How well do isolated lignins mimic the inhibitory behaviour of cell wall lignins during enzymatic hydrolysis of hydrothermally treated softwood?

Abstract

Lignin in pretreated lignocellulosic substrates frequently inhibits enzymatic hydrolysis by non-productively binding hydrolytic enzymes. Isolated lignins are commonly used to study these lignin-enzyme interactions. To determine how well isolated lignins mimic the inhibitory behaviour of in situ lignins, we compared inhibition by in situ lignins within hydrothermally pretreated Pinus radiata wood to inhibition by the corresponding isolated lignins added to bleached kraft pulp. This was done as a function of pretreatment severity, enzyme cocktail and dose, and response to added polyethylene glycol. Two different types of isolated lignins, PTL (protease treated lignin-rich residue) and EMAL (enzymatic mild acidolysis lignin), were compared. The inhibitory effect of isolated lignins increased with both pretreatment severity and the amount of lignin added, and was associated with greater condensation and more phenolic groups in the lignins. Overall, isolated lignins provide a good predictor of the inhibitory behaviour of in situ lignins, provided other factors including the origin of the isolated lignin, and amount and accessible surface area of lignin are taken into account.