Structural and Behavior Changes of Herbaceous and Hardwood Biomass during Steam Explosion Pretreatment and Enzymatic Hydrolysis

Steam explosion (SE) was used to pretreat rice straw (RS) and Caragana korshinskii Kom. (CKK). Enzymatic hydrolysis of pretreated RS and CKK, and a pure cellulose (bacterial cellulose, BC) were performed and compared. The characteristics and changes of different substrates during pretreatment and enzymatic hydrolysis were observed. After SE pretreatment, the hemicellulose content of RS and CKK was decreased from 21.7% to 4.9% and 17.9% to 6.2%, respectively. The cellulose percent of RS and CKK was increased to 45.1% and 38.4%, and the enzymatic hydrolysis conversion of cellulose was increased 1.1 times and 0.9 times, respectively. Although the composition and enzymatic yield of different substrates varied, their enzymatic hydrolysis rates showed a similar declining trend during enzymatic hydrolysis. The adsorption capacities of substrates on the enzyme were increased by pretreatment. The enzymatic hydrolysis efficiency was closely related to the enzyme adsorption capacities of substrates at the initial stage (1 h). The BC and SE pretreated RS first adsorbed and subsequently desorbed the enzyme, while the untreated RS and CKK had weak adsorption capacity and formed irreversible adsorption with the enzyme. The changes in crystallinity after enzymatic hydrolysis suggested that there was no direct correlation between the crystallinity and digestibility of cellulose.