The flow properties of ketchup were assessed upon addition of commonly used food thickeners: guar, xanthan and CMC gum at three different concentrations (0.5%, 0.75% and 1%) and four temperatures (25, 35, 45 and 55 °C). The ketchup without supplementation served as a control. All ketchup formulations exhibited non-Newtonian, pseudoplastic behaviour at all temperatures and hydrocolloid levels. The Power-law and Herschel-Buckley model were successfully applied to fit the shear stress versus shear rate data. The flow behaviour indices, n and n′, varied in the range of 0.189–0.228 and 0.216–0.263, respectively. The consistency coefficients, k and k′, were in the range of 8.42–27.22 and 6.56–20.10 Pa s n, respectively. The addition of hydrocolloids increased the yield point (τ0) and apparent viscosity of the ketchup in comparison to that of the control. The Arrhenius equation was successfully used to describe the effects of temperature on the apparent viscosity of the prepared formulations. The E a value appeared in the range between 5492.6 and 21475.8 J mol−1. [ABSTRACT FROM AUTHOR]
The viscoelastic property and scaling behavior of acid (glucono-delta-lactone)-induced soy protein isolate (SPI) gels were investigated at various ionic strengths (0-800 mM) and five protein concentrations ranging between 4% and 8% (w/w). The infinite storage modulus (G '(infinity)) and the gelation start time (t(g))which indicate the progress of gelation process exhibited strong ionic strength dependence. The storage modulus and critical strain were found to exhibit a power-law relationship with protein concentration. Rheological analysis and confocal laser scanning microscopy (CLSM) analysis were applied to estimate the fractal dimensions (D-f) of the gels and the values were found to vary between 2.319 and 2.729. The comparison of the rheological methods and the CLSM image analysis method showed that the Shih, Shih, Kim, Liu, and Aksay (1990) model was better suited in estimating the D-f value of acid-induced SPI gel system. (C) 2012 Elsevier Ltd. All rights reserved.