Biocatalytic Upcycling ofBiomass with Proteases and Glucanases to Produce Chitin

The large-scale production of citric acid using Aspergillus niger generates substantial quantities of fungal biomass, which remains an underutilized resource. In this study, we developed a tailored enzyme-based strategy to valorize A. niger biomass by selectively extracting chitin, while generating glucose-rich hydrolyzates suitable for fermentation. Comprehensive screening of 16 commercial proteases and glucanases led to the identification of optimal enzyme combinations and process conditions. At a 30 L scale, this process yielded a chitin-rich fraction representing 27% of the initial biomass. The extracted chitin was characterized using X-ray diffraction and ¹³C solid-state nuclear magnetic resonance (NMR) spectroscopy, revealing high crystallinity and purity. The chitin content of the chitin-rich fraction was quantified using newly established NMR calibration curves based on distinct carbon signals associated with the acetamido group (C-2, CH₃, and C═O) and estimated to be on the order of 74%. The chitin-rich fraction was subsequently converted into chitosan with a degree of deacetylation of ∼55% (45% yield on a dry matter basis) and colloidal chitin (60% yield on a dry matter basis), with product properties similar to those of corresponding products derived from crustacean chitin. This study demonstrates the feasibility of enzyme-only extraction of fungal chitin and provides a scalable, sustainable approach for converting fungal biomass into high-value bioproducts.