Dendrimer-like nanoparticles based β-galactosidase assembly for enhancing its selectivity toward transgalactosylation

• Dendrimer-like hierarchically porous silica nanoparticles (HPSNs) was fabricated, functionalized and characterized.
• Amino-functionalized HPSNs was favorable for adsorption.
• HPSNs-NH2-β-galactosidase assembly can be reused up to 10 continuous cycles.
• HPSNs-NH2-β-galactosidase generated higher GOS yield than free counterpart.
• HPSNs-NH2-β-galactosidase favored transgalactosylation over hydrolysis.

Functional nanomaterials have been pursued to assemble nanobiocatalysts since they can provide unique hierarchical nanostructures and localized nanoenvironments for enhancing enzyme specificity, stability and selectivity. Functionalized dendrimer-like hierarchically porous silica nanoparticles (HPSNs) was fabricated for assembling β-galactosidase nanobiocatalysts for bioconversion of lactose to galacto-oligosaccharides (GOS). The nanocarrier was functionalized with amino (NH2) and carboxyl (COOH) groups to facilitate enzyme binding, benchmarking with non-functionalized HPSNs. Successful conjugation of the functional groups was confirmed by FTIR, TGA and zeta potential analysis. HPSNs-NH2 showed 1.8-fold and 1.1-fold higher β-galactosidase adsorption than HPSNs-COOH and HPSNs carriers, respectively, with the highest enzyme adsorption capacity of 328 mg/g nanocarrier at an initial enzyme concentration of 8 mg/ml. The HPSNs-NH2 and β-galactosidase assembly (HPSNs-NH2-Gal) demonstrated to maintain the highest activity at all tested enzyme concentrations and exhibited activity up to 10 continuous cycles. Importantly, HPSNs-NH2-Gal was simply recycled through centrifugation, overcoming the challenging problems of separating the nanocarrier from the reaction medium. HPSNs-NH2-Gal had distinguished catalytic reaction profiles by favoring transgalactosylation, enhancing GOS production of up to 122 g/l in comparison with 56 g/l by free β-galactosidase. Furthermore, it generated up to 46 g/l GOS at a lower initial lactose concentration while the free counterpart had negligible GOS production as hydrolysis was overwhelmingly dominant in the reaction system. Our research findings show the amino-functionalized HPSNs can selectively promote the enzyme activity of β-galactosidase for transgalactosylation, which is beneficial for GOS production.