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81.
Stability of proteinase from Carica papaya latex in dense gases
Maja Leitgeb, Mateja Primožič, Željko Knez, 2005, izvirni znanstveni članek

Opis: Proteinase from Carica papaya latex was tested on its thermal stability at atmospheric pressure and in supercritical carbon dioxide, near-critical propane and dimethyl-ether. In supercritical carbon dioxide at 300 bar thermalactivation of the examined proteinase was improved in the comparison toatmospheric pressure. In propane and dimethyl-ether (300 bar) activity of the examined proteinase decreased. Influence of compressionžexpansion cycles on residual activity of the same proteinase in supercritical carbon dioxide (300 bar and 50 °C) was studied, as well. Different ways of transition from supercritical to low-pressure-state were used which affected residual activityof the proteinase.Addition of water in the system increased activity of proteinase from C. papaya, which was incubated in supercritical carbon dioxide for 24 h. Optimum amount of water was found to be between 0.5 and 0.7 g/L.
Ključne besede: chemical processing, high pressure technology, supercritical CO2, proteinase, thermal stability, pressure stability, enzyme activity, water content, dense gases
Objavljeno v DKUM: 01.06.2012; Ogledov: 1823; Prenosov: 27
URL Povezava na celotno besedilo

82.
Enzymatic reactions in high-pressure membrane reactors
Maja Leitgeb, Mateja Primožič, Željko Knez, 2005, izvirni znanstveni članek

Opis: In the studies on the stability of biocatalysts in a high-pressure batch stirred tank reactor, changes in biocatalyst activity due to pressurizationždepressurization steps were observed. An interesting alternative to overcome this inconvenience is using the high-pressure continuous membrane reactors, where just a single compression and expansion step is necessary. The aim of the research was to carry out the enzyme-catalyzed reactions in high-pressure membrane reactors. At first, high-pressure enzyme-catalyzed hydrolyses of oleyl oleate and sunflower oil were performed in a high-pressure continuous enzymatic flat-shape membrane reactor. Additionally, cellulase from Humicola insolens was covalently immobilized on tubular membrane, and enzyme-catalyzed hydrolysis of carboxy-methyl cellulose was carried out in a high-pressure continuous enzymatic tubular membrane reactor. The membrane-stability tests for flat-shape polysulfon membranes before and after treatment with supercritical CO2 or subcritical propane were done, as well.
Ključne besede: chemical processing, high pressure technology, membrane reactors, biotechnology
Objavljeno v DKUM: 01.06.2012; Ogledov: 1588; Prenosov: 78
URL Povezava na celotno besedilo

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Supercritical fluids as solvents for enzymatic reactions
Maja Leitgeb, Mateja Primožič, Željko Knez, 2007, pregledni znanstveni članek

Opis: Enzymes may act in different solvent systems. Water as the solvent in vivo may be replaced partially or mostly with other solvents, such as micro-emulsions, organic solvents, reversed micelles, ionic liquids and supercritical fluids (SCFs).Several types of enzymatic reactions were performed in SCFs. Influence of SCFs on enzyme stability and activity is presented on different examples; on different reaction systems (hydrolysis, transesterification...) and on the use of non-immobilized (Subtilisin carlsberg, Aspergillus niger...) as well as immobilized enzymes. Several types of high-pressure enzymatic reactors (batch-, stirred-tank-, extractive semibatch-, recirculating batch-, semicontinuous flow-, continuous packed-bed-, and continuous-membrane reactors) have been used for the performance of enzymatic reactions. In the studies on stability of biocatalysts in a high-pressure batch-stirred tank reactor changes in biocatalysts activity due to pressurization/depressurization steps were observed. Interesting alternative to overcome this inconvenience is the use of the high-pressure continuous membrane reactors, where just single compression and expansion step is necessary.
Ključne besede: enzymatic reactions, supercritical carbon dioxide, high-pressure, enzyme stability, high-pressure reactors
Objavljeno v DKUM: 31.05.2012; Ogledov: 3115; Prenosov: 144
.pdf Celotno besedilo (177,49 KB)
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87.
Proteinase-catalyzed hydrolysis of casein at atmospheric pressure and in supercritical media
Mateja Primožič, Maja Leitgeb, Željko Knez, 2006, izvirni znanstveni članek

Opis: In the presented work, reaction parameters for hydrolysis of casein, catalyzed by Carica papaya latex at atmospheric and high pressure, were optimized. Casein is a remarkably efficient nutrient, supplying not only essential amino acids, but also some carbohydrates, calcium, phosphorus and therefore is very important for the food industry. Different reaction parameters such as temperature, stirring rate, casein and enzyme concentration were studied to found the optimal conditions for the reaction. Reactions were performed at atmospheric pressure; an influence of temperature/pressure on the casein hydrolysis in supercritical carbon dioxide (SC CO2) was also investigated to improve the reaction rates. Higher conversions were achieved when the reactions were performed in SC CO2, even though casein was not soluble in this medium.
Ključne besede: chemical processing, high pressure technology, supercritical CO2, enzymatic reactions, proteinase, Carica papaya latex
Objavljeno v DKUM: 31.05.2012; Ogledov: 2078; Prenosov: 46
URL Povezava na celotno besedilo

88.
Enzyme-catalyzed reactions in different types of high-pressure enzymatic reactors
Mateja Primožič, Maja Leitgeb, Muzafera Paljevac, Željko Knez, 2006, izvirni znanstveni članek

Opis: The enzyme-catalyzed hydrolysis of carboxy-methyl cellulose (CMC) was performed in three different types of reactors; in a batch stirred-tank reactor (BSTR) operating at atmospheric pressure, in a high-pressure batch stirred-tank reactor (HP BSTR) and in a high-pressure continuous tubular-membrane reactor (HP CTMR). In the high-pressure reactors aqueous SC C02 was used as the reaction medium. The aim of our research was optimization of the reaction parameters for reaction performance. All the reactions were catalyzed by cellulase from Humicola insolens. Glucose production in the high-pressure batch stirred-tank reactor was faster than in the BSTR at atmospheric pressure. The optimal temperature for the reaction performed in the BSTR at atmospheric pressure was 30°C, while the optimal temperature for the reaction performed in SC C02 was 32°C. The influence of the application of tubular ceramic membranes in the high-pressure reaction system was studied on the model reaction of CMC hydrolysis at atmospheric pressure and in SC C02. The reaction was catalyzed by cellulase from Humicola insolens covalently linked to the surface of the ceramic membrane. The hydrolysis of CMC in SC C02 and at atmospheric pressure was performed for a long time period. The reaction carried out in SC C02 was more productive than the reaction performed at atmospheric pressure.
Ključne besede: chemical processing, enzymatic reaction, cellulase, supercritical carbon dioxide, high-pressure batch reactor, high-pressure membrane reactor
Objavljeno v DKUM: 31.05.2012; Ogledov: 1992; Prenosov: 332
.pdf Celotno besedilo (454,51 KB)
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