# Bioconversion of Apple Pomace to _Meyerozyma guilliermondii_ and _Scheffersomyces stipitis_ Biomass
## 3 Results and Discussion
### Sugars, Organic Acids, and Alcohols in the Post-Cultivation Effluents  
Tables 5-7 show the content of selected simple sugars, organic acids, glycerol, and ethanol in the AP hydrolysates.  
\begin{table}
\begin{tabular}{l c c c c c} \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{**CEL**} & \multirow{2}{*}{**GLU**} & **XYL** & **ARA** & **GA** \\  & & & **[g/L]** & & \\ \hline MgWE30 & 0.411 \(\pm\) 0.0218 & 0.01 \(\pm\) 0.0002 & 0.04 \(\pm\) 0.0018 & 0.433 \(\pm\) 0.0073 & 3.307 \(\pm\) 0.0722 \\ MgAE30 & 0.685 \(\pm\) 0.0117 & n.d. & 0.04 \(\pm\) 0.0016 & 0.376 \(\pm\) 0.0142 & 6.506 \(\pm\) 0.1486 \\ MgWE50 & 0.358 \(\pm\) 0.0119 & 0.01 \(\pm\) 0.0002 & 0.04 \(\pm\) 0.001 & 0.634 \(\pm\) 0.0157 & 5.733 \(\pm\) 0.1525 \\ MgAE50 & 0.061 \(\pm\) 0.0027 & 0.131 \(\pm\) 0.0032 & 0.11 \(\pm\) 0.0036 & 0.04 \(\pm\) 0.0013 & 1.707 \(\pm\) 0.0725 \\ SsAE30 & 0.821 \(\pm\) 0.0213 & n.d. & 0.01 \(\pm\) 0.0002 & 0.01 \(\pm\) 0.0004 & 6.166 \(\pm\) 0.0897 \\ SsWE30 & 0.118 \(\pm\) 0.0043 & 0.111 \(\pm\) 0.0029 & 0.06 \(\pm\) 0.0027 & 0.02 \(\pm\) 0.0007 & 3.141 \(\pm\) 0.0916 \\ SsWE50 & 0.02 \(\pm\) 0.0001 & 0.151 \(\pm\) 0.0025 & 0.05 \(\pm\) 0.002 & 0.02 \(\pm\) 0.0005 & 1.972 \(\pm\) 0.06 \\ SsAE50 & 0.427 \(\pm\) 0.0177 & 0.149 \(\pm\) 0.0037 & n.d. & 0.04 \(\pm\) 0.0009 & 1.366 \(\pm\) 0.0627 \\ \hline \end{tabular}
\end{table}
Table 5: Sugars and galacturonic acid content in the post-cultivation effluents.  
Considering the presence of the acids analysed in the post-culturing effluents from the yeast cultures _M. guillermondii_ and _S. stipitis_ (Table 6), only trace amounts of citric acid were observed in the range of 0.000-0.066 g/L. The succinic acid concentration oscillated between 0.01 g/L (MgWE50 sample) and 0.094 g/L for the MgAE30 sample. The presence of lactic acid in the culture leachate was at a level of 0.006 g/L (MgWE30)-0.032 g/L (SsAE50). The formic acid content varied considerably in the post-culturing leachates, ranging from 0.045 g/L in the MgAE30 sample to 0.134 g/L for the SsAE50 effluent. Only traces of acetic acid between 0.002 g/L and 0.023 g/L were determined in culture leachates, compared to the 0.858-1.178 g/L observed for the AE and WE hydrolyses before cultivation.  
Analysis of the acid concentration results before and after cultivation (Table 6) showed that citric, lactic, and acetic acid concentrations decreased during cultivation. In contrast, such consistency was not observed for succinic and formic acid. To evaluate the organic acid balance before and after cultivation, it must be remembered that the final concentration of these acids results from the possible activity of yeast strains and the undesired bacteria from the possible contaminations.  
Samples after the cultivation of the yeast _Meyerozyma guillermondii_ and _Scheffersomyces stipitis_ contained trace amounts of glycerol (0.024 g/L or less)--Table 7. After the culture of _Meyerozyma guillermondii_ cells, the highest ethanol concentration was recorded in sample MgAE50 (0.061 g/L). After the culture of yeast _Scheffersomyces stipitis_, the highest alcohol content was obtained in sample SsAE50 (0.113 g/L). The low ethanol results obtained in the post-culture effluents may suggest that the yeast carried out the expected process of efficient biomass culture rather than alcoholic fermentation. The observation of a reduction in glycerol concentration during culture is also promising, probably because it was assimilated by the yeast cells and used for energy and building cell mass.