## 3 Results and Discussion  
### EOP Hydrolysate Composition and Detoxification  
Table 1 displays the composition in monomeric sugars of the hydrolysate obtained from sulfuric acid pretreatment of EOP. As seen, a hydrolysate rich in hemicellulose sugars was generated, with a total sugar concentration of 37.1 g/L. Among the sugars detected, the most abundant one was xylose, accounting for 64% of the total sugars contained in the acid hydrolysate. Therefore, this hydrolysate shows potential to be used as media for xylitol production, as xylitol can be biologically generated from xylose through fermentation with different microorganisms [4,5]. The inhibitor compounds composition of the EOP hydrolysate is also shown in Table 1. According to [PERSON] et al. [11], the specific type of lignocellulosic biomass, as well as the pretreatment conditions used, influence the type and concentrations of inhibitor compounds originated. In this study, under the work conditions employed, an insignificant presence of HMF (0.1 g/L) and low concentration of formic acid (0.8 g/L) were found, while a higher concentration of furfural (1.9 g/L) was detected. HMF and furfural are known to be generated as a result of the hexose and pentose degradation, respectively, coming from the formic acid from furfural [15]. Our results indicate a significant effect of acid pretreatment conditions in xylose decay, though hexoses were affected to a minor extent. On the other hand, acetic acid and total phenols were detected in much higher levels (5.6 and 4.1 g/L, respectively). Acetic acid comes from acetyl groups contained in the hemicellulose fraction, whereas the lignin breakdown could lead to the generation of phenolic compounds [15]. According to [PERSON] et al. [6], raw EOP contains 2.1% acetyl groups in its composition that explain the presence of acetic acid in the hydrolysate. The inhibitory effect of compounds, such as furans, acetic acid, and phenolic compounds, on the metabolism of xylitol-producing microorganisms has been previously reported, and several detoxification methods have been tested [20,21]. In this work, treatment with activated charcoal and ion-exchange resin were assayed to reduce the presence of these type of compounds in EOP hydrolysate. The efficiency of each detoxification method was evaluated considering its effect on the reduction of toxic compounds and resulting loss of sugars (Figure 1) and, specially, on its fermentability for xylitol production. The sugar and toxic compound concentrations obtained as a result of each detoxification method are showed in Table 1. \begin{table}
\begin{tabular}{l c c c} \hline \hline  & \multicolumn{3}{c}{**Detoxification Method**} \\ \cline{2-4}
**CarbohyDrates (g/L)** & **None** & **Activated Charcoal** & **Ion-Exchange Resin** \\ \hline Glucose & \(4.89\pm 0.04\) & \(4.45\pm 0.03\) & \(4.85\pm 0.14\) \\ Xylose & \(23.72\pm 0.53\) & \(22.66\pm 0.04\) & \(23.70\pm 0.13\) \\ Galactose & \(4.42\pm 0.36\) & \(3.45\pm 0.07\) & \(4.39\pm 0.14\) \\ Arabinose & \(3.36\pm 0.21\) & \(3.10\pm 0.01\) & \(3.35\pm 0.07\) \\ Mannose & \(0.69\pm 0.03\) & \(0.39\pm 0.06\) & \(0.67\pm 0.01\) \\ \hline
**Inhibitor compounds (g/L)** & & & \\ \hline Formic acid & \(0.79\pm 0.07\) & \(0.14\pm 0.03\) & \(0.16\pm 0.01\) \\ Acetic acid & \(5.59\pm 0.02\) & \(5.36\pm 0.00\) & \(3.51\pm 0.01\) \\ HMF & \(0.11\pm 0.00\) & n.d. & n.d. \\ Furfural & \(1.89\pm 0.10\) & \(0.31\pm 0.03\) & \(0.58\pm 0.04\) \\ Total phenols & \(4.08\pm 0.20\) & \(1.25\pm 0.02\) & \(0.63\pm 0.01\) \\ \hline \hline \end{tabular} n.d.: non-detected.  
\end{table} 
Table 1: Sugar and inhibitor compound concentrations in acid hydrolysate before and after detoxification. According to [PERSON] et al. [22], treatment by activated charcoal is considered one of the more economical and effective detoxification methods.