Handbook of Size Exclusion Chromatography and Related ...

Figure 9 VIS spectrum of potato maltodextrin (——) with starting-type of branching
characteristics. Introduction of additional branching positions by branching enzyme to the
initial potato maltodextrin at 208C (—B—); introduction of more branching positions
by branching enzyme to the initial potato maltodextrin at 48C (—O—); first derivative
of spectra illustrates a shift of absorption maximum (zero-intercept) and a broadening of
absorbance in the wavelength range below 550 nm for increasing scb characteristics of
polyiodide–glucan complexes. Absorbance maxima: potato maltodextrin, 540 nm;
branching-enzyme modified maltodextrin at 208C, 520 nm, branching-enzyme modified
maltodextrin at 48C, approx. 460 nm.
Branching characteristics for glucan mixtures or individual fractions in a
first approach may be estimated by determining complexation potential of helical
glucans with polyiodide anions. Experimentally, 125 mg of freshly sublimated
iodine is dissolved in the presence of 400 mg kJ in 1000 mL demineralized water
and diluted 1 : 1 with 0.1 M acid to ensure a final pH 4.5–5.0 when mixed with the
alkaline eluate from SEC. Polyiodide anions complexed in the helical starch
glucan segments shift the extinction maximum from Emax 525 nm of free aqueous
iodine to higher wavelengths (64,65). In fact, the shift is also controlled by the
length of helical segments and by the number of available helical segments;
however, correlation of E640 values is an appropriate indication for lcb-glucans.
Correlation of scb-glucans with E 525 values is supported by corresponding
maxima in ORD/CD-spectra for a(1 ! 4)-glucans with dp , 40 (66,67). The
(E640/E525) ratio also indicates branching characteristics of complexed glucans,
glucan fractions, or glucan fragments as lcb/scb-glucan ratio.
© 2004 by Marcel Dekker, Inc.