Variation in amylose fine structure of starches from different botanical sources.

The molecular structures of amylose and amylopectin have an impact on functional properties of starch-containing food. This is the first study comparing amylose size distributions from various plant sources. Chain-length distributions (CLDs) of amylose and amylopectin branches ("fine structure") are characterized using size-exclusion chromatography [sometimes termed gel permeation chromatography (GPC)] and parametrized by both biosynthesis-based and empirical fits, to understand the starch biosynthesis mechanism and identify associations with starch digestibility. All starches show bimodal amylose weight CLDs, varying with plant sources, with potato tuber and sweet potato root starch having relatively longer branches than the others. The digestograms of all starches fit first-order kinetics. Unlike what has been seen in cooked grains/flours, amylose and amylopectin fine structures have no association with the digestibility of freshly gelatinized starch. This suggests that the observed effect in cooked grains/flours arises from a secondary interaction between amylose fine structure and higher order structural features.