Cell Wall Chemical and Structural Changes of Wood by Steam Explosion to Increase Fungal Growth for Myco-Composite Production

The production of myco-composites, sustainable materials formed by fungal growth through lignocellulosic substrates, requires efficient fungal colonization of the feedstock. This study highlights the potential of steam explosion (SE) as an effective pretreatment to enhance the bioavailability of beech wood components for myco-composite production. Wood samples were subjected to steam explosion under four different severities (R_0 3.36; R_0 3.65; R_0 3.94; R_0 4.24), and their chemical composition and microstructure were analyzed by dynamic image analysis, scanning electron microscopy, drop shape analysis, near-infrared spectroscopy, and anionic chromatography. By modifying the chemical composition and microstructure of wood particles, SE improves substrate accessibility for fungal colonization and generates a nutrient medium with minimal inhibitory compounds, promoting optimal fungal growth. Our findings reveal that Trametes versicolor exhibits its highest growth rate and larger hyphal diameters (1.3 vs 0.5 μm) on beech wood particles treated at intermediate severities (R_{0 3.36–3.94}) with growth rates increasing by 46% compared to condition R_0 4.24 and 138% compared to untreated beech. These results were correlated with a reduction in fine particles (0.7 vs 11.6% at R_0 4.24) and better water absorption (28 vs 5% at R_0 4.24). The myco-composite produced with R_0 3.65 showed 69% thickness recovery compared to 32% (R_0 3.36) and 41% (R_0 4.24). Fungal growth inhibition occurred at R₀ > 3.7, emphasizing the critical window for pretreatment severity. These results demonstrate the importance of substrate characterization in balancing digestibility and nutrient integrity, providing a pathway for the efficient and sustainable myco-composite production from wood and recalcitrant biomass.