Studies on Gamma-Irradiation of High Amylose Corn Starch

Part I. Effects of gamma-irradiation on physicochemical properties of corn starches of various amylose content

Abstract

Amylomaize VII, amylomaize V, normal corn, waxy corn and potato starches were irradiated with ⁶⁰Co-gamma rays at the dose levels from 2×10⁴ to 100×10⁴ rad to determine the changes in physicochemical properties by irradiation.
Irradiated starches were characterized by determination of amylography, specific viscosity, blue value, pH, acidity, carbonyl content, reducing value and limit of β-amylolysis.
Irradiated starches showed a decrease in viscosity and blue value, and an increase in reducing value with increasing dose levels. These results were seemed to indicate the degradation of starch molecule. A slight oxidation of starch was suggested by a decrease in pH and an increase in acidity and carbonyl content.
Amylomaize VII and amylomaize V starches were less sensitive than the other starches in terms of irradiation effects. The rheological properties determined by amylography and Ostwald viscometer changed at the lowest dose(5×10⁴ rad)and the other properties changed above 20×10⁴rad.
The limits of β-amylase hydrolysis of normal corn, waxy corn and potato starches increased slightly by irradiation(100×10⁴ rad). On the other hand, β-amylolysis limits of amylomaize VII and amylomaize V starches were lower about 5.5% and 2.5% respectively than that of non-irradiated samples. The decrease of β-amylolysis imit enlarged with increasing amylose contelnt.