Effect of NaCl, CaCl2, and sucrose on the rheological properties of agar from Gracilaria in Vietnam

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Agar is a polysaccharide extracted mainly from Gracilaria. Agar is widely used in the food industry as a viscous agent, thickness, emulsifier or food stabiliser. The presence of NaCl, CaCl2 or sucrose influences in sol-gel transition, viscosity of the agar solution or gel strength of the agar. Agar forms a gel at high concentration or lower one if there is the presence of NaCl, CaCl2 or sucrose. Gelling temperature (Tg) of agar solution at 0.2 wt% increasing at 36, 36 or 38°C upon addition of 300 mM NaCl, 100 mM CaCl2, or 30% sucrose, respectively. The viscosity of the 0.2% agar solution increased insignificantly when the ionic strength was below 100 mM, but increased sharply above 100 mM. The gel strength increases with added NaCl, CaCl2 up to 100 mM, 30 mM, respectively; then they drop slightly at higher concentrations of NaCl, CaCl2. Meanwhile, the viscosity of agar solution only increases at sucrose concentrations above 10%. Gel strength increased with increasing sucrose concentration, being 1.2 to 1.8 times higher if 30% sucrose was added.