Pasting and rheological properties of water caltrop starch as affected by the addition of konjac glucomannan, guar gum and xanthan gum

Water caltrop starch (WCS) isolated from the dehydrated water caltrop (DWCS) showed higher content of protein and ash as compared to starch isolated from fresh water caltrop (FWCS), leading to slightly lower starch purity. However, the pasting profiles of DWCS and FWCS are similar under a constant solid content of 4% (w/w). WCS/ gum mixed systems contain 0.3%-0.9% gum generally showed higher pasting temperature, peak viscosity, and final viscosity than the starch alone system. The increase in peak and final viscosity during rapid-viscosity analysis was most pronounced for WCS/gum mixed systems with konjac glucomannan (KG), followed by guar gum (GG) and xanthan gum (XG). All WCS/gum mixed systems showed shear thinning and thixotropic char-acteristics. The extent of pseudoplasticity and shear stability, as evidenced by the smaller flow behavior index (n) and area of the hysteresis loop, was most pronounced for WCS/gum mixed system with XG, followed by mixed systems with GG and KG. Dynamic viscoelastic analysis revealed that the addition of gum increased both the storage and loss moduli of WCS, and lowered the frequency dependence of the loss factor significantly. However, the loss factor of WCS/gum mixed systems was generally higher than that of the starch alone system, implying the addition of gums modified the rheological characteristic of WCS to more viscous dominant behavior.