Recyclable solid-phase biocatalyst with improved stability by sol–gel entrapment of β-d-galactosidase

• Alkyl substituted silane precursors were used for entrapment of β-d-galactosidase.
• The highest activity in optimized immobilization conditions was 84 μmol min−1 g−1.
• The entrapped β-d-galactosidase demonstrated increased pH and temperature stability.
• More than 60% residual activity was preserved after 5 reutilizations.

β-d-Galactosidase from Kluyveromyces lactis was for the first time immobilized by entrapment in hybrid organic-inorganic sol–gel materials with microporous structure, obtained from alkoxy silanes and alkyl substituted alkoxy silanes, in different combinations. The immobilization matrix was tailored by fine tuning of several parameters, such as: nature of alkyl group of silane precursors, molar ratio of silane precursors, nature of additives, protein concentration. Unlike other enzymes, β-d-galactosidase showed the best catalytic activity at low alkyl group content in the sol–gel matrix, at a molar ratio of 7:1 between the tetraalkoxysilane alkyl-trialkoxysilane precursor. The immobilized enzyme demonstrated enhanced storage, pH and thermal stability compared to the soluble enzyme. The composite sol–gel materials were characterized by transmission electron microscopy, scanning electron microscopy, fluorescence confocal microscopy, and porosity measurement. The biocatalyst was successfully reused in five reaction cycles, maintaining more than 60% of the initial activity.

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