## 3 Results and Discussion
### Downstream Processing  
In order to obtain a purified fraction of XOS for potential food applications, the hydrolysates obtained during hydrothermal pretreatment and enzymatic treatments must \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **Temperature** \\ **(\({}^{\circ}\)C)** \\ \end{tabular} } & **Severity** & \multirow{2}{*}{\
\begin{tabular}{c} **Solid** \\ **Recovery** \\ **(\%)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Sugars in Filtrates** \\ **(HTP and Alkaline) (g)** \\ \end{tabular} } & \multicolumn{3}{c}{**Enzyme Hydrolysates (Combined**} & \multicolumn{3}{c}{**Sugar**} \\  & & & **(HTP and Alkaline) (g)** & & & \multicolumn{3}{c}{**Enzymatic and Alkali Enzymatic**} & \multicolumn{3}{c}{**Recovery**} \\  & & & & & & & & ** Treatments) (g)** & & & \\ \hline \multicolumn{10}{c}{G \({}^{\mathrm{a}}\)} & \({\mathrm{X}}^{\mathrm{b}}\) & \({\mathrm{A}}^{\mathrm{c}}\) & \({\mathrm{T}}^{\mathrm{d}}\) & \({\mathrm{G}}^{\mathrm{a}}\) & \({\mathrm{X}}^{\mathrm{b}}\) & \({\mathrm{A}}^{\mathrm{c}}\) & \({\mathrm{T}}^{\mathrm{d}}\) & (g) \({}^{\mathrm{e}}\) & (\%) \({}^{\mathrm{f}}\) \\ \hline
140 & 2.35 & 88.9 & 0.49 & 0.88 & 0.25 & 1.62 & 24.98 & 14.99 & 2.92 & 42.89 & 44.5 & 64.8 \\ \hline
160 & 2.94 & 87.84 & 3.73 & 3.6 & 0.9 & 8.23 & 14.48 & 10.11 & 2.51 & 27.1 & 35.3 & 51.4 \\ \hline
180 & 3.53 & 76.8 & 3.48 & 3.90 & 1.38 & 8.76 & 28.21 & 23.23 & 4.44 & 55.88 & 64.6 & 94 \\ \hline \hline \end{tabular}  
* G: released glucose; \({}^{\mathrm{b}}\) \({\mathrm{X}}\): released xylose; \({}^{\mathrm{c}}\) \({\mathrm{A}}\): released arabinose; \({}^{\mathrm{d}}\) \({\mathrm{T}}\): total sugars; \({}^{\mathrm{e}}\) sum of sugars in the hydrolyses + alkaline and combined enzymatic and alkali hydrolyses; \({}^{\mathrm{f}}\) Percentage of sugar recovery, calculated by (sugar recovery (g)/carbohydrate in the raw material (g)).  
\end{table} 
Table 4: Material balances from hydrothermal pretreatment followed by alkali, enzymatic and combined alkali enzymatic treatments. be refined. A variety of compounds like monosaccharides, acetic acid, furfural and HMF from pentose and hexose dehydration, soluble inorganic compounds or protein-derived products could appear in the hydrolyses [34]. Commercial xylo-oligosaccharides have a purity in the range of 75-95% [12]. The literature shows that purification and separation of XOS requires several processing steps, consisting of physicochemical treatments [62]. Adsorption was employed in combination with other treatments for the refining of XOS, intended to remove undesired compounds and separate oligo from monosaccharides. Chromatographic separation was carried out for XOS purification at an analytical level, yielding high purity fraction, while ion exchange was used for purification of XOS alone or in multi-step processing [12; 34; 62; 63]. In this work, refining experiments were carried out in two steps: a first step of adsorption using the surface-active material activated charcoal or the polymer adsorber resin PUROLITE MN-502 to remove phenols and reduce the concentration of salt ions. The hydrolysate resulting after alkaline and enzymatic hydrolysis of the residues treated at the severity factor of 3.53 was used for the downstream processing experiments. As observed in Table 5, statistically significant differences were obtained when comparing removal of sulphate, phosphate and cations (K\({}^{+}\), Mg\({}^{2+}\), Ca\({}_{2}\)\({}^{+}\), NH\({}_{4}\)\({}^{+}\)N) by activated charcoal or the MN-502 resin, the latter showing higher efficiency. For instance, phosphate concentrations reduced from the initial 59 mg/L in the hydrolysate to 16 mg/L or 23 mg/L after 2 h of decolorization with the resin or the activated charcoal, respectively. Sulphate concentrations dropped almost to half, from 80 mg/L to 40 mg/L after treatment with the resin, showing statically significant differences when compared to the filtrate resulting after decolorization with charcoal (54 mg/L).