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Handbook of Size Exclusion Chromatography and Related ...

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Figure 29 Brabender viscosity for (a) wheat glucans (—B—): Broad<br />

disintegration ! parallel reorganization <strong>of</strong> supermolecular structures; pronounced<br />

reorganization on cooling; (b) waxy maize glucans (—†—): more sharp<br />

disintegration ! minor reorganization <strong>of</strong> supermolecular structures; constant shear<br />

deformation; applied temperature program: heating, 30 ! 908C within 40 min; holding,<br />

908 for 15 min; cooling, 90 ! 308C within 40 min.<br />

tend to re-establish supermolecular structures, neither in the high temperature<br />

holding nor in the subsequent cooling period. Quite different behavior is observed<br />

for lcb-dominated starch glucans: their disintegration is achieved much more<br />

easily than that for scb-glucans; however, the tendency <strong>of</strong> liberated lcb-glucans to<br />

re-establish supermolecular structures is much more pronounced. The level <strong>of</strong><br />

glucan/glucan interaction after disintegration remains constant at the initially<br />

elevated level as long thermal stress is kept constant (holding period) <strong>and</strong> even<br />

increases in the cooling period, significantly exceeding the level <strong>of</strong> initial<br />

disintegration status. Thus, however less perfectly stabilized compared to scbglucans,<br />

lcb-glucans tend to form new supermolecular structures <strong>and</strong> show a<br />

significant re-organization capability.<br />

5.5 Supermolecular Structures <strong>of</strong> Starch Glucans: Dynamic<br />

Light Scattering<br />

Dynamic light scattering (DLS)/photon correlation spectroscopy (PCS)<br />

experiments for starch glucan solutions provide data about diffusive mobility <strong>of</strong><br />

glucan molecules <strong>and</strong> supermolecular structures formed by glucan molecules. In<br />

particular, translational diffusion <strong>of</strong> glucans <strong>and</strong> glucan aggregates causes Doppler<br />

© 2004 by Marcel Dekker, Inc.

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