Browsing by Author "Doutch, J"

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    Characterisation of large scale structures in starch granules via small-angle neutron and X-ray scattering
    (Elsevier Science Ltd, 2013-01-02) Doutch, J; Gilbert, EP
    Small angle scattering (SAS) techniques have a distinguished track record in illuminating the semi-crystalline lamellar structure of the starch granule. To date, there have been few attempts to use SAS techniques to characterise larger-scale structures reported from imaging techniques such as growth rings, blocklets or pores, nor how these structures would modulate the well-known scattering arising from the semi-crystalline lamellar structure. In this study, SAS data collected over an extended q range were gathered from dry and hydrated starch powders from varied botanical sources. The use of neutrons and X-rays, as well as comparing dry and hydrated granules, allowed different levels of contrast in scattering length density to be probed and therefore selected structural regions to be highlighted. The lowest q range, 0.002-0.04 (A) over circle (-1), was found to be dominated by scattering from the starch granules themselves, especially in the dry powders; however an inflection point from a low contrast structure was observed at 0.035 (A) over circle (-1). The associated scattering was interpreted within a unified scattering framework with the inflexion point correlating with a structure with radius of gyration similar to 90A (A) over circle - a size comparable to small blocklets or superhelices. In hydrated starches, it is observed that there is an inflection point between lamellar and q(-4) power-law scattering regions at approximately 0.004 (A) over circle (-1) which may correlate with growth rings and large blocklets. The implications of these findings on existing models of starch lamellar scattering are discussed. © 2013, Elsevier Ltd.
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    Relations between molecular, crystalline, and lamellar structures of amylopectin
    (American Chemical Society, 2012-12-01) Witt, T; Doutch, J; Gilbert, EP; Gilbert, RG
    Chain (branch) length distributions (CLD) from size-exclusion chromatography of a series of waxy starches were parametrized using both an empirical and a biosynthesis-based method and correlated with their crystalline amorphous lamellar properties obtained from X-ray scattering. Correlations were best seen with the biosynthesis-based parametrization. This showed for the first time that the following links between the CLD and lamellar parameters, the average interlamellar repeat distance and the distribution of these distances, were decreased by an increase in the proportion of very short branches and were increased by an increase in the proportion of intermediate and longer chains; further, the shoulder and linear sections of the CLD were found to affect the lamellar repeat distance and distribution. These effects are rationalized in terms of branch-length effects on the production of crystallites and :he presence of portions of longer branches in the amorphous regions. © 2012 The American Physical Society
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    Structural changes from native waxy maize starch granules to cold-water sluble phrodextrin during thermal treatment
    (Americal Chemical Society, 2014-04-29) Bai, Y; Doutch, J; Gilbert, EP; Shi, YC
    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. © 2020 American Chemical Society