Kinetics of Enzymatic Hydrolysis of Irradiated Potato Starch byα-Amylase and Glucoamylase

In order to understand the enzymatic hydrolysis characteristics of irradiated potato starch,potato native starch and potato starch treated with60Co-γ ray at dosage of 400 kGy were hydrolyzed by α-amylase and glucoamylase.The effects of pH,hydrolysis temperature and enzyme dosage on hydrolysis rate were investigated. Based on the Michaelis-Menten equation,the kinetic parameters were obtained by the Lineweaver-Burk method. The results indicated that hydrolysis rate of irradiated potato starch was obviously higher than that of native starch. Individual enzymatic hydrolysis processes obeyed the Michaelis-Menten model,and the Michaeli constant( Km) of α-amylase were 11. 343 mg·mL-1( native starch) and 9. 386 mg·mL-1( irradiated starch),and maximum reaction velocity( Vmax) of α-amylase were 0.406 mg( mL·min)-1( native starch) and 1. 079 mg( mL·min)-1( irradiated starch),respectively. The Michaeli constant( Km) of glucoamylase were 10. 307 mg·mL-1( native starch) and 8. 905mg·mL-1( irradiated starch),and maximum reaction velocity( Vmax) of glucoamylase were 0. 338 mg( mL · min)-1( native starch) and 0. 821 mg( mL·min)-1( irradiated starch),respectively. The hydrolysis product glucose was a competitive inhibitor against the enzymes with an inhibitory constant( Ki) of 1. 298 mg·mL-1( native starch) and 0. 934 mg·mL-1( irradiated starch). It indicated that irradiation greatly increased enzymatic hydrolysis activity of potato starch.