17-51: Effect of additive in improving saccharification of thermo-mechanically pre-treated Pinus radiata and molecular level investigation of additive effect

In New Zealand, 90 % of the 1.7 M ha plantation forest estate is Pinus radiata, which offers a good source of renewable, inexpensive and readily available lignocellulosic biomass. Ironically, woody biomass, especially softwood, is recalcitrant to enzymatic hydrolysis and therefore is a challenging substrate for effective conversion to sugar. One approach to overcome the recalcitrant nature of softwood is to supplement with additives. In this work we have tested different surfactants as additives and found that polyethyleneglycol (PEG) with molecular weight 4000 was the most effective giving 17 % improvement in saccharification. There was no additive effect by PEG above molecular weight of 4000 and concentration above 0.02 g/g of substrate. A five time reduction in enzyme dose was achieved by addition of 0.02 g of PEG-4000 per g of substrate and still obtains similar cellulose conversion. Fluorescence imaging and spectroscopy elucidated molecular level interactions between PEG and lignin which is mainly derived from secondary walls, with little or no penetration of PEG into fragments derived from the middle lamella. The middle lamella consists mainly of lignin with smaller amounts of hemi-cellulose with little or no cellulose. Therefore, the inability of PEG to penetrate middle lamella is almost irrelevant to glucose yield. The very large surface area inside the porous secondary wall and binding of PEG to lignin present in this region account for improved yield by decreasing the non-specific binding of enzyme to these surfaces.