Lactic Acid Bacteria Isolated from Fermented Doughs in Spain Produce Dextrans and Riboflavin

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 <i>rrs</i> and <i>pheS</i> gene sequences as LAB belonging to four species (<i>Weissella cibaria</i>, <i>Leuconostoc citreum</i>, <i>Leuconostoc falkenbergense</i> and <i>Leuconostoc mesenteroides</i>). Six selected strains from the <i>Leuconostoc</i> (3) and <i>Weissella</i> (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 <i>L. citreum</i> polymer showed an unusually high degree of branching. Quantification of the riboflavin and the EPS productions showed that the <i>W. cibaria</i> 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 <i>L. falkenbergense</i>.