Abstract
Many lactic acid bacteria (LAB) produce metabolites with applications in the food industry, such as dextran-type exopolysaccharides (EPS) and riboflavin (vitamin B2). Here, 72 bacteria were isolated from sourdoughs made by Spanish bread-makers. In the presence of sucrose, colonies of 22 isolates showed a ropy phenotype, and NMR analysis of their EPS supported that 21 of them were dextran producers. These isolates were identified by their random amplified polymorphic DNA (RAPD) patterns and their rrs and pheS gene sequences as LAB belonging to four species (Weissella cibaria, Leuconostoc citreum, Leuconostoc falkenbergense and Leuconostoc mesenteroides). Six selected strains from the Leuconostoc (3) and Weissella (3) genera grew in the absence of riboflavin and synthesized vitamin B2. The EPS produced by these strains were characterized as dextrans by physicochemical analysis, and the L. citreum polymer showed an unusually high degree of branching. Quantification of the riboflavin and the EPS productions showed that the W. cibaria strains produce the highest levels (585–685 μg/and 6.5–7.4 g/L, respectively). Therefore, these new LAB strains would be good candidates for the development of fermented foods bio-fortified with both dextrans and riboflavin. Moreover, this is the first report of riboflavin and dextran production by L. falkenbergense.
Highlights
Lactic acid bacteria (LAB) occur naturally in fermented foods, such as “mother doughs” or bakery doughs from bakers’ stores
After 48 h of incubation, colonies were observed by Transmission Electron Microscopy (TEM), and EPS was detected surrounding the bacterial cells (Figure 3), as we have previously described for other W. cibaria and Leuconostoc strains [11,41,66]
22 LAB strains, isolated from different fermented doughs, were identified as belonging to the Lactobacillus, Leuconostoc, and Weissella genera and 21 of them were identified as dextran-producing bacteria
Summary
Lactic acid bacteria (LAB) occur naturally in fermented foods, such as “mother doughs” ( named Type I sourdoughs) or bakery doughs from bakers’ stores. The microorganisms and their metabolites isolated from these fermented matrices are classified as qualified presumption of safety (QPS), generally regarded as safe (GRAS), and considered as nontoxic and food-grade microorganisms [1]. Great attention is given to the discovery and characterization of new LAB strains that are able to biosynthesize postbiotics [4] such as exopolysaccharides (EPS) to exploit their functional properties in foods, especially in bread [5,6,7,8,9]. The EPS produced in situ by some LAB species are of interest because of their contribution to the rheology of the doughs and to the texture of the products, especially in gluten-free breads [7,8,13,14]
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