The Effect of Different Ratios of Starch and Freeze–Thaw Treatment on the Properties of Konjac Glucomannan Gels

Abstract

The composite gels of konjac glucomannan (KGM) and corn starch (CS) were prepared and treated by the freeze–thaw method. For KGM–CS gels, as the starch ratio rose from 0 to 100%, storage modulus (G′) decreased by 97.7% (from 3875.69 Pa to 87.72 Pa), degradation temperature decreased from 313.32 °C to 293.95 °C, and crystallinity decreased by 16.7%. For F–KGM–CS gels, G′ decreased by 99.0% (from 20,568.10 Pa to 204.09 Pa), degradation temperature increased from 289.68 °C to 298.07 °C, and crystallinity decreased by 17.1% with more starch content. The peak in infrared spectroscopy shifted to a higher wavenumber with more starch and to a lower wavenumber by freezing the corresponding composite gels. The detected retrogradation of the composite gels appeared for KGM–CS with 80% starch and F–KGM–CS with 40% starch. The endothermic enthalpy of free water rose by 10.6% and 10.1% with the increase in starch for KGM–CS and F–KGM–CS, respectively. The results of moisture distribution found that bound water migrated to free water and the water-binding capacity reduced with more starch. The results demonstrated that the molecular interaction in composite gels was weakened by starch and strengthened by freezing.