Enzymatic Hydrolysis of Steam Treated Aspen Wood: Influence of Partial Hemicellulose and Lignin Removal Prior to Pretreatment

Aspen wood chips were treated with acidified chlorite to remove 90% of the lignin, or were extracted with concentrated alkali to remove 500 of the hemicellulose. Samples of the original chips, the resulting low-lignin aspenwood (LLA) and the low-hemicellulose aspenwood (LLA) were treated with saturated steam at 240°C for 20–180 s. Chemical analysis and enzymatic hydrolysis of the resulting water-washed substrates showed that, after 40 s of steaming, the rate and extent of enzymatic hydrolysis correlated better with removal of alkali-insoluble lignin than with removal of xylan. The original wood, LLA and LHA had similar crystallinity indices which increased in the water-insoluble fractions with time of steaming. Carbohydrate degradation products (“pseudo-lignin”) formed in equal amounts on steaming original wood or LLA, indicating furfural-lignin condensation to be not involved. Development of accessibility in LHA resembled that in original aspenwood, despite the absence of acetic acid for autohydrolysis.