Influence of lignin addition on the enzymatic digestibility of pretreated lignocellulosic biomasses

• Effects of hydrophilic and hydrophobic lignin on enzymatic hydrolysis were compared.
• Sulfonated lignin enhanced enzymatic hydrolysis of AS and GL pretreated samples.
• SED of GL pretreated masson pine increased from 42% to 75% with SL addition.
• SL on enhancing hydrolysis may associate with hydrophilic groups in residual lignin.
• Hydrophobic interaction between lignin and enzyme may drive the enzyme adsorption.

The presence of lignin in lignocellulosic biomass is correlated with its enzymatic digestibility. Their correlation and mechanism have been investigated widely but have not been elucidated clearly. In this study, hydrophilic sulfonated lignin and hydrophobic kraft lignin were introduced into the enzymatic hydrolysis process to investigate their effects on the enzymatic digestibility of different pretreated lignocellulose. The influence of lignin addition on the enzymatic digestibility varied with both introduced lignin type and the pretreatment methods of substrates. Slight enhancement of enzymatic hydrolysis was observed for all substrates by adding kraft lignin. The addition of sulfonated lignin could effectively improve the enzymatic digestibility of green liquor and acidic bisulfite pretreated materials, but had little effect on sulfite–formaldehyde pretreated samples. The enzymatic digestibility of green liquor pretreated masson pine increased from 42% without lignin addition to 75% with 0.3 g/g-substrate sulfonated lignin addition.