An optimum combined severity factor improves both the enzymatic saccharification yield and the functional lignin structure

Liquid hot water (LHW) pretreatment has become an interesting alternative among the known pretreatment approaches. In this study, an extended combined severity factor (CSF) as LHW pretreatment severity was used to make a balance between the enzymatic hydrolysis of cellulose and the potential application value of lignin. The results, mainly from the degradation of carbohydrates, the enzymatic saccharification of cellulose, and the characterization of lignin by FTIR, TGA, 31P NMR, and 2D HSQC NMR, demonstrated that a CSF of approximately 8.37 was the optimum pretreatment severity to facilitate the cellulose enzymatic hydrolysis and obtain functional lignin. Hemicellulose was removed for > 74.7% with a negligible glucose concentration of 1.19 g/L. The pretreated substrates were subsequently enzymatically hydrolyzed reaching a saccharification yield of 83.92%. The obtained lignin exhibited excellent structural properties, such as a higher hydroxyl (OH) content (2.34 mmol/g of aliphatic hydroxyl and 2.43 mmol/g of phenolic OH) and more β-O-4 aryl ether linkages (27.86%). In a word, this study hence provides useful guidance for the enzymatic saccharification of cellulose and the extraction of functional lignin using LHW pretreatment.