Browsing by Subject "Weissella confusa"

Dextrans are polysaccharides and mainly produced from lactic acid bacteria, which have great values in industrial applications. Dextrans with different molar mass and branches have different applications. In this thesis, the effects of different reaction factors on the molar mass and composites of dextrans had been studied. Weissella confusa VTT E-90392 dextransucrase was used to synthesize dextran with sucrose as substrates. The effects of sucrose concentration, enzyme concentration, reaction time, temperature and pH on dextran macromolecular properties were detected. Sucrose concentration, enzyme concentration and reaction time were selected as the most influential factors for the subsequent response surface modeling to analyze how they affect dextran properties, according to experimental design. 18 reaction conditions were conducted and the product mixtures containing dextran were analyzed by HPSEC. The effects of the three reaction factors on dextran production were also studied. The predictive contour plot showed that dextran conversion was positively proportional to the enzyme concentration and increased in the early stage, but decreased in the late stage. In the preliminary study of the effects of various factors on dextran profile, two or three main dextran size populations eluting at different volumes were found in HPSEC analysis. The 1st dextran size population (eluted around 10.5 ml) had the highest Mw ranging from 7 × 107 to 2 × 108 g/mol. The 2nd dextran size population (eluted at around 12.5 ml) had Mw ranging from 2 × 107 to 4×107 g/mol. Besides, there seemed to be a 3rd dextran size populations (eluted at 16.2 ml to 17.5 ml) and the Mw was within the widest range (5 × 106 g/mol to 1.3 × 107 g/mol).We kept the samples' 4 factors constant and one factor changed and compared the effect of each factor. Under conditions: low sucrose, dextransucrase concentration, low temperature, low pH or short reaction time, the amount of the 2nd dextran size population was in equal or higher amount than the 1st one and 3rd one hardly appeared. On the contrary, the 1st size population became predominant over 2nd one, and the 3rd one started to form. In the modeling experiments, the overall effects of reaction time, sucrose concentration and enzyme concentration on the molar mass and amounts of different dextran size populations were studied. In our study, as the sucrose and enzyme concentration increased, the 2nd dextran size population decreased. The amount of 3rd one was positively proportional to the sucrose and enzyme concentrations. At the early stage of reaction, the amount of 3rd one was positively proportional to the reaction time, but the amount of 3rd one was negatively proportional to the reaction time. We hypothesize that as the reaction proceeds, 2nd dextran size population can be elongated into the 1st population. It was not clear whether the 2nd dextran size population could combine with themselves to form 1st one (internal insertion) or the 2nd one could only be inserted with D-glucosyl units one by one (external insertion). At the end of synthesis, dextran can be degraded possibly by hydrolyzing D-glucosyl units externally, because there should be more than 3 dextran populations if the dextran was internally broken. Based on the above results, it might give some new clue about the process of dextran synthesis and the way the dextran was hydrolyzed.

Oligosaccharides and dextran can both be produced from sucrose during sourdough fermentation when using dextran producing lactic acid bacteria (LAB). Both dextran and oligosaccharides increase the softness and volume of bread. Since they both are produced simultaneously, the exact effects of dextran and oligosaccharides in sourdough cannot be differentiated. The production of oligosaccharides and dextran can, however, be affected by modifying the concentrations and ratio of sucrose and acceptor and changing the used pH and temperature. The aim of this master’s thesis was to improve the functionality of syrups used in baking by optimizing the production of maltosylisomaltooligosaccharides (MIMO) by oligosaccharides and dextran producing LAB Weissella confusa. The used fermentation temperatures were 20℃ and 30℃. Sucrose concentrations in syrups were 0%, 10% and 20%. Native syrup was used as a control sample. The optimized, functionalized syrup with 20% added sucrose was further used in bread production to evaluate its ability to increase volume and decrease hardness of bread. Breads with added optimized and functionalized syrup, syrup with 0% added sucrose and native syrup as well as control wheat bread were baked. The volume of functionalized syrup containing bread was expected to increase and hardness to decrease compared to other breads. The oligosaccharide production in syrups was qualitatively whereas mono- and disaccharides quantitatively evaluated by high performance anion exchange chromatography with pulse amperometric detection (HPAEC-PAD). Dextran content was evaluated after enzymatic degradation using HPAEC-PAD. The technological impact in bread was evaluated by measuring of the specific volume and texture profile analysis (TPA) of breads containing dextran and MIMO. The results were compared to the breads containing syrup with 0% added sucrose, native syrup and control wheat bread. An increased production of MIMO was obtained by increasing sucrose concentration from 10% to 20%. The peaks of short-chain MIMO decreased, and long-chain MIMO increased as sucrose concentration increased. Temperature did not affect MIMO production. Unlike expected, the volume of functionalized syrup containing bread decreased, and the hardness increased compared to control, bread containing syrup with 0% sucrose or bread with native syrup. This could be due to decreased yeast activity due to increased osmotic pressure, which was caused by a low water amount and yet high sugar content. In further studies, the baking conditions of functionalized syrup containing bread should be optimized to increase the activity of yeast and also the use of functionalized syrup fermented with 10% sucrose should be evaluated in baking.