A rheological study on the effects of heating rate and dispersing method on the gelling characteristics of curdlan aqueous dispersions

Dynamic viscoelastic measurements were performed to investigate the effect of heating rate on the gelling characteristics of curdlan aqueous dispersions. Thermal scanning rheological measurements showed that the final dynamic storage modulus (G′) of the dispersion after heating to 90°C and subsequent cooling to 30°C increased with rising heating rate, while the final dynamic mechanical loss tangent (tan δ) decreased. This was attributed predominantly to the increase in thermo-reversible component or the number of junction zones between curdlan molecules accomplished with hydrogen bonds in the gelled system. The measurements also indicated that the final G′ of the dispersion decreased with increasing incubation time at 55°C, while the final tan δ increased. These results suggested that the behavior of curdlan within its swelling temperature range should play an important role in the gelation and that heating history should determine the number of junction zones in the gel and/or the amount of total bonding energy stored there. These suggestions were supported by a difference in the gelling characteristics between alkali-neutralized dispersion (i.e. dissolving curdlan particles in an alkaline solution beforehand) and water dispersion; the final G′ for the former was larger than that for the latter after the heating and cooling process, while the final tan δ for the former was smaller.