Enhanced enzymatic saccharification of corn stover via lignin structural modulation by 1,4-butanediol/dilute acid pretreatment

Dilute acid (DA) pretreatment induces lignin condensation and surface deposition, limiting enzymatic saccharification. Hence, 1,4-butanediol (1,4-BDO) was incorporated into DA pretreatment of corn stover (CS) at 1,4-BDO/DA ratios of 20/100, 40/80, and 60/60 (v/v). Structural changes of residual lignin and their impact on enzymatic hydrolysis of pretreated-CSs were explored. Lignin removal and hemicellulose retention increased as 1,4-BDO/DA ratio rose. Glucose yield increased from 50.0% (DA control) to 64.4% (CS-40/80) using cellulase alone, and reached 80.3% with a xylose yield of 48.1% by xylanase supplementation. HSQC NMR and FTIR suggested that 1,4-BDO promoted α-etherification of lignin, which protected β-O-4 linkages and mitigated condensation, thereby reducing lignin thermal stability and hydrophobicity. Cellulase binding capacity of lignin decreased from 97.9 to 77.2 mg/g as 1,4-BDO/DA ratio increased. Lignin inhibition was mitigated more markedly at a higher 1,4-BDO/DA ratio. The suppressed condensation, reduced phenolic OH content, and lowered hydrophobicity likely accounted for this alleviated lignin inhibition. The highest yields at the 40/80 ratio suggested that both the 1,4-BDO proportion and acid strength might be key to enhancing hydrolysis. These findings confirmed that 1,4-BDO/DA pretreatment could modify lignin structure and mitigate its inhibitory effect, offering a reference for diol-assisted acidic pretreatment.