Effect of dilute alkali pretreatment on structural features and enhanced enzymatic hydrolysis of Miscanthus sinensis at boiling temperature with low residence time

The aim of this work was to evaluate the effect of dilute sodium hydroxide for conversion of Miscanthus sinensis to fermentable sugars at boiling temperature with low residence time. Various concentrations of NaOH (0.75%–2.5%) were applied for treatment of Miscanthus in an autoclave at 105 °C for 10 min. The non-cellulosic surface granules composed of lignin, waxes, and partly of hemicelluloses were exhibited in pretreated Miscanthus. The scanning electron microscopy, atomic force microscopy, and Fourier transform infrared spectroscopy studies showed that the 2.5% NaOH-treated Miscanthus exposed cellulose fibres and surface granules were removed, probably due to comprehensive disruption of the linkages between lignin and carbohydrates. The cellulose crystalline index was increased from the water-treatment to 2.0% NaOH-treatments and remarkably lowered by the 2.5% NaOH-treatment. Chemical component analysis showed that the level of cellulose increased to 70% and lignin was reduced to 4.2% by 2.5% NaOH-treated sample. The greatest removal of lignin and hemicellulose from pre-hydrolysate liquors was 74% and 55%, respectively. The reducing sugar yield with cellulase 15 FPU, β-glucosidase 30 IU, and xylanase 6 FXU g−1 substrate was estimated as 73% and 87% for 2.0% and 2.5% NaOH-treated samples respectively. The 2.5% NaOH-treatment is judged to be effective for disrupting Miscanthus recalcitrance in this pretreatment regime.

► Miscanthus sinensis treated with various concentrations of NaOH at 105 °C for 10 min.
► AFM study shows surface granules were removed by 2.5% NaOH-treatment.
► Cellulose crystalline index (CrI) was lowered by 2.5% NaOH-treated sample.
► Cellulose fibres were destructured by 2.5% NaOH-treatment.
► 2.5% NaOH disrupted Miscanthus recalcitrance and enhanced enzymatic saccharification.