Extraction and optimization of chitosan yield and deacetylation quality from mushroom mycelium waste

Abstract

The growing mushroom industry generates substantial quantities of residual mycelial biomass, much of which is discarded despite its potential as a source of value-added biopolymers. This study investigated the extraction of fungal chitosan from Pleurotus ostreatus mycelium waste and statistically evaluated the deacetylation process using Response Surface Methodology based on a Box-Behnken Design. Three process variables, sodium hydroxide concentration (30–50%), reaction time (2–4 h), and temperature (100–150 °C), were evaluated for their effects on degree of deacetylation (DDA) and chitosan yield. A total of 17 experimental runs were conducted, and the resulting quadratic models showed strong predictive performance, with R² values of 0.9740 for DDA and 0.9974 for yield. The DDA model was significantly influenced by NaOH concentration, process time, the interaction between process time and temperature, and quadratic effects of NaOH concentration and temperature. Yield was more sensitive to process severity and was significantly affected by all linear terms and multiple interaction effects. The highest DDA, 80.36%, was obtained at 50% NaOH, 2 h, and 125 °C, whereas the highest chitosan yield, 21.85%, was achieved at 30% NaOH, 3 h, and 100 °C. ATR-FTIR analysis confirmed the characteristic functional groups of chitosan, including O–H/N–H, C–H, amide I, amide II, amide III, and C–O bands. Thermogravimetric analysis revealed a major decomposition stage between 200 and 350 °C with approximately 46% weight loss and a residual mass of approximately 43% at 600 °C. SEM analysis showed an aggregated flaky morphology with a compact layered structure, while EDX confirmed the presence of carbon, oxygen, and nitrogen as the principal constituent elements of chitosan. These findings demonstrate that mushroom mycelium waste is a viable alternative feedstock for fungal chitosan production and highlight the need to balance chitosan quality and recovery under best processing conditions.