The use of lactic acid bacteria for developing functional foods is increasing for their ability to synthesize beneficial metabolites such as vitamin B (riboflavin, RF) and postbiotic compounds. Here, the spontaneous mutant FS54 B2 was isolated by treatment of the dextran-producing Weissella confusa FS54 strain with roseoflavin. FS54 B2 overproduced RF (4.9 mg/L) in synthetic medium. The FMN riboswitch is responsible for the regulation of RF biosynthesis, and sequencing of the coding DNA revealed that FS54 B2 carries the G131U mutation. FS54 B2 retained the capacity of FS54 to synthesize high levels of dextran (3.8 g/L) in synthetic medium. The fermentation capacities of the two Weissella strains was tested in commercial oat-, soy- and rice-based beverages. The best substrate for FS54 B2 was the oat-based drink, in which, after fermentation, the following were detected: RF (2.4 mg/L), dextran (5.3 mg/L), potential prebiotics (oligosaccharides (panose (5.1 g/L), isomaltose (753 mg/L) and isomaltotriose (454 mg/L)) and the antioxidant mannitol (16.3 g/L). pH-lowering ability and cell viability after one month of storage period were confirmed. As far as we know, this is the first time that an RF-overproducing W. confusa strain has been isolated, characterized and tested for its potential use in the development of functional beverages.

Gluten consumption causes several immunological and non-immunological intolerances in susceptible individuals. In this study, the dextran-producing Weissella cibaria BAL3C-5 and its derivative, the riboflavin-overproducing strain BAL3C-5 C120T, together with a commercial bakery yeast, were used to ferment gluten-free (GF)-doughs obtained from corn and rice flours at two different concentrations and supplemented with either quinoa, buckwheat, or chickpea to obtain laboratory-scale GF bread. The levels of dextran, riboflavin, and total flavins were determined in the fermented and breads. Both strains grew in fermented doughs and contributed dextran, especially to those made with corn plus quinoa (~1 g/100 g). The highest riboflavin (350–150 µg/100 g) and total flavin (2.3–1.75 mg/100 g) levels were observed with BAL3C-5 C120T, though some differences were detected between the various doughs or breads, suggesting an impact of the type of flour used. The safety assessment confirmed the lack of pathogenic factors in the bacterial strains, such as hemolysin and gelatinase activity, as well as the genetic determinants for biogenic amine production. Some intrinsic resistance to antibiotics, including vancomycin and kanamycin, was found. These results indicated the microbiological safety of both W. cibaria strains and indicated their potential application in baking to produce GF bread.