Structural changes from native waxy maize starch granules to cold-water-soluble pyrodextrin during thermal treatment.
The structural changes occurring during the thermal conversion of insoluble native waxy maize starch granules to cold-water-soluble pyrodextrin under acidic conditions have been investigated by multiple techniques, including synchrotron small-angle X-ray scattering (SAXS), wide-angle X-ray scattering, differential scanning calorimetry, and gel permeation chromatography. In a mixture of water/glycerol (20/80, w/w), the SAXS characteristic peak at ca. 0.6 nm(-1) decreased in intensity as pyrodextrin solubility increased. The peak disappeared as pyrodextrin solubility reached 100%. Starch crystal size, its associated melting enthalpy, and pyrodextrin molecular size decreased as solubility increased. Although starch structure changed during thermal conversion, the pyrodextrins appeared identical to the native starch when observed in glycerol under a normal and polarized light microscope. It is proposed that the starch backbone is hydrolyzed by acid in the amorphous region and the crystalline region with starch molecules being hydrolyzed into small molecular fractions but persisting in a radial arrangement.
Department of Grain Science and Industry, Kansas State University , Manhattan, Kansas 66506, United States.
Yanjie
Y
Bai
Liming
L
Cai
James
J
Doutch
Elliot P
EP
Gilbert
Yong-Cheng
YC
Shi
D002152:Calorimetry, Differential Scanning; D003912:Dextrins / Q000737:chemistry*; D015394:Molecular Structure; D010936:Plant Extracts / Q000737:chemistry*; D012995:Solubility; D013213:Starch / Q000737:chemistry*; D013816:Thermodynamics; D014961:X-Ray Diffraction; D003313:Zea mays / Q000737:chemistry*
D003912:Dextrins; D010936:Plant Extracts; D013213:Starch
dextrin; pyrodextrin; small-angle X-ray scattering; starch structure; thermal treatment