Influence of Different Sugars and Initial pH on β-Glucan Formation by Lactobacillus brevis TMW 1.2112.

We wanted to identify key factors influencing the extent of β-glucan production by Lactobacillus brevis TMW 1.2112, which has been isolated from viscous, spoiled beer and which could contribute to viscosity increases of spoiled beverages via exopolysaccharide (EPS) production. In this way, we analyzed the influence of different initial pH values and carbohydrate sources on growth of and slime/β-glucan formation by this strain. In a screening of 48 carbohydrates, 14 fermentable sugars which enabled growth were identified. These sugars were further investigated regarding their EPS formation-promoting properties. The hexose-based mono- and di-saccharides enabled slime formation, while all pentoses failed to cause any thickening effect. The strongest slime formation was observed upon growth on D-maltose, the weakest on D-fructose. A lower initial pH (4.3) caused significant higher viscosities than an initially higher one (pH 6.2). This effect was independent from the carbohydrate supplied. Although the thickening of nutrient media by L. brevis TMW 1.2112 strongly depended on the initial pH and the available carbon source, all isolated polysaccharides were exclusively composed of glucose moieties and exhibited highly similar elution profiles after separation via asymmetric flow field-flow fractionation independently of the provided carbon source. Our results suggest that the extent of β-glucan/slime formation by special L. brevis strains isolated from the brewery environment is strongly influenced by the initial pH and the availability of certain EPS formation-promoting sugars with maltose being the most favored carbohydrate for the regulated and directive biosynthesis of capsular β-glucan.