## 3 Results and Discussion
### Comparative Analysis of SHF and SSF Configurations for 2,3-BDO Production from Carrot Discard  
To assess the feasibility of using carrot discard (CD) as a feedstock, two process configurations--separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF)--were evaluated for both _B. licheniformis_ and _B. amyloliquefaciens_. For the SHF process, an initial enzymatic hydrolysis of the CD yielded a sugar-rich hydrolysate with a total sugar content of 67.7 g/L. The composition was as follows (in g/L): glucose, 41.5; fructose and galactose, 24.2; arabinose, 2.0; formic acid, 0.3; and acetic acid, 0.7. In contrast, the SSF strategy involved conducting the hydrolysis and fermentation steps concurrently in a single vessel. The performance of both strains under each configuration is detailed in Table 3 and Figure 3.  
Under the SHF configuration, _B. licheniformis_ completely consumed all available sugars from the CD hydrolysate within 46 h (Figure 3a), showing a preference for glucose (depleted in 28 h) over fructose, galactose, and arabinose (depleted in 46 h) (Figure S4). This phenomenon is characteristic of catabolite repression, a well-documented regulatory \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Microorganism**} & \multirow{2}{*}{\begin{tabular}{c} **Process** \\ **Conf.** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Time** \\ **(h)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Sugar** \\ **(ptake** \\ **(\%)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **2,3-BDO** \\ **(g/L)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Ethanol** \\ **(g/L)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Acetoin** \\ **(g/L)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Bioomass** \\ **(g/L)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Y2,3-BDO** \\ **(600 nm)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **P2,3-BDO** \\ **(g/g)** \\ \end{tabular} } \\ \hline _B. licheniformis_ & SHF & 46 & 100 (100) & 10.9 \(\pm\) 0.8 & 0.4 \(\pm\) 0.3 & 24.2 \(\pm\) 0.4 & 18.7 \(\pm\) 0.0 & 0.17 & 0.236 \\  & SSF & 22 & 60.2 (51.0) & 0.9 \(\pm\) 0.0 & 1.5 \(\pm\) 0.2 & 3.7 \(\pm\) 0.3 & - & 0.02 & 0.040 \\ _B. amyloliquefaciens_ & SHF & 56 & 81.2 (100) & 16.7 \(\pm\) 1.6 & 0.2 \(\pm\) 0.1 & 8.0 \(\pm\) 0.2 & 14.6 \(\pm\) 0.0 & 0.33 & 0.298 \\  & SSF & 56 & 46.4 (46.4) & 4.1 \(\pm\) 0.0 & 0.5 \(\pm\) 0.0 & 3.1 \(\pm\) 0.0 & - & 0.14 & 0.074 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Sugar uptake (%), fermentation products concentration (g/L), biomass OD (600 nm), 2,3-butanediol yield (Y2,3-BDO/subarray, g/g) and 2,3-butanediol productivity (P2,3-BDO, expressed as g/L-h), at the time of maximum 2,3-butanediol production, obtained in fermentation assays of carrot discard in SHF (separate hydrolysis and fermentation) and SSF (simultaneous saccharification and fermentation) configurations by _B. licheniformis_ and _B. amyloliquefaciens_. Data in parentheses refer to sugar uptake at the end of the fermentation process (144 h). mechanism in many bacteria. In the presence of a preferred carbon source like glucose, the expression and activity of enzymes required for the transport and metabolism of secondary sugars are repressed [26]. For example, the metabolism of pentoses such as xylose is often inhibited by glucose through the repression of key enzymes like xylose reductase and xylitol dehydrogenase. Only after glucose has been substantially depleted from the medium are these enzymatic pathways derepressed, allowing for the consumption of the remaining sugars. This pattern of sequential sugar utilization is consistent with numerous studies on 2,3-BDO production from mixed-sugar feedstocks. [PERSON] et al. [21] observed a much higher glucose uptake rate compared to pentose uptake by _B. licheniformis_ DSM 8785 during fermentation of sorghum stalk biomass. Similarly, [PERSON] et al.