## 2 Results and Discussion
### The potentialities of GC\(\times\)GC-ToFMS in the Identification of Broas Volatile Compounds  
In a previous study on _proas_ volatile composition by GC-MS (1D) [27], only 16 out of the 128 volatiles described in the present work were detected (Table 1), which confirms that GC\(\times\)GC-ToFMS provides a much higher potential for the detection and identification of food volatiles [63; 64]. It should also be noted that, in this work, a relatively high signal-to-noise (S/N) threshold (100) was used, which limited the number of detected compounds. Figures 2 and 3 illustrate the advantages of GC\(\times\)GC-ToFMS, which allowed the separation of analytes with similar volatility and common product ions through the secondary \({}^{2}\)D column. Considering the set of columns used (non-polar/polar), the decrease in volatility (high \({}^{1}\)t\({}_{\text{R}}\)) is mainly related to the increase in the number of carbons [64; 65]. In contrast, the increase in the \({}^{2}\)t\({}_{\text{R}}\) corresponds to increasing polarity [64; 65]. For instance, 2-butyl-tetrahydrofuran (F31) was not detected in the previous study [27]. This compound was co-eluted with 2-nonanone (\({}^{1}\)t\({}_{\text{R}}\): 715 s), and both presented similar mass spectra, with identical product ions at \(m/z\) 71 and 43 (Figure 3). However, since they present different polarities, their separation was achieved through the \({}^{2}\)D column. 2-Butyl-tetrahydrofuran (F31) exhibits a slightly lower Log P than 2-nonanone (Log P: 2.93 and 3.08, respectively), which supports its relatively high polarity, and, therefore, the higher retention time in the \({}^{2}\)D (\({}^{2}\)t\({}_{\text{R}}\). 0.77 vs. 0.56 s). Thus, despite the high similarity index of 2-nonanone with the library spectra (89%) obtained in the previous analysis by GC-MS [27], the compound 2-butyl-tetrahydrofuran also contributed to the peak area considered for 2-nonanone. Without the high resolving power of GC\(\times\)GC, the separation, identification, and relative quantitation of these two compounds would have been a challenge. Another example is the identification of methylpentylfuran (F27). This compound was not commonly detected in foods but was previously tentatively identified in _proas_ by GC-MS [27]. The results obtained in the present work corroborate this earlier identification. The mass spectrum of F27 showed a high similarity index with the spectra from methylpentylfuran from the Wiley database (Table 1). Furthermore, this compound showed a very low retention time of 0.50 s in the \({}^{2}\)D column (Figure 4), suggesting its low polarity, which was confirmed by its calculated Log P of 4.43. Although methylpentylfuran usually refers to 3-methyl-2-pentylfuran, F27 can also correspond to other isomers, such as 2-methyl-5-pentylfuran or 4-methyl-2-pentylfuran. In addition, several other volatiles belonging to chemical families, which usually arise during baking, were eluted at this \({}^{1}\)t\({}_{\text{R}}\) (705 s), namely furfurylfuran (F28), 2-formyl-3-methylthiophene (Tp4), 2-acetylthiophene(Tp5) and furnaceol (Fo20). Since they show different polarities (Log P of 2.52, 1.38, 1.28 and -0.33, respectively), they were separated through the \({}^{2}\)D column (\({}^{2}\)t\({}_{\text{R}}\): 0.95, 1.31, 1.56 and 4.02, respectively). As shown in Figure 4A, the peak intensities of methylpentylfuran (F27) and 3-nonanone were much higher than F28, Tp4, Tp5 and Fo20. Thus, it would not have been possible to identify these compounds without the orthogonal separation through the \({}^{2}\)D column [64; 65]. The identification of volatile sulfur compounds (Figure 4B) is particularly relevant since they are typically present in foods at extremely low levels, often at sub-parts-per-billion concentrations, but provide background sensory nuances to the flavor and are often considered \"character-impact compounds\" [13].