# Shedding Light on the Volatile Composition of _Broa_, a Traditional Portuguese Maize Bread
## 1 Introduction
Apart from lipid oxidation, aldehydes can also be formed inside the yeast cells, by the degradation of flour amino acids via the Ehrlich pathway, and originate the corresponding alcohols, acids and esters [16; 17; 20]. Different volatile compounds can be formed, depending on the LAB and yeasts present in the dough [11; 16; 22; 23]. Ketones, such as geranylacetone, can be originated from carotenoids' oxidation, which have been described in maize baked products and other cereal breads [11; 24]. In addition to color development, browning reactions produce compounds that contribute to the flavor of bakery products [5]. In particular, Maillard products are formed through a reaction between amino acids and reducing sugars, leading to the formation of brown pigments (melanoidins), and a large number of volatile compounds [5; 6; 20]. This process consists of mainly three stages: (1) sugar degradation, where compounds such as furans, pyrones, furfurals, furanones and pyranones are formed, followed by (2) amino acids' degradation (Strecker reaction), which generates mainly aldehydes, acids and alcohols, and (3) further interactions, originating colored melanoidins and other volatiles, such as pyrroles, pyridines and pyrazines [25]. These volatiles are considered important for the overall aroma profile of breads, as they generally have low odor thresholds and contribute to the desirable aroma properties [11; 17; 19; 20; 26]. Caramelization reactions are originated through sugars' degradation in the absence of amino acids and provide compounds especially related to caramel flavor [5; 19]. Low levels of volatiles from non-enzymatic browning reactions and high levels of lipid oxidation products contribute to the formation of off-flavors in breads [18]. Some studies have reported that variations in wheat flour odor directly affect bread flavor [23; 27]. Moreover, phenolic compounds may also contribute to the volatile composition of foods, influencing both the Maillard and lipid oxidation reactions [28; 29; 30; 31]. In particular, the presence of ferulic acid in whole wheat breads has been reported as the main reason for the difference in the aroma of breads prepared from whole and refined wheat flours [28]. As ferulic acid is particularly abundant in maize, where it can be at least 10 times higher than in other grains [32], it is expected that the volatile composition of _bras_ may be especially affected by their phenolic composition. Additionally, these compounds exhibit antioxidant properties, contributing to the prevention of non-communicable diseases [33] that are generally regarded as a major public health concern. Several studies have been published on the identification of key volatiles responsible for odor quality in maize-based foods, such as popcorn and cornflakes [24; 34; 35; 36; 37]. However, to the best of our knowledge, the volatile composition of maize-based sourdough breads has never been studied. The main objectives of this work were to: (1) characterize _bras_' volatile composition in order to identify volatiles that may influence consumer's choice, and to (2) shed light on the characteristics of traditional maize varieties responsible for their better suitability for _bras_ production. In particular, the influence of (2a) soluble phenolic compounds, (2b) total carotenoids content and (2c) volatiles from maize flours on _bras_' volatile composition was evaluated. This knowledge is important to both the baking industry and maize breeders, as cereals' composition contribution to odor can possibly become a future quality parameter in breeding [27].