Structure and Rheological Behaviour of Agar Extracted From Madagascar Sea Coast Algae

Polysaccharide from an original red algae (Gelidium sp) was extracted with hot water, clarified, and precipitated in presence of ethanol. NMR spectroscopic analyses and chromatographic separation after complete hydrolysis showed that this polysaccharide was composed predominantly of a repeating-unit based on 4-O-3,6-anhydro-α-L-galactopyranose and 3-O-β-D-galactopyranose confirming their agar nature. The Gelidium sp agar (representing 16 w % on the basis of dried crude algae) has a regular chemical structure and forms strong gels in aqueous medium. Its rheological behavior is examined as a function of polymer concentration and temperature.