ISSN:
1573-5176
Keywords:
agar
;
Gracilaria
;
structure
;
quality
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract Agar polymers synthesized by species of the genus Gracilaria constitute a complex mixture of molecules, containing several extremes in structure. Sulphate hemi-esters, methyl ethers and pyruvic ketals can alter in a number of ways the structural regularity of agar based on strictly 3-O-linked β-l-galactopyranose and 4-O-linked α-l-galactopyranose residues. In comparison with agars from Gelidium and Pterocladia, agars from Gracilaria can have higher degrees of sulphation, methoxylation and pyruvylation. The gelling ability of agars from most of Gracilaria species is considerably improved by adopting, before extraction, an alkali pretreatment which converts α-l-galactose 6 sulphate into 3,6-anhydro-α-l-galactose. Native agars obtained from Gracilaria cannot be classified, with few exceptions, as bacteriological grade agar as they have a high content of methoxyls and consequently high gelling temperatures. On the contrary, the genus Gracilaria is considered the most important source of food and sugar-reactive grade agars. Among techniques which can be used to study algal polysaccharides, combined 1H and 13C nuclear magnetic resonance spectroscopy represent the most effective and powerful method for the investigation of the chemical structure of agarocolloids.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00003999
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