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Handbook of Size Exclusion Chromatography and Related ...

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structures, excluded volumes, <strong>and</strong> the way to fill excluded volumes, is <strong>of</strong>ten<br />

underestimated (53). Key characteristics for this molecular level are branching<br />

characteristics. It is well known that the ratio <strong>of</strong> lcb/scb-glucans (amylose-type/<br />

amylopectin-type) inparticularcontrolsmacroscopicstarchqualities (54,55).Bad<br />

solubilityinaqueousmedia,hightendencyforretrogradation<strong>and</strong>gelatinization<strong>of</strong><br />

amylose-type nb/lcb-glucans is aswell known as the potential <strong>of</strong> such starches to<br />

form gels <strong>and</strong> films. Amylopectin-type scb-glucans on the other h<strong>and</strong> are soluble<br />

in aqueous media as long they are not organized in supermolecular H-bond<br />

stabilized clusters. Additionally, scb-glucans are capable <strong>of</strong> fixing a high<br />

percentage <strong>of</strong> water <strong>and</strong> are less sensitive towards varying environmental<br />

conditions (56–63).<br />

Investigation <strong>of</strong> branching characteristics includes determination <strong>of</strong> a<br />

complex package <strong>of</strong> parameters:<br />

. Type <strong>of</strong> branching pattern; composition <strong>of</strong> branching pattern for starch<br />

glucan fractions sampled with respect to identical excluded volume;<br />

identicalmolecularweight(degree<strong>of</strong>polymerization); identical internal<br />

stabilization; identical potential for formation <strong>of</strong> supermolecular<br />

characteristics;<br />

. Number <strong>and</strong>/or percentage <strong>of</strong> branching position within individual<br />

glucan molecules <strong>and</strong> type <strong>of</strong> distribution <strong>of</strong> number <strong>of</strong> branching<br />

positions in supermolecular domains;<br />

. Heterogeneity/homogeneity <strong>of</strong> branching positions within individual<br />

glucan molecules <strong>and</strong> distinct supermolecular domains;<br />

. Degree <strong>of</strong> local symmetry (crystallinity) due to certain types <strong>of</strong><br />

branchingcharacteristics;influence<strong>of</strong> increasedbranchingtosymmetry<br />

<strong>and</strong> interactive properties.<br />

However, the experimental approaches to branching characteristics are rather<br />

laborious <strong>and</strong> <strong>of</strong>ten result in rough estimations only:<br />

. Destructive techniques: pure chemical directed <strong>and</strong>/or enzymatically<br />

catalyzed step-by-step fragmentation followed by fragment analysis <strong>and</strong><br />

recalculation <strong>of</strong> mean molecules as a puzzle from fragment<br />

characteristics;<br />

. Complexing/staining<strong>of</strong>starchglucans(nativeglucans,glucanfractions,<br />

glucan fragments) with polyiodide anions in hydrophobic caves <strong>of</strong><br />

terminal helical starch glucan branches, <strong>and</strong> spectroscopy in terms <strong>of</strong><br />

extinction-ratio E640/E525 provides relative information about lcb/scbcharacteristics<br />

<strong>of</strong> investigated samples (Fig. 9); application to fractions<br />

from semipreparative SEC (Fig. 10a, b) yields apr<strong>of</strong>ile <strong>of</strong> lcb/scb-ratio<br />

with respect to glucan fractions with decreasing excluded volume.<br />

© 2004 by Marcel Dekker, Inc.

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