Handbook of Size Exclusion Chromatography and Related ...

y previous swelling in diluted aqueous SO2 (diluted alkali or acetate buffer pH
6.5, 0.02 M). Swelling is followed by wet milling with a homogenizer and
separation of starch and nonstarch materials by several sieving steps. Gluten, in
particular, is separated by sedimentation on asloped separation channel where
gluten iswashed out by water, and starch granules are accumulated at the bottom.
Wheatstarchgranulesareacquiredbyrinsingofdoughmadeofwheatflourwitha
little water.
Starch granules from potato tubers are purified rather simply by washing,
peeling, and smashing of the tubers, suspending the pulp in pure water and
separating starch from fibers by sieving. After centrifugation, water-soluble
componentsareremovedwiththesupernatant.Eithertheresultingmixofdifferent
sizes of granules is taken to analysis or an additional separation procedure is
applied: pooling of granules according their dimension by sedimentation in pure
water (Fig. 6a, b)
To achieve molecular level analysis/characterization of starch glucans,
isolation and dissolution, without generating artifacts, is required. Therefore,
starch granules are typically dispersed in sodium or potassium hydroxide (0.5–
2 M). Sonication and microwave heating have been suggested to improve
“dissolution”, however, these techniques support formation of artifacts and
occurrence of uncontrolled destruction phenomena (49,50). For analytical
purposes, dispersing in 90% aqueous dimethylsulfoxide (DMSO) is favorable.
The glucan fraction dissolves in DMSO (0.5–1% wt/vol) when stirred for at least
15 hours (overnight) at 708C. For distinct dissolution experiments dissolution
temperature and periods of dissolution were varied between 50–958C and 4–200
hours, respectively. After centrifugation (3000 rpm, 15 min) a clear starch glucan
containing supernatant is achieved. In contrast with NaOH or KOH, proteins and
lipids are insoluble in DMSO and for further processing no neutralization is
required. DMSO-dissolved starch samples may be stored for several weeks
without significant aging effects such as degradation, aggregation, or
retrogradation.
4 STARCH GLUCAN CHARACTERISTICS AND
THE SEC CONCEPT
Simplified starch glucans, similar to most polysaccharides, fill up volume [Ve;
Eq. (1)] in a more or less regular way controlled by a fine-tuning mechanism on a
molecular level which modifies coherent domains according to changing external
and internal challenges. Major facets of macroscopic technological starch qualities
therefore have to be correlated with molecular-level glucan features such as:
. Conformation [mc; Eq. (1)]: molecular symmetries in terms of helices,
beta-sheets, branching pattern (short-chain, long-chain branches,
© 2004 by Marcel Dekker, Inc.