Mechanochemical Top-Down Isolation of Chitin Nanofibrils from Oyster Mushrooms

Chitin, as a widely found polymer from renewable carbon feedstock, is a good candidate to foster sustainable circular economies. Particularly, nanochitin from fungal sources offers multiple environmental benefits over conventional crustacean- or insect-derived chitins. This study explores routes for the scalable isolation of chitin nanofibrils from oyster mushrooms (Pleurotus ostreatus). Chemical treatments including alkaline treatments (1.25 m NaOH), mild or more severe bleaching (4% to 8% v/v H2O2), are implemented with or without a high-pressure homogenization top-down isolation step. Obtained dispersions were examined for their physicochemical properties, including morphology, crystallinity, rheology, Z-potential, gelling/sedimentation characteristics, and antibacterial activity. While high-pressure homogenization facilitated chemically processed biomass nanofibrillation, exposure to harsher bleaching treatment resulted in an inherent nanofibrillation. Colloidal stability varied substantially as evaluated by sedimentation, and gelation concentrations ranged between 2 and 4 wt %. Such behavior is explained by a greater fibrillation of chitin in combination with the preservation of native glucans. This study builds on ongoing efforts to optimize the top-down isolation of fungal nanochitin and foster its utilization using conventional routes for lignocellulosic processing, opening novel routes to develop sustainable biobased materials.