## 3 Results and Discussion  
### Chemical Characterization of Feedstock and Processed Solids  
The tight structure of wheat straw cell wall is hard to hydrolyze without pretreatment processes that could overcome the recalcitrance of lignocellulosic for the enzyme action. In this work, hydrothermal pretreatment (HTP), alkaline treatment and enzymatic treatment, or the combinations thereof, were used to improve the accessibility of the enzymes to the WS. Hydrothermal treatment was chosen due to the advantages highlighted in the literature, such as low cost, reduced chemical consumption due to the increase in acetic acid and water ionization that catalyze the process and facilitate depolymerization of the wheat straw structure, production of oligosaccharides and monosaccharides with decreased formation of degradation products, and the formation of residues that could further be fractioned [21].  
Milling was applied to reduce the particle size and improve the hydrolysis by increasing the surface area [21]. The chemical composition of wheat straw is shown in Table 1. The holocellulose of wheat straw accounts for 68.67 \(\pm\) 0.4% of the total weight and consists of 27.67 \(\pm\) 0.1% hemicelluloses and 36% \(\pm\) 0.3 celluloses. Lignin was quantified as acid detergent lignin 12.91 \(\pm\) 0.8%, ash 5 \(\pm\) 0.1% and extractives 1.2 \(\pm\) 0.1%. During the HTP, the hemicelluloses decreased with the severity factor, from 24.7 \(\pm\) 0.2% at 2.35 when treated at 140 \({}^{\circ}\)C for 15 min, to 11.3 \(\pm\) 0.1% at a severity factor of 2.94 when HTP reached 180 \({}^{\circ}\)C. The dissolution of hemicellulose was caused by the ionization of water and formation of acetic acid [55]. Consequently, cellulose increased with the severity factor, from 45.12 \(\pm\) 0.1% to 51 \(\pm\) 0.5%. As for lignin, the content increased with the severity factor, with the highest content of 9.9% at 180 \({}^{\circ}\)C (Table 1). The pH profile after HTP shows the treatment severity and indicates the solubility of hemicelluloses in the liquid phase. The pH of the filtrate at the severity factor of 2.35 decreased from 5.2 to 4.5 at the severity of 2.94 (160 \({}^{\circ}\)C, 15 min) to 3.9 at the severity of 3.53 (180 \({}^{\circ}\)C, 15 min). Similar results were obtained by [PERSON] et al. in 2018, who applied hydrothermal pretreatment combined with ethanol extraction to obtain oligosaccharides from wheat straws [10]. They observed that hemicellulose decreased with the HTP increasing temperature (from 27.06% \(w/w\) at 120 \({}^{\circ}\)C to 25.09% \(w/w\) at 140 \({}^{\circ}\)C and 3.09% \(w/w\) at 180 \({}^{\circ}\)C), while cellulose content increased with the increase of temperature from 120 \({}^{\circ}\)C to 180 \({}^{\circ}\)C.  
Chemical Characterization of Hydrolysates after HTP, Alkaline and Enzymatic Treatments of the Solid Residues  
Hydrothermal pretreatment was shown to degrade the hemicellulose present in the WS, improving the accessibility of cellulose to enzymes, with the formation of soluble sugars, xylose oligomers (xylo-oligosaccharides \"XOS\"), weak acids, furan derivatives and phenolic compounds. The results concerning the production of soluble sugars (glucose, xylose and arabin) and xylo-oligosaccharides are presented in Tables 2 and 3, respectively. In Supplementary File S1 the results obtained by other researchers in terms of wheat straw fractioning, sugars, xylo-oligosaccharides and inhibitor release are described.