Kinetics of Enzymatic Hydrolysis of Wheat Starch by α-Amylase and Glucoamylase for Preparation of Microporous Starch

In order to understand the kinetic characteristics of the synergistic hydrolysis of wheat starch by α-amylase and glucoamylase for preparing microporous starch,the effects of pH,reaction temperature and enzyme dosage on hydrolysis rate during the hydrolysis of wheat type A granular starch by both enzymes were investigated and the Michaelis constants(Km) for the individual and combined enzymatic hydrolysis of wheat starch were determined.Both individual enzymatic hydrolysis processes obeyed the Michaelis-Menten equation,and the Km and Vmax(maximum reaction velocity) were 9.548 mg/mL and 0.659 mg/(mL.min) for and α-amylase,and 12.676 mg/mL and 0.555 mg/(mL min) for glucoamylase,respectively.The hydrolysis product glucose was a competitive inhibitor against the enzymes with an inhibitory constant(Ki) of 4.288 mg/mL.Maximum hydrolysis was reached when 5 mg/mL of wheat type A granular starch was hydrolyzed with 10 U/mL of α-amylase and 20 U/mLof glucoamylase under the conditions of 55 ℃ and pH 4.5 for 25 min.As a result,2.54 mg/mLof reducing sugar was produced.In conclusion,α-amylase and glucoamylase can be used together to hydrolyze wheat starch for the preparation of microporous starch and their combination shows significantly higher hydrolysis efficiency than individual use.