## 4 Discussions
### Bread Fermentation Performance Tests  
The tested sourdough samples exhibited a dough rising capacity (DRC) exceeding 100%, indicating their capability to produce bread dough. The higher specific volume observed in the FS1 and FS3 doughs may be attributed to the increased CO2, as suggested by [25], resulting from adequate dough acidification, which enhances the gluten's gas-retaining ability. Conversely, the excessive acidity of the FS2 and FDS2 sourdoughs hindered their fermentation performance, a phenomenon elucidated by [22], who explained it as the inhibitory effect of acidity on the main yeasts responsible for CO2 production. The authors of [26] also reported a similar trend, in which firm-consistency sourdoughs like the FS2 fresh sourdough promoted the production of acetic acid, which had a strong negative influence on the yeast activity. The FDS2 dough exhibited a reduced specific volume in comparison to its fresh FS2 counterpart. This phenomenon can be elucidated, according to [27], by the adverse impact of the simultaneous presence of an acidic pH and a high ethanol concentration on yeast growth. The delay in proofing observed in phase I of the freeze-dried sourdoughs (approximately \(\pm\)200 min) can be attributed to the presence of injured and stressed cells, which are found in reduced numbers in freeze-dried sourdoughs, as explained by [28] in their study. To address this issue, the authors of [24] suggest employing pretreatments such as rehydration or the refreshment of leavens to activate them effectively and ensure their fermentative activity. Additionally, the use of cryoprotective agents during the freeze-drying process is recommended. It is also worth noting that the acidity level of fresh sourdough appears to have a significant impact on the fermentation capabilities of its freeze-dried counterpart. For instance, FS2, with a TTA of 39.24, exhibited a shorter bread-making time compared to FDS2, which has a TAA of 74.20. The extended fermentation time observed in the doughs of the freeze-dried sourdoughs can be elucidated through the findings of [29]. They proposed that this phenomenon is attributed to the presence of organic acids generated by rapidly proliferating bacteria, which inhibit the fermentation activity of less acid-tolerant species. Furthermore, in [12], Caglar reported a high mortality rate among microorganisms due to the freeze-drying process. Conversely, an extended fermentation period enables certain freeze-dried sourdoughs to approach the level of dough rise achieved by specific fresh sourdoughs. The decline in dough volume observed in certain sourdough types during phase IV can be attributed to the rupture of the network and the release of CO\({}_{2}\) outward; this phenomenon is indicative of the dough reaching its point of porosity. The FS1 dough requires less bread-making time than FS3, confirming the significant role of hydration in the microbial ecology and the metabolic function of the sourdough. However, the FDS3 dough exhibited a shorter bread-making time than FDS1. This discrepancy could be attributed to a higher mortality rate of the microorganisms in the FDS1 sourdough, resulting from its slightly elevated hydration level and the consequent cell wall rupture of the microorganisms during freezing, which precedes the freeze-drying process [30; 31]. From these observations, it can be inferred that while the liquid form of the fresh sourdough holds promise for bread making, its freeze-dried form may not be necessary yield the same benefits. The kinetics of dough rise are analogous with the release of CO\({}_{2}\), thus affirming its important role in dough expansion, which aligns with the findings presented by [32] in their study. Nevertheless, when an equal amount of CO\({}_{2}\) is liberated, the extent of dough expansion varies notably among different dough compositions, especially during phases II (swelling) and III (stability); this variation can be attributed to the discrepancies in their gas retention capacities and elasticity stemming from leavening agents.