Thermal deactivation of a commercial α-amylase from Bacillus licheniformis used in detergents

We have studied experimentally the enzymatic hydrolysis of soluble starch with a commercial α-amylase from Bacillus licheniformis (commercial enzyme Termamyl 300 L Type DX) at pH 7.5 within the temperature range of 60–75 °C. To follow the reaction we applied a procedure based on the iodometric method of measuring α-amylase activity. We found for each of the temperatures studied that at the same treatment intensity the different enzyme concentrations and reaction times assayed gave practically the same conversion values, whereas these values were altered according to the length of time the enzyme solutions were previously kept at reaction temperature. Therefore, the thermal denaturation of the enzyme can be fitted to a second-order kinetic. We have established a way of calculating the deactivation constant for each temperature both for the experiments made with different waiting times before the reaction and for those with different treatment intensity. Finally, we fitted the thermal-deactivation constant against temperature according to Arrhenius’ equation, obtaining an activation energy of 172 kJ/mol.