Amylolysis of maize mutant starches

Starches from single and double maize mutants were subjected to enzymatic degradation by porcine pancreatic alpha -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. (C) 2001 Society of Chemical Industry.