## 3 Results
### Biosynthesis of Volatile Organic Compounds
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \multirow{2}{*}{**Concentration**} & \multicolumn{3}{c}{_K. barnettii_ D1} & \multicolumn{3}{c}{_H. warnum_ D9} & \multicolumn{3}{c}{_W. anomalous_ D11} & \multirow{2}{*}{\(p\)-Value} \\ \cline{2-2} \cline{4-9}  & **1\%** & **5\%** & **10\%** & **1\%** & **5\%** & **10\%** & **1\%** & **5\%** & **10\%** \\ \hline Isobutyl alcohol & 17,141.45 a & 9907.40 c & 14,178.41 b & 3176.63 f & 4981.82 e & 7024.62 d & 4498.99 e & 633.78 d & 9776.04 c & -0.0001 \\ \hline
3-Methylbutanol & 48,380.42 a & 28,138.90 c & 38,570.89 b & 5034.51 fg & 9762.78 e & 18,812.46 d & 4960.63 fg & 6854.48 f & 10,728.03 e & -0.0001 \\ \hline
2-Methylbutanol & 17,640.24 a & 10,474.98 c & 14,265.84 b & 3183.62 e & 3704.44 e & 5601.32 d & 1539.72 f & 2005.29 f & 3019.58 e & -0.0001 \\ \hline
2-Phenylethanol & 12,195.62 a & 12,201.57 a & 9234.97 a & 5160.35 a & 6219.84 a & 9238.05 a & 6829.36 a & 6487.31 a & 8175.67 a & 0.0356 \\ \hline
1-Propanol & 1140.57 cde & 706.45 f & 571.25 f & 1921.53 b & 1090.56 de & 560.58 f & 1354.83 c & 1759.63 b & 2399.34 a & -0.0001 \\ \hline \end{tabular}
\end{table} 
Table 10: SHS-GC-MS analysis of higher alcohols formed during fermentation of hydrolysed apple pomace at 15 \({}^{\circ}\)C. Detailed report, including ion chromatograms after qualitative analysis, is shown in Supplementary Materials (“Supplementary reports S4–S6”). \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \multirow{2}{*}{**Concentration**} & \multicolumn{3}{c}{_K. barnettii_ D1} & \multicolumn{3}{c}{_H. warnum_ D9} & \multicolumn{3}{c}{_W. anomalous_ D11} \\ \cline{2-9}  & **1\%** & **5\%** & **10\%** & **1\%** & **5\%** & **10\%** & **1\%** & **5\%** & **10\%** \\ \hline Untreated AP & 240.51 & 232.83 & 240.41 & 319.93 & 374.08 & 334.41 & 10.41 & 23.55 & 8.78 \\ \hline Hydrolysed AP & 389.12 & 196.10 & 290.61 & 364.82 & 265.08 & 193.57 & 2.51 & 2.78 & 3.55 \\ \hline \multicolumn{9}{c}{Carbonyl compounds} \\ \hline Untreated AP & 5.54 & 1.80 & 1.13 & 5.62 & 5.47 & 4.19 & 1.75 & 2.18 & 1.71 \\ \hline Hydrolysed AP & 6.08 & 3.93 & 3.87 & 15.53 & 19.77 & 11.11 & 14.54 & 16.04 & 26.89 \\ \hline \multicolumn{9}{c}{Alcohols} \\ \hline Untreated AP & 36.89 & 42.96 & 50.41 & 27.49 & 14.90 & 19.57 & 16.67 & 36.95 & 12.90 \\ \hline Hydrolysed AP & 96.50 & 61.43 & 76.82 & 18.48 & 25.76 & 41.24 & 19.18 & 23.64 & 34.10 \\ \hline \end{tabular}
\end{table} 
Table 11: Summary concentrations of VOCs formed during fermentation of untreated and hydrolysed apple pomace at 15 \({}^{\circ}\)C.  
centration obtained from the sample after fermentation with _Wickerhamomyces anomalous_ D11 was very low compared to the other examined strains. The samples collected from other strains gave higher amounts of ethyl acetate at 1% inoculation. Considering other esters, the most notable changes in biosynthesis were observed for 3-methylbutyl acetate, 2-methylbutyrateacetate, 2-phenylethyl acetate, methyl acetate, and ethyl propionate. These compounds were produced generally in higher concentrations during the fermentation of hydrolys apple pomace. In this fermentation medium, one additional compound, ethyl hexanoate, was detected. However, in all samples, it was quantified only in trace amounts. The summary concentrations of esters did not correlate with the inoculum level, as different amounts were detected at different inoculum levels with no increasing or decreasing tendencies. Only in the case of samples fermented by _H. uvarum_ D9 was a decreasing tendency observed as the amount of inoculum increased. Besides esters, the summary concentrations of carbonyl compounds quantified during the experiment were higher compared to the samples of untreated apple pomace. This is due to the higher concentration of acetaldehyde quantified in all analysed samples, particularly in samples with _H. uvarum_ D9 and _W. anomalous_ D11. The amounts of other compounds remained at a similar level or were even lower. A relationship between the total amount of carbonyl compounds and the inoculum size for given strains was also observed.