Novel submicron colloidal gels from agro-waste extracts, microalgal polysaccharides and gellan gum: A strategy to produce active coating formulations

The discovery and formulation of natural products increasingly rely on advanced technologies to identify novel therapeutic and functional properties. This study presents a submicron colloidal gel system combining gellan gum (KF) from Sphingomonas elodea , an aqueous polysaccharide extract from Chlorella vulgaris (CHLA), and antioxidant-rich polar extracts from hazelnut skins (HS) and chestnut burs (CHES). The aim is to create bioactive formulations for use as natural functional coatings. Differential scanning calorimetry (DSC) identified critical glass transition and gelation temperatures for KF and CHLA, which are essential for stable gel formation. Below these thresholds, colloidal dispersion is incomplete or unstable. When appropriately heated, the system forms submicron-scale dispersions (400-450 nm, DLS) and develops gel networks upon cooling. The presence of divalent cations modulates KF aggregation, promoting higher-order helix conformations and enhancing hydrogen bonding. Interestingly, KF/CHLA gels can form even in the absence of added cations. Scanning Electron Microscopy reveals well-structured, interconnected 3D networks. Rheological analyses demonstrate a clear transition from liquid-like to gel-like behavior. Notably, identifying the optimal inclusion point, during which bioactive extracts are added, ensures their integration without compromising the gel’s structural integrity. These findings underscore the rheological and technological properties of the system, establishing it as a flexible, eco-sustainable platform for developing functional coatings and natural delivery systems. The combination of microbial and agrowaste-derived components opens promising avenues for health-related applications [ 1 ] [ 2 ] [ 3 ]. Aknowledgment Agritech National Research Center, funded by the European Union Next-GenerationEU (PNRR – M4C2, Investment 1.4, D.D. 1032, 17/06/2022, Project CN00000022), and PRIN 2022 project “MIGLIORARE” (code P2022WT79B, CUP N. D53D2302209 0001). Publication History Article published online: 05 March 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany