title: Rice starch granule amylolysis--differentiating effects of particle size, morphology, thermal properties and crystalline polymorph.
abstract: The underlying mechanism of amylolysis of rice starch granules was investigated using isolated starch granules from wild-type, as well as SBEIIb mutant and down-regulated lines. Fused granule agglomerates isolated from mutant and transgenic lines were hydrolysed at similar rates by amylases, and had similar crystalline patterns and thermal properties as individual granules. Surface pores, a feature previously only reported for A-polymorphic starch granules, were also observed in B- and C-polymorphic rice starch granules. Although the microscopic patterns of hydrolysis among granules with different crystalline polymorphs were qualitatively similar, the extent and the rate of amylolysis were different, suggesting that B-type crystalline polymorphs are intrinsically more resistant to enzymatic hydrolysis than A-type in rice starch granules. It is proposed that the slightly longer branch lengths of amylopectin which leads to the formation of more stable B-type double helical structures compared to their A-type counterparts is the major parameter, with other factors such as granule size, surface pores and interior channels having secondary roles, in determining the rate of enzymatic hydrolysis of rice starch granules.
authors.affiliation: Centre for Nutrition and Food Sciences, ARC Centre of Excellence in Plant Cell Walls, Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, St Lucia, QLD 4072, Australia. Electronic address: s.dhital@uq.edu.au.
authors.forename: Sushil
authors.initials: S
authors.lastname: Dhital
authors.affiliation: Plant Industry and Food Futures Flagship, Commonwealth Scientific and Industrial Research Organisation (CSIRO), P.O. Box 1600, Canberra, ACT 2601, Australia. Electronic address: v.butardo@irri.org.
authors.forename: Vito M
authors.initials: VM
authors.lastname: Butardo
authors.affiliation: Plant Industry and Food Futures Flagship, Commonwealth Scientific and Industrial Research Organisation (CSIRO), P.O. Box 1600, Canberra, ACT 2601, Australia. Electronic address: steve.jobling@csiro.au.
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Jobling
authors.affiliation: Centre for Nutrition and Food Sciences, ARC Centre of Excellence in Plant Cell Walls, Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, St Lucia, QLD 4072, Australia. Electronic address: m.gidley@uq.edu.au.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Gidley
mesh_terms: D015061:1,4-alpha-Glucan Branching Enzyme / Q000235:genetics / Q000378:metabolism; D000681:Amylases / Q000378:metabolism; D015536:Down-Regulation; D006868:Hydrolysis; D007700:Kinetics; D009154:Mutation; D012275:Oryza / Q000737:chemistry*; D010316:Particle Size; D013213:Starch / Q000737:chemistry*; D013696:Temperature
chemical_list: D013213:Starch; D015061:1,4-alpha-Glucan Branching Enzyme; C116400:starch-branching enzyme IIb; D000681:Amylases
keywords: Amylopectin; Amylose; Amylose Extender; Digestibility; High amylose; Starch structure