Table_9_Lactic Acid Bacterium Population Dynamics in Artisan Sourdoughs Over One Year of Daily Propagations Is Mainly Driven by Flour Microbiota and Nutrients.DOCX

This study aimed to: (i) assess at what extent traditional, daily propagated, sourdough can be considered a stable microbial ecosystem; (ii) ascertain the drivers of stability/variability. For this purpose, samples of sourdough, flour and environment were collected over 1 year from three different bakeries located in Altamura, Castellana Grotte, and Matera. Culture-dependent and –independent analyses were carried out on all the samples. In addition, sourdough and flour were subjected to biochemical characterization. In all the sourdoughs sampled at the same bakery, cell density of lactic acid bacteria fluctuated of one-two log cycles. However, 16S metagenetic analysis showed that sourdough bacterial microbiota was remarkably stable, in terms of species. Yet, some differences were found during time at intra-specific level. Indeed, bacterial strains succeeded in a 1-year lapse of time or even in 6-months, such as in the case of strains isolated from Altamura sourdough samples. Residual carbohydrates, lactic acid, ethanol and free amino acids varied in the same sourdough collected at different sampling times. These variations could be attributed to combination of various factors, such as fermentation temperature and strain succession. In addition, concentration of flour nutrients varied over 1 year and, in some cases, in a shorter time lapse. This may have favored certain strains over others. For this reason and also because of its inherent contamination by lactic acid bacteria, we found flour as the major driver of strains succession.

本研究旨在：(i) 评估传统每日续养的酸面团（sourdough）可被视为稳定微生物生态系统的程度；(ii) 明确其稳定性与变异性的驱动因子。为此，研究团队历时1年，从位于阿尔塔穆拉（Altamura）、卡斯特拉纳格罗泰（Castellana Grotte）和马泰拉（Matera）的三家不同面包坊采集了酸面团、面粉及环境样本。对所有样本均开展了依赖培养与非依赖培养的分析。此外，还对酸面团与面粉进行了生化特性表征。在同一家面包坊采集的所有酸面团样本中，乳酸菌的细胞密度波动幅度为1~2个对数循环。然而，16S宏基因组分析显示，从物种层面而言，酸面团的细菌菌群整体呈现显著稳定性。但在种内水平上，随时间推移仍存在一定差异。例如，部分细菌菌株可在长达1年甚至6个月的周期内持续存续，如从阿尔塔穆拉地区酸面团样本中分离得到的菌株。在不同采样时间采集的同一酸面团样本中，残留碳水化合物、乳酸、乙醇及游离氨基酸的含量存在明显变化。这类差异可归因于多种因素的共同作用，包括发酵温度与菌株演替。此外，面粉中的营养物质浓度在1年周期内，乃至更短的时间跨度内亦会发生波动，这可能会使特定菌株相较于其他菌株更具生长优势。基于上述原因，再加上面粉本身会受到乳酸菌的污染，研究团队发现面粉是驱动菌株演替的主要因素。