12-4 |
Significance of the viscoelastic characteristics of curdlan gel on its diffusion properties |
K. L. ROBBINS and Y. M. Lo. Dept. of Animal & Food Sciences, Univ. of Delaware, 040 Townsend Hall, 531 S. College Ave., Newark, DE 19717-1303 Curdlan, a bacterial polysaccharide, forms gels with similar structures by neutralization of alkaline solutions or by heating aqueous suspensions. The unique gelling mechanism of curdlan makes it a potentially important matrix for nutraceutical and life science applications, which require precise control of diffusion properties. Although not with curdlan, the effect of viscosity on dynamic flavor release has been identified with other polysaccharides. We hypothesize that due to its b-1,3-linkages the diffusion properties of curdlan gel are dependent on its viscoelastic behavior. Our objective was to characterize the diffusion properties of curdlan gel with respect to its viscoelastic properties. Curdlan gels were formed by cooling of heated water suspension (80¢XC). Transient and oscillatory studies were conducted with a Bohlin rheometer. The optical density (640 nm) of water suspensions containing curdlan beads (3 mm diameter) co-extruded with FD&C Blue #1 dye into 5% CaCl2 was monitored. The gels were examined using scanning electron microscopy (SEM). Opposite to the late-time period, the diffusion coefficients of curdlan gels during early release increased with increasing concentration, suggesting the formation of a network structure different from a typical gel. The oscillatory experiments showed typical gel-like behavior; storage modulus dominated loss modulus, both increased linearly with increasing frequency (1-100 rad/s). However, the phase lags were higher at low frequency for all curdlan gels, indicating a tendency toward more fluid-like behavior at low deformation rate. The sensitivity of gels to strain increased with increasing curdlan concentration (2-8%). It was thus speculated and later proved by SEM that there were reservoir domains in the gel structure capable of trapping the dye, and hence upon release more dye was released from gels containing more curdlan polymers. Results from this study provide the foundation for determining the structure and function relationship of curdlan, which is crucial to its applicability.
Session 12, Food Engineering: Rheology and Texture
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