Microbial Ecology Dynamics in Portuguese Broa Sourdough

Abstract

This research effort aimed at a better understanding of microbial phenomena taking place during time in spontaneous sourdough fermentation for broa, a traditional Portuguese bread. Unlike most microbiological studies of sourdough, viable counts obtained were not limited to Lactobacillus and yeasts, but encompassed also molds, Gram‐negative rods, endospore‐(non)forming Gram‐positive rods and catalase‐positive/negative Gram‐positive cocci. This less conventional approach unveiled the ubiquitous Bacillus genus throughout spontaneous broa sourdough fermentation. Presumptive yeasts, Lactobacillus and Bacillus were found to low levels after kneading, but became dominant by the end of regular (no aeration) fermentation. They apparently inhibit undesired rods and Staphylococcus, which were found to relatively high numbers after kneading. By 24 h of fermentation, lactic acid cocci accounted for an important fraction of biodiversity, and pH decreased significantly reaching about 4.1. Aeration accelerated the microbial dynamics. In terms of total viable counts, such a long‐term fermentation appeared to reach a quasi‐stationary state. Practical Applications Microbial studies encompassing a large set of culture media and incubation conditions were previously undertaken in samples of maize and rye flours, and sourdoughs for broa obtained from 14 artisanal producers and in two seasons. Microbial counts and identification unfolded a complex wild microbiota, and fermentation played a major effect upon all microbial groups. Flours and mother‐dough microbiota were characterized during storage afterward. A similar approach was followed here to ascertain the microbiological profile of a wide range of microorganisms throughout long‐term sourdough fermentation, in attempts to answer the questions: how microorganisms evolve, and how they respond to increasing aeration. These studies provide an innovative way to look at sourdough systems and microbial dynamics therein. Results showed the importance of increasing fermentation time to take full advantage of ecological competition against undesirable microorganisms, and emphasized the need for further studies to reveal the role of Bacillus in sourdough fermentations.

Lactic Acid Bacteria Isolation from Spontaneous Sourdough and Their Characterization Including Antimicrobial and Antifungal Properties Evaluation

“…Thirteen LAB strains were identified, chiefly Leuconostoc mesenteroides, Lactobacillus plantarum, Enteroccocus pseudoavium, Lactobacillus casei, Lactobacillus curvatus, Lactobacillus farraginis, Pediococcus pentosaceus, Pediococcus acidilactici, Lactobacillus paracasei, Lactobacillus plantarum, Lactobacillus coryniformis, Lactobacillus brevis, and Lactobacillus uvarum. The LAB community found in the sourdough after a spontaneous fermentation is mainly brought about by the adventitious microbiota existing in the flour or flours [1][2][3][4]10]. Sourdough microbial composition can be more or less stable for years [42].…”

“…In fact, the competitive and synergetic consortia of acid tolerant yeasts and LAB usually reach rapidly viable counts above those of the adventitious microbiota initially present in the flour or flours. Nevertheless, other ubiquitous microorganisms present in the flours are likely to stay viable in some sourdoughs [1][2][3][4]10]. Previous researchers have shown that microbial diversity in sourdoughs can varied according to different geographic location [43].…”

“…However, it should be emphasized that the metabolic pathways for carbohydrates can be changed by the same microbial strain throughout time, depending on the environment and growth conditions, for instance during the depletion of certain substrates and the production of metabolites that became substrates to the others throughout a batch or fed-batch fermentation-thus making difficult the full elucidation and control of metabolic pathways. As examples, the metabolic pathways will depend in the complexity of the growth medium, temperature, time, water activity, and acidity, interactions between microorganisms in co-culture starters or natural sourdough systems, among many other variables [1][2][3][4]10]. Yet and particularly, when complex substrates (containing other substrates rather than the fermentable hexoses) are present in a growth medium, its fermentation may yield organic acids, acetate and CO 2 at distinct ratios-which is very often to occur in industrial processes.…”

“…Yet, the inhibitory action of LAB is not limited to lactic and acetic acids and a wide range of other metabolites excreted to the growth medium may possess antagonistic properties against several prokaryotic bacteria and/or eukaryotic yeasts and molds. As already cited, among those metabolites are formic acid, free fatty acids, ammonia, ethanol, hydrogen peroxide, diacetyl, acetoin, 2,3-butanediol, acetaldehyde, benzoate, bacteriolytic enzymes, bacteriocins and BLIS, as well as several other less known inhibitory substances [1,3,4,10,41,[58][59][60][61][62][63][64]. Furthermore, the antimicrobial effect of LAB can also be significantly influenced by numerous physical, chemical and nutritional environmental factors [65,66].…”

“…In addition to the previous benefits, the use of starter cultures in bread making and other fermented food may be of interest to attain several other advantages, such as the reduction of production costs, fermentation times and risk of spoilage, to increase shelf-life, to predict microbial metabolic activities and to improve the control of the biotechnological processes, and to improve sensory quality and food safety, among others. Moreover, regarding the use of sourdough biotechnology, behind the technological advantages, it also holds a high potential to improve nutritional value and health-promoting effects of the final food products, including reduction of the glycemic response, increase of minerals bioavailability and promoting the formation of bioactive compounds (e.g., prebiotic oligosaccharides) [1,2,67].…”