Figure 4.

Effect of pH on the relative enzyme activity at 50 °C. Fe₃O₄-CS-immobilized enzyme (0.2 g), Fe₃O₄-CS-THP-immobilized enzyme (0.2 g) or the free enzyme (1 mL) was added to 100 mL of 5% (w·v⁻¹) lactose at 50 °C in a 500 mL Erlenmeyer flask and incubated at various pH from 3.0 to 8.0 in an orbital shaker bath at 200 rpm for 10 min. The relative activity was determined by measuring the production of glucose. The buffer used in this set of reactions were 0.1 M sodium acetate buffer (pH 3.0~5.6) and 0.1 M potassium dihydrogen orthophosphate (pH 5.8~8.0). The data are averaged from three samples. (●) Fe₃O₄-CS-immobilized enzyme; (○) Fe₃O₄-CS-THP-immobilized enzyme; (▼) free enzyme.