Abstract
The effect of drying on the enzymatic hydrolysis of cellulose was determined by analysis of porosity and crystallinity. Fiber hornification induced by drying produced an irreversible reduction in pore volume due to shrinkage and pore collapse, and the decrease in porosity inhibited enzymatic hydrolysis. The drying effect index (DEI) was defined as the difference in enzymatic digestibility between oven- and never-dried pulp, and it was determined that more enzymes caused a higher DEI at the initial stage of enzymatic hydrolysis and the highest DEI was also observed at the earlier stages with higher enzyme dosage. However, there was no significant difference in the DEI with less enzymes because cellulose conversion to sugars during hydrolysis did not enhance enzymatic hydrolysis due to the decrease in enzyme activity. The water retention value (WRV) and Simons’ staining were used to measure pore volume and to investigate the cause of the decrease in enzymatic hydrolysis. A decrease in enzyme accessibility induced by the collapse of enzymes’ accessible larger pores was determined and this decreased the enzymatic hydrolysis. However, drying once did not cause any irreversible change in the crystalline structure, thus it seems there is no correlation between enzymatic digestibility and crystalline structure.
Highlights
Biorefinery platforms using biomass have been studied widely in recent years because of their low carbon footprint [1]
The effect of drying on enzymatic hydrolysis was evaluated by enzymatic digestibility, which was determined by the amount of sugars released during enzymatic hydrolysis with 10 FPU/g-pulp of cellulase
The drying effect index (DEI) was defined as the difference in enzymatic digestibility between the OD and ND pulps and it was concluded that more enzymes cause a higher DEI at the initial stage of enzymatic hydrolysis, and the highest
Summary
Biorefinery platforms using biomass have been studied widely in recent years because of their low carbon footprint [1]. Most of the platform chemicals can be produced from sugars, which indicates that low cost sugar production from biomass is important to achieve a low carbon footprint [4]. Lignocellulosic biomass has been suggested as the feedstock for sustainable sugar production and various conversion processes including pretreatment and saccharification have been studied to facilitate effective sugar production from lignocellulosic biomass [5,6,7]. Sustainable sugar is mainly produced by enzymatic saccharification and pretreatment must be performed to improve enzyme accessibility to cellulose [8,9]. The pretreatment exposes cellulose by partial removal of hemicellulose and lignin, and it facilitates enzyme access to cellulose. The exposed cellulose is likely to be partially dried and the cellulose drying affects its
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