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    Adsorption Isotherm and Kinetic Modelling of ?-Galactosidase Immobilization onto a Basic Resin (Duolite A568)
    (Asian Journal Of Chemistry, 2011) Gurdas, Sevim; Gulec, Haci Ali; Mutlu, Mehmet
    This study aimed to determine adsorption characteristics of Aspergillus oryzae beta-galactosidase onto a basic resin Duolite A568. The experimental data were analyzed by the Langmuir and Freundlich isotherm to describe the adsorption equilibrium. The equilibrium data fitted well with the Langmuir model which confirmed that the Duolite A568 was favourable for adsorption of P-galactosidase enzyme under conditions studied. The maximum adsorption capacity was found to be (5.1 +/- 0.49) x 10(-2) mg/g at 35 degrees C. The kinetic data were fitted. to pseudo-second-order kinetic model of Ho by linear and non-linear regression methods. The enthalpy change (Delta H degrees), the entropy change (Delta S degrees) and the Gibb's free energy change (Delta G degrees) for the:sorption processes were calculated to be 15.5 kJ/mol, 30.4 J/mol K and -9.4 kJ/mol, respectively. The positive Delta H degrees value indicated that the adsorption process was endothermic. Delta G degrees and Delta S degrees values showed that adsorption process occurred by physical mechanism and spontaneously.
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    Immobilization of Aspergillus oryzae ?-Galactosidase on Low-pressure Plasma-modified Cellulose Acetate Membrane Using Polyethyleneimine for Production of Galactooligosaccharide
    (Korean Soc Biotechnology & Bioengineering, 2010) Gulec, Haci Ali; Gurdas, Sevim; Albayrak, Nedim; Mutlu, Mehmet
    The aim of this study was to produce galacto-oligosaccharides (GOS) from lactose using beta-galactosidase from Aspergillus oryzae immobilized on a low-pressure plasma-modified cellulose acetate (CA) membrane Specifically, a novel method was developed for multilayer enzyme immobilization involving polyethyleneimine (PEI)-enzyme aggregate formation and growth on a CA membrane A large amount of enzyme (997 mu g/cm(2) membrane) was immobilized with 66% efficiency The K(m) value for the immobilized enzyme was estimated to be 48 mM, which indicates decreased affinity for the substrate, whereas the Vmax value was smaller The immobilized enzyme showed good storage and operational stability The half-life of the immobilized enzyme on the membrane was about 1 month at 30 degrees C and similar to 60 h at 60 degrees C Maximum GOS production of 27% (w/w) was achieved with 70% lactose conversion from 320 g/L of lactose at pH 4 5 and 60 degrees C Trisaccharides were the major types of GOS formed and accounted for about 75% of the total GOS produced Based on these results, immobilized enzyme technology could be applied to GOS production from lactose
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    Immobilization of Aspergillus oryzae ?-Galactosidase onto Duolite A568 Resin via Simple Adsorption Mechanism
    (Springer, 2012) Gurdas, Sevim; Gulec, Haci Ali; Mutlu, Mehmet
    In this study, a rapid, simple and economic method of enzyme immobilization was developed to hydrolyze lactose. Duolite A568 resin was used for the immobilization of beta-galactosidase via simple adsorption mechanism. The effects of immobilization parameters such as time, pH, and temperature were studied. Immobilization parameters for maximum enzyme activity were estimated at 35 A degrees C temperature, pH 4.5, 5 mg/mL enzyme concentration, and approximately 60 min immobilization time. A significant amount of enzyme was immobilized with high catalytic activity. Enzyme immobilization procedure explained in this study slightly affected the enzyme kinetic. The value of Michaelis constant K (m) for immobilized enzyme was significantly larger, indicating decreased affinity by the enzyme for its substrate. It was observed that both free and immobilized enzyme showed maximum activity at 65 A degrees C reaction temperature. Immobilized beta-galactosidase was significantly more active at all temperatures as compared to its free form. However, optimal pH of immobilized enzyme was slightly affected by immobilization procedure. The optimum pH of immobilized enzyme was shifted up 0.5 unit to a more alkaline value of 6.0 compared to the free enzyme.