Operational Stability of Glucoamylase in Continuously Operated Ultrafiltration Membrane Reactor – Experimental Methods and Mathematical Model

The rate of a reaction catalyzed by enzymes is influenced by various factors, including temperature, pH, chemical substances, etc.1 In this work, the influence of temperature on enzyme operational stability was studied. Temperature deactivation of an enzyme is usually defined as a transformation of an active enzyme into denaturated (deactivated) form, described by an irreversible first-order reaction2–5. Denaturation of most proteins occurs in the temperature range of 45 – 50 °C. Due to temperature increase, the energy level of atoms in a protein molecule grows higher and denaturation, i.e. thermodenaturation6,7,8, occurs when the atoms attain enough energy to break the connections inside the globular protein structure1. This causes the loss of the protein’s biological activity, which is directly related to molecule conformation9. The Van’t Hoff rule applies to enzyme catalyzed reactions, as well as to chemical reactions. This means that a temperature increase of 10 °C increases the reaction rate by two to three times2,10. Further temperature increase causes a decrease in the reaction rate11,12 due to the limited stability of proteins8,10. Therefore, an increase in temperature increases the reaction rate but also the rate of deactivation, i.e. it decreases enzyme stability2. The dependence of the reaction rate on temperature shows a maximum. The temperature at which the maximum of the reaction rate is achieved is not an optimal temperature, because at that point starts the irreversible process of denaturation10. Enzyme deactivation is also influenced by the time of exposure to elevated temperature10,13,14. Therefore, the temperature maximum of an enzyme is not a constant value10. The reaction of maltose hydrolysis catalyzed by Dextrozyme was studied in this work. Dextrozyme is a mixture of glucoamylase and pullulanase. Glucoamylase catalyzes the maltose hydrolysis, and pullulanase prevents the reverse reaction. Hence, the enzyme of main interest in this system was glucoamylase, and its operational stability was studied at different temperatures. Levenspiel15 suggested two methods for the investigation of catalyst operational stability in a continuous process. The first method involves attaining constant conversion in a continuously operated reactor, which is achieved by decreasing the flow rate, i.e. increasing the residence time. Fast and efficient analysis is essential for rapid response to Operational Stability of Glucoamylase in Continuously Operated Ultrafiltration Membrane Reactor – Experimental Methods and Mathematical Model