Immobilization of ?-galactosidase on galactose-containing polymeric beads

Industrial application of ?-galactosidase requires efficient methods to immobilize the enzyme, yielding a biocatalyst with high activity and stability compared to free enzyme. An ?-galactosidase from tomato fruit was immobilized on galactose-containing polymeric beads. The immobilized enzyme exhibited an activity of 0.62 U/g of support and activity yield of 46%. The optimum pH and temperature for the activity of both free and immobilized enzymes were found as pH 4.0 and 37 °C, respectively. Immobilized ?-galactosidase was more stable than free enzyme in the range of pH 4.0-6.0 and more than 85% of the initial activity was recovered. The decrease in reaction rate of the immobilized enzyme at temperatures above 37 °C was much slower than that of the free counterpart. The immobilized enzyme shows 53% activity at 60 °C while free enzyme decreases 33% at the same temperature. The immobilized enzyme retained 50% of its initial activity after 17 cycles of reuse at 37 °C. Under same storage conditions, the free enzyme lost about 71% of its initial activity over a period of 7 months, whereas the immobilized enzyme lost about only 47% of its initial activity over the same period. Operational stability of the immobilized enzyme was also studied and the operational half-life (t1/2 was determined as 6.72 h for p-nitrophenyl ?-d-galactopyranoside (PNPG) as substrate. The kinetic parameters were determined by using PNPG as substrate. The Km and Vmax values were measured as 1.07 mM and 0.01 U/mg for free enzyme and 0.89 mM and 0.1 U/mg for immobilized enzyme, respectively. The synthesis of the galactose-containing polymeric beads and the enzyme immobilization procedure are very simple and also easy to carry out. © 2009 Elsevier Inc. All rights reserved.