## 3 Results and Discussion
### Volatiles
#### 3.3.2 Minor Volatiles  
In total, 30 compounds (including esters, organic acids, and alcohols) were identified (Table 5). The nature of kefir culture and the fermentation temperature significantly affected (\(p<0.05\)) ester, alcohol, miscellaneous, and total volatiles' content, while strong interactions (\(p<0.05\)) between the two factors were observed in most cases. On the contrary, organic acids concentration was significantly (\(p<0.05\)) affected only by the nature of the kefir \begin{table}
\begin{tabular}{l c c c c c c c c c c} \hline \hline
**Nature of** & \begin{tabular}{c} **Fermentation** \\ **Dried Kefir** \\ **C** \\ \end{tabular} & \begin{tabular}{c} **Repeated** \\ **Batches** \\ **(C)** \\ \end{tabular} & \begin{tabular}{c} **Acetaldehyde** \\ **(mg/L)** \\ \end{tabular} & \begin{tabular}{c} **Ethyl** \\ **(mg/L)** \\ \end{tabular} & \begin{tabular}{c} **1-Propanol** \\ **(mg/L)** \\ \end{tabular} & \begin{tabular}{c} **Isobutanol** \\ **(mg/L)** \\ \end{tabular} & \begin{tabular}{c} **1-Hexanol** \\ **(mg/L)** \\ \end{tabular} & \begin{tabular}{c} **Amyl** \\ **Alcohol** \\ **(mg/L)** \\ \end{tabular} & \
\begin{tabular}{c} **Isoamyl** \\ **(mg/L)** \\ \end{tabular} &
\begin{tabular}{c} **Methanol** \\ **(mg/L)** \\ \end{tabular} \\ \hline \multirow{3}{*}{Free cells} & 30 & 1-3 & **44**-**88** & 20-32 & 26-37 & 33-42 & 1-3 & 18-22 & 60-87 & 9-21 \\  & 20 & 4-6 & 20-50 & 10-36 & 23-32 & 28-38 & 2-4 & 14-22 & 51-77 & 5-18 \\  & 5 & 7-8 & 13-18 & 12-15 & 11-14 & 10-12 & 5-7 & 6-8 & 18-23 & 12-13 \\ \hline \multirow{3}{*}{Imobilized cells on apple pieces} & 30 & 1-3 & 63-96 & 28-35 & 36-71 & 38-65 & 2-3 & 18-56 & 150-180 & 7-15 \\  & 20 & 4-6 & 15-21 & 33-67 & 57-10 & 51-94 & 3 & 24-70 & 89-20 & 8-21 \\ \cline{1-1}  & 5 & 7-8 & 18-25 & 6-7 & 23-30 & 21-25 & 2 & 11-13 & 48-55 & 5-7 \\ \cline{1-1}  & 30 & 1-3 & 50-97 & 18-37 & 35-61 & 38-83 & 2-3 & 17-51 & 137-166 & 4-17 \\ \cline{1-1}  & 20 & 4-6 & 7-15 & 33-65 & 56-57 & 51-67 & 1-3 & 24-40 & 89-146 & 5-8 \\ \cline{1-1}  & DCM & 5 & 7-8 & 14-15 & 11-12 & 14-19 & 14-20 & 2 & 8-10 & 38-41 & 12-15 \\ \cline{1-1}  & 30 & 1-3 & 29-41 & 7-17 & 31-44 & 30-47 & 2-3 & 14-38 & 70-133 & 10-21 \\ \cline{1-1}  & 20 & 4-6 & 9-15 & 37-56 & 32-69 & 29-58 & 1-2 & 15-42 & 60-139 & 6-14 \\ \cline{1-1}  & 35 & 7-8 & 14-23 & 10-12 & 27-39 & 22-30 & 1-2 & 13-17 & 60-66 & 3-5 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Major volatiles of low alcohol wines fermented by repeated batch fermentations at various temperatures (5–30 \({}^{\circ}\)C) using thermally-dried free or immobilized kefir culture. culture. In general, a decrease was observed in total volatiles' concentration at lower fermentation temperatures, although not significantly in all cases [20]. Fatty acid esters like ethyl hexanoate, ethyl octanoate, ethyl decanoate, and 2-phenylethyl acetate (responsible for the fruity notes) are considered important for wine bouquet [61], and were detected in all samples. Their synthesis is favored on higher temperatures, while an increase of their levels has previously been associated with cell immobilization [18; 54; 62]. Likewise, 3-methylbutyl acetate (known to contribute banana-like scents) was detected in all samples, while ethyl butyrate (responsible for apple-peel attributes), 2-methylbutyl acetate (responsible for peer flavors), ethyl dodecanoate (responsible for dried fruit, smokey, earthy, and toasty aromas) [54; 58; 63; 64], ethyl propanoate and isobutyl acetate (known for their fresh and fruity character), were detected in most of the samples. Interestingly, the highest ester concentrations (\(p<0.05\)) were observed in fermentations performed at 30 \({}^{\circ}\)C with immobilized cells on DCM, compared to wines produced by immobilized cells on other supports and free cells. Organic acids are known for their low odor threshold limit and their potential impact on wine flavor [64].