## 3 Results and Discussion
### Total Reducing Sugars (TRS) After Pretreatment  
Reducing sugars represent the most significant carbohydrate components liberated during pretreatment, and they are susceptible to use in subsequent fermentation processes. In this study, the effectiveness of HTP in the reducing sugars production is shown in Figure 3. The treatment duration exhibited a significant impact on the solubilization of sugar. The concentration of TRS increased over time with all biomasses. Significantly, OP demonstrated the maximum concentration, reaching 19.1 gTRS/L after 30 min of treatment. This was followed by SBP at 10.1 gTRS/L, BSG at 5.8 gTRS/L, and the lowest concentration of 1.5 gTRS/L with RH.  
In comparison to the literature, this study has demonstrated the effectiveness of auto-hydrolysis in the extraction of reducing sugars from lignocellulosic biomass. [PERSON] et al. [35] reported that a recovery of 14.5 gTRS/L was achieved from BSG after 30 min of hydrothermal treatment at 103 \({}^{\circ}\)C, using 0.15 M H\({}_{2}\)SO\({}_{4}\) and a biomass loading of 5% (\(w/v\)). Furthermore, other investigations [36] reported a maximum of 13.34 gTRS/L under the following optimal conditions: 3.87% (\(w/w\)) solid loading, 1% (\(w/w\)) acid concentration, a reaction time of 48.4 min, and a processing temperature of 121 \({}^{\circ}\)C in a steam autoclave. Concurrently, another study [37] obtained a yield of 0.3 gTRS/g of OP using auto-hydrolysis  
Figure 3: Total reducing sugar (TRS) expressed as g/L of HTP biomasses (OP, BSG, SBP, and RH). Note: Unt—Untreated.  
at 120 \({}^{\circ}\)C for 30 min. The study used 2.5 g of biomass suspended in 100 mL of water and 0.075 mL of H\({}_{2}\)SO\({}_{4}\). In comparison, the present study achieved a yield of 0.23 gTRS/g from OP using a green solvent (water) under similar thermal conditions.  
Accordingly, in this study, the increase in monosaccharide concentration over time can be explained by the effectiveness of the thermal treatment in disrupting the complex bonded structure in the biomass, yielding sugars. Temperature and pressure during the process are critical factors in the degradation of structural components and their conversion into value-added compounds [38; 39]. However, solubilization and sugar yield can be significantly influenced by fiber composition, specifically the proportions of soluble fiber, cellulose, and hemicellulose, which are the main reservoir for simple reducing sugars.  
Notably, OP contains a significant proportion of soluble compounds, including approximately 30% cellulose and hemicellulose. This composition facilitated the liberation of high concentrations of monosaccharides after treatment.  
In contrast, BSG and SBP exhibited increased TRS yields after 30 min of treatment, with BSG producing approximately 3 times and SBP producing 2.5 times that of the initial concentrations. Moreover, these results are consistent with the lignocellulosic structures of sugar beets and brewers. Specifically, BSG contains approximately 50% of (cellulose and hemicellulose), while sugar beets contain around 44%. Furthermore, a proportion of the soluble sugars was possibly converted into a secondary product as VFAs, a process that can influence the final yield of reducing sugar obtained.  
Conversely, the lowest TRS concentrations in RH could be attributed to their high lignin content. Lignin creates a complex, resistant structure that limits the accessibility to cellulose and hemicellulose, thus affecting sugar liberation.