# Shedding Light on the Volatile Composition of _Broa_, a Traditional Portuguese Maize Bread
## 3 Results and Discussion
### Characterization of the Volatile Composition of Broas
\begin{table}
\begin{tabular}{c c c} \hline
**Chemical Class** & **Compound** & **Suggested Origin** \\ \hline \multicolumn{3}{c}{**Cluster 1:** B6, B7, B8} \\ \hline Furans & 2-Pentyfuran \({}^{*}\) (\(-\)) & Lipid oxidation, from (\(E\))-2-nonenal [17] \\ \hline \multirow{4}{*}{Hydrocarbons} & 1-Chlorooctadecane (\(+\)) & \\  & Undecane (\(+\)) & \\  & Decane (\(+\)) & \\  & 3,7-Dimethyldecane (\(+\)) & Lipid oxidation [21] \\  & 3-Methylundecane (\(+\)) & \\  & 2,4-Dimethyl-1-decene (\(+\)) & \\ \hline \multirow{2}{*}{Pyrroles} & 1-Furfurylpyrrole (\(+\)) & Last stages of the Maillard reaction [19] \\ \cline{2-3}  & 2-Acetylpyrrole (\(+\)) & Maillard reaction, from oxidation of 2-acetyl-1-pyrroline [21] \\ \hline \multirow{2}{*}{Alcohols} & 2-Hexyl-1-octanol (\(+\)) & Yeast fermentation or reduction of aldehydes from lipid oxidation [17] \\ \hline Pyranones & Maltol (\(+\)) & Degradation of disaccharides, such as maltose or lactose [21] \\ \hline Furfurals & 5-Methylfurfurral \({}^{*}\) (\(+\)) & Degradation of sugars [11; 20] \\ \hline \multicolumn{3}{c}{**Cluster 2:** B3, B4, B11} \\ \hline \multirow{2}{*}{Ketones} & 3-Octen-2-one (\(-\)) & Lipid oxidation [20], fermentation [20] or sugar \\ \cline{2-3}  & \multicolumn{1}{c}{degradation [11]} \\ \hline \multirow{3}{*}{Aldehydes} & Octanal \({}^{*}\) (\(-\)) & Lipid oxidation [15] \\ \cline{2-3}  & 2,4-Decadienal (\(E\),\(E\)) \({}^{*}\) (\(-\)) & Lipid oxidation of linoleic acid [28] \\ \cline{2-3}  & Benzaldehyde \({}^{*}\) (\(-\)) & Ehrlich pathway or Strecker degradation, from \\ \cline{2-3}  & \multicolumn{1}{c}{phenylalanine [17; 25], or auto-oxidation of 2,4-decadienal [18]} \\ \hline \multirow{3}{*}{Hydrocarbons} & 3-Ethyl-2-methyl-1,3-hexadiene (\(-\)) & \\ \cline{1-1}  & Tetradecane (\(+\)) & Lipid oxidation [21] \\ \cline{1-1} \cline{2-3}  & 1-Tetradecene (\(+\)) & \\ \hline \end{tabular}
\end{table} 
Table 4: _Bros\({}^{\prime}\)_ volatile compounds that contributed to discriminate the different clusters. Figure 5: Dendrogram of cluster analysis of _bros_. _Broas_ were differentiated mainly by their content in volatiles from lipid oxidation and formed during baking. In particular, clusters 3 and 4 were characterized by higher amounts in volatiles from lipid oxidation. As observed for maize flours, the _broa_ prepared from the commercial maize variety (B12) was discriminated from all the others, belonging to cluster 4 (Figure 5 and Table 4). This sample was characterized by higher amounts in some aldehydes, alcohols and alkanes, suggesting that more lipid oxidation reactions [20; 21] had occurred, probably due to the different genetic origin of the corresponding maize flour (F12), as previously discussed. It was also characterized by lower contents in methylpentylfuran. Although it was not possible to confirm the identification of methylpentylfuran, it is possible that it had been originated by lipid oxidation, such as 2-pentylfuran [15; 17], and/or during the Maillard reaction, such as other furans [19]. On the contrary, cluster 3 (B1, B2, B5, B9 and B10) was characterized by higher contents in methylpentylfuran and, similar to cluster 4, by higher amounts in several low-odor threshold aldehydes derived from lipid oxidation. Cluster 2 (B3, B4 and B11) was characterized by lower amounts in volatiles from lipid oxidation and/or fermentation reactions [15; 21; 28], namely 3-ethyl-2-methyl-1,3-hexadiene, 3-octen-2-one, octanal and benzaldehyde. The lower amounts in 2,4-decadien observed in these samples can explain their lower benzaldehyde contents,since benzaldehyde can be formed by the auto-oxidation of 2,4-decadienal (_E_,_E_) [18]. Finally, _bros_ B6, B7 and B8 belonged to cluster 1, characterized by higher contents in compounds resulting from the baking process, particularly maltol, 1-furfurylpyrrole, 2-acetylpyrrole and 5-methylfurfurral. The correlations among _bros_' volatiles were also evaluated (Supplementary Table S6).