Browsing by Subject "lakkaasi"
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(2016)The literature part of the thesis discusses about Agaricus mushrooms and the structure and function of laccase and tyrosinase. Also the potential and existing applications of these enzymes were reviewed. In experimental part the activity levels of tyrosinase and laccase were measured in two 28 day cultivations. Medium in the cultivation was 2% (w/v) malt extract broth and in other cultivations the medium was 1.5% (w/v) soybean meal. In soybean meal medium seven white rot fungi were cultivated and in malt broth six Agaricus strains were cultivated. Agaricus bisporus FBCC396 strain was cultivated in pure malt broth and with 25 µM copper addition. The laccase activity from culture media and tyrosinase activity, both monophenolase and diphenolase activities, were measured in seven different time points (day 7, 11, 14, 18, 21, 24 and 28). Tyrosinase activity was measured with bound quinone method from all samples. Diphenolase activity from samples from soybean meal cultivations was measured also with free quinone method in addition to bound quinone method. Morphological identification of all strains was confirmed with the ITS region sequencing. Also attempts to isolate the copper binding regions of laccase and tyrosinase genes were made, and the sequences from isolated copper binding regions were compared to existing data in gene databases. The highest laccase activity was measured from Phlebiopsis gigantea FBCC730 culture broth in soybean meal cultivation and in malt broth cultivation the highest laccase activity was measured from A. bisporus FBCC396 strain with the addition of copper in the culture medium. The highest tyrosinase activities were measured from Agrocybe praecox and P. gigantea mycelium extracts, which had both highest mono- and diphenolase activities. Both used tyrosinase activity measurement methods had their own difficulties and uncertainties, and neither results are absolutely reliable, mainly due to overlapping activities of phenol oxidising enzymes
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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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