α‐Amylolysis of Large Barley Starch Granules

The α‐amylolysis of large (volume average 16 μm) barley starch granules was studied by measuring the amount of carbohydrates solubilizing during hydrolysis, and the changes in morphology and molecular structure of the granule residues by scanning electron microscopy, particlesize analysis, size‐exclusion chromatography, X‐ray diffraction, and differential scanning calorimetry. X‐ray diffraction showed that, in the earlier stages of α‐amylolysis, both amorphous and crystalline parts of the granules were equally solubilized. More extensive hydrolysis caused a gradual decrease in A‐type crystallinity and degradation of the granular structure. Scanning electron microscopy revealed that hydrolysis proceeded through pinholes, and pitted and partially hollow granule residues were formed. The lipid‐complexed amylose was less susceptible to α‐amylolysis than free amylose and amylopectin. Lipid‐complexed amylose started leaching out of the granule residues only after half of the starch had solubilized due to the α‐amylase treatment. Even though scanning electron microscopy indicated that there were intact granules left throughout the hydrolysis, the results obtained suggested that α‐amylolysis of large barley starch granules proceeded rather evenly among the granules.