Influence of extrusion and digestion on the nanostructure of high-amylose maize starch.
An in-depth characterization of the structural changes undergone by high-amylose starch after extrusion and digestion with a pancreatic alpha-amylase has been carried out. The combination of USAXS, SAXS, XRD, and SEM techniques has provided a wide "picture" of the morphological transformations of starch, covering a length scale from approximately 0.3 nm to approximately 230 microm. Depending on the extrusion conditions, either gelatinization was attained ("mild" conditions) or single-amylose helix formation was induced ("extreme" conditions). SAXS experiments demonstrated that upon contacting the extruded materials with water, retrogradation took place. A new type of molecular organization with a characteristic repeat length of 5 nm was observed in the dry resistant starch fractions from the extruded high-amylose starch. The crystalline morphology of the resistant starch fractions, as observed by XRD, varied from B-type crystallinity for the "mild" extruded starch to a mixture of C- and V-type crystallinity in the case of "extreme" extrusion.
Lopez-Rubio
Amparo
A
Bragg Institute, Australian Nuclear Science and Technology Organization, PMB 1, Menai, NSW 2234, Australia. amparo.lopez.rubio@ansto.gov.au
Htoon
Aung
A
Gilbert
Elliot P
EP
D000688:Amylose / Q000032:analysis*; D003461:Crystallography; D008855:Microscopy, Electron, Scanning; D049329:Nanostructures; D013213:Starch / Q000737:chemistry* / Q000648:ultrastructure*; D014961:X-Ray Diffraction; D003313:Zea mays / Q000201:enzymology*
D013213:Starch; D000688:Amylose