Highly methylated agar from Gracilaria edulis (Gracilariales, Rhodophyta)

摘要

The structure and gelling properties of alkali-modified agar from G. edulis (collected from the Philippines) were investigated. 1H and 13C NMR experiments revealed a basic repeating unit of alternating 3-linked 6-O-methyl-beta-D-galactopyranose and4-linked 3,6-anhydro-alpha-L-galactopyranose. Partial methylation at O-2 of the anhydrogalactose moiety was also revealed. Meanwhile, the O-4 of the methylated galactose residue was detected to exhibit partial sulfation by NMR and FT-IR spectroscopy. Thegel strength and syneresis index of the extracted agar were considerably enhanced by the addition of sodium, potassium, and calcium ions. The ion-driven gelation and peculiar sulfate position conferred the agar's similarity to kappa-carrageenan.