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  • Title: Influence of extrusion and digestion on the nanostructure of high-amylose maize starch.
    Author: Lopez-Rubio A, Htoon A, Gilbert EP.
    Journal: Biomacromolecules; 2007 May; 8(5):1564-72. PubMed ID: 17394285.
    Abstract:
    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.
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