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

Abstract

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.

A review of sourdough starters: ecology, practices, and sensory quality with applications for baking and recommendations for future research

“…As in wild grasslands, a mature starter’s final ecology hinders colonization by new species (introduced during refreshments) in ways that are not yet clear, but closely connected to organic acid production and other competitive behaviors. While some researchers have explored microbial succession in starters over time ( Minervini et al, 2018 ), we do not conclusively know how the long-term age of a starter affects its microbial community and functional characteristics. Exploring the relationship between a starter’s age and its microbial ecology, resiliency to land management changes, and sensory quality may be an interesting direction for future research.…”

“…Flour helps to introduce microorganisms into the sourdough medium ( Reese et al, 2020 ). Flour also supplies different nutrients (i.e., carbohydrates and amino acids) and non-nutrients (i.e., phenolic acids, amylase, ash), the presence and concentrations of which can influence bacteria and yeast species survival ( Vogelmann & Hertel, 2011 ; Minervini et al, 2014 ; Minervini et al, 2018 ; Gänzle, 2014 ). For example, different bacteria and yeast preferentially digest different saccharides, which can influence species co-occurrence through either mutualism or antagonism ( Gracia-Lázaro et al, 2018 ).…”

“…We suspect that the overall age of a starter influences which species are present in the starter, the day-to-day potential for fluctuations in the ecology of the system, and the genes on which microorganisms rely. For example, Minervini et al (2018) reported intra-species changes and slightly increasing yeast counts over a one-year period of sampling Italian bakery starters, suggesting that older starters may be better leavening agents. Undoubtedly, this is just one of many kinds of changes that occurs with starters over time.…”

Sourdough production: fermentation strategies, microbial ecology, and use of non-flour ingredients

“…Backslopped spontaneous sourdough productions starting from scratch go through a three-step fermentation cascade with respect to the growth of the bacterial communities in the flour-water mixture, in particular LAB ; Van der Meulen et al 2007;De Vuyst et al 2009Ercolini et al 2013;Minervini et al 2014;De Vuyst, Van Kerrebroeck, and Leroy 2017;Oshiro, Zendo, and Nakayama 2021). The microbial load of the flour [< 4 to 7 log (CFU/g)] and its nutrient availability, as well as the physicochemical parameters of the flour-water mixture, such as temperature, DY, pH, total titratable acidity and oxygen tension, and the fermentation time, determine the start and course of the microbiology of a backslopping process for sourdough production (Corsetti 2013;De Vuyst, Van Kerrebroeck, and Leroy 2017;Minervini et al 2018;Oshiro et al 2020). Hence, fermentation of the flour-water mixture starts with autochthonous, sourdough nonspecific bacteria, such as proteobacteria, staphylococci and diverse LAB species, belonging to the enterococci, lactococci, and streptococci.…”

Microbial community dispersal in sourdough

“…They had also been mentioned in studies describing flour microbiota, and the results were in accordance with those of De Angelis et al ( 2019) who compared the microbiotas of soft and durum wheat flour using culture independent methods. Minervini et al (2018a) analyzed the microbiotas of three different flours, and found the species F. sanfranciscensis in every sample (4% of all the strains isolated from the flour). This was higher than what we found, and could have been related to bias affecting the culture independent analyses, where rare species can go undetected.…”