Rheological properties of corn starch-xanthan gum mixtures

摘要: Corn starch is used to thicken foods. Addition of a gum modifies food texture and minimizes syneresis. Xanthan Gum (XG) produced from Xanthomonas campestris is being used extensively as a thickening agent. Our objectives were to determine the effects of concentration of XG and three starches on the rheological characteristics: flow behavior and vane yield stress of their mixtures. XG, intrinsic viscosity 112.3 L/g, was used over the concentration range: 0 to 1%. Dispersions of the starches: waxy corn (WCS), cross-linked waxy maize (CLWM) and cold water swelling corn (CWS) with a concentration of 6% were used. Starch-XG dispersions were heated at 80C for 10 min using a Rotavapor, and cooled in a water-ice bath. A six-blade vane (diameter 4 cm, height 6 cm) attached to a Rotovisco RV30 viscometer (Haake) was used to determine, in order: the static yield stress (YSS), the flow curve over 0-90 s-1, and the dynamic yield stress (YSD) at 20C; YSS and YSD were determined at 0.05 s-1. In general, all the dispersions were shear-thinning fluids with yield stress whose behavior was well described by the Herschel-Bulkley model. Yield stress of WCS-0.35% XG was higher than that of WCS alone. Increase in XG concentration from 0.35 to 1.0% did not result in large increase in yield stress. The mixture: WCS-0.35% XG had higher angular deformation than those with 0.5, 0.7, and 1% XG. Yield stress of the CLWM-XG mixtures decreased dramatically with XG concentration: ex: YSS= 59.3 Pa at 0% XG to 31.7 Pa at 1% XG. In contrast, values of angular deformation of YSS and YSD increased. Static yield stress of CWS-gum mixtures was about 30 …