# Shedding Light on the Volatile Composition of _Broa_, a Traditional Portuguese Maize Bread
## 3 Results and Discussion
### Characterization of the Volatile Composition of Broas
#### 3.4.1 Contribution of Phenolic Compounds for _Bros_' Volatile Composition  
Some phenolic compounds, particularly free phenolic acids present in the outer layers of cereal grains, such as ferulic acid, may directly contribute to breads' flavor [74], increasing their bitterness and astringency [30]. However, previous studies have demonstrated that the contribution of phenolic compounds to breads' flavor is mainly due to their influence on their volatile composition [28; 29; 30]. Although most of maize phenolic compounds are insoluble and linked to arabinoxylans [32], it is believed that only the soluble phenolics are able to influence the volatile composition of breads [28; 75]. Therefore, the main soluble phenolics of maize flours and _broas_ were quantitated (Supplementary Table S3) and correlated with _broas_' volatile composition (Supplementary Table S8). Some examples of the influence of phenolic compounds on _broas_ volatiles are represented in Figure 4, and Supplementary Figures S4 and S5. Significant negative correlations were found between phenolic compounds from maize flours and _broas_ and several volatiles derived from lipid oxidation reactions. In particular, strong negative correlations (R < -0.7, \(p\) < 0.05) were found between _broas_' diferuloyl putrescine and counaroyl feruloyl putrescine contents and alkanes (octane, 2,6 dimethylundecane and 2,6,11-trimethyldodecane) and alcohols (1-octen-3-ol, 1-heptanol, 1-octanol). Negative correlations were also obtained between phenolic compounds and 1-nonanol and 1-octanol. Therefore, phenolic compounds seamed to inhibit lipid oxidation reactions not only in maize flours, as previously discussed, but also in _proas_ and possibly during bread making, as described for other breads [30; 33; 73; 76]. However, positive correlations (R > 0.57, \(p\) < 0.05) were found between both free ferulic acid and coumaroyl feruloyl putrescine in maize flours and several lipid oxidation aldehydes [15; 20; 44] in _proas_, such as hexanal, 4-heptenal, heptanal, nonanal, decanal and benzaldehyde. Some studies have reported that phenolics, including ferulic acid, can actually increase the generation of lipid oxidation volatiles [30], possible because they begin to show pro-oxidant behavior at higher concentrations [30; 73]. Conversely, [PERSON] et al. [28] have demonstrated that the addition of ferulic acid to refined breads did not influence the generation of lipid oxidation products. The effectiveness of an antioxidant can be influenced by its location in the food matrix, survival during food processing, interactions with other food components [31] and by different hydrophilic properties of some antioxidants [30; 73; 77]. However, the mentioned aldehydes could have also been formed during baking [11] and not exclusively from lipid oxidation reactions. Negative correlations were also found between phenolic compounds and some volatiles originated by yeast and/or bacteria during fermentation, such as ethyl hexanoate, ethyl octanoate, 1-hexyl acetate, benzyl alcohol, 2-methyl-1-butanol and \(\gamma\)-nonalactone [15; 17; 20; 22], suggesting that hydroxycinnamic acids and hydroxycinnamic acid amides inhibited amylases and yeast activity, as it has already been described for ferulic acid [30]. These findings can also explain the positive correlations among aldehydes and phenolic compounds and the negative correlations among alcohols and phenolic compounds, since aldehydes can be reduced to alcohols by the activity of LAB and yeasts [20]. Thus, if these reduction reactions were inhibited by phenolic compounds, the levels of alcohols would be lower, whereas an increase in aldehydes' content would be expected. On the contrary, significant positive correlations were found among phenolic compounds and furan derivatives from browning reactions (Maillard and caramelization reactions, Supplementary Figure S4), namely, furfural, furfuryl alcohol, 2-acetylfuran and 5-methylfurfural.