36D-19 |
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G. TABILO-MUNIZAGA1, C. Saenz2, B. Escobar2, A. M. Estevez3, M. P. Lira3, L. Garrido1, and R. Quezada1. (1) Dept. of Food Engineering, Univ. del Bío Bío, PO Box 447, Chillán, Chile, (2) Dept. Agroindustria y Enología, Facultad de Ciencias Agronómicas, Univ. de Chile, PO Box 1004, Santiago, Chile, (3) Dept. Agroindustria y Enología, Facultad de Ciencias Agronómicas, Univ. de Chile, PO Box 1004, Santiago, Chile The main goal of this study was to evaluate the effect of calcium on flow and viscoelastic properties of 0.4 and 0.6% w/v dispersions of P. chilensis (Mol.) Stunt seed gum, at temperatures of 5,10,20,40,60 and 80° C. The flow and viscoelastic properties were evaluated in rotational and oscillatory mode. Shear rate-shear stress rheograms were done for each treatment. Corrected flow curves were fitted with the Herschel-Bulkley model and flow index (n), consistency index (K), and yield stress were reported. Viscoleastic properties of seed gum dispersions were characterized using small amplitude oscillatory shear. A constant torque and an angular frequency of 10 s-1 were used. Amplitude was measured and 20 points were recorded within the range of 0.5 to 10 nNm. Next, a frequency sweep test was performed with constant strain. The angular frequency (s-1) was carried out over a range of frequencies of 100 to 1 1/s. Storage moduli (G'), loss moduli (G") and deflection angle (δ) of P. chilensis (Mol.) Stuntz seed gum dispersions were obtained through the frequency sweep test. Results showed that Herschel-Bulkley model was good for describing rheological behavior of P. chilensis (Mol.) Stuntz dispersions with a correlation coefficient >0.99. P. chilensis (Mol.) Stuntz seed gum dispersions showed pseudoplastic behavior and time dependency. No effect was found in flow index values (n) by calcium concentration (0.4 and 0.6% w/v) and temperature (5 to 80° C), however yield stress values were significantly increased (p<0.05). Viscoelastic parameters showed that seed gum dispersions behave as gels, where G' values were greater than G” values in all cases. Presence of calcium significantly (p<0.05) improved viscoelastic properties of P. chilensis (Mol.) Stuntz dispersions. Moreover, the magnitude of elastic modulus and complex viscosity increased with the increase of concentration.
Session 36D, Food Engineering: Rheology
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |