Lignin as a sustainable biopolymer for food: extraction, functionality, food safety and future perspectives

Lignin, an abundant byproduct of the pulp, paper, and biorefinery industries, has a complex chemical structure containing phenolic, carboxylic, and methoxyl functional groups that confer tunable reactivity and functional properties. These characteristics enable lignin to act as an antioxidant, antimicrobial, UV-shielding agent, emulsifier, Pickering particle, and reinforcing component in films and hydrogels. This review examines the growing role of lignin as a sustainable biopolymer for food and food-related applications. It integrates current knowledge on lignin extraction, structure-function relationships, emulsion applications, bioactive delivery systems, antioxidant and antimicrobial applications, and cytotoxicity. Opportunities and limitations are discussed in the context of food-grade processing and safety requirements. Future research directions are outlined to guide the safe and effective use of lignin in food systems. Over the past five years, advances in extraction technologies, fractionation, and chemical modification have reshaped the potential of lignin for food packaging, emulsion stabilization, and bioactive delivery systems. However, challenges remain. Plant source, extraction method, and molecular heterogeneity strongly influence lignin solubility, cytotoxicity, and interfacial behavior, creating variability that complicates standardization for food use. Emerging findings on gastrointestinal interactions and cell-line cytotoxicity highlight the need for systematic toxicological assessment and clearer regulatory pathways, as the lack of standardized safety evaluation remains a major barrier to the direct application of lignin in food.