Composition and distribution of carrabiose moieties in hybrid kappa-/iota-carrageenans using carrageenases.

Hybrid kappa/iota-carrageeans extracted from Gigartina skottsbergii, Chondracanthus chamissoï, and Chondrus crispus were incubated with Pseudoalteromonas carrageenovora kappa-carrageenase and Alteromonas fortis iota-carrageenase. The degradation products as well as the resistant fraction were fully characterized by chromatography, NMR, and mass spectrometry. The low percentage of degradation observed after treatment by the iota-carrageenase suggests that long segments of iota-carrabiose or block of iota-carrageenan are low in abundance. The degradation products of the kappa-carrageenase allow discriminating three modes of kappa-carrabiose distribution: blocks of kappa-carrabiose, kappa-carrabiose rich fraction containing iota-carrabiose units probably randomly distributed, and iota-carrabiose rich fraction which corresponds to the resistant fraction. The proportions of each fraction were related to the botanical origin as well as the place of growth of the seaweed.