The Evolution of Cellulose Crystallinity During the Entire Wheat Straw Organosolv Biorefinery Process and Its Relationship with Enzymatic Hydrolysis

Cellulose crystallinity is frequently associated with lignocellulosic biomass digestibility, yet its development during multistep biorefinery processing and its relationship with enzymatic hydrolysis remain difficult to isolate. This study investigated the evolution of cellulose crystallinity in wheat straw (Triticum aestivum) during Hot-Water Pretreatment (HWP), Water Pretreatment (WP), Organosolv extraction, sequential washing, and drying, and related these changes to enzymatic glucose yield. Crystallinity was determined using X-ray diffraction and an ATR-FTIR-based PLS model, while enzymatic hydrolysis was evaluated by HPLC-based glucose quantification. HWP caused a temperature-dependent decrease in crystallinity from 47.5 ± 1.3% in untreated straw to 27.0 ± 2.2% at 120 °C, whereas WP at room temperature caused no significant change. However, without subsequent Organosolv extraction, both pretreatments alone resulted in low glucose yields of approximately 10%, indicating that cellulose crystallinity is only one of several factors governing enzymatic hydrolysis efficiency. During washing after Organosolv extraction, crystallinity increased from 40.6 ± 2.1% to 54.2 ± 1.3%, whereas, under the tested conditions, glucose yield was more closely associated with the estimated residual ethanol concentration than with the change in crystallinity. Drying had the strongest effect, increasing crystallinity by up to 53.6% relative to the wet state. Overall, cellulose crystallinity should be considered as one of several interacting factors governing enzymatic digestibility, and sample moisture history must be carefully controlled when comparing crystallinity data.