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