3.3 Impact of the third constituent in ChCl-DHBA DES system on
enzymatic hydrolysis of sorghum stover
The pretreatment efficiency of each DES was evaluated by measuring
fermentable sugar production via enzymatic hydrolysis. The average value
and standard deviation are in Figure 3 and Supplementary
Materials with Table S3 for glucan conversion and Table
S4 for xylan conversion, respectively. Overall, both binary and ternary
ChCl-DHBA DESs improved the glucan and xylan conversion in sorghum
stover. Over 80% of glucan conversion and over 40% of xylan conversion
were obtained with the DES pretreated WT and TG biomass. Especially the
glucan conversion yields of TG biomass pretreated by both binary and
ternary DESs (ChCl-DHBA, ChCl-DHBA-W, and ChCl-DHBA-EG) after 72
h-enzymatic hydrolysis ranged 98-100%, which were higher than
pretreated WT biomass had. It is well-known that xylan removal and
delignification are well correlated with glucan conversion in previous
studies.40,41 However, the enzymatic hydrolysis
results in this study were not well correlated with their
delignification and xylan removal efficiency. Other factors, such as
possible pseudo lignin deposition and cellulose crystallinity, could be
possible reasons.42-44
The glucan conversions of binary DES pretreated biomass were 85%
(pretreated WT) and 98% (pretreated TG). The addition of the
solvent-based third constituents further improved the glucan conversion
of the binary DES pretreated biomass. ChCl-DHBA-W pretreated WT sorghum
stover showed 97% of glucan conversion, while ChCl-DHBA-EG pretreated
one showed a similar yield (89%) with binary ChCl-DHBA DES. The effect
of ternary DES on xylan convolution was more pronounced. The ChCl-DHBA-W
and ChCl-DHBA-EG DES pretreated WT biomass had 11% and 15% higher
xylan conversion than the binary DES pretreated one. The ternary DES
pretreated TG biomass also had 17-35% enhancement in xylose production
compared to binary DES pretreated one.
Two types of solvent-based third constituents, water in ChCl-DHBA-W DES
and ethylene glycol in ChCl-DHBA-EG DES, further increased glucan and
xylan efficiency of the ChCl-DHBA DES pretreated biomass in both WT and
TG biomass. ChCh-DHBA-W DES pretreated biomass showed similar glucan
conversion to WT (97%) and TG (98%). The ChCl-DHBA-W DES exhibited the
highest glucan and xylan conversion with WT sorghum stover. This DES
also resulted in notably high xylan conversion (81%) with TG biomass.
Another ternary DES, ChCl-DHBA-EG DES, showed higher glucan and xylan
conversion (89% and 57%) than ChCl-DHBA DES (85 and 42%) with the
pretreated WT. The ChCl-DHBA-EG DES provided superior sugar conversion
with the pretreated TG biomass (99%) compared to the WT biomass (88%)
even though the chemical composition changes in WT and. TG biomass were
similar (Figure 1 , Table 1, and Table S1 )