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 dispersio ns. Thermal scanning rheological measurements showed that the final dynamic storage modulus (G') of the dispersion after heating to 90 degrees C and s ubsequent cooling to 30 degrees C increased with rising heating rate, while the final dynamic mechanical loss tangent (tan delta) decreased. This was attributed predominantly to the increase in thermo-reversible component or the number of junction zones between curdlan molecules accomplished with hy drogen bonds in the gelled system. The measurements also indicated that the final G' of the dispersion decreased with increasing incubation time at 55 degrees C, while the final tan delta increased. These results suggested th at the behavior of curdlan within its swelling temperature range should pla y an important role in the gelation and that heating history should determi ne the number of junction zones in the gel and/or the amount of total bondi ng energy stored there. These suggestions were supported by a difference in the gelling characteristics between alkali-neutralized dispersion (i.e. di ssolving curdlan particles in an alkaline solution beforehand) and water di spersion; the final G' for the former was larger than that for the latter a fter the heating and cooling process, while the final tan delta for the for mer was smaller. (C) 2000 Elsevier Science Ltd. All rights reserved.