The maximum cellulose conversion of 45.82% and reducing sugar yield of 0.293 g/g upon hydrolysis were obtained.
The developed process resulted in a maximum cellulose conversion of xylan-removed SB, 98.69 ± 1.30%, and a maximum extracted SB xylan conversion into XOS (xylobiose and xylotriose) of 57.36 ± 0.79% that was the highest SB xylan conversion reported in the literature, employing cellulase from Penicillium oxalicum EU2106 and recombinant endo-β-1,4-xylanase in Pichia pastoris.
The initial hydrolysis rates and maximum cellulose conversions to total glucose plus cellobiose for the three cellulose treatments were found to be greatest with NaOH, followed by ammonia at 25°C, then ammonia at 130°C cellulose, with the lowest rates for the initial cellulose I.
The maximum overall cellulose conversion of 83.09% was observed at 185°C, 2.5% acid usage, and 3 minutes of residue time.
In our study, we found that partially delignified fiber and vessels remained in the pith fraction, and might also account for the maximum level of cellulose conversion of around 63-66%.
The results of Figures 8 and 9 provide a strong argument that, for a given substrate, the accessible surface area defines the maximum rate of cellulose conversion by providing an upper limit to the extent at which a sessile population of thin biofilms can grow.
It is worth noting though that the initial enzyme loadings for this study were set so that glucose yields would not approach theoretical maximum levels (below 85% total cellulose conversion), so that the effects of enzyme recycle could be observed in both the positive and negative direction from the control no recycle condition.
In non-pretreated samples, the cellulose conversion reached a maximum of 31% after 72 hours of hydrolysis for the clone with the lowest lignin content, 16.8%.
Despite differences in absolute enzyme loading levels and maximum extents of ethanol production and cellulose conversion reached, Figures 2 and 3 show that all four enzyme systems perform well in SSF mode and have the capability to achieve cellulose to glucose conversion levels of 90% or higher in 7 days or less provided they are dosed at sufficiently high levels.
Considering the cellulose loss due to the pretreatment (maximum of 30%, depending on the process), the total cellulose conversion increases significantly from 22.0% (value for the untreated bagasse) to 72.4%.
However, under this low cellulase loading, the cellulose conversion was < 10% of the theoretical maximum, and at higher cellulase loading (0.6 FPU/g filter paper, giving ~20% cellulose conversion), the synergistic activity was insignificant [ 11].
