# Shedding Light on the Volatile Composition of _Broa_, a Traditional Portuguese Maize Bread
## 3 Results and Discussion
### Characterization of the Volatile Composition of Broas  
The volatile compounds present in _broas_ were mainly derived from lipid oxidation (Figure 4) and originated during bread making (fermentation (Supplementary Figure S4) and non-enzymatic browning reactions (Supplementary Figure S5). It is known that the increase of lipid oxidation products in breads is associated with (1) higher fermentation temperatures [15], (2) the use of wholegrain flours, such as in broas preparation, probably due to the additional lipid material in cereal germ [28], and (3) the presence of oxidative yeasts naturally present in sourdoughs, such as _Candida_ spp. [16]. 4-Heptrenal (\(Z\)) and 2,4-decadienal (\(E\),\(E\)) were detected in _broas_, but not in maize flows. Both aldehydes have been reported as primary odorants to contribute to the flavor of wheat bread [56], and 2,4-decadienal has also been described as an important popcorn volatile [24]. They have also been described as lipid oxidation products and could have been formed during fermentation, due to the metabolic activity of yeasts and lactic acid bacteria [6]. Since 2,4-decadienal was particularly abundant in the commercial wheat flour used for _broas_ preparation, it could also have been derived from the lipid oxidation of linoleic acid [28] present in this flour. Benzaldehyde was detected in all _broas_ despite being only detected in the commercial maize flour. It may have been produced by auto-oxidation of 2,4-decadienal [18] or formed from phenylalanine through the Ehrlich pathway and/or Strecker degradation (Supplementary Figure S4) [17; 25]. Other compounds were also detected in _broas_, but not in maize flours, as acids (acetic and hexanoic acids), esters (ethyl hexanoate, ethyl octanoate, 1-hexyl acetate), ketones (octen-2-one, 3-hydroxy-2-butanone, 2-methyl-3-octanone and 3,5-ocatadien-2-one) and furanones (\(\gamma\)-N-caprolactone and \(\gamma\)-nonalactone). These compounds may have been originated by yeast and/or bacteria during fermentation [15; 17; 20; 22]. Acetic acid is a well-known main product of fermentation by LAB and its concentration is higher when sourdough is used in breads; formulation [20], such as in the preparation of _broa_. In spite of being volatilized during baking [11], acetic acid may be a product of Maillard or caramelization reactions [17; 20]. Furanones can also be products of carbohydrate dehydration and fragmentation that occurs during baking [21; 25]. Other compounds may have been formed during the early steps of the Maillard reaction (sugar dehydration or fragmentation), such as furans, pyranones and furfurals [5; 19; 25; 71], and in the last stages of the reaction, such as pyrroles and pyrazines (Supplementary Figure S4) [19]. \(p\)-Vinylguaiaicol was also detected in _broas_, but not in maize flours. It has been described as an important odorant in other breads and baked products, derived from ferulic acid decarboxlation [8; 28; 29]. On the contrary, some compounds were lost after processing, such as \begin{table}
\begin{tabular}{c c c} \hline
**Chemical Class** & **Compound** & **Suggested Origin** \\ \hline Terpenes & Limonene (+) & Plant metabolism and signaling [70] \\ \hline Alcohols & 1-Octanol & Lipid oxidation [17] \\ \hline Hydrocarbons & Pentadecane & Lipid oxidation [21] \\  & 3-Ethyl-2-methyl-1,3-hexadiene & Lipid oxidation [21] \\ \hline Furans & 2-PentyIfuran & Lipid oxidation, from (\(E\))-2-nonenal [15; 17] \\ \hline \end{tabular} (+) Compounds present in higher concentrations (\(p<0.05\)). (\(-\)) Compounds present in lower concentrations (\(p<0.05\)).  
\end{table} 
Table 3: _Cont._aldehydes, alcohols and ketones, which may have been volatilized during baking [16; 20], or participated in further reactions during bread making [35]. The contribution of a compound to the final bread aroma depends not only on its concentration, but also on its odorant power, which is determined by its odor threshold, or odor activity value (OAV) [11].