Influence of in-situ synthesized exopolysaccharides on the quality of gluten-free sorghum sourdough bread.

The majority of gluten-free breads on the market are of poor sensory and textural quality. Exopolysaccharides (EPS) formed from sucrose during sourdough fermentation can improve the technological properties of gluten-free breads and potentially replace hydrocolloids. In this study, the influence of in situ formed EPS on dough rheology and quality of gluten-free sorghum bread was investigated. Dextran forming Weissella cibaria MG1 was compared to reuteran producing Lactobacillus reuteri VIP and fructan forming L. reuteri Y2. EPS containing bread batters were prepared by adding 10% and 20% of sourdough. As control served batters and bread containing sourdoughs fermented without sucrose and batters and bread without sourdough addition. The amount of EPS formed in situ ranged from 0.6 to 8.0 g/kg sourdough. EPS formed during sourdough fermentation were responsible for the significant decrease in dough strength and elasticity, with in situ formed dextran exhibiting the strongest impact. Increased release of glucose and fructose from sucrose during fermentation enhanced CO2 production of yeast. Organic acids in control sourdough breads induced hardening of the bread crumb. EPS formed during sourdough fermentation masked the effect of the organic acids and led to a softer crumb in the fresh and stored sorghum bread. Among EPS, dextran showed the best shelf life improvements. In addition to EPS, all three strains produced oligosaccharides during sorghum sourdough fermentation contributing to the nutritional benefits of gluten-free sorghum bread. Results of this study demonstrated that EPS formed during sourdough fermentation can be successfully applied in gluten-free sorghum flours to improve their bread-making potentials.

Bacterial species identification from MALDI-TOF mass spectra through data analysis and machine learning.

At present, there is much variability between MALDI-TOF MS methodology for the characterization of bacteria through differences in e.g., sample preparation methods, matrix solutions, organic solvents, acquisition methods and data analysis methods. After evaluation of the existing methods, a standard protocol was developed to generate MALDI-TOF mass spectra obtained from a collection of reference strains belonging to the genera Leuconostoc, Fructobacillus and Lactococcus. Bacterial cells were harvested after 24h of growth at 28°C on the media MRS or TSA. Mass spectra were generated, using the CHCA matrix combined with a 50:48:2 acetonitrile:water:trifluoroacetic acid matrix solution, and analyzed by the cell smear method and the cell extract method. After a data preprocessing step, the resulting high quality data set was used for PCA, distance calculation and multi-dimensional scaling. Using these analyses, species-specific information in the MALDI-TOF mass spectra could be demonstrated. As a next step, the spectra, as well as the binary character set derived from these spectra, were successfully used for species identification within the genera Leuconostoc, Fructobacillus, and Lactococcus. Using MALDI-TOF MS identification libraries for Leuconostoc and Fructobacillus strains, 84% of the MALDI-TOF mass spectra were correctly identified at the species level. Similarly, the same analysis strategy within the genus Lactococcus resulted in 94% correct identifications, taking species and subspecies levels into consideration. Finally, two machine learning techniques were evaluated as alternative species identification tools. The two techniques, support vector machines and random forests, resulted in accuracies between 94% and 98% for the identification of Leuconostoc and Fructobacillus species, respectively.

Structural analysis of enzyme-resistant isomaltooligosaccharides reveals the elongation of α-(1→3)-linked branches in Weissella confusa dextran.

Weissella confusa VTT E-90392 is an efficient producer of a dextran that is mainly composed of α-(1→6)-linked D-glucosyl units and very few α-(1→3) branch linkages. A mixture of the Chaetomium erraticum endodextranase and the Aspergillus niger α-glucosidase was used to hydrolyze W. confusa dextran to glucose and a set of enzyme-resistant isomaltooligosaccharides. Two of the oligosaccharides (tetra- and hexasaccharide) were isolated in pure form and their structures elucidated. The tetrasaccharide had a nonreducing end terminal α-(1→3)-linked glucosyl unit (α-D-Glcp-(1→3)-α-D-Glcp-(1→6)-α-D-Glcp-(1→6)-α-D-Glc), whereas the hexasaccharide had an α-(1→3)-linked isomaltosyl side group (α-D-Glcp-(1→6)[α-D-Glcp-(1→6)-α-D-Glcp-(1→3)]-α-D-Glcp-(1→6)-α-D-Glcp-(1→6)-α-D-Glc). A mixture of two isomeric oligosaccharides was also obtained in the pentasaccharide fraction, which were identified as (α-D-Glcp-(1→6)-α-D-Glcp-(1→3)-α-D-Glcp-(1→6)-α-D-Glcp-(1→6)-α-D-Glc) and (α-D-Glcp-(1→6)[α-D-Glcp-(1→3)]-α-D-Glcp-(1→6)-α-D-Glcp-(1→6)-α-D-Glc). The structures of the oligosaccharides indicated that W. confusa dextran contains both terminal and elongated α-(1→3)-branches. This is the first report evidencing the presence of elongated branches in W. confusa dextran. The (1)H and (13)C NMR spectroscopic data on the enzyme-resistant isomaltooligosaccharides with α-(1→3)-linked glucosyl and isomaltosyl groups are published here for the first time.

In situ production and analysis of Weissella confusa dextran in wheat sourdough.

Several lactic acid bacteria belonging to the genera Leuconostoc, Lactobacillus, and Weissella have been introduced to wheat sourdough baking for in situ production of exopolysaccharides. This is considered a novel method for improving the shelf-life, volume and nutritional value of bread without additives. However, in situ production of exopolysaccharides during sourdough fermentation is challenged by simultaneous acidification due to metabolic activities of the bacteria, which may significantly diminish the positive technological impact of exopolysaccharides. In this study, the growth, activity and in situ production of dextran by Weissella confusa VTT E-90392 in wheat sourdoughs were investigated. Furthermore, the influence of dextran-enriched sourdoughs, at the addition level of 43%, on the subsequent bread quality was established. W. confusa efficiently produced dextran from the added sucrose in wheat sourdough without strong acid production. A new specific enzyme-assisted method for in situ analysis of dextran in sourdoughs was developed. With this method, we could for the first time proof significant (11-16 g/kg DW) production of polymeric dextran in sourdoughs. Concomitant formation of shorter isomaltooligosaccharides by W. confusa was also detected. The produced dextran significantly increased the viscosity of the sourdoughs. Application of dextran-enriched sourdoughs in bread baking provided mildly acidic wheat bread with improved volume (up to 10%) and crumb softness (25-40%) during 6 days of storage. Hence, W. confusa is a promising new strain for efficient in situ production of dextrans and isomaltooligosaccharides in sourdoughs without strong acidification.