# Water-Soluble Sugars of Pedigreed Sorghum Mutant Stalks and Their Recovery after Pretreatment
## 3 Results and Discussion
### Sugar Recovery after Dilute Acid Pretreatment
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Raw Biomass**} & \multicolumn{6}{c}{**Pretreatment Hydrolysate**} & \multirow{2}{*}{**Glucose**} & \multirow{2}{*}{**Fructose**} \\ \cline{2-2} \cline{4-11}
**Sample** & & & & & & & & **Sugar** & **Geos** & **Fructose** \\
**Identity** & & & & & & & & & **Degradation** & **(g/L)** & **(\%)** & **(\%)** \\ \cline{2-11}
**Sucrose** & **Glucose** & **Fructose** & **Glucose** & **Fructose** & **Xylose** & **Arabinese** & **HMF** & **Furfural** \\ \hline E18A & 0.13a  & 0.1a & 0.08a & 0.16a & 0.14a & 4.3a & 0.56a & 0a & 0.07a & 97.4a & 97.0a \\ E18B & 0.16a & 0.16a & 0.07a & 0.23a & 0.14a & 4.42a & 0.51a & 0.04a & 0.06a & 96.2a & 93.9a \\ E20A & 0.12a & 0.08a & 0.07a & 0.14a & 0.12a & 4.28a & 0.59a & 0.02a & 0.06a & 96.9a & 92.8a \\ E20B & 0.26a & 0.11a & 0.09a & 0.23a & 0.20a & 3.9a & 0.52a & 0.03a & 0.05a & 96.4a & 91.5a \\ E25A & 0.27a & 0.15a & 0.16a & 0.28a & 0.28a & 4.07a & 0.55a & 0.04a & 0.05a & 98.8a & 95.4a \\ E25B & 0.28a & 0.17a & 0.19a & 0.3a & 0.31a & 3.99a & 0.81a & 0.07a & 0.06a & 97.3a & 94.4a \\ E30A & 0.57b & 0.49a & 0.47a & 0.77b & 0.69b & 3.52b & 0.66a & 0.24a & 0.06a & 99.8a & 91.8a \\ E30B & 0.77b & 0.4a & 0.42a & 0.73b & 0.68b & 4.12a & 0.75a & 0.23a & 0.06a & 93.5a & 84.9b \\ E35A & 1.42b & 0.78b & 0.89b & 1.39b & 1.33b & 3.51b & 0.53a & 0.39b & 0.05a & 93.8a & 83.5b \\ E35B & 0.82b & 0.83b & 1.07b & 1.21b & 1.29b & 3.49b & 0.54a & 0.38b & 0.05a & 97.9a & 87.4b \\ E40A & 1.78b & 0.78b & 0.95b & 1.48b & 1.51b & 3.17b & 0.53a & 0.45b & 0.04a & 89.1b & 82.5b \\ E40B & 1.63b & 1.23b & 1.44b & 1.82b & 1.52b & 3.11b & 0.44b & 0.48b & 0.04a & 89.4b & 67.7b \\ E45A & 3.36b & 1.32b & 1.29b & 2.55b & 1.68b & 2.66b & 0.49b & 0.55b & 0.05a & 85.5b & 56.9b \\ E45B & 3.05b & 1.24b & 1.40b & 2.39b & 1.78b & 2.52b & 0.40b & 0.66b & 0.04a & 87.0b & 61.2b \\ E52A & 5.20b & 1.15b & 1.10b & 3.20b & 2.06b & 2.28b & 0.37b & 0.79b & 0.03b & 86.0b & 56.1b \\ E52B & 4.75b & 1.17b & 1.08b & 2.85b & 2.06b & 2.39b & 0.34b & 0.72b & 0.04a & 81.0b & 60.1b \\ \hline \multicolumn{11}{c}{Note: Samples E25A and E25B are wild-type sorghum used as control; the remaining samples are pedigreed sorghum mutant stalks.  } \\ \end{tabular}
\end{table} 
Table 2: Water-soluble sugars in the raw biomass and recovery of sugars after pretreatment. For wild-type sorghum, approximately 98% and 95% recovery was achieved for glucose and fructose, respectively. However, as the water-soluble sugar content in the sorghum stalks increased, significant amounts of sugars were lost during the dilute acid pretreatment, especially for fructose. When the water-extractive content was greater than 35% (_w/w_), fructose recovery was usually less than 60% and 5-HMF concentration was significantly higher (>0.7 g/L). In contrast, the glucose recoveries of all the selected sorghum samples were higher than 80%, which further proved that fructose was easier to degrade than glucose, as found in other studies [24; 25]. For sorghum mutants with high water-extractive content (>35%, _w/w_), a pre-washing step was beneficial to recover the present water-soluble sugars before performing the pretreatment process in order to avoid sugar losses or degradation during the pretreatment stage [23; 28]. However, for those sorghum mutants with less water-extractive content, a single-step, one-pot process was recommended to reduce processing cost and minimize wastewater disposal since a majority of sugars can be recovered after dilute acid pretreatment with minimal amount of degradation products. For high water-extractive biomass, an integrated bioprocess of combined advanced solid-state fermentation technology (ASSF) and alkaline pretreatment can be used to convert all the present sugars, including sucrose and structural carbohydrate.