Effects of temperature on the hydrolysis of lactose by immobilized beta-galactosidase in a capillary bed reactor

The effects of temperature on the hydrolysis of lactose by immobilized beta-galactosidase were studied in a continuous flow capillary bed reactor. Temperature affects the rates of enzymatic reactions in two ways. Higher temperatures increase the rate of the hydrolysis reaction, but also increase the rate of thermal deactivation of the enzyme. The effect of temperature on the kinetic parameters was studied by performing lactose hydrolysis experiments at 15, 20, 25, 30, and 40 degrees C. The kinetic parameters were observed to follow an Arrhenius-type temperature dependence. Galactose mutarotation has a significant impact on the overall rate of lactose hydrolysis. The temperature dependence of the mutarotation of galactose was effectively modelled by first-order reversible kinetics. The thermal deactivation characteristics of the immobilized enzyme reactor were investigated by performing lactose hydrolysis experiments at 52, 56, 60, and 64 degrees C. The thermal deactivation was modelled effectively as a first order decay process. Based on the estimated thermal deactivation rate constants, at an operating temperature of 40 degrees C, 10% of the enzyme activity would be lost in one year.

Formation of oligosaccharides during enzymatic lactose: Part I: State of art

Enzymatic lactose hydrolysis by beta-galactosidase (lactase) was investigated with respect to the formation of oligosaccharides. An analysis of the formation of oligosaccharides and their control is important in the development of technical applications for enzymatic lactose hydrolysis. The available literature data on transfer reactions of lactase were reviewed, compared, and presented in a concise tabular form. Mechanisms and possible ways of modelling enzymatic lactose hydrolysis, including formation of oligosaccharides, are presented.

Synthesis of β-Galactooligosaccharides from Lactose Using Microbial β-Galactosidases

  Galactooligosaccharides (GOSs) are nondigestible oligosaccharides and are comprised of 2 to 20 molecules of galactose and 1 molecule of glucose. They are recognized as important prebiotics for their stimulation of the proliferation of intestinal lactic acid bacteria and bifidobacteria. Therefore, they beneficially affect the host by selectively stimulating the growth and/or activity of a limited number of gastrointestinal microbes (probiotics) that confer health benefits. Prebiotics and probiotics have only recently been recognized as contributors to human health. A GOS can be produced by a series of enzymatic reactions catalyzed by β-galactosidase, where the glycosyl group of one or more D-galactosyl units is transferred onto the D-galactose moiety of lactose, in a process known as transgalactosylation. Microbes can be used as a source for the β-galactosidase enzyme or as agents to produce GOS molecules. Commercial β-galactosidase enzymes also do have a great potential for their use in GOS synthesis. These transgalactosyl reactions, which could find useful application in the dairy as well as the larger food industry, have not been fully exploited. A better understanding of the enzyme reaction as well as improved analytical techniques for GOS measurements are important in achieving this worthwhile objective.

Effects of temperature on lactose hydrolysis by immobilized beta-galactosidase in plug-flow reactor

The hydrolysis of lactose using immobilized beta-galactosidase (from Aspergillus niger) on phenol-formaldehyde resin was studied at temperatures between 8 and 60 degrees C and initial lactose concentrations ranging from 2.5 to 20.0%. A model involving enzyme-galactose complex similar to Michaelis-Menten kinetics with competitive product (galactose) inhibition is suitable to describe the lactose hydrolysis reaction. A small degree of lack of fit between the model and the data was found to be due to the formation of oligosaccharides. Thermal deactivation of lactase follows first-order reaction mechanism. The effect of temperature on the reaction and the deactivation rate constants follows the Arrhenius relationship. The Oligosaccharide formation was not significantly affected by the temperature when the initial lactose concentration was 5%. A design equation for the plug-flow immobilized lactase reactor was developed from the reaction and the deactivation kinetics and was used to find the optimal operating temperature. The optimal temperature was found to be dependent on the operating time but not on the lactose concentration or the conversion. The optimal operating temperature is 60 degrees C when operating time is short but is close to 35 degrees C for a long operating time. A preliminary economic analysis indicates that the optimal operating temperature is 43, 38.5, and 33 degrees C when the operating time is 300 days, 1000 days, and infinity, respectively.

Hydrolysis of lactose by free and immobilized beta-galactosidase from Thermus sp. strain T2

The hydrolysis of lactose by a beta-galactosidase from the thermophilic microorganism Thermus sp. strain T2, both in solution and immobilized on a commercial silica-alumina, has been studied. The enzyme has been previously produced by Escherichia coli JM101 harboring the plasmid pBGT1, which contains the codifying gene under the promoters lpp(P) and lac(PQ). The enzyme was immobilized on the support activated with tris-hydroxymethylphosphine (THP). Activity and stability of the free and the immobilized enzyme towards pH and temperature were tested. To study the activity at different pH and temperature values, lactose was used as substrate. To check the stability, the enzyme was incubated either in buffer BP or in a solution of lactose in buffer BM at different pH and temperatures, being the remaining activity tested by withdrawing samples and determining their activity toward ONPG at 70 degrees C in buffer BP. Afterward, runs were performed to obtain kinetic models adequate for the description of the hydrolysis of lactose by the free and the immobilized enzyme. These data were fitted to the kinetic models proposed (all based on the Michaelis-Menten mechanism) by non-linear regression, being the models and their parameters compared to determine the effect of the immobilization on the kinetic behavior of the enzyme. Both the free and the immobilized enzyme are competitively inhibited by galactose, while glucose inhibited only the action of the free enzyme, in an uncompetitive way. The immobilization step seems to eliminate the inhibition by glucose. Moreover, the immobilization reduced to a half the inhibitory action of galactose. In general, the immobilization reduced the activity of the enzyme, but increased its thermal stability. Finally, a comparison between the kinetic behavior of this thermophilic enzyme and enzymes of mesophile microorganisms previously studied by us (E. coli and K. fragilis) and by other authors (Aspergillus niger) is performed.

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.