Amylolysis of maize mutant starches

Starches from single and double maize mutants were subjected to enzymatic d egradation by porcine pancreatic alpha -amylase. The maize mutants covered a broad range of macromolecular composition and crystalline structure relat ive to fractional crystallinity level (from 0.19 to 0.48) and polymorphic t ype (with various proportions of A-, B- and V-type allomorphs). Regardless of amylose content or crystallinity level, starches with a predominant B-cr ystalline type were more resistant to amylolysis than others, and initial r ates of hydrolysis were lower for B-type than A-type starches. Final hydrol ysis 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 cha ins or crystal defects also appeared to increase initial hydrolysis rates, although lower initial rates and final hydrolysis extents were mainly relat ed to the amount of B-type crystallites. Unexpectedly, hydrolysis residues were composed of both amorphous and B-type crystalline regions. These obser vations suggest that resistance to amylolysis is related to the distributio n of B-type crystallites within the granule rather than to the relative pro portion of B-type crystallites. (C) 2001 Society of Chemical Industry.