Starch hydrolysis by the synergistic action of amylase and glucoamylase

Abstract

Starch hydrolysis is highly investigated chemical process which is usually carried out in two stages: the first step is liquefaction catalyzed by  -amylase, and the second step is the saccharification process catalyzed by glucoamylase. High energy demand of saccharification and liquefaction processes results in the necessity to study them on lower temperatures. Since amylase exhibits lower activity at lower temperature ( 50 °C for glucoamylase used in this work) and addition of calcium ions can caused the inhibition or deactivation effect on this enzyme. Impact of calcium ions on the starch hydrolysis catalyzed by synergistic action of amylase and glucoamylase was studied in this work. For that purpose two amylases -Termamyl and Liquozyme and glucoamylase – Dextrozyme were used. The experiments were performed at pH 5.5 and 65 oC. These conditions were chosen as a compromise for the activity of both enzymes. Before investigation of synergistic action of amylase and glucoamylase, enzymes were studied separately. Amylases were studied in the reaction of starch hydrolysis and glucoamylase was studied in the reaction of maltose hydrolysis. For each system mathematical model was developed. α -amylase deactivation rate was described by two-step model that assumed formation of an intermediate before complete deactivation. First order kinetics was used to describe glucoamylase deactivation. All experiments were performed with and without presence of calcium ions. It was found out that calcium ions contributed to the operational stability of native form of both amylases. In the case of Termayml presence of calcium did not affect the intermediate form of enzyme, while for Liquozyme intermediate, it had slightly negative impact. From the results it was concluded that possible inhibition and deactivation of glucoamylase with calcium ions could be excluded. Integrated process of liquefaction and saccharification was successfully performed and nearly 100 % conversion of starch to glucose was achieved. Among investigated amylases, Termamyl is most promising for use in the integrated process of starch hydrolysis since its deactivation rate is more than 100 times lower than that of the Liquozyme.