## 3 Results and Discussion
### Cellulose Isolation  
Table 1 reports the results of the cellulose isolation from wheat process following the two different protocols of Figure 1, based on the characterization of the solid residue obtained at the end of the whole process, then after acid or auto-hydrolysis, basic hydrolysis and bleaching. Even though the fiber residue from auto-hydrolysis appears to be better in color as well as texture (Figure 2), its purity (cellulose content) is slightly lower in the auto-hydrolysis process when compared to the acid hydrolysis method (Table 1). Interestingly, the hemicellulose, acetic acid, acid soluble and acid insoluble lignin content of auto-hydrolyzed fiber is lower than those of the acid hydrolyzed sample. This means that the auto-hydrolysis process leads to a better delignification of the final cellulose material, which results both in a better quality of the cellulose and in a possible higher lignin recovery form the obtained liquor [36]. On the other hand, the final lower purity of cellulose coming from auto-hydrolysis could be explained by the formation of pseudo-lignin compounds during biomass pretreatment processes [50]. These compounds, derived from sugar degradation products, cannot be \begin{table}
\begin{tabular}{l c c} \hline  & **Auto-Hydrolysis** & **Acid Hydrolysis** \\ \hline Fiber residue yield (g/100 g\({}_{\text{wheat straw dm}}\)) & 20.41 \(\pm\) 0.22 & 17.56 \(\pm\) 0.37 \\ Cellulose (g/100 g\({}_{\text{fiber residue dm}}\)) & 77.79 \(\pm\) 0.85 & 85.98 \(\pm\) 1.84 \\ Cellulose yield (g/100 g\({}_{\text{wheat straw dm}}\)) & 15.88 \(\pm\) 0.17 & 15.10 \(\pm\) 0.32 \\ Cellulose recovery (g/100 g\({}_{\text{cellulose wheat straw dm}}\)) & 47.01 \(\pm\) 0.51 & 44.70 \(\pm\) 0.92 \\ Hemicellulose (g/100 g\({}_{\text{fiber residue dm}}\)) & 1.01 \(\pm\) 0.02 & 2.05 \(\pm\) 0.11 \\ Acetic acid (g/100 g\({}_{\text{fiber residue dm}}\)) & 0.19 \(\pm\) 0.02 & 0.59 \(\pm\) 0.01 \\ Acid soluble lignin (g/100 g\({}_{\text{fiber residue dm}}\)) & 0.90 \(\pm\) 0.04 & 1.09 \(\pm\) 0.03 \\ Acid insoluble lignin (g/100 g\({}_{\text{fiber residue dm}}\)) & 5.47 \(\pm\) 0.50 & 12.43 \(\pm\) 0.24 \\ \hline \end{tabular}
\end{table} 
Table 1: Characterization of the final fiber residue obtained after acid/alkaline fractionation process of wheat straw (with initial auto-hydrolysis or conventional acid hydrolysis) in terms of cellulose, hemicellulose, lignin and acetic acid content. Values are reported as mean values (\(n=3\)) \(\pm\) sd. evaluated using structural carbohydrates analytical method. For these reasons, furthers studies need to be conducted in order to properly assess these compounds. However, the cellulose recovery is comparable and so the greener auto-hydrolysis process could be very interesting from an industrial point of view. These kinds of pretreatment processes were often used to recover cellulose with lower purity to be used for successive fermentation, for instance for bioethanol production [51] or for further enzymatic hydrolysis [52]. For this reason, there are few scientific works concerning the recovery of high pure cellulose from wheat straw. [PERSON] and [PERSON] [53] studied a process to produce highly purified cellulose from wheat straw using sequential treatments of dewaxed straw (i.e., wheat straw after extraction with ethanol and toluene) with potassium hydroxide under ultrasonic irradiation. The final fiber residue yield is equal to 37%, then higher than in the present study (Table 1). The main issue is that the proposed process was performed using ultrasound technology, which presents very high costs at industrial scale. Moreover, the final fiber residue yield of auto-hydrolysis process proposed in this work can be further increased by improving both solids recovery yield and optimizing the operating conditions of the process. [PERSON] et al. (1998) [54] investigated a fractionation of wheat straw by steam-explosion technique, instead of auto-hydrolysis, followed by an alkali delignification and a final bleaching step to produce a high pure cellulose.