Highly methylated agar from Gracilaria edulis (Gracilariales, Rhodophyta)

The structure and gelling properties of alkali-modified agar from Gracilari a edulis were investigated. H-1 and C-13 NMR experiments revealed a basic r epeating unit of alternating 3-linked 6-O-methyl-beta-D-galactopyranose and 4-linked 3,6-anhydro-alpha-L-galactopyranose. Partial methylation at O-2 o f the anhydrogalactose moiety was also revealed. Meanwhile, the O-4 of the methylated galactose residue was detected to exhibit partial sulfation by N MR and FT-IR spectroscopy. The gel strength and syneresis index of the extr acted agar were considerably enhanced by the addition of sodium, potassium, and calcium ions. The ion-driven gelation and peculiar sulfate position co nferred the agar's similarity to kappa-carrageenan.