Article,
The influence of the conformational state of kappa- and iota-carrageenan on the rate of acid hydrolysis
Carbohydr. Res., (July 1996)
Abstract
kappa- and iota-carrageenan were hydrolysed in 0.1 M HCl in the presence
of LiI (kappa-) or LiCl (iota-). The rate constant for the hydrolysis
determined from the decrease in the specific viscosity k' = Delta(c/eta(sp))/Delta
t increased by a factor 200 and 10 for kappa- and iota-carrageenan,
respectively, when passing above the conformational transition temperature
(T-m). The rate constant determined from the increase in the number
of reducing end-groups (k) increased by a factor 10 for kappa-carrageenan,
whereas no increase was observed for iota-carrageenan. The activation
energy (E(a)) for kappa-carrageenan increased from 120 to 190 kJ/mol
upon conformational ordering, whereas for iota-carrageenan the activation
energy was 135 kJ/mol in both conformational states. The activation
energies were virtually independent of the ionic strength. The results
indicate that the stability properties of kappa- and iota-carrageenan
as reflected by viscosity or molecular weight decay is determined
by differences in the nature of the ordered and disordered conformation,
respectively, rather than differences in the hydrolytic stability
of glycosidic linkages. The results are best described in terms of
a multiple-stranded structure of the ordered conformations of both
kappa- and iota-carrageenan.
Tags
- ;
- ;;
- acid
- and
- aqueous-solution;
- conformation;
- depolymerization;
- dynamics
- equilibria;
- hydrolysis
- kappa-
- kinetics;
- l-carrageenan;
- measurements;
- model;
- of
- polysaccharide
- polysaccharides
- polysaccharides;
- rates
- transition;
- viscosity
- xanthan;
- [isi:]
