The influence of the conformational state of κ- and τ-carrageenan on the rate of acid hydrolysis

κ- And τ-carrageenan were hydrolysed in 0.1 M HCl in the presence of Lil (κ-) or LiCl (τ-). The rate constant for the hydrolysis determined from the decrease in the specific viscosity [k′ = Δ(c/ηsp)/Δt] increased by a factor 200 and 10 for κ- and τ-carrageenan, respectively, when passing above the conformational transition temperature (Tm). The rate constant determined from the increase in the number of reducing end-groups (k) increased by a factor 10 for κ-carrageenan, whereas no increase was observed for τ-carrageenan. The activation energy (Ea) for κ-carrageenan increased from 120 to 190 kJ/mol upon conformational ordering, whereas for τ-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 κ- and τ-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 κ- and τ-carrageenan.