Browsing by Subject "dekstraani"

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  • Viljanen, Janne (Helsingfors universitet, 2012)
    Exohomopolysaccharides (HOPS) are polysaccharides that are composed solely of glucose or fructose monomers and which are classified according to the linkage type between the monomers (e.g., dextran ?-[1?6]). Several different lactic acid bacteria (LAB) strains produce HOPS from sucrose. It is known that maltose can influence the synthesis of HOPS which can lead to formation of oligosaccharides. In fermented foods, HOPS and oligosaccharides can have both technological impact and prebiotic properties. The aim of this thesis was to investigate the synthesis of HOPS and oligosaccharides in mMRS broths and in oat bran gruel. Lactobacillus reuteri FUA 3048, Lb. reuteri LTH 5448, Weissella cibaria 10M and W. confusa DSM 20194 were used as starter cultures. HOPS and oligosaccharide yields in mMRS broths were analysed by ethanol precipitation and acid hydrolysis. An enzyme assisted method was used in order to quantify linear dextran content in freeze-dried oat gruels. Oligosaccharide profiles were analysed with high performance anion exchange chromatography with pulsed amperometric detetection. In mMRS broths, which contained 25 g/l sucrose (S-mMRS), LAB strains synthesised exosaccharides at concentrations of 0.9–2.3 g/l. Addition of maltose (34 g/l) significantly increased exosaccharide yield. This can be explained by strong malto-oligosaccharide (e.g., panose) synthesis. W. cibaria 10M produced 0.94 g/l linear dextran in S-mMRS broth and at 0.74 g/l in maltose containing broth and W. confusa DSM 20194 synthesised 1.7 g/l linear dextran in both broths. In oat gruel matrix (34 g/l maltose) W. confusa DSM 20194 synthesised 4.6 g/100 g dextran in freeze-dried gruel. In lower maltose concentrations dextran yield increased. Oligosaccharide profiles indicated that Weissella strains and the Lb. reuteri FUA 3048 strain synthesised gluco-oligosaccharides and Lb. reuteri LTH 5448 strain produced erlose. The results of this thesis give further insight in to role of maltose in HOPS synthesis in food matrices.
  • Nihtilä, Hanna (Helsingin yliopisto, 2019)
    Brewers’ spent grains (BSG) are by-products of the brewing industry. Utilization of BSG in food applications is challenging, due to its poor technological characteristics. Because of their water retaining properties, interactions with matrix components and impact on texture formation, bacterial exopolysaccharides (EPS) represent a promising tool for improvement of BSG properties. Among bacterial exopolysaccharides, dextran produced in situ by lactic acid bacteria (LAB) during fermentation has shown major improvements in technological and sensorial features of products prepared from various types of plant materials. The nutritious composition of BSG may support the growth of LAB and enable in situ dextran production. The aim of this study was to establish and examine the synthesis of dextran by LAB in BSG. Sixteen dextran producing LAB strains were screened for viscosity formation in BSG fermentation. The strains showing the highest viscosity formation were further assessed for fermentation performance. The more suitable fermentation temperature was traced by comparing the viscosifying performance of selected starters at 20 and 25 °C. Dextran amount was determined semi-quantitatively from selected fermented samples showing optimal results, and the presence of oligosaccharides was assessed. Sucrose, glucose, maltose and fructose amounts were analyzed to observe the relation between sugar consumption and dextran and oligosaccharides formation. Weissella confusa strains A16 and 2LABPTO5 and Leuconostoc pseudomesenteroides strain DSM20193 appeared the most promising starters for viscosity formation and thus dextran synthesis in this matrix. From the examined fermentation temperatures, strains showed the highest potential for dextran synthesis at 25 °C. The amount of synthesized dextran ranged from 1.1 to 1.7 % w/w (of the wet weight of the whole sample matrix). The rheological properties of BSG were modified via LAB fermentation and dextran synthesis, resulting in more viscous texture, and its applicability in food systems was thus potentially enhanced.
  • Pynnönen, Henna (Helsingfors universitet, 2009)
    Methylation analysis by Ciucanu and Kerek (1984) and Hakomori (1964) and the meaning of circumstances in the reaction, reaction parameters and structure of the sample were reviewed in this study. The experimental work consisted of methylation analysis of glucose, cellobiose, isomaltose, pullulan, commercial dextran and dextrans produced by lactic acid bacteria Weissella confusa and Leuconostoc citreum. The success of the methylation was controlled using the IR-method. Methylated samples were treated by methanolysis and acid hydrolysis. The structure analyses were carried out with GC-MSspectra. Two different columns: DB-1 and HP-5 were compared in the GC-analysis. Two hours methylation in the ultrasonic bath gave good methylation results. It was easy to control the methylation by IR-method. OH-peak (3400 cm-1) was absent and CH3- peaks (2900 and 2800 cm-1) were high after successful methylation. IR-spectroscopy is a valuable tool to check if methylation has been successful. Samples could be remethylated before hydrolysis and derivation if necessary. After methanolysis there were ?- and ?-pyranose forms from each methylated monosaccharides. Due to reduction after the acid hydrolysis method, there was only one methylated form from each product. The structures of glucose, cellobiose, isomaltose and pullulan were solved by both hydrolysis methods. Recovery of these samples was good but the deviation was large. The structure of commercial dextran and dextran produced by W. confusa were solved by methanolysis method and partly by acid hydrolysis method. Recovery of these samples was poor. The methylation succeeded only in one of the dextran samples produced by L. citreum. The methylation analysis of dextrans could be developed in the future by increasing the temperature and the time of mixing and by adding some glycerol.
  • Alasalmi, Krista (Helsingin yliopisto, 2019)
    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.
  • Ahola-Iivarinen, Elina (Helsingfors universitet, 2016)
    In the literature review of this study, the focus was on biofilms that certain microbes produce, and their potential use in food industry. Biofilms consist of microbial cells and extracellular products, e.g., polysaccharides. Pullulan as an exopolysaccharide has many industrial applications and the aim of this study was to explore a new potential alpha-glucan, dextran, and especially its ability to form a stand-alone film. Pullulan and dextran were separately mixed in de-ionized water. The dynamic viscosities of dextran and pullulan solutions were determined. Film formation of dextran was not successful, not even with sorbitol as a plasticizer. The optical properties, water vapor and oxygen permeabilities and tensile strengths of pullulan films were studied. Additionally, Whatman42-filter material was coated with or immersed in dextran solution. Hence the changes in tensile strength and permeability values between a well-known material and dextran treated material could be detected. Pullulan films had low haze values (2.1–3.9%) and they were transparent to UVA-, UVB- and visible light. The tensile strength values of pullulan films were 47–53 MPa. For filter paper, the corresponding values were 10 MPa and application of dextran coating increased it to 15–19 MPa. All polysaccharide solutions exhibited Newtonian behavior and their relative viscosities were <10 mPa, 5% pullulan with viscosity around 20 mPa as an exception. Pullulan solutions had higher viscosities than dextran solutions. The air permeabilities were 10–50 ml/min for pullulan films, 10 ml/min for dextran-sorbitol film, 200 ml/min for dextran film and 200–500 ml/min for Whatman42 material. The oxygen permeability values for pullulan films were <0,1 cm3·μm m-2·d-1·kPa-1. Based on results in this study, pullulan films are impermeable to oxygen. As the films tolerated water vapor poorly, pullulan might be a potential component in packages made of composite materials, as individual packaging material in dry environment or possibly chemically modified to obtain better resistance to water vapor. Our results show that without additional modifications dextran does not form a continuous self-supporting films in these conditions.