Browsing by Subject "polysakkaridi"
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(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.
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(2017)The literature review of this master’s thesis dealt with polysaccharide based hydro- and aerogels and their preparation methods and characterization. TEMPO/laccase-catalyzed oxidation was also included in the literature review. The aim of the experimental part of this thesis was to prepare hydrogels by TEMPO/laccase-catalyzed oxidation and study how the oxidation changed the rheological and chemical characteristics of the polysaccharides. The hydrogels were also dried to produce hydrogels via lyophilization and their characteristics were determined. The degree of oxidation of the hydrogels was analyzed by the GC-MS method. The viscoelastic properties of the hydrogels were studied by oscillation measurements. The compressive modulus of the aerogels was determined by means of a compression test. The morphology of the aerogels was studied with the help of a scanning electron microscopy (SEM). The studied polysaccharides were arabinoxylan, glucomannan, galactomannan and xyloglucan. Due to the oxidation, a change in the viscoelastic behaviour could be seen between the native and oxidised polysaccharides. The rheological test revealed that the native polysaccharides were viscous liquids (G' > G'') and oxidized polysaccharides formed elastic hydrogels (G' > G''). The degree of oxidation of the hydrogels varied 3,3–11,7 %. The hydrogels were dried using two different freezing methods, unidirectional and conventional, and they were freeze-dried into aerogels without significant shrinkage. The density of the aerogels varied 0,017–0,030 g/mm3. The compressive modulus of the aerogels was 108‒1184 kPa depending on the polysaccharide. The SEM images revealed that unidirectional freezing resulted in pores that were parallelly oriented with the freezing direction. Unidirectionally frozen aerogels were stronger than conventionally frozen aerogels when the compression was oriented against the freezing direction. This was the first time that TEMPO/laccase catalyzed oxidation was used to prepare arabinoxylan and glucomannan hydro- and aerogels. The arabinoxylan and glucomannan aerogels were mechanically stronger than previously studied aerogels that have been prepared by enzymatic oxidation.
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