36D-25 |
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D. TANJORE and C. R. Daubert. Dept. of Food Science, North Carolina State Univ., 127 Withers Hall, Box 7624, Raleigh, NC 27695-7624 The Brookfield YR–I is an affordable instrument that uses the vane technique for yield stress measurement. Previous research established that the vane method can also be used to obtain the shear modulus. In the present study, the Brookfield viscometer was used to provide viscoelastic properties, including the phase angle, storage, and loss moduli. The objectives of this study were to 1) test the new technique for measuring the viscoelastic phase angle based on the torque–time response; 2) measure the storage and loss moduli following an approximation for vane strain. To test the new approach, gelatin gels were selected as the model system and prepared at concentrations ranging from 2.5% to 4% w/v in water. Viscoelastic properties for the model systems were analyzed and compared using the new Brookfield method and a more conventional controlled stress rheometer. For 4% gelatin gels, the phase angle measured with the Brookfield were observed to range between 2.3 and 5.0 degrees and the shear modulus ranged between 160.5 and 207.5 Pa. Across similar strain rates, the results from dynamic testing using the stress controlled rheometer, showed the phase angle to range between 1.2 and 3.4 degrees and the shear modulus ranged between 152.5 and 176.5 Pa. The noticeable overlap of the viscoelastic parameters obtained from both instruments at a 95% confidence level signifies statistical similarity. These results show that Brookfield viscometers can provide reliable viscoelastic property information. The application of this technique permits the evaluation of viscoelastic properties through an affordable approach.
Session 36D, Food Engineering: Rheology
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |