Immobilization and characterization of β‐galactosidase in thermally reversible hydrogel beads

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Abstract
β-Galactosidase has been immobilized within thermally reversible hydrogel beads and has been studied in batch and packed bed reactor systems. The enzyme was entrapped in a copolymer hydrogel of N-isopropylacrylamide (NIPAAm) and acrylamide (AAm) as beads were formed in an inverse suspension polymerization. A reversible deswelling and reswelling of the hydrogel matrix was induced by first warming and then cooling through 37–40°C, which is the lower critical solution temperature, LCST, of the backbone copolymer. The optimum temperature for maximum activity of the immobilized enzyme-gel bead system was found to be 30–357deg;C in a batch mode and 40°C in a packed bed reactor, which were both below the 50°C optimum for the free enzyme. These differences are understandable, since the mass transfer rates of substrate and product within the pores of the gel matrix are controlled mainly by the temperature, so therefore it is the temperature which governs the overall activity of the immobilized enzyme system. It was also found that when the operational temperature in the packed bed reactor was cycled between temperatures below (35°C) and above (45°C) the copolymer gel LCST, the activity of the immobilized enzyme almost fully recovered after each cycle. In fact, the enzyme-gel system exhibited a complete “shut-off” in activity at 50°C which was the temperature where the free enzyme showed its maximum activity. The thermal cycling operation of LCST enzyme-gel beads can be used to enhance overall activity and productivity of a packed bed reactor, when compared to isothermal operation of this reactor. This is due to the thermally induced “pumping” which enhances mass transfer rates of substrate in and product out of the gel beads.

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