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Abstract

Agar polysaccharides extracted from two Thai species of Gracilaria (G. fisheri and G. edulis) and one Japanese species (Gracilaria sp.) were investigated by physical and chemical analysis, and 1 H, 13 C NMR and FT-IR spectroscopy. Agar with partial 6-O-methylated on 3-linked β-D-galactopyranosyl, 2-O-methylated on 4-linked 3,6-anhydro-α-L-galactopyranosyl and 4-O-methyl-α-L-galactopyranosyl units attached to the C6 of 3-linked D-galactopyranosyl units were isolated from G. fisheri. The large parts of 6-O-methylated on 3-linked β-D-galactopyranosyl units and partial methylation on C2 of 4-linked 3,6-anhydro-α-Lgalactopyranosyl units were observed in the agar extracted from G. edulis which corresponded with higher gelling temperature (»60 C°). In contrast, the Japanese agar extracted from Gracilaria sp. showed a typical pattern of agarobiose with partial methylation at C6 of the D-galactopyranosyl units. All agars extracted exhibited sulfate substitution at different positions in the polymers. High sulfate contents were obtained in native agar of G. fisheri (4.56%) and G. edulis (7.54%) that mainly branched at C-4 of the D-galactopyranosyl unit. The presence of this unit was responsible for poor gelling ability of the agar polymers. Alkali treatment was effective both in removing alkali-labile sulfate and increasing the gel strength in Gracilaria sp. (334.5 ± 14.1 g/cm 2) whereas only a slight effect was noted on G. fisheri (228.27 ± 48.18 g/cm 2) and G. edulis (239.95 ± 28.35 g/cm 2). Further investigation may need to determine the constituent sugars and an alternative utilization of the Thai gracilaroids.

Natural Gums as Oleogelators

“…It consists of two monomers: agarose and agaropectin. Agaropectin contains molecules of D-galactose and galacturonic acid, to which a variable number of sulfate (VI) residues are attached, while agarose is an unbranched polysaccharide formed by molecules of α-(1→4)-3,6-dihydro-L-galactose and β-(1→3)-D-galactose [ 75 , 77 ].…”

Progress in Modern Marine Biomaterials Research

“…-diol, are known as water-soluble, gel-forming polysaccharide extracts from agarophyte members of the Rhodophyta [209]. Agar is derived from the polysaccharide agarose, which forms the supporting structure in the cell walls of certain species of algae, and which is released on boiling.…”

“…Another 30 g sample was incubated in 2 L of 5% NaOH solution at 80 • C for 2 h. The algae were washed in running tap water for 30 min to remove excess NaOH. The alkali-treated algae were neutralized in 2% H 2 SO 4 solution for 1 h, then washed in running tap water overnight until complete elimination of the acid" [209]. Agar scaffolds preparation for tissue engineering was also reported: "0.02% agar was soaked in distilled water for 30 min at room temperature and then boiled to 80 • C with stirring for 2 h until it completely turned into a transparent homogeneous solution.…”

Enzymatic desulfation of the red seaweeds agar by Marinomonas arylsulfatase

“…7a and 8a, respectively. The signals from α anomeric proton at δ 5.13 and 5.27 were assigned to LA and α-L-galactose-6-sulfate (L6S), respectively [31]. H-1 of β-D-galactose (G′) was linked to L6S, and that of G was linked to LA at δ 4.43 and 4.54, respectively [24].…”