From biowaste to innovation: Development of composite nanoparticles from lignin-rich agricultural byproduct

Transforming organic waste into valuable compounds supports the principles of a circular economy. Compost tea (CT) and humic substances (HS), derived from agri-food wastes, are a potential source of lignin, the most abundant plant-origin polymer characterized by several beneficial properties and potential for the creation of sustainable nanomaterials, such as nanoparticles (NPs). Our research introduces a novel approach by producing NPs directly from lignin-rich agricultural byproduct, that is aqueous extracts of composted green waste to promote eco-friendly NPs production. Dissolved organic fractions from composted artichoke, CT-ART and HS-ART were characterized, and the optimal conditions for producing NPs from these materials via controlled nanoprecipitation were identified. To improve the properties of the NPs, composite systems were successfully generated by combining these lignin-rich materials with zein. Overall characterization underscored the association between the components and the pivotal role of zein in reducing compost-based NP size (~200 nm), improving simultaneously the monodispersity (PDI ~0.1) and the stability of the dispersion. Through freeze-drying NPs-based long-term stable dry powders were produced and demonstrated robust antioxidant and antimicrobial activity. These findings show that biowaste and natural polymers like zein can create stabilized compost-based NPs for use in nutraceutical and pharmaceutical applications, aligning with the "waste-to-wealth" concept.