Suchergebnisse

Magnetized polysiloxane coated with polyaniline (mPOS–PANI) was used as a support for β-galactosidase immobilization via glutaraldehyde. The galactooligosaccharides (GOS) production by this derivative was investigated under different initial lactose concentrations (5–50%) and temperatures (30–60 °C). The initial lactose concentration in the reaction media affected the total amounts of produced GOS and their time course production was described as a "bell-shaped" curve as a result of the balance between transgalactosylation and hydrolysis. No significative difference was observed for the free and immobilized enzymes. The reaction rates for lactose hydrolysis and GOS formation increased with increasing temperature from 30 °C to 60 °C, but GOS production at all lactose conversion levels was almost unchanged with changing temperature. The mPOS–PANI matrix was also characterized by scanning electronic microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometry (VSM), thermomagnetization, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). ; European Union Programme of High Level Scholarships for Latin America - Programme Alban ((Scholarship No. E05D057787BR) ; Brazilian National Research Council ...

β-Galactosidase from Kluyveromyces lactis was covalently immobilized onto a mPOS–PVA, using glutaraldehyde as activating agent and its properties were evaluated. The enzymatic water insoluble derivative displayed the same optimum pH (6.5) and optimum temperature (50 °C) of the soluble enzyme. The apparent Km app and activation energy for both soluble and immobilized enzyme derivative were found to be not significantly different. The mPOS–PVA β-galactosidase preparation presented a higher operational and thermal stability than the soluble enzyme. This immobilized β-galactosidase also was effective in hydrolyzing lactose from milk. Hence, one can conclude that mPOS–PVA is an attractive and efficient support for β-galactosidase immobilization. ; Alban, the European Union Programme of High Level Scholarships for Latin America; Brazilian National Research Council ...

β-Galactosidase from Aspergillus oryzae is an enzyme with a wide industrial application, mostly in the hydrolysis of lactose and, more recently, in the synthesis of oligosaccharides. Several advantages are associated with the application of immobilized enzymes on magnetic supports. In this work, β-galactosidase was covalently immobilised onto a Polysiloxane- Polyvinyl Alcohol Magnetic Composite (mPOS-PVA), Magnetic Polysiloxane with Polyaniline (mPOS-PANI), Magnetized Dacron (DACRON) and Magnetite with Polyaniline (MAG-PANI) using glutaraldehyde as activating agent being the synthesis of GOS evaluated and compared at different temperatures (30, 40, 50 and 60 oC) and various initial lactose concentration (50, 100, 200, 300, 400 and 500 g/L). The kinetic parameters obtained by fitting the experimental data were compared in order to determine the effect of the immobilization process with different supports on the synthesis of oligosaccharides. These results clearly demonstrate that all supports may be used for β-galactosidase immobilization as, besides improving the enzyme hydrolytic and GOS synthesis properties, its separation from the obtained reaction products is easy to accomplish. ; Programme Alβan, European Union Programme of High Level Scholarships for Latin America ; Brazilian National Research Council ...

The synthesis of galacto-oligosaccharides (GOS) by the action of Aspergillus oryzae β-galactosidase free and immobilized on magnetic polysiloxane-polyvinyl alcohol (mPOS-PVA) was studied. A maximum GOS concentration of 26% (w/v) of total sugars was achieved at near 55% lactose conversion from 50%, w/v lactose solution at pH 4.5 and 40 °C. Trisaccharides accounted for more than 81% of the total GOS produced. GOS formation was not considerably affected by pH and temperature. The concentrations of glucose and galactose encountered near maximum GOS concentration greatly inhibited the reactions and reduced GOS yield. GOS formation was not affected by enzyme immobilization in the mPOS-PVA matrix, indicating the absence of diffusional limitations in the enzyme carrier. Furthermore, this water insoluble magnetic derivative was reutilized 10-times and retained about 84% of the initial activity. In addition, the kinetic parameters for various initial lactose concentrations were determined and compared for the free and immobilized enzyme. ; David F. M. Neri gratefully acknowledges support by the Programme Alpan, the European Union Programme of High Level Scholarships for Latin America (Scholarship No. E05D057787BR). Luiz B. Carvalho Jr. is recipient of a scholarship of the Brazilian National Research Council ...

Bioconversions using enzymes immobilized in magnetic supports present significant advantages due to the easy separation of the enzyme from the reaction mixture and the simplicity and low cost of the support preparation. The characterization of the oligosaccharide mixture obtained by the action of b-galactosidase covalently attached, via glutaraldehyde, to a hydrazideeDacronemagnetite composite is presented. The fractionation of the oligosaccharide mixture by high performance liquid chromatography, followed by the analysis of the purified compounds by mass spectrometry and nuclear magnetic resonance spectroscopy permitted the identification of glucose, galactose, lactose and a hexose disaccharide containing a 1/6 linkage. Also, the following GOS were identified: b-D-Galp-(1/6)-b-D-Galp-(1/4)- Glcp, b-D-Galp-(1/4)-[b-D-Galp-(1/6)]-Glcp and b-D-Galp-(1/6)-b-D-Galp-(1/6)-b-D-Galp-(1/4)- Glcp. When GOS yield (26.2%) and kinetics of biotransformation of lactose by the Dacron immobilized b-galactosidase were compared with values obtained for the enzyme immobilized in other magnetic supports, similar behaviour was observed ; David F.M. Neri gratefully acknowledges support by Alban, the European Union Programme of High Level Scholarships for Latin America (Scholarship No. E05D057787BR). Luiz B. Carvalho Jr. is recipient of a scholarship from the Brazilian National Research Council (CNPq). M.R.M. Domingues acknowledges financial support provided to the project POCI/QUI/59337/2004. Duarte P. M. Torres acknowledges Fundacao para a Ciencia e a Tecnologia (Portugal) for the PhD Grant received (reference ...