Dynamic rheological study of Sterculia striata and karaya polysaccharides in aqueous solution

Chichá polysaccharide is the dry exudate from Sterculia striata, which belongs to the same family of karaya polysaccharide. S. striata polysaccharide (SSP) contains (mol%) rhamnose (23.8), galactose (19.3), xylose (7.7), uronic acid (49.2), and acetyl groups (9.6). Dynamic rheological analysis of SSP, deacetylated SSP (DSSP), and karaya polysaccharide (KP) in aqueous solution has been carried out. SSP behaves as a weak gel in the concentration range of 2-4% and as a true gel at higher concentrations. Karaya polysaccharide behaves as a true gel at concentrations higher than 2%, and forms a gel than stronger than that of SSP at the same polysaccharide concentration. The addition of 0.1 M NaCl to both polysaccharides decreases their gel strength, however, more pronouncedly that of the SSP solution. The presence of acetyl groups is necessary to promote interactions between polysaccharide chains, which make gels strong. No sharp conformational transition has been observed for either SSP or KP samples by thermal rheological analysis.