title: Mechanism for starch granule ghost formation deduced from structural and enzyme digestion properties.
abstract: After heating in excess water under little or no shear, starch granules do not dissolve completely but persist as highly swollen fragile forms, commonly termed granule "ghosts". The macromolecular architecture of these ghosts has not been defined, despite their importance in determining characteristic properties of starches. In this study, amylase digestion of isolated granule ghosts from maize and potato starches is used as a probe to study the mechanism of ghost formation, through microstructural, mesoscopic, and molecular scale analyses of structure before and after digestion. Digestion profiles showed that neither integral nor surface proteins/lipids were crucial for control of either ghost digestion or integrity. On the basis of the molecular composition and conformation of enzyme-resistant fractions, it was concluded that the condensed polymeric surface structure of ghost particles is mainly composed of nonordered but entangled amylopectin (and some amylose) molecules, with limited reinforcement through partially ordered enzyme-resistant structures based on amylose (for maize starch; V-type order) or amylopectin (for potato starch; B-type order). The high level of branching and large molecular size of amylopectin is proposed to be the origin for the unusual stability of a solid structure based primarily on temporary entanglements.
authors.affiliation: Centre for Nutrition and Food Sciences, Queensland Alliance for Agriculture and Food Innovation, The University of Queensland , St. Lucia, Brisbane, Queensland 4072, Australia.
authors.forename: Bin
authors.initials: B
authors.lastname: Zhang
authors.forename: Sushil
authors.initials: S
authors.lastname: Dhital
authors.forename: Bernadine M
authors.initials: BM
authors.lastname: Flanagan
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Gidley
mesh_terms: D000681:Amylases / Q000737:chemistry; D000687:Amylopectin / Q000737:chemistry*; D000688:Amylose / Q000737:chemistry*; D004063:Digestion; D008970:Molecular Weight; D010936:Plant Extracts / Q000737:chemistry*; D011487:Protein Conformation; D003313:Zea mays / Q000737:chemistry*
chemical_list: D010936:Plant Extracts; D000688:Amylose; D000687:Amylopectin; D000681:Amylases
keywords: enzyme-resistant fraction; gelatinization; glucan conformation; polymer entanglement; starch granule ghosts; α-amylase