title: Molecular, mesoscopic and microscopic structure evolution during amylase digestion of extruded maize and high amylose maize starches.
abstract: Extrusion processing of cereal starch granules with high (>50%) amylose content is a promising approach to create nutritionally desirable resistant starch, i.e. starch that escapes digestion in the small intestine. Whilst high amylose content seems to be required, the structural features responsible for the slow digestion of extrudates are not fully understood. We report the effects of partial enzyme digestion of extruded maize starches on amylopectin branch length profiles, double and single helix contents, crystallinity and lamellar periodicity. Comparing results for three extruded maize starches (27, 57, and 84% apparent amylose) that differ in amylase-sensitivity allows conclusions to be drawn concerning the rate-determining features operating under the digestion conditions used. Enzyme resistance is shown to originate from a combination of molecular and mesoscopic factors, including both recrystallization and an increase in very short branches during the digestion process. This is in contrast to the behaviour of the same starches in the granular form (Shrestha et al., 2012) where molecular and mesoscopic factors are secondary to microscopic structures in determining enzyme susceptibility. Based on the structure of residual material after long-time digestion (>8h), a model for resistant starch from processed high amylose maize starches is proposed based on a fringed micelle structure with lateral aggregation and enzyme susceptibility both limited by attached clusters of branch points.
authors.affiliation: Centre for Nutrition and Food Sciences, ARC Centre of Excellence in Plant Cell Walls, The University of Queensland, St. Lucia, Brisbane, Qld 4072, Australia; Commonwealth Scientific and Industrial Research Organisation, Food Futures National Research Flagship, Riverside Corporate Park, North Ryde, NSW, Australia; School of Science and Health, The University of Western Sydney, Richmond, NSW, Australia.
authors.forename: Ashok K
authors.initials: AK
authors.lastname: Shrestha
authors.affiliation: Bragg Institute, Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DSC, NSW 2232, Australia; Commonwealth Scientific and Industrial Research Organisation, Food Futures National Research Flagship, Riverside Corporate Park, North Ryde, NSW, Australia.
authors.forename: Jaroslav
authors.initials: J
authors.lastname: Blazek
authors.affiliation: Centre for Nutrition and Food Sciences, ARC Centre of Excellence in Plant Cell Walls, The University of Queensland, St. Lucia, Brisbane, Qld 4072, Australia.
authors.forename: Bernadine M
authors.initials: BM
authors.lastname: Flanagan
authors.affiliation: Centre for Nutrition and Food Sciences, ARC Centre of Excellence in Plant Cell Walls, The University of Queensland, St. Lucia, Brisbane, Qld 4072, Australia.
authors.forename: Sushil
authors.initials: S
authors.lastname: Dhital
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation, Food Futures National Research Flagship, Riverside Corporate Park, North Ryde, NSW, Australia.
authors.forename: Oscar
authors.initials: O
authors.lastname: Larroque
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation, Food Futures National Research Flagship, Riverside Corporate Park, North Ryde, NSW, Australia.
authors.forename: Matthew K
authors.initials: MK
authors.lastname: Morell
authors.affiliation: Bragg Institute, Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DSC, NSW 2232, Australia.
authors.forename: Elliot P
authors.initials: EP
authors.lastname: Gilbert
authors.affiliation: Centre for Nutrition and Food Sciences, ARC Centre of Excellence in Plant Cell Walls, The University of Queensland, St. Lucia, Brisbane, Qld 4072, Australia. Electronic address: m.gidley@uq.edu.au.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Gidley
mesh_terms: D000688:Amylose / Q000737:chemistry*; D013213:Starch / Q000737:chemistry*; D003313:Zea mays / Q000737:chemistry*
chemical_list: D013213:Starch; D000688:Amylose
keywords: Amylose; Chain length; Digestibility; Extrusion; Maize; Starch structure