Hydrolysis of lactose in skim milk by immobilized ?-galactosidase in a spiral flow reactor

Calcium alginate entrapped preparations of Aspergillus oryzae beta galactosidase: its stability and applications in the hydrolysis of lactose

Insoluble concanavalin A-beta galactosidase complex was obtained by using jack bean extract and this complex was crosslinked with glutaraldehyde, in order to maintain the integrity of complex in the presence of its substrate or products. Concanavalin A-beta galactosidase complex retained 92% of the initial enzyme activity whereas crosslinked complex showed 88% activity. Entrapment of concanavalin A-beta galactosidase complex into calcium alginate beads provided suitability to use this preparation in reactors. Temperature- and pH-optima of the various immobilized beta galactosidase preparations were the same as its soluble counterpart. Entrapped crosslinked concanavalin A-beta galactosidase complex retained more than 50% activity after 1h exposure with 4.0 M urea at room temperature. Moreover, entrapped crosslinked concanavalin A-beta galactosidase complex retained 81 and 62% of the original enzymatic activity in the presence of 5% calcium chloride and 5% galactose, respectively. Entrapped crosslinked concanavalin A-beta galactosidase complex preparation was more superior in the continuous hydrolysis of lactose in a batch process as compared to the other entrapped preparations. This entrapped crosslinked concanavalin A-beta galactosidase complex retained 95% activity after seventh repeated use and 93% of its original activity even after 2 months storage at 4 degrees C.

Kinetics of lactose hydrolysis by beta-galactosidase of Kluyveromyces lactis immobilized on cotton fabric

A mathematic model for describing the Michaelis-Menten-type reaction kinetics with product competitive inhibition and side-reaction is proposed. A multiresponse nonlinear simulation program was employed to determine the coefficients of a four-parameter rate expression. The rate expression was compared with the conventional Michaelis-Menten reaction rate models with and without product inhibition. Experimental data were obtained using beta-galactosidase of Kluyveromyces lactis immobilized on cotton fabric in a batch system at a temperature of 37 degrees C and at various initial concentrations of dissolved lactose ranging from 3-12.5% (w/v). The reaction is followed by concentration changes with time in the tank. Samples were obtained after the outlet stream of the packed bed reactor is mixed in a well-stirred tank. High-performance liquid chromatography (HPLC) was applied to monitor the concentrations of all the sugars (reactants as well as products). The four-parameter rate model is featured with a term to describe the formation of trisaccharides, a side-reaction of the enzymatic hydrolysis. The proposed model simulates the process of lactose hydrolysis and the formation of glucose and galactose, giving better accuracy compared with the previous models.

Development of an ultrahigh-temperature process for the enzymatic hydrolysis of lactose. IV. Immobilization of two thermostable beta-glycosidases and optimization of a packed-bed reactor for lactose conversion

Recombinant hyperthermostable beta-glycosidases from the archaea Sulfolobus solfataricus (Ss beta Gly) and Pyrococcus furiosus (CelB) were covalently attached onto the insoluble carriers chitosan, controlled pore glass (CPG), and Eupergit C. For each enzyme/carrier pair, the protein-binding capacity, the immobilization yield, the pH profiles for activity and stability, the activity/temperature profile, and the kinetic constants for lactose hydrolysis at 70 degrees C were determined. Eupergit C was best among the carriers in regard to retention of native-like activity and stability of Ss beta Gly and CelB over the pH range 3.0-7.5. Its protein binding capacity of approximately 0.003 (on a mass basis) was one-third times that of CPG, while immobilization yields were typically 80% in each case. Activation energies for lactose conversion by the immobilized enzymes at pH 5.5 were in the range 50-60 kJ/mol. This is compared to values of approximately 75 kJ/mol for the free enzymes. Immobilization expands the useful pH range for CelB and Ss beta Gly by approximately 1.5 pH units toward pH 3.5 and pH 4.5, respectively. A packed-bed enzyme reactor was developed for the continuous conversion of lactose in different media, including whey and milk, and operated over extended reaction times of up to 14 days. The productivities of the Eupergit C-immobilized enzyme reactor were determined at dilution rates between 1 and 12 h(-1), and using 45 and 170 g/L initial lactose. Results of kinetic modeling for the same reactor, assuming plug flow and steady state, suggest the presence of mass-transfer limitation of the reaction rate under the conditions used. Formation of galacto-oligosaccharides in the continuous packed-bed reactor and in the batch reactor using free enzyme was closely similar in regard to yield and individual saccharide components produced.

Continuous superporous agarose beds in radial flow columns

Continuous superporous agarose beds constitute a new support material for chromatography, biocatalysis and electrophoresis. The bed consists of a single piece of agarose gel, homogeneously transected by flow-carrying pores, which easily can be varied in the range of 10-100 microm. In this work, large diameter beds (60 mm) were prepared and used in specially designed radial flow columns. The basic chromatographic properties of the beds were investigated by size-exclusion chromatography experiments. In an affinity chromatography application one bed was derivatized with Cibacron Blue 3GA and used for the purification of lactate dehydrogenase from a crude bovine heart extract. In a biotransformation application one bed was provided with immobilized beta-galactosidase and used in the production of lactose-free milk.

Kinetic modeling of lactose hydrolysis with an immobilized beta-galactosidase from Kluyveromyces fragilis

The kinetic model of the hydrolysis of lactose with a beta-galactosidase from Kluyveromyces fragilis immobilized on a commercial silica-alumina (KA-3, from Südchemie) has been determined. A wide experimental range of the main variables has been employed: temperature, concentrations of substrate, and products and concentration of enzyme. The runs were performed in a complex buffer with the salt composition of milk. The effect of pH and temperature on the stability and the activity of the enzyme have been studied. The optimum pH for the enzyme activity was, approximately, seven. The immobilized enzyme was more stable than the free one at acidic pH, but more instable at basic pH. The maximum temperature used for the hydrolysis runs performed to select the kinetic model was 40 degrees C, so inactivation of the enzyme during the kinetic runs has been avoided. Agitation, concentration of enzyme in the solid and particle size were selected to ensure that the overall rate was that of the chemical reaction. Eleven kinetic models were proposed to fit experimental data, from first order to more complex ones, such as those taking into account inhibition by one of the compounds involved in the hydrolysis reaction. Applying statistical and physical criteria, a Michaelis-Menten model with a competitive inhibition by galactose has been selected. The model is able to fit the experimental data correctly in the wide experimental range studied. Finally, the model obtained is compared to the one selected in a previous work for the hydrolysis of lactose with the free enzyme.

Development of an ultra-high-temperature process for the enzymatic hydrolysis of lactose. I. The properties of two thermostable beta-glycosidases

Recombinant beta-glycosidases from hyperthermophilic Sulfolobus solfataricus (SsbetaGly) and Pyrococcus furiosus (CelB) have been characterized with regard to their potential use in lactose hydrolysis at about 70 degrees C or greater. Compared with SsbetaGly, CelB is approximately 15 times more stable against irreversible denaturation by heat, its operational half-life time at 80 degrees C and pH 5.5 being 22 days. The stability of CelB but not that of SsbetaGly is decreased 4-fold in the presence of 200 mM lactose at 80 degrees C. CelB displays a broader pH/activity profile than SsbetaGly, retaining at least 60% enzyme activity between pH 4 and 7. Both enzymes have a similar activation energy for lactose hydrolysis of approximately 75 kJ/mol (pH 5.5), and this is constant between 30 and 95 degrees C. D-Galactose is a weak competitive inhibitor against the release of D-glucose from lactose (Ki approximately 0.3 M), and at 80 degrees C the ratio of Ki, D-galactose to Km,lactose is 2.5 and 4.0 for CelB and SsbetaGly, respectively. SsbetaGly is activated up to 2-fold in the presence of D-glucose with respect to the maximum rate of glycosidic bond cleavage, measured with o-nitrophenyl beta-D-galactoside as the substrate. By contrast, CelB is competitively inhibited by D-glucose and has a Ki of 76 mM. The transfer of the galactosyl group from lactose to acceptors such as lactose or D-glucose rather than water is significant for both enzymes and depends on the initial lactose concentration as well as the time-dependent substrate/product ratio during batchwise lactose conversion. It is approximately 1.8 times higher for SsbetaGly, compared with CelB. Overall, CelB and SsbetaGly share their catalytic properties with much less thermostable beta-glycosidases and thus seem very suitable for lactose hydrolysis at >/=70 degrees C.

Hydraulic Permeability of Immobilized Bacterial Cell Aggregates

A dense aggregate of cells was retained in a reactor by a supported porous membrane. A continuous flow of nutrient medium was maintained through the cell aggregate and membrane. The hydraulic resistance of the cell aggregate was monitored throughout experiments with either growing or chemically cross-linked cells, under conditions of varying flow rates. Digital image analysis was used to characterize the sizes, separations, and orientations of several thousand individual cells in electron micrographs of chemically cross-linked cell aggregates. Two nonlinear phenomena were observed. First, the hydraulic resistance varied in direct relation to and reversibly with flow rate. Second, in constant flow-rate experiments the hydraulic resistance increased with time at a faster rate than could be attributed to cell growth. Both of these phenomena were dependent upon and could be explained by the ability of cells to move with respect to one another, under the influences of Brownian motion and of convection. Such relative motion could allow changes in net alignment of cells in the direction of flow and in the volume fraction of cells in the aggregate. This explanation is consistent with image analysis data. The observed sensitivity of hydraulic resistance to flow rate was inconsistent with a model that assumed elastic deformation of individual cells, and no evidence of cell deformation was found in electron micrographs.