Characterization of growth and exopolysaccharide production of selected acetic acid bacteria in buckwheat sourdoughs

- Levan-producing acetic acid bacteria (AAB) were applied in buckwheat sourdoughs.
- High amounts of levan were produced in buckwheat sourdoughs by AAB.
- Initial sucrose concentrations and dough yields influenced the levan production.
- The size of in situ produced levans was influenced by the fermentation time.

Sourdough technology is a promising approach to improve the quality of gluten-free (GF) breads. It offers replacement of currently used structure-forming commercial hydrocolloids by in situ produced exopolysaccharides (EPS). Acetic acid bacteria (AAB) can produce EPS of extremely high molecular weight, which are promising candidates for structure formation in breads. In this work, an alternative aerobic GF cereal fermentation by the levan producing AAB strains Gluconobacter albidus TMW 2.1191, Kozakia baliensis NBRC 16680 and Neoasaia chiangmaiensis NBRC 101099 was established in buckwheat doughs containing molasses as a natural source of sucrose. All three strains reached up to 109 CFU/g dough at 48 h and produced 16-20 g/kg flour of fructans. The efficiency of EPS production was strain dependent and was additionally affected by initial molasses concentrations, inoculum sizes and dough yields, which influenced the respective bacterial growth and levan forming capabilities. G. albidus was the most competitive strain to grow in the buckwheat doughs, accordingly, the levan produced by this strain was further examined for its molecular mass and size determination. The structural analysis of levans from G. albidus in buckwheat doughs at 24 and 48 h revealed the changes in particle sizes during fermentation. The ability of AAB strains to grow well and to produce high amounts of levan in situ in buckwheat-molasses doughs has opened a new possibility of using AAB doughs as a natural ingredient for quality improvement of GF baked products.