100-3 |
Estimating steady shear viscosity of fish muscle protein paste at different concentrations |
W. B. YOON1, S. Gunasekaran1, and J. W. Park2. (1) Dept. of Biological Systems Engineering, Univ. of Wisconsin, Madison, 460 Henry Mall, Madison, WI 53706, (2) Astoria Food Laboratory, Oregon State Univ., 2001 Marine Dr., Rm. 253, Astoria, OR 97103 Steady shear viscosity is an important physical parameter in processing of many biopolymer solutions and pastes. At high concentrations, biopolymers are in a highly entangled state. Their weak solid-like behavior makes it difficult to measure their steady shear viscosity. The Cox-Merz rule can be used to estimate steady shear viscosity by superimposing dynamic viscosity determined from small amplitude shear oscillatory measurements. The objectives of this study were to: 1) investigate shear rate dependence of steady shear viscosity of fish muscle protein paste as a function of protein concentration and 2) examine the validity of the Cox-Merz rule to estimate steady shear viscosity at high shear rates. Alaska pollock surimi was used to study the viscosity of fish muscle protein. The total moisture content was adjusted from 75 to 95% (w/w) to vary the protein concentration. A controlled-stress rheometer was used for dynamic and continuous shear viscosity measurements. Dynamic shear viscosity measurements were performed within the linear region (applied strain<0.005) at frequencies in the range of 0.01 to 10 Hz. For steady shear viscosity, the applied stress was carefully controlled to obtain shear rates in the range of 10-4 to 10-1 s-1. The concentration dependence of zero shear viscosity was scaled by a power-law relationship with an exponent of 3.51. The universality of viscosity was empirically obtained as a function of concentration by introducing and superimposing dimensionless variables. Both steady shear and dynamic viscosity showed strong shear thinning behavior and was well described by the Carreau model. The Cox-Merz rule was applicable to estimate steady shear viscosity with a horizontal shift factor. The power-law exponent determined from the concentration dependence of zero shear viscosity shows that concentrations used in this study were in semi-dilute regime. The shear thinning behavior of surimi paste was due to entanglement of the flexible actomyosin macromolecules.
Session 100, Seafood Technology: Texture, Chemistry
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