework of potential recycling-by-design and a circular economy, demonstrating how controlled enzymatic conversion can produce high-value intermediates for green chemistry, biomaterials, energy recovery, and environmental remediation. By comparing these biopolymers side by side, we identify common principles, challenges, and technological opportunities to transform enzymatic degradation into a key driver of circular bioeconomy strategies. To ensure relevance and accuracy, only recent research published since 2015 has been included, focusing on the latest advances in enzymatic degradation and sustainable applications. This synthesis fills a critical knowledge gap, serving as a valuable resource for researchers, industries, and policymakers seeking to develop innovative, sustainable materials that align with the principles of green chemistry and environmental responsibility.