Phase and polymorphic transitions of starches at low and intermediate water contents

Abstract

The plasticizing and structuring roles of water are described for native and hydrolysed starch at different temperatures between the glass and melting transition temperatures. Water, which acts as a plasticizer of amorphous regions, is also present in the crystallites and improves the crystallinity, increasing the resolution of X-ray diffraction diagrams. Polymorphic conversions and crystallinity modifications may be induced by hydrothermal treatments at temperatures below the melting temperature of the most stable form among the recognized allomorphs, i.e. the B-type water-rich crystalline hydrate of tuber and amylose starches, the A-type lower hydrate of natural cereal starches and the complexed single helical forms obtained in less polar environments either hydrated (Vh) or anhydrous (Va). The conditions needed to obtain various solid state conversions are given for Vh to Va or Vh to B-type at ambient temperature and B to A upon heating. In all cases for given temperature and hydration conditions, the kinetics depend on the chain length involved. In contrast to the situation with short independent chains obtained by acid hydrolysis of starch, which can rearrange themselves easily, annealing and 'heat moisture treatments' never increase the crystallinity of native starches although their melting behavior is strongly modified. These different transitions are discussed in terms of glass transition and melting temperatures, composition and known structures of starchy substrates.

Characterization of Starch Polymorphic Structures Using Vibrational Sum Frequency Generation Spectroscopy

“…46,47 For the V to B transition, Buleon et al noted that "the double helical conformation, usually proposed for Atype and B-type structures, is questionable. It is unlikely that any drastic conformational change such as defolding/refolding is provoked by such mild treatment as rehydration, unless the helical conformations ascribed to both V h -and B-types are not very different..." 48 It is not easy to conceive of a simple way to make the transition from antiparallel single helices to parallel double helices in solids with such low mobility (without complete melting and recrystallization). 49 It should be noted that the transitions between A and B, both of which are considered double-helix structures, are much more difficult.…”

B→A Allomorphic Transition in Native Starch and Amylose Spherocrystals Monitored by In Situ Synchrotron X-ray Diffraction

“…24 On the other hand, B-crystallites would melt and the chains would recrystallize into allomorph A. 21 In the recent years, synchrotron radiation has successfully been used to study structural transitions in starch. In situ series of small-and wide-angle X-ray scattering (SAXS and WAXS) spectra were recorded to monitor the variation in lamellar and crystal structure, respectively, during hydrothermal treatments.…”

Ultrasonic investigation of wheat starch retrogradation

“…The ultrasonic attenuation can be caused both by wave scattering and absorption. In the case of the concentrated starch system analysed in this work, the scattering contribution is negligible, because the dimensions of the amylopectin crystals, typically in the order of 10-100s of nm (Buleon et al, 1998a(Buleon et al, , 1998bJenkins et al, 1993), are far smaller than the wavelength of the ultrasonic waves used for the experiment at 10 MHz, which varies between 183 and 195 lm depending on the ultrasonic velocity in the starch samples. Therefore, only wave absorption is responsible for the wave attenuation observed in the wheat starch extrudates.…”

“…texture and flavour perception (Buleon et al, 1998a, Buleon, Le Bail, Colonna, & Bizot, 1998b), nutritional (susceptibility to enzymic hydrolysis (Farhat et al, 2001)) and processing (shredding, cutting, etc.) characteristics.…”

“…Amylose is essentially a linear polymer, while amylopectin is a highly branched macromolecule. Amylopectin, whose content varies from 70 to 85% depending on starch botanical source, is assumed to be the main responsible of the crystallinity of the native starch granules (Buleon, Colonna, Planchot, & Ball, 1998a, 1998bJenkins, Cameron, & Donald, 1993;Miles, Morris, Orford, & Ring, 1985).…”