Sustainable Production of Bioactive Chitosan from Fermented Rice Bran and Husk via Solid-State Fermentation

Sustainable production of high-quality chitosan from agro-industrial by-products remains a challenge in biotechnology. This study aimed to improve chitosan production from fermented rice bran and rice husk using Rhizopus oryzae in solid-state fermentation (SSF), and evaluated the physicochemical and biological properties of the resulting biopolymer. A full factorial design (23) was applied to assess key fermentation parameters, including moisture content, substrate composition, and nitrogen supplementation. Among the tested conditions, the highest chitosan yield was at 55% moisture, 50% rice husk, and 1.8 g/L urea. The obtained chitosan was characterized for degree of deacetylation (DD) using FTIR and NMR, and molecular weight (MW) by viscometry. Antimicrobial activity was tested against Gram-positive and Gram-negative bacteria, and antioxidant capacity was measured via DPPH and ABTS assays. The chitosan exhibited a high DD (86.4 ± 0.6%) and a MW of 59.65 kDa, values comparable to commercial standards. It showed strong antimicrobial activity, particularly against Gram-negative strains. Antioxidant assays confirmed concentration-dependent activity, reaching 94% DPPH inhibition at 5.00 mg mL−1. Overall, the results demonstrate that agro-industrial residues can be effectively transformed into high-quality, bioactive chitosan, offering a sustainable and circular alternative to conventional production routes.