Browsing by Subject "hapanleivonta"

Sourdough baking is a process used for thousands of years and it’s still used to this day. Sourdough is a mixture of flour and water that has been fermented with lactic acid bacteria (LAB) and yeasts and it’s used to leaven the bread. Some of sourdough LAB produce exopolysaccharides (EPS) from sucrose in their metabolism. Dextran, which consists of α-(1→6) linked glucosyl units is the most common EPS. EPS produced by LAB have been widely studied to have different positive impacts on bread texture. The aim of this thesis was to screen the sourdough samples for EPS producing LAB and to analyze the structures of those EPS as accurately as possible. In the experimental part LAB were isolated from the sourdough samples and grown on MRS agar containing sucrose. All EPS forming colonies were then isolated from the plates and purified to obtain pure strains. The EPS produced by the strains were hydrolyzed enzymatically by dextranase and glucosidase after which their monosaccharides and enzyme resistant oligosaccharides were analyzed by HPAEC-PAD. The structures of the EPS were also analyzed with NMR. 13 EPS producing strains were isolated from the sourdough samples. Based on the HPAEC-PAD results all samples were found to be dextran because the enzymes were able to hydrolyze them. From the enzyme resistant oligosaccharide chromatograms it was seen that there were four different chromatographic profiles so there were four different EPS structures. NMR results confirmed that all EPS were dextrans. The NMR results also confirmed that there were four different structures among the EPS samples. All EPS had α-(1→3) linked branches. Two samples also had α-(1→2) linked branches. This research gave information about the EPS production by the sourdough’s LAB and also the structures of those EPS.