3.1. Physicochemical and Microbiological Characterization of Bulgarian Sourdoughs
Regarding TTA, only sample D8 is within the recommended values, with TTA of 15.6. The other four samples had lower TTA values, which could be primarily attributed to the higher dry matter content (that, in turn, influences the dominant microorganisms) but also to other factors such as the number of backsloppings and other parameters employed in the preparation method.
The LAB viable counts of the analyzed sourdoughs were between 9.92 ± 0.96 (D11) and 11.68 ± 0.58 log CFU/g (D5), and the yeast viable counts in the sourdoughs varied from 7.72 ± 0.34 (D11) to 9.59 ± 0.68 log CFU/g (D9). The high TTA could not be linked to the LAB viable counts alone. It may be affected by the homo-/heterofermentative character of the predominant LAB strains in sourdoughs as a major factor for the type and amount of organic acids produced during fermentation, as well as other related endogenous and exogenous baking parameters, such as the fermentation time and temperature, type of cereal and its extraction rate, dough yield, fermentation quotient, number of backsloppings, etc. It was interesting to find that sample D8, which had the lowest DM content, also harbored the highest ratio between LAB and yeast viable counts (2680). This could also be correlated with the lowest pH and highest TTA values recorded for this sample. Samples D5 and D12, which had similar DM values, showed similar LAB-to-yeast ratios, suggesting a link between DM content and the high prevalence of lactic acid bacteria over yeast.
3.4. Bacterial Communities in the Studied Sourdough Samples
The samples in our study were not representative enough to make conclusions regarding all of these factors. Yet, the results from different samples originating from the same bakery show that the production location (environment) is related to the presence of some common species. For example, Lacticaseibacillus casei (Lactobacillus casei) and Loigolactobacillus coryniformis (Lactobacillus coryniformis) were mainly presented in samples D8 and D9 taken from one bakery (Bansko town, Southwest Bulgaria), and Companilactobacillus farciminis (Lactobacillus farciminis) and Weissella cibaria were found in both sourdoughs from Ruse town, North Bulgaria (at the Danube River). Sourdough specificity related to location is an important feature that could be used for sourdough metagenomic authentication. However, we observed that samples from different bakeries prepared from white wheat flour shared common species. For example, Lactobacillus delbrueckii was in almost equal proportions in samples D5 (Smolyan, South Bulgaria) and D8 (Ruse, North Bulgaria). Ligilactobacillus agilis (Lactobacillus agilis), Limosilactobacillus fermentum (Lactobacillus fermentum), and Leuconostoc mesenteroides were the most common in these two sourdoughs. However, some specific species were found only in specific samples, independent of the bakery, such as Pediococcus parvulus in sample D12, Schleiferilactobacillus perolens (Lactobacillus perolens) in sample D5, and Ligilactobacillus salivarius (Lactobacillus salivarius) in sample D11, which could be attributed to other factors.
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