Kinetics of thermal inactivation of chitin-immobilized lactase (CIL) was studied in the absence and presence of catalytic modulators. Results were in good agreement with two-phase series mechanism of inactivation. The inhibitory product galactose was a positive modulator of enzyme thermal stability, while the opposite held for the substrate lactose. Differential equations were developed and solved to describe packed-bed reactor operation with CIL, considering lactose and galactose modulation. The model was experimentally validated in a laboratory packed-bed reactor. A more stable CIL has been developed and their kinetic (V max K m , K I ) and inactivation parameters (k i ) have been determined as explicit functions of temperature. A strategy for temperature optimization of CIL reactor operation is presented in which the experimental information gathered has been included.