## 3 Results
### Volatile Organic Compounds Profiling  
The VOCs profiling of sourdoughs and following dough samples revealed significant quantitative and qualitative differences, which can be attributed to the different microflora of each of the two systems A and B, given that the ingredients used were the same. Sourdoughs were characterized by much higher total VOCs, as can be inferred from Figure 6. Indeed, the volatiles produced in the sourdough undergo a dramatic dilution from the addition of ingredients. It is noteworthy that the significantly higher (1.5-fold) VOCs levels, expressed as total chromatographic area, observed in MB (4.76 \(\times\) 10\({}^{7}\)) compared with MA (3.16 \(\times\) 10\({}^{7}\)), are followed by significantly higher levels also recovered in IMPB (2.26 \(\times\) 10\({}^{7}\)) and FINB (1.88x10\({}^{7}\)) samples compared with IMPA (1.62 \(\times\) 10\({}^{7}\)) and FINA (1.56 \(\times\) 10\({}^{7}\)), respectively, even if the difference is slightly reduced to 1.2-fold. The relative abundance of chemical classes of VOCs in the volatile fraction of samples is shown in Figure 7. As much as >80% of the volatile fraction of sourdoughs was made up of alcohols and esters together, while aldehydes and acids each represented about 6-7% of the total chromatographic area. Figure 5: Neighbor-joining phylogenetic tree obtained by 16S multiple alignment. A gamma distribution was applied to model the rate variation among sites. The node numbers indicate the percentage of replicates in which taxa clustered at the same distance (bootstrap test). References species used in the dataset are reported, in the figure, using their former name and the associated NCBI id. Given the recent re-organization of the Lactobacillus genus, the different genera are highlighted with different colors and named using the new taxonomical nomenclature, according to [PERSON] et al. [11]. Interestingly, the VOCs profile of MA was characterized by a balanced level of esters and alcohols, while in MB samples the alcohols prevailed; this finding agrees with the presence of _S. cerevisiae_ in B samples. The relative composition of the volatile fraction changed after formulation and leavening, the most noteworthy changes being the increase in aldehydes from 6-7% to 17-23% of the total VOCs, a reduction in esters to 5-7%, and the development of ketones, represented by acetoin (3-hydroxy, 2-butanone), which was not detected in the sourdough samples. The main aliphatic aldehydes found were acetaldehyde, characterizing the VOC profile of all samples and showing an evident increasing trend from MB to FINB samples (Table 5). To a lower extent, there were 2-butenal, only found in fermented dough samples, hexanal, the product of lipid oxidation by the lipoxygenase pathway [44], and heptenal, retrieved only in MA and MB samples; they accounted for about 4% and 0.3-0.7%, respectively. These aldehydes could not be detected in further steps, according to previous reports [16]; however, the hexanal loss was not followed by a corresponding 1-hexanol increase during maturation. Figure 6: Mean total chromatographic area of the identified volatile organic compounds (VOCs) in sourdoughs and dough samples A and B.  
Figure 7: Relative abundance (%) of the chemical classes of volatile organic compounds (VOCs), determined in sourdough and dough samples at different steps of _Panettone_ preparation. Among aromatic aldehydes, phenylacetaldehyde accounted for about 5.5-7.6% of total VOCs in dough samples, while benzaldehyde accounted for 0.5-2%. The B samples always showed higher relative abundances of these compounds, while none of them were detectable in sourdough samples, suggesting the contribution of dough ingredients in their formation. Among esters, ethyl acetate represented about 40% and 21% of the total VOCs of sourdoughs MA and MB, respectively, followed by isoamyl acetate (about 2%), ethyl lactate (1.5-2%), and ethyl hexanoate, while their concentration was dramatically reduced in the leavened products.