Abstract: 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/mL of glucoamylase under the conditions of 55 ℃ and pH 4.5 for 25 min. As a result, 2.54 mg/mL of 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.

Key words: wheat type A granular starch, microporous starch, α-amylase, glucoamylase, kinetics