ScienceAsia 32 Supplement 1 (2006): 011-017 |doi: 10.2306/scienceasia1513-1874.2006.32(s1).011
Physical and Chemical Characterization of Agar
Polysaccharides Extracted from the Thai and Japanese
Species of Gracilaria
Jantana Praiboon,a* Anong Chirapart,b Yoshihiko Akakabe,c Orapin Bhumibhamond and Tadahiko Kajiwarac
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 1H, 13C NMR and
FT-IR spectroscopy. Agar with partial 6-O-methylated on 3-linked -D-galactopyranosyl, 2-O-methylated
on 4-linked 3,6-anhydro--L -galactopyranosyl and 4-O-methyl--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 -D-galactopyranosyl units and partial methylation on C2 of 4-linked 3,6-anhydro--L -
galactopyranosyl units were observed in the agar extracted from G. edulis which corresponded with higher
gelling temperature (>> 60 Co). 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/cm2) whereas only a slight effect was noted on G. fisheri (228.27 48.18 g/cm2) and G. edulis (239.95
28.35 g/cm2). Further investigation may need to determine the constituent sugars and an alternative
utilization of the Thai gracilaroids.
a Department of Biotechnology, Faculty of Agro-industry, Kasetsart University, Bangkok 10900, Thailand.
b Department of Fishery Biology, Faculty of Fishery, Kasetsart University, Bangkok 10900, Thailand.
c Department of Biological Chemistry, Faculty of Agriculture, Yamaguchi University, Yamaguchi 753-8515,
d Schools of Agroindustry, Mae Fah Luang University, Chiang Rai 57100, Thailand.
* Corresponding author, E-mail: email@example.com