Mixed gels - Physical Gels from Biological and Synthetic Polymers - page 315

0.02 mW

G

F

E

D

C

B

20 30 50

Temperature (°C)

40 60 70 80 90

Figure 10.15 DSC cooling curves for mixtures with various ratios of κ -carrageenan and glucomannan (0.6% total
polysaccharide concentration) in 0.05M KCl. Scanning rate was 0.1°C min − 1 . Ratio of κ -
carrageenan concentration to konjac glucomannan concentration: (A) 0.1/0.5; (B) 0.2/0.4;
(C) 0.3/0.3; (D) 0.4/0.2; (E) 0.45/0.15; (F) 0.5/0.1; (G) 0.6/0. Reprinted with permission from
Williams et al.( 1993 ) © 1993 American Chemical Society.

the peak at higher temperature indicated an interaction between carrageenan and gluco-
mannan, and the one at lower temperature was due to gelation of the excess carrageenan.
ESR results showed that as the temperature is reduced the mobilities of the spin labels
decrease more rapidly than for konjac glucomannan alone, signifying a greater reduction
in segmental motion, presumably brought about through interaction of konjac gluco-
mannan and -carrageenan molecules.

Using 133 Cs NMR measurements, Piculell et al.( 1994 ) found enhanced chemical
shifts and line broadening in

κ

-carrageenan gels containing KGM or LBG. They attrib-
uted this to the association between mannans and (aggregated)

κ

-carrageenan helices in
the gel mixtures. They also pointed out that the ordered conformation of

κ

κ -carrageenan

and its degree of speci c ion binding was the same with or without the addition of

galactomannans. In agreement with early

findings by Dea et al.( 1972 ), they also found

that the conformational ordering of -carrageenan on cooling occurred at a higher

temperature in the mixture with LBG, but otherwise the shift results for the two systems
were quite similar. They concluded that the Cs line broadening was suggestive of a
binding isotherm, where the available

κ

' sites ' for mannan association were saturated at

high concentrations, and that the additional line broadening seen in mixtures of

κ -carrageenan with LBG was indeed due to the formation of mixed aggregates.

Gellan mixtures
Gellan konjac glucomannan

Miyoshi et al.( 1996 ) used rheometry and DSC to study the interaction between gellan
gum and KGM with and without NaCl and CaCl 2 . As seen in Figure 10.16 , a mixture of
gellan and KGM at a ratio of 0.3/0.5 showed gel-like behaviour at 0°C, while no other

-