β-Galactosidase of Aspergillus oryzae immobilized in an ion exchange resin combining the ionic-binding and crosslinking methods: Kinetics and stability during the hydrolysis of lactose

Aspergillus oryzae β-D-galactosidase immobilization on glutaraldehyde pre-activated amino-functionalized magnetic mesoporous silica: Performance, characteristics, and application in the preparation of sesaminol

Aspergillus oryzae β-D-galactosidase (β-Gal) efficiently hydrolyzes sesaminol triglucoside into sesaminol, which has higher biological activity. However, β-Gal is difficult to be separate from the reaction mixture and limited by stability. To resolve these problems, β-Gal was immobilized on amino-functionalized magnetic nanoparticles mesoporous silica pre-activated with glutaraldehyde (Fe3O4@mSiO2-β-Gal), which was used for the first time to prepare sesaminol. Under the optimal conditions, the immobilization yield and recovered activity of β-Gal were 57.9 ± 0.3 % and 46.5 ± 0.9 %, and the enzymatic loading was 843 ± 21 Uenzyme/gsupport. The construction of Fe3O4@mSiO2-β-Gal was confirmed by various characterization methods, and the results indicated it was suitable for heterogeneous enzyme-catalyzed reactions. Fe3O4@mSiO2-β-Gal was readily separable under magnetic action and displayed improved activity in extreme pH and temperature conditions. After 45 days of storage at 4 °C, the activity of Fe3O4@mSiO2-β-Gal remained at 92.3 ± 2.8 %, which was 1.29 times than that of free enzyme, and its activity remained above 85 % after 10 cycles. Fe3O4@mSiO2-β-Gal displayed higher affinity and catalytic efficiency. The half-life was 1.41 longer than free enzymes at 55.0 °C. Fe3O4@mSiO2-β-Gal was employed as a catalyst to prepare sesaminol, achieving a 96.7 % conversion yield of sesaminol. The excellent stability and catalytic efficiency provide broad benefits and potential for biocatalytic industry applications.

Sodium carbonate versus borate buffer for lactase quenching, laboratory work

A laboratory exercise for undergraduate advanced students of enzymology and biocatalysis is presented. Since enzyme assays can be quenched or continuous, this experiment compares the performance of two quenching agents for lactase, in a continuous setup. Enzymatic activity of β-galactosidase (Aspergillus oryzae) was determined based on the release of 4-nitrophenol from 4-nitrophenyl β-D-galactopyranoside using a microplate reader. Sodium carbonate and borate buffer were tested as quenching agents, and experimental control was the unstopped assay. Based on released 4-nitrophenol, enzyme activity, and rate constant k, the students could assess the performance of each termination agent. The experiment promotes disciplinary and transversal competencies, including research-based learning, critical thinking, and introduce the students to high-throughput techniques that are common in the research and development environment.

Challenges and perspectives of the β-galactosidase enzyme

The enzyme β-galactosidase has great potential for application in the food and pharmaceutical industries due to its ability to perform the hydrolysis of lactose, a disaccharide present in milk and in dairy by-products. It can be used in free form, in batch processes, or in immobilized form, which allows continuous operation and provides greater enzymatic stability. The choice of method and support for enzyme immobilization is essential, as the performance of the biocatalyst is strongly influenced by the properties of the material used and by the interaction mechanisms between support and enzyme. Therefore, this review showed the main enzyme immobilization techniques, and the most used supports for the constitution of biocatalysts. Also, materials with the potential for immobilization of β-galactosidases and the importance of their biotechnological application are presented. KEY POINTS: • The main methods of immobilization are physical adsorption, covalent bonding, and crosslinking. • The structural conditions of the supports are determining factors in the performance of the biocatalysts. • Enzymatic hydrolysis plays an important role in the biotechnology industry.

Immobilization of Aspergillus oryzae β-galactosidase in cation functionalized agarose matrix and its application in the synthesis of lactulose

Aspergillus oryzae β-galactosidase was immobilized in in-house quaternary ammonium agarose (QAA) and used for the first time in the synthesis of lactulose. A biocatalyst was obtained with a specific activity of 24,690 IU_H∙g^-1; protein immobilization yield of 97% and enzyme immobilization yield of 76% were obtained at 30 °C in 10 mM phosphate buffer pH 7 for standard size agarose at 100 mg_protein∙g_support^-1 which the maximum protein load of QAA. Highest yield and specific productivity of lactulose were 0.24 g∙g^-1 and 9.78 g∙g^-1 h^-1 respectively, obtained at pH 6, 100 IU_H∙g lactose^-1 enzyme/lactose ratio and 12 lactose/fructose molar ratio. In repeated-batch operation with the immobilized enzyme, the cumulative mass of lactulose per unit mass of contacted protein and cumulative specific productivity were higher than obtained with the soluble enzyme since the first batch. After enzyme activity exhaustion, the enzyme was desorbed and QAA support was reused without alteration in its maximum enzyme load capacity and without detriment in yield, productivity and selectivity in the batch synthesis of lactulose with the resulting biocatalyst. This significantly decreases the economic impact of the support, presenting itself as a distinctive advantage of immobilization by ionic interaction.

Calcium pectinate-agar beads as improved carriers for β-d-galactosidase and their thermodynamics investigation

Polyethyleneimine (PEI) glutaraldehyde-refined calcium pectinate (CaP)-agar beads were presented as improved covalent immobilization matrices. The CaP-agar beads exhibited incremented mechanical stability which facilitated their handling. The beads' concoction and activation processes were honed using the Box-Behnken design which recommended utilizing 5.4% agar, and a 2.95% PEI solution of pH 8.67. The honed CaP-agar beads established a more efficient ionic interaction with PEI which enabled the immobilization of more enzyme while utilizing less PEI than that required to activate the neat CaP beads. Furthermore, the activated CaP-agar beads granted superior operational stability to the immobilized enzyme, β-d-galactosidase (βgal), where it preserved 86.84 ± 0.37% of its precursive activity during its thirteenth reusability round. The CaP-agar immobilized βgal (iβgal) also showed incremented storage stability where it preserved 85.05 ± 3.32% of its precursive activity after 38 days of storage. The thermal stability of the iβgal was shown to be superior to that of the free enzyme as the iβgal exhibited incremented thermodynamic parameters, such as the t _1/2 values, the D values, the thermal denaturation activation energy, the enthalpies, and the Gibb's free energies. The βgal's immobilization onto the activated CaP-agar beads also shifted the enzyme's optimal pH from 4.6-5.1 to 3.3-4.9, whereas its optimal temperature was retained at 55 °C. The procured biocatalyst was exploited to efficiently hydrolyze the lactose in whey permeate.

Structure-activity relationships on the study of β-galactosidase folding/unfolding due to interactions with immobilization additives: Triton X-100 and ethanol

Improving the enzyme stability is a challenge for allowing their practical application. The surfactants are stabilizing agents, however, there are still questions about their influence on enzyme properties. The structure-activity/stability relationship for β-galactosidase from Bacillus circulans is studied here by Circular Dichroism and activity measurements, as a function of temperature and pH. The tendency of preserving the β-sheet and α-helix structures at temperatures below 65°C and different pH is the result of the balance between the large- and short-range effects, respecting to the active site. This information is fundamental for explaining the structural changes of this enzyme in the presence of Triton X-100 surfactant and ethanol. The enzyme thermal stabilization in the presence of this surfactant responds to the rearrangement of the secondary structure for having optimal activity/stability. The effect of ethanol is more related with changes in the dielectric properties of the aqueous solution than with protein structural transformations. These results contribute to understand the effects of surfactant-enzyme interactions on the enzyme behavior, from the structural point of view and to rationalize the surfactant-based stabilizing strategies for β-galactosidades.

Manipulation of nanofiber-based β-galactosidase nanoenvironment for enhancement of galacto-oligosaccharide production

The nanoenvironment of nanobiocatalysts, such as local hydrophobicity, pH and charge density, plays a significant role in optimizing the enzymatic selectivity and specificity. In this study, Kluyveromyces lactis β-galactosidase (Gal) was assembled onto polystyrene nanofibers (PSNFs) to form PSNF-Gal nanobiocatalysts. We proposed that local hydrophobicity on the nanofiber surface could expel water molecules so that the transgalactosylation would be preferable over hydrolysis during the bioconversion of lactose, thus improve the galacto-oligosaccharides (GOS) yield. PSNFs were fabricated by electro-spinning and the operational parameters were optimized to obtain the nanofibers with uniform size and ordered alignment. The resulting nanofibers were functionalized for enzyme immobilization through a chemical oxidation method. The functionalized PSNF improved the enzyme adsorption capacity up to 3100 mg/g nanofiber as well as enhanced the enzyme stability with 80% of its original activity. Importantly, the functionalized PSNF-Gal significantly improved the GOS yield and the production rate was up to 110 g/l/h in comparison with 37 g/l/h by free β-galactosidase. Our research findings demonstrate that the localized nanoenvironment of the PSNF-Gal nanobiocatalysts favour transgalactosylation over hydrolysis in lactose bioconversion.

Detailed analysis of galactooligosaccharides synthesis with β-galactosidase from Aspergillus oryzae

The synthesis of galactooligosaccharides (GOS) catalyzed by β-galactosidase from Aspergillus oryzae (Enzeco) was studied. Using 400 g/L of lactose and 15 U/mL, maximum GOS yield, measured by HPAEC-PAD, was 26.8% w/w of total carbohydrates, obtained at approximately 70% lactose conversion. No less than 17 carbohydrates were identified; the major transgalactosylation product was 6'-O-β-galactosyl-lactose, representing nearly one-third (in weight) of total GOS. In contrast with previous reports, the presence of at least five disaccharides was detected, which accounted for 40% of the total GOS at the point of maximum GOS concentration (allolactose and 6-galactobiose were the major products). A. oryzae β-galactosidase showed a preference to form β(1→6) bonds, followed by β(1→3) and β(1→4) linkages. Results were compared with those obtained with β-galactosidases from Kluyveromyces lactis and Bacillus circulans. The highest GOS yield and specific productivity were achieved with B. circulans β-galactosidase. The specificity of the linkages formed and distribution of di-, tri-, and higher GOS varied significantly among the three β-galactosidases.

Potential applications of carbohydrases immobilization in the food industry

Carbohydrases find a wide application in industrial processes and products, mainly in the food industry. With these enzymes, it is possible to obtain different types of sugar syrups (viz. glucose, fructose and inverted sugar syrups), prebiotics (viz. galactooligossacharides and fructooligossacharides) and isomaltulose, which is an interesting sweetener substitute for sucrose to improve the sensory properties of juices and wines and to reduce lactose in milk. The most important carbohydrases to accomplish these goals are of microbial origin and include amylases (α-amylases and glucoamylases), invertases, inulinases, galactosidases, glucosidases, fructosyltransferases, pectinases and glucosyltransferases. Yet, for all these processes to be cost-effective for industrial application, a very efficient, simple and cheap immobilization technique is required. Immobilization techniques can involve adsorption, entrapment or covalent bonding of the enzyme into an insoluble support, or carrier-free methods, usually based on the formation of cross-linked enzyme aggregates (CLEAs). They include a broad variety of supports, such as magnetic materials, gums, gels, synthetic polymers and ionic resins. All these techniques present advantages and disadvantages and several parameters must be considered. In this work, the most recent and important studies on the immobilization of carbohydrases with potential application in the food industry are reviewed.