Brewers' spent grain as substrate for dextran biosynthesis by Leuconostoc pseudomesenteroides DSM20193 and Weissella confusa A16

Abstract

Background: 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. 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.

Results: The 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.

Conclusions: Selected 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.

Keywords: Brewers’ spent grain; Dextran; Fermentation; Lactic acid bacteria.

Fig. 1

Kinetics of acidification, bacterial growth and viscosity during fermentation of EPS + and EPS− BSG. Change in pH, bacterial growth and viscosity at T0, T4, T6, T8, T10, T12, T16, T20 and T24 (hours) during fermentation of control (EPS−) and sucrose supplemented (EPS+) BSG by Leuconostoc pseudomesenteroides DSM20193 (a) and Weissella confusa A16 (b)

Fig. 2

Synthesis of maltosyl-isomaltooligosaccharides (MIMO) during fermentation of EPS− and EPS+ BSG. Synthesis of MIMO by Leuconostoc pseudomesenteroides DSM20193 (a) and Weissella confusa A16 (b) during fermentation of control (EPS−) and sucrose supplemented (EPS+) BSG at T0 T6 T10 T16 and T24 (hours). Maltose (Mal). panose (Pan). maltotriose (Mal-tri) and maltotetraose (Mal-tet) are indicated in the plot. Chromatograms are plotted with HPAEC-PAD response (nC) in Y axis and retention time (min) in X axis

Fig. 3

Transcriptional analysis of dextransucrase encoding genes during fermentation of EPS− and EPS+ BSG. Relative expression of three dextransucrase encoding genes (dsrD1, dsrD2 and dsrD3) present in Leuconostoc pseudomesenteroides DSM20193 (a) and one dextransucrase gene (dsrW1) present in Weissella confusa A16 (b) against housekeeping gene recA were determined at T0, T10, T16 and T24 (hours) during fermentation of control (EPS−) and sucrose supplemented (EPS+) BSG