Accessibility of barley starch granules to α-amylase during different phases of gelatinization

The effect of the degree of gelatinization of barley starch granules on their accessibility to α-amylolysis was studied. The limited ability of Bacillus licheniformis and porcine pancreatin α-amylases to hydrolyse raw barley starch was reflected in the small release of soluble carbohydrates during α-amylolysis at 30°C. Annealing of starch for 3 hours below 50°C did not increase enzymic accessibility. At the higher pre-heating temperatures of 55 and 60°C, the amount of solubilized carbohydrates increased during subsequent α-amylase treatment at 30°C. The increase in enzymic accessibility could well be explained by the reduced order and crystallinity of starch, which was also detected by thermal analysis. The first change observed in the molecular size distribution of α-amylase-treated barley starch granules was detected as a decrease in the amylopectin moiety only after pre-heating at a temperature of 50°C or higher. The α-amylolysis at 30°C increased the solubility of the residual starch granules at 85°C.