## 4 Conclusions  
The VOCs produced by LB672 growing in a defined medium containing either glucose or fructose as a carbon source under different fermentation conditions were assessed using PTR-ToF-MS, and the compounds detected were confirmed using HS-SPME-GC-MS, fastGC-PTR-ToF-MS, and/or the literature data. For the first time, PTR-ToF-MS was used to track the generation of fermentation VOCs in a defined medium. VOC production by LB672 \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**No** & **Flavour Standards** & **Molecular Formula** & **Molecular Weight** & **RI** & **RT (s)** &
\begin{tabular}{c} **Main/Fragment Ions** \\ **Checked** \\ \end{tabular} \\ \hline
1 & Ethyl acetate & C\({}_{4}\)H\({}_{8}\)O\({}_{2}\) & 88 & 888 & 58 & 89.060, 61.028, 43.018 \\
2 & 2-Butanone & C\({}_{4}\)H\({}_{8}\)O\({}_{3}\) & 72 & 918 & 60 & 73.065 \\
3 & Ethanol & C\({}_{2}\)H\({}_{6}\)O\({}_{3}\) & 46 & 932 & 59 & 47.049 \\
4 & Ethyl butanoate & C\({}_{6}\)H\({}_{12}\)O\({}_{2}\) & 116 & 1023 & 68 & 117.091, 89.060, 43.054 \\
5 & 2-Methyl propanol & C\({}_{4}\)H\({}_{10}\)O\({}_{3}\) & 74 & 1092 & 69 & 57.07 \\
6 & 2-Hexanone & C\({}_{6}\)H\({}_{12}\)O\({}_{3}\) & 100 & 1100 & 78 & 101.096 \\
7 & 2-Heptanone & C\({}_{7}\)H\({}_{12}\)O\({}_{3}\) & 114 & 1182 & 84.5 & 115.112 \\
8 & 3-Methyl butanol & C\({}_{5}\)H\({}_{12}\)O\({}_{3}\) & 88 & 1209 & 82.2 & 71.086 \\
9 & Ethyl hexanoate & C\({}_{8}\)H\({}_{16}\)O\({}_{2}\) & 144 & 1233 & 89 & 145.122, 117.091 \\
10 & 2-Nonanone & C\({}_{9}\)H\({}_{18}\)O\({}_{3}\) & 142 & 1390 & 109 & 143.143 \\
11 & Ethyl octanoate & C\({}_{10}\)H\({}_{20}\)O\({}_{2}\) & 172 & 1435 & 111.5 & 127.112, 145.122 \\
12 & Acetic acid & C\({}_{2}\)H\({}_{4}\)O\({}_{2}\) & 60 & 1449 & 112.5 & 61.028, 43.018 \\
13 & Benzaldehyde & C\({}_{7}\)H\({}_{6}\)O\({}_{3}\) & 106 & 1520 & 115.5 & 107.049 \\
14 & Ethyl decanoate & C\({}_{12}\)H\({}_{24}\)O\({}_{2}\) & 200 & 1638 & 146 & 201.233, 155.107 \\
15 & Phenylethyl alcohol & C\({}_{8}\)H\({}_{10}\)O\({}_{3}\) & 122 & 1906 & 218 & 105.070 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Flavour standards checked in fastGC PTR-ToF-MS.  
was strongly influenced by the carbon source and fermentation time and temperature. The VOCs detected were mainly acids, alcohols, aldehydes, esters, furrans, ketones, and sulphur compounds. Overall, the defined medium containing glucose (DM) generated higher concentrations of the VOCs of interest after 7 days of fermentation at 35 \({}^{\circ}\)C compared to at 25 \({}^{\circ}\)C and fructose-containing defined medium (DMFr) at both temperature conditions. This study suggests that the production of target VOCs in plant-based fermentations may be enhanced by altering the carbon source or fermentation conditions. This knowledge could be applied to the production of target VOC, on an industrial scale, through the fermentation of plant-based substrates. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/molecules29143275/s1](https://www.mdpi.com/article/10.3390/molecules29143275/s1)]([https://www.mdpi.com/article/10.3390/molecules29143275/s1](https://www.mdpi.com/article/10.3390/molecules29143275/s1)), Table S1: The VOCS (\(m/z\)) detected by PTR-ToF-MS after LB672 fermentation that significantly (\(p<\) 0.05) distinguished between defined medium compositions (carbon sources) (M), fermentation time (0 and 7 days) (T) and temperature (either at 25 or 35 \({}^{\circ}\)C) (Temp), and their interaction effects., Table S2: The mean concentration (ppbV) of selected VOCs (\(m/z\)) after 7 days of fermentation by LB672 across defined medium compositions (DM: glucose added, DMFr: fructose added) at either 25 or 35 \({}^{\circ}\)C. Values are presented as mean \(\pm\) standard error (\(n=4\)). Conceptualisation, P.S. and P.B. ; methodology, S.R., I.K., P.S., F.B. and P.B. ; investigation, S.R. ; formal analysis, S.R., I.K. and E.B. ; data curation, S.R., I.K. and E.B. ; writing--original draft, S.R. ; writing--review and editing, S.R., I.K., P.S., E.B., F.B. and P.B.