Lignin-associated factors impede enzymatic hydrolysis of hydrothermally pretreated birch and poplar wood

Pretreatment is a critical step in processing wood for various applications, particularly in the production of biofuels, biochemicals, and biomaterials. Our previous study shows that the enzymatic hydrolysis efficiency of hydrothermally pretreated birch (80.8 %) is markedly superior to that of poplar (21.5 %) treated in the same conditions (180°C, 50 min). Based on that, this study investigated the effects of lignin-related factors on the enzymatic hydrolysis of hydrothermally pretreated birch and poplar wood. The milled wood lignin (MWL) and lignin-carbohydrate complex (LCC) were extracted from birch and poplar wood before and after pretreatment. The two factors—non-productive binding and physical blocking derived from lignin that primarily influence the efficiency of enzymatic hydrolysis of biomass are specifically analyzed in this study. By the enzymatic hydrolysis test of holocellulose, it was confirmed that the physical blocking caused by surface lignin and LCC in pretreated birch is significantly lower than that in poplar either in an enzyme loading of 10 FPU/g or 25 FPU/g. The data of surface lignin coverage, LCC composition, and LCC contents in birch and poplar samples supports this result. Moreover, the addition of isolated lignin on Avicel test proved that the lignin from pretreated birch has less non-productive binding than that from poplar. These two factors together contributed to the higher efficiency of enzymatic hydrolysis of hydrothermally pretreated birch than poplar.