## 3 Results and Discussion
### Hydrothermal Pretreatment (HTP): Organic Matter Solubilization  
As presented in Figure 2, the solubilization efficiency of OP, SBP, BSG, and RH was examined under hydrothermal pretreatment conditions of 120 \({}^{\circ}\)C for a duration of 10 min, 20 min, and 30 min. The hydrolysis degree was determined by measuring soluble chemical oxygen demand (sCOD, g O\({}_{2}\)/L) and dissolved organic carbon (DOC, g C/L). The results demonstrate a gradual increase in the concentration of soluble compounds over time, with a maximum sCOD and DOC reported after 30 min for most substrates. In terms of sCOD, the highest solubilization was exhibited by OP (57.3 g O\({}_{2}\)/L), followed by SBP and BSG (42.4 and 29.8 g O\({}_{2}\)/L, respectively), while RH exhibited the lowest solubilization performance (9.2 g O\({}_{2}\)/L). Regarding DOC values, the concentrations measured after 20 and 30 min of pretreatment were relatively similar across all biomasses. For OP, DOC reached 15.2 g C/L at 20 min and 14.1 g C/L at 30 min. SBP showed values of 11.1 and 10.9 g C/L at the same point, while BSG recorded 8.7 and 9.2 g C/L, respectively. The RH treatment demonstrated the lowest DOC concentration, not exceeding 1.5 g C/L after 30 min of treatment. This phenomenon may be attributed to the composition of the intrinsic structure of individual biomasses. Substrates such as OP, which are rich in soluble fiber and have lower lignin content, show faster and more significant hydrolysis. In contrast, RH, containing high lignin content, exhibited limited solubilization, confirming the limiting role of complex lignocellulosic structures during HTP. \begin{table}
\begin{tabular}{c c c c c} \hline
**Parameter** & **SBP** & **BSG** & **RH** & **OP** \\ \hline VS (g/kg) & 739.03 \(\pm\) 0.2 & 261.06 \(\pm\) 0.2 & 772.04 \(\pm\) 0.1 & 195.06 \(\pm\) 0.1 \\ TS (g/kg) & 833.05 \(\pm\) 0.5 & 280.01 \(\pm\) 0.4 & 915.00 \(\pm\) 0.0 & 206.02 \(\pm\) 0.8 \\ sCOD (g/kg) & 10.60 \(\pm\) 0.20 & 21.90 \(\pm\) 0.70 & 1.29 \(\pm\) 0.00 & 41.10 \(\pm\) 0.40 \\ DOC (g C/kg) & 4.09 \(\pm\) 0.10 & 7.93 \(\pm\) 0.10 & 0.52 \(\pm\) 0.10 & 10.10 \(\pm\) 0.00 \\ TVFA (g H-Ac/kg) & 0.87 \(\pm\) 0.00 & 1.39 \(\pm\) 0.00 & 0.03 \(\pm\) 0.00 & 0.43 \(\pm\) 0.00 \\ Total protein (g/kg) & 1.40 \(\pm\) 0.00 & 1.30 \(\pm\) 0.00 & 0.30 \(\pm\) 0.00 & 1.40 \(\pm\) 0.00 \\ Total polyphenols (gGalic Acid/kg) & 0.09 \(\pm\) 0.00 & 0.08 \(\pm\) 0.00 & 0.05 \(\pm\) 0.00 & 1.03 \(\pm\) 0.00 \\ pH (pH units) & 4.37 \(\pm\) 0.10 & 5.44 \(\pm\) 0.20 & 5.54 \(\pm\) 0.50 & 4.17 \(\pm\) 0.30 \\ NDF-Soluble fibers * (\%) & 42.20 \(\pm\) 1.40 & 38.00 \(\pm\) 1.10 & 16.50 \(\pm\) 1.20 & 66.80 \(\pm\) 1.20 \\ Cellulose (\%) & 21.10 \(\pm\) 1.40 & 16.30 \(\pm\) 0.40 & 32.85 \(\pm\) 0.40 & 15.70 \(\pm\) 2.20 \\ Hemicellulose (\%) & 22.50 \(\pm\) 0.40 & 33.70 \(\pm\) 0.50 & 22.20 \(\pm\) 0.60 & 9.11 \(\pm\) 0.80 \\ Lignin (\%) & 3.50 \(\pm\) 0.00 & 7.01 \(\pm\) 0.90 & 14.0 \(\pm\) 1.00 & 1.26 \(\pm\) 0.10 \\ Rest (\%) & 10.70 \(\pm\) 1.40 & 4.99 \(\pm\) 1.10 & 14.5 \(\pm\) 0.30 & 7.13 \(\pm\) 0.30 \\ \hline \end{tabular} (*) NDF-Soluble fibers: primarily composed of proteins, pectin, starch, and mucilages.  
\end{table} 
Table 1: Physicochemical characterization of the biomasses. Figure 2: Solubilization of organic matter, estimated as sCOD and DOC, for HTP. Note: Unt—Untreated. The hydrothermal conditions facilitate the disruption of biomass through auto-catalytic reactions, whereby water under pressure functions as both a thermal catalyst and a reactant, thereby facilitating bond disruption and molecular degradation. Consequently, the efficiency of solubilization is significantly influenced by the composition of the fibers, particularly the lignin content, which exhibits resistance to depolymerization under these conditions. According to the literature, autoclave-based thermal pretreatment demonstrates effectiveness in enhancing solubilization and hydrolysis of lignocellulosic substrates.