Browsing by Subject "dextran"

Plant-based milks can be unstable during storage due to the colloidal structure of these drinks. In general, e-coded additives are used to increase the viscosity of the drinks and hence, improve stability. Oat beta-glucan, microbially or enzymatically produced exopolysaccharides, such as dextran, and flaxseed mucilage are natural hydrocolloids that are known to have the ability to increase viscosity. These hydrocolloids could potentially be used to replace e-coded additives. The aim of this thesis was to study the stabilizing potential of oat beta-glucan, exopolysaccharides, and flaxseed mucilage in oat drinks. Oat drinks with added hydrocolloids were compared to control samples that were oat drink without added hydrocolloids and oat drinks with pectin at concentrations of 0.2% and 0.4%. Oat beta-glucan, exopolysaccharides, and flaxseed mucilage were added to the prepared drinks by replacing 10% of water with the extracts. Additionally, stabilizing properties of isolated and freeze-dried microbially produced dextran was studied by adding it to the drinks at concentrations of 1.5%, 1.0% and 0.5%. Stability of the oat drinks was assessed during a 14−day storage period by measuring the viscosity, pH, and phase separation. Results of this study demonstrated the stabilizing potential of the natural hydrocolloids. The addition of hydrocolloids increased the viscosity in all samples. The inclusion of natural hydrocolloids led to a similar stability, and in some cases also significantly lower viscosity, compared to pectin added drinks. Oat beta-glucan had a remarkable positive impact on the stability of oat drinks. This was most likely due to the network formation of oat beta-glucan molecules, which decreased the sedimentation of colloidal particles. Enzymatically produced dextran also improved the stability of oat drinks, which might be attributed to the viscosity-increasing -capacity of dextran. However, the stabilizing role of microbially produced exopolysaccharides was not shown. For future study, the molecular interactions of natural hydrocolloids in the colloidal solution should be investigated.

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.

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.

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.

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.