Amylolysis of maize mutant starches

Starches from single and double maize mutants were subjected to enzymatic degradation by porcine pancreatic α‐amylase. The maize mutants covered a broad range of macromolecular composition and crystalline structure relative to fractional crystallinity level (from 0.19 to 0.48) and polymorphic type (with various proportions of A‐, B‐ and V‐type allomorphs). Regardless of amylose content or crystallinity level, starches with a predominant B‐crystalline type were more resistant to amylolysis than others, and initial rates of hydrolysis were lower for B‐type than A‐type starches. Final hydrolysis extents were less than 35% for predominant B‐type starches, 60% for C‐type ones and more than 70% for predominant A‐ or V‐type ones. Dangling chains or crystal defects also appeared to increase initial hydrolysis rates, although lower initial rates and final hydrolysis extents were mainly related to the amount of B‐type crystallites. Unexpectedly, hydrolysis residues were composed of both amorphous and B‐type crystalline regions. These observations suggest that resistance to amylolysis is related to the distribution of B‐type crystallites within the granule rather than to the relative proportion of B‐type crystallites.