Browsing by Subject "entsymaattinen hydrolyysi"

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  • Rahikainen, Jenni (Helsingfors universitet, 2009)
    Environmental concerns and limited availability of fossil hydrocarbons have boosted the research of renewable feedstocks and their processing into fuels and chemicals. Currently, vast majority of transportation fuels and bulk chemicals are refined from crude oil, but renewable lignocellulosic plant biomass has long been recognised as potential feedstock for liquid fuel and chemical production. Several alternative processes exist for biomass refining, lignocellulose-to-ethanol process being among the most studied processes. First, lignocellulose is pretreated in order to deconstruct the recalcitrant structures of plant cell walls and expose cellulosic fibrils. Subsequently, biotechnical process utilises cellulolytic enzymes of fungal origin to depolymerise cellulose down to glucose monomers and oligomers. Monomeric sugars serve as a source for platform chemicals in further conversions. Lignocellulose consists mainly of cellulose, hemicellulose and lignin. It is generally accepted that lignin has an inhibitory effect during enzymatic hydrolysis of cellulose and part of this effect is caused by irreversible cellulase adsorption on lignin. Fungal cellulase system consists of several enzyme components that contribute to the effective degradation of insoluble cellulosic substrate. Cellulases are traditionally divided to three groups according to enzymatic activity: exoglucanases, endoglucanases and ?-glucosidases. Different enzyme components are shown to have different affinity to lignin which enables screening or engineering of weak lignin-binding enzymes. However, too little is still known about enzyme-lignin interactions and competitive nature of enzyme binding on lignin. In this study, lignin-rich residues were isolated from steam pretreated spruce (SPS) using three different methods: enzymatic hydrolysis, acid hydrolysis and alkali extraction. Lignin residues were characterized and used in adsorption studies with commercial cellulase preparations from Trichoderma reesei (Celluclast 1.5L) and Aspergillus niger (Novozym 188). Enzyme activity measurements and protein analytics were employed to reveal competitive adsorption of cellulases and catalytic activity of solid-bound enzymes. Results showed that T. reesei enzymes had high affinity on lignocellulosic SPS and all SPS-derived lignins, but enzyme activity measurements revealed considerably divergent competitive adsorption patterns. Among all the isolated lignins, lignin-rich residue obtained by enzymatic hydrolysis of SPS and subsequent protease purification was evaluated as most suited adsorption substrate for further adsorption studies and screening purposes. ?-glucosidases from T. reesei and A. niger were shown to have highly distinctive adsorption behaviour on the lignin-rich substrates: A. niger ?-glucosidase lacked affinity to lignin, whereas T. reesei ?-glucosidase adsorbed to all lignin-rich particles. Lignin-bound Trichoderma reesei endoglucanases and CBH I exoglucanase were shown to retained high activity towards soluble substrates used in activity measurements. On the contrary, same enzymes were unable to processively hydrolyze insoluble crystalline cellulose.
  • Lakkavaara, Eero (Helsingin yliopisto, 2020)
    The literature review focused on the chemical composition of oats, the functional properties of oat components and the foods manufactured from oat ingredients. The factors affecting the technological and the nutritional properties of oat β-glucan have been previously studied. However, the effect of enzymatic hydrolysis on oat β-glucan has not been widely examined. The aim was to study the effect of β-glucanase concentration, hydrolysis time and temperature on the hydrolysis rate of oat β-glucan. During the experimental work an Arena-method was developed to analyse the concentration of β-glucan. The required amount of experiments was determined using statistical CCF design of experiment. The total number of experiments was 36 and 96 analyses were conducted in the experimental work. The viscosity, the concentration of β-glucan and the concentration of dietary fibre were analysed from the hydrolysed suspensions. Based on the results, the effects of the process variables on the hydrolysis of β-glucan were evaluated. Hydrolysis of β-glucan was a relatively fast reaction with the β-glucanase used in the study. Hydrolysis temperature and the concentration of the enzyme had the most significant effects on the hydrolysis of β-glucan. Based on the viscosity curves, the molecular weight of oat β-glucan was significantly decreased. The hydrolysed β-glucan did not increase the viscosity and was not indicating shear-thinning behavior. However, most of the β-glucan hydrolysates were dietary fibre by definition.