36D-20 |
|
P. ACHAYUTHAKAN1, M. Suphantharika2, and M. A. Rao1. (1) Food Science and Technology, Cornell Univ., 630 W. North Street, 14456 Geneva, NY 14456, (2) Dept. of Biotechnology, Mahidol Univ., Rama 6 Road, 10400 Bangkok, Thailand 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% higher than control. Increasing XG in the mixtures did not affect YSS. However, YSD decreased at high XG concentration. Rheological behavior of the corn starch-XG mixtures depended on the type of starch and the XG concentration. It appears that the state of the starch granule plays an important role in rheology of the mixtures.
Session 36D, Food Engineering: Rheology
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |