Analysis of an Immobilized β-Galactosidase Reactor with Competitive Product Inhibition Kinetics

Abstract

The present study deals with the immobilization of Kluyveromyces lactis β-galactosidase on a weak ionic exchange resin (Duolite A568) as polymer support. β-Galactosidase was immobilized using the adsorption method. A kinetic study of the immobilized enzyme was performed in a packed-bed reactor. The adsorption of the enzyme followed a typical Freundlich adsorption isotherm. The adsorption parameters of k and n were 14.6 and 1.74, respectively. The initial rates method was used to characterize the kinetic parameters of the free and immobilized enzymes. The Michaelis-Menten constant (Km) for the immobilized enzyme (120 mM) was higher than it was for the free enzyme (79 mM). The effect of competitive inhibition kinetics was studied by changing the concentration of galactose in a recycling packed-bed reactor. The kinetic model with competitive inhibition by galactose was best fitted to the experimental results with Vm, Km, and KI values of 46.3 mmolmin -1 mg -1 , 120 mM, and 24.4 mM, respectively. In a continuous packed-bed reactor, increasing the flow rate of the lactose solution decreased the conversion efficiency of lactose at different input lactose concentrations. Continuous operation of 11 days was conducted to investigate the stability of a long-term operation. The retained activity of the immobilized enzymes was 63% and the half-life of the immobilized enzyme was found to be 15 days.

Synthesis of Lactulose in Continuous Stirred Tank Reactor With β-Galactosidase of Apergillus oryzae Immobilized in Monofunctional Glyoxyl Agarose Support

“…They explained that due to the short reaction time, mass transfer of the substrate into the immobilized enzyme molecules was reduced affecting both its transgalactosylation and hydrolysis. The reduction in X Lactose ( Figure 7D ) has also been reported by Kang (2013) for the hydrolysis of lactose with K. lactis β-G immobilized in Duolite A568, and by Mayer et al (2010) for the synthesis of lactulose in CPBR with Pyrococcus furiosus β-G immobilized in an anionic-exchange resin and in Eupergit C.…”

“…The reduction in X Lactose (Figure 7D) has also been reported by FIGURE 7 | Effect of feed flowrate on yields (Y Lactulose , Y TOS , and Y T ) (A-C), lactose conversion (X Lactose ) (D), productivity of lactulose (π Lactulose ) (E) and selectivity (S LU/TOS ) (F) during the synthesis of lactulose with glyoxyl-agarose immobilized β-galactosidase from A. oryzae in continuous stirred tank reactor operation at 50 • C, pH 4.5, 50% w/w inlet concentration of sugar substrates and reactor enzyme load of 29.06 IU H •mL −1 , at fructose/lactose molar ratios of: 4 ( ), 8 ( ), and 16 ( ). Kang (2013) for the hydrolysis of lactose with K. lactis β-G immobilized in Duolite A568, and by Mayer et al (2010) for the synthesis of lactulose in CPBR with Pyrococcus furiosus β-G immobilized in an anionic-exchange resin and in Eupergit C.…”