Kinetic behavior of microencapsulated beta-galactosidase.

Escherichia coli beta-D-galactosidase (E.C. 3.2.1.23) was immobilized in cellulose nitrate membrane microcapsules and the reaction kinetics with o-nitrophenyl-beta-D-galactopyranoside (ONPG), lactose, and whole milk were studied using both continuous stirred tank and packed bed reactor configurations. The results of the experiments gave effectiveness factors of 0.3 for ONPG, 0.6 to 0.7 for lactose in solution, and close to unity for lactose in milk. Using a coupled mass transfer and kinetic model, it was possible to estimate the permeability of the microcapsule membrane from the reactor data. Membrane permeabilities on the order of 5 X 10(-3) and 3 X 10(-4) cm/sec were estimated for ONPG and lactose, respectively. It was determined that the membrane was the limiting mass transfer resistance for the overall reaction. The analysis showed that within the microcapsule, the reaction is reaction rate limited for lactose and slightly diffusion limited for ONPG.