Autohydrolysis and microwave ionic liquid pretreatment of Pinus radiata: Imaging visualization and analysis to understand enzymatic digestibility

Abstract

Sequential pretreatments provide advantages of every single process towards a complete biomass fractionation. In this work, autohydrolysis and IL microwave pretreatments are sequentialy studied, and their effect to enhance enzymatic hydrolysis is analyzed. Mild, intermediate and severe autohydrolysis are combined with four IL temperatures (50, 80, 120 and 150 °C). Pretreated solids are enzymatically hydrolyzed and compared in terms of chemical composition and morphology. Digital image analysis is employed to numerically determine the heterogeneity of the solids using surface fractal dimension and lacunarity parameters. In this study, the negative effect of intermediate and severe autohydrolysis, over the subsequent IL pretreatment is demonstrated. Mild autohydrolysis and high IL conditions (AH150IL120) results in digestibilities of 78.8 g of glucan/100 g of glucan introduced. High surface fractal values (in the range of 2.5461–2.7124) and low lacunarities (0.0818–0.2563) enhance the enzymatic accessibility of pine wood. Furthermore, the negative effect of softwood lignin accumulation in the surface is observed using confocal fluorescence microscopy.