# Bioconversion of Apple Pomace to _Meyerozyma guilliermondii_ and _Scheffersomyces stipitis_ Biomass
## 3 Results and Discussion
### Sugars, Organic Acids, and Alcohols in the AP Hydrolysates

Table 2: Sugars and galacturonic acid content in the AP hydrolysates. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{1}{c}{**Sample**} & **CA** & **SA** & **LA** & **FA** & **AA** \\  & & & **[g/L]** & & \\ \hline W & 0.185 \(\pm\) 0.007 & 0.127 \(\pm\) 0.0016 & 1.27 \(\pm\) 0.0415 & 0.067 \(\pm\) 0.0019 & 0.262 \(\pm\) 0.0043 \\ A & 0.043 \(\pm\) 0.0023 & 0.091 \(\pm\) 0.0038 & 1.2 \(\pm\) 0.0098 & 0.083 \(\pm\) 0.001 & 1.115 \(\pm\) 0.0374 \\ WE50 & 0.184 \(\pm\) 0.0082 & 0.054 \(\pm\) 0.0011 & 1.18 \(\pm\) 0.0096 & 0.042 \(\pm\) 0.001 & 0.905 \(\pm\) 0.0275 \\ AE50 & 0.085 \(\pm\) 0.0026 & 0.062 \(\pm\) 0.0018 & 1.11 \(\pm\) 0.024 & 0.056 \(\pm\) 0.002 & 1.141 \(\pm\) 0.0244 \\ WE30 & 0.215 \(\pm\) 0.0063 & 0.007 \(\pm\) 0.0003 & 1.19 \(\pm\) 0.0541 & 0.045 \(\pm\) 0.0018 & 0.858 \(\pm\) 0.0337 \\ AE30 & 0.101 \(\pm\) 0.003 & 0.09 \(\pm\) 0.0015 & 1.24 \(\pm\) 0.061 & 0.065 \(\pm\) 0.0023 & 1.178 \(\pm\) 0.0386 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Organic acid content in the AP hydrolysates. of xylose in the samples ranged from 4.96 g/L (sample WE30) to 7.92 g/L (AE30 sample). The amount of arabinose observed in the WE and AE samples ranged from 5.15 g/L for the WE30 sample to 5.669 g/L for the AE30 sample. It can be seen that 2% sulphuric acid significantly supported the decomposition of the apple pomaces matrix. However, we predicted that the general increase in the efficiency of enzymatic hydrolysis would be observed for samples pretreated with sulphuric acid instead of water (for the exact temperature); in the results of the statistical comparison (including the variance and \(p\)-value comparison) of WE30-AE30 and WE50-AE50, some of the results for specific sugars do not support such a general conclusion. For example, the glucose concentration in the WE30 sample was significantly higher \(p\) < 0.05 (19.311 \(\pm\) 0.8692 g/L) than in the AE30 sample (14.866 \(\pm\) 0.6147 g/L). For the same sugar, the concentrations in WE50 and AE50 were 18.55 \(\pm\) 0.6058 g/L and 18.325 \(\pm\) 0.8415 g/L, respectively, and the difference was not statistically significant (\(p\) > 0.05). However, the specific sugar concentrations are the results of the unique combination of substrate characteristics and the hydrolysis course; the considerable concentration, promising for yeast yield, was that the galacturonic acid, the derivative of pectins present in the AP, and reported also by others [69; 70; 71]. The purpose of conducting enzyme hydrolysis at a temperature of 30 \({}^{\circ}\)C, which is approximately 20 \({}^{\circ}\)C below the optimal for the preparation of Cellic CTec2 [72], was to investigate whether performing this stage at 50 \({}^{\circ}\)C is necessary for maximising hydrolysis efficiency and achieving the final SCP yield. These temperatures are not tolerated by yeast cells, making it impossible to implement a time- and energy-saving process of simultaneous saccharification and SCP cultivation. However, the results presented in Table 2 suggest promising prospects for this approach, as the sugar concentrations released during the hydrolysis of pretreated AP samples at 30 \({}^{\circ}\)C are comparable to those obtained at 50 \({}^{\circ}\)C.  
The final concentrations of specific sugars after pretreatment and enzymatic hydrolysis are not only influenced by the efficiency of the enzymes but also by the substrate load ratio (SL) (substrate: working liquid) used. In our study, this parameter was close to 10% (\(w/v\)). [PERSON] et al. reported a glucose content in the AP hydrolysate up to 4 g/L but for 2% SL (\(w/v\)), which is a lower value than 19.311 \(\pm\) 0.8692 g/L of glucose obtained in our WE30 sample. However, [PERSON] et al. [73] reported glucose concentrations of up to 30 g/L in hydrolysates obtained with a mild sulphuric acid solution at SL ratios of 20-30%. Our findings regarding sugar content in hydrolysates are also supported by [PERSON] et al. [74].