## 3 Results and Discussion
### Chemical Characterization of Feedstock and Processed Solids
#### 3.2.1 Sugar Release  
The release of soluble sugars during HTP increased with the severity factor, from 0.17 \(\pm\) 0.1 g/L at a severity factor of 2.35 to 0.89 \(\pm\) 0.6 g/L at log R\({}_{0}\) = 3.53. The depolymerization of hemicellulose occurred due to the hydrolytic action of the hydronium ions, which cleaved the acetyl groups to generate acetic acid [42]. The acetic acid content increased with the severity factor, from 0.15 \(\pm\) 0.02 g/L at a severity factor of 2.35 (140 \({}^{\circ}\)C, 15 min) to 1.32 \(\pm\) 0.01 g/L at a severity factor of 3.53 (180 \({}^{\circ}\)C, 15 min), as observed in Figure 2a. [PERSON] et al. [18] observed the same trend after liquid hot water pretreatment of waste wheat straw for fermentable sugars and acetic acid, which increased with the rising temperature. Additionally, the authors obtained higher yields of sugars, with 15.8 g/L fermentable sugars at 180 \({}^{\circ}\)C for 40 min compared to our work, due to the different processing conditions. [PERSON] et al. applied the same hydrothermal treatment as in our work but for longer residence time (0.5 h) and further applied an acid treatment with sulfuric acid to the hydrolysates to determine the oligosaccharide concentrations; they obtained higher yields of oligosaccharides than monosaccharides, which increased with the severity of the treatment from 2.49 g/kg at 120 \({}^{\circ}\)C to 61.69 g/kg at 180 \({}^{\circ}\)C [10]. Similarly, [PERSON] et al. reported comparable concentrations of monosaccharides to our work after HTP treatment of wheat straw at temperatures between 160 and 205 \({}^{\circ}\)C for 15 min (0.1 g/L xylose in the hydrolysate treated at 160 \({}^{\circ}\)C; 4.4 g/L xylose at the highest temperature of 205 \({}^{\circ}\)C) [56]. \begin{table}
\begin{tabular}{c c c c c} \hline  & **WS** & **R\({}_{\bf 140}\)** & **R\({}_{\bf 160}\)** & **R\({}_{\bf 180}\)** \\ \hline Severity factor & & 2.35 & 2.94 & 3.53 \\ \hline Hemicellulose & 27.67 \(\pm\) 0.1 & 24.7 \(\pm\) 0.2 & 25.3 \(\pm\) 1 & 11.3 \(\pm\) 0.1 \\ \hline Celluloses & 36.0 \(\pm\) 0.3 & 45.12 \(\pm\) 0.1 & 49.6 \(\pm\) 0.1 & 51.1 \(\pm\) 0.5 \\ \hline Lignin (ADL a) & 12.91 \(\pm\) 0.8 & 6.1 \(\pm\) 0.4 & 9.67 \(\pm\) 0.8 & 9.90 \(\pm\) 1 \\ \hline Holocellulose & 68.67 \(\pm\) 0.4 & 69.828 \(\pm\) 0.3 & 74.9 \(\pm\) 1 & 62.4 \(\pm\) 0.6 \\ \hline Ash & 5.0 \(\pm\) 0.1 & 1.2 \(\pm\) 0.1 & 1 \(\pm\) 0.2 & 0.8 \(\pm\) 0.1 \\ \hline Extractives & 1.2 \(\pm\) 0.1 & 0.6 \(\pm\) 0.1 & 0.8 \(\pm\) 0.2 & 1.4 \(\pm\) 0.1 \\ \hline Others & 17.22 \(\pm\) 0.1 & 11.18 \(\pm\) 0.1 & 1.47 \(\pm\) 0.1 & 2.3 \(\pm\) 0.2 \\ \hline Yield & 100 & 88.9 \(\pm\) 0.8 & 87.84 \(\pm\) 1.4 & 76.8 \(\pm\) 0.7 \\ \hline \end{tabular}  
* ADL: acid detergent lignin; R140: residues after the HTP at 140 \({}^{\circ}\)C; R160: residues after the HTP at 160 \({}^{\circ}\)C; R180: residues after the HTP at 180 \({}^{\circ}\)C.  
\end{table} 
Table 1: Chemical composition (% DM) of the raw material (WS) and pre-treated residues after the hydrothermal pretreatment. The solid residues after HTP were used to carry out the alkaline and enzymatic treatments. The alkaline treatment was shown to improve the removal of lignin and hemicellulose and swelling of the cellulose fibers [57]. Glucose release was highest at 160 \({}^{\circ}\)C (3.73 \(\pm\) 0.28 g/L); however, the differences between the pretreatment temperatures were not statistically significant. Xylose and arabinse had the highest release at the