Table 4 shows the concentrations of the reducing end groups
and impurities such as furfurals and HMFs after the extraction process.
Acidic hydrolysis of the G. corneum extract, where the soluble
carbohydrate concentration was 3.5%, was performed with the
addition of 0.5–1% oxalic acid. The amount of reducing sugars
formed in the extracts is shown in Table 5. When fermentation
was carried out without removing furan compounds from the
hydrolysates of G. corneum extracts, ethanol production by S. cerevisiae
No. 9 was severely inhibited. The removal efficiency of the
furans was 62–90% by steam stripping, while HMF was removed
at levels of 4–17%. The loss of reducing sugars in the process was 11–16%. As shown in Fig. 2, an ethanol volume percentage of 5.8%
(v/v), corresponding to ethanol weight percentage of 4.58% (w/v),
was obtained from 12.3% reducing sugars in G. corneum hydrolysates
after 96 h of fermentation. Finally, over 20% (w/w) ethanol
from the dissolved carbohydrates in the extracts was obtained. Enzyme
saccharification of galactan, the main components of the extracts,
may help reduce the formation of fermentation inhibitors
such as furans and HMF, and may help increase ethanol yield
and simplify the saccharification process. Further study in this area
is necessary.