Abstract
BackgroundLactic acid bacteria can synthesize dextran and oligosaccharides with different functionality, depending on the strain and fermentation conditions. As natural structure-forming agent, dextran has proven useful as food additive, improving the properties of several raw materials with poor technological quality, such as cereal by-products, fiber-and protein-rich matrices, enabling their use in food applications. In this study, we assessed dextran biosynthesis in situ during fermentation of brewers´ spent grain (BSG), the main by-product of beer brewing industry, with Leuconostoc pseudomesenteroides DSM20193 and Weissella confusa A16. The starters performance and the primary metabolites formed during 24 h of fermentation with and without 4% sucrose (w/w) were followed.ResultsThe starters showed similar growth and acidification kinetics, but different sugar utilization, especially in presence of sucrose. Viscosity increase in fermented BSG containing sucrose occurred first after 10 h, and it kept increasing until 24 h concomitantly with dextran formation. Dextran content after 24 h was approximately 1% on the total weight of the BSG. Oligosaccharides with different degree of polymerization were formed together with dextran from 10 to 24 h. Three dextransucrase genes were identified in L. pseudomesenteroides DSM20193, one of which was significantly upregulated and remained active throughout the fermentation time. One dextransucrase gene was identified in W. confusa A16 also showing a typical induction profile, with highest upregulation at 10 h.ConclusionsSelected lactic acid bacteria starters produced significant amount of dextran in brewers’ spent grain while forming oligosaccharides with different degree of polymerization. Putative dextransucrase genes identified in the starters showed a typical induction profile. Formation of dextran and oligosaccharides in BSG during lactic acid bacteria fermentation can be tailored to achieve specific technological properties of this raw material, contributing to its reintegration into the food chain.
Highlights
Lactic acid bacteria can synthesize dextran and oligosaccharides with different functionality, depending on the strain and fermentation conditions
At T10, dextran amount was slightly higher in EPS + Brewers’ spent grain (BSG) fermented with W. confusa A16 (0.9 g/100 g) than with L. pseudomesenteroides DSM20193 (0.7 g/100 g fermented BSG), and it kept increasing until 24 h, reaching similar values of 1.2 and 1.1 g/100 g of BSG fermented with L. pseudomesenteroides DSM20193 and W. confusa A16, respectively
BSG was used as a substrate for dextran biosynthesis in situ during Lactic acid bacteria (LAB) fermentation, with the aim of assessing the possibility to increase its applicability as food ingredient
Summary
Lactic acid bacteria can synthesize dextran and oligosaccharides with different functionality, depending on the strain and fermentation conditions. As natural structure-forming agent, dextran has proven useful as food additive, improving the properties of several raw materials with poor technological quality, such as cereal by-products, fiber-and protein-rich matrices, enabling their use in food applications. Among the well-known benefits of LAB fermentation, the synthesis of exopolysaccharides in situ successfully modified the functionality of cereal by-products, fiberand protein-rich matrices [6, 7]. Most of these studies have used LAB belonging to Leuconostoc and Weissella spp. as starters for the fermentation, due to their ability to produce dextran in large amount [8]
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