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D. B. GENOVESE and M. A. Rao. Food Science & Technology, Cornell Univ., New York State Agricultural Experiment Station, 630 W. North St., Geneva, NY 14456-1371

Starch gels can be considered as a continuous amylose-containing network reinforced by dispersed swollen granules. Elastic modulus, G', of colloidal gels follows a power law relationship with volume fraction of flocculated particles, f. Shih et al (1990) developed a scaling theory where the exponential factor is related to the fractal dimension, D, of the flocs. In this case, D is a measure of particle's surface deviation from smoothness. A pre-exponential coefficient, G' at f=1, was defined in this work as the elastic modulus when the starch dispersion (SD) is close-packed.

The role of: (1) morphological-structural characteristics of the granules, and (2) composition of the continuous phase, on the rheological behavior of SDs was studied.

Two starch varieties at different concentrations were analyzed: cross-linked waxy maize (CLWM) and tapioca. SDs were prepared by heating starch-water mixtures during 10 min, at 80 C in the case of CLWM, and 70 C in the case of tapioca. Dynamic oscillatory rheological tests were conducted on the SDs at 20 C. Volume fractions of granules were determined by the Blue Dextran exclusion method.

Values of D=2.81 for CLWM (0.51f=1 for CLWM SD was an order of magnitude greater than that for tapioca SD. The higher strength of CLWM granules along with additional experiments, indicate that G' at f=1 is mainly dependent on the granule rigidity, while the amylose content in the continuous phase plays a secondary role in the rheological behavior.

Roughness of starch granule's surface was quantitatively characterized by means of D. The proposed parameter, G' at f=1, may be a useful tool to characterize the rigidity of the granules.

Session 43, Food Engineering: Rheology and texture
9:00 AM - 12:00 PM, Monday AM

2003 IFT Annual Meeting - Chicago,