Bioconversion of Mushroom Chitin-Rich Waste into Valuable Chitin Oligosaccharides Using a Combined Approach of Biocatalysis and Precision Fermentation

The shift toward a circular economy has increased efforts to derive valuable chemicals from renewable resources, including chitin-rich waste. Mushroom cultivation generates significant waste, particularly the stalks left behind on breeding beds, which contain a substantial amount of chitin with untapped potential. This research establishes a proof of concept for valorizing this waste stream by converting it into valuable chitin oligosaccharides, which have applications across food, feed, agriculture, and pharmaceuticals. Using a combined approach of enzymatic saccharification with five chitinolytic enzymes, followed by precision fermentation of the resulting <i>N-</i>acetyl-d-glucosamine (GlcNAc), we successfully produced defined chitinpentaose. Chitin extracted from <i>Agaricus bisporus</i> brown demonstrated the highest saccharification efficiency, achieving a GlcNAc conversion of 31 ± 1% (w/w). Our findings highlight the necessity of purifying the saccharification product to ensure product specificity during fermentation, although the production strain's growth remained suboptimal compared to commercially available GlcNAc. Using an engineered <i>E. coli</i> strain, we achieved pure chitinpentaose, with a yield of 0.0327 g/L at a 10 mL scale and production levels (g/OD₆₀₀) comparable to those obtained with HPLC-grade commercial GlcNAc. This study provides a foundation for further research aimed at improving biocatalyst recycling and optimizing the growth phase, thereby enhancing the cost-efficiency and scalability of this sustainable bioconversion process.