Common Rheological Models Research Articles

ON‐LINE RHEOLOGICAL CHARACTERIZATION OF PIZZA SAUCE USING TUBE VISCOMETRY

ABSTRACTThe performance of a tube process viscometer was evaluated forits ability to characterize the rheological properties of pizza sauce. Tube flow was described using common rheological models (Power Law, Herschel‐Bulkley, Casson and Bingham plastic) and model parameters were compared to laboratory rheometer data. Derived model parameters (tube) and measured pressure drop data were both correlated with other off‐line instruments, namely the Bostwick Consistometer and Brookfield viscometer. Bingham Plastic model parameters of viscosity and yield stress as generated from the tube viscometer were found to be comparable to the rheometer generated equivalents. Measured pressure drop readings using linear and Power law regression showed good predictive capability (R2 >0.99 & 0.93) of Brookfield and Bostwick Consistometer readings respectively. It can be concluded that tube viscometry would result in effective real time rheological characterization of tomato‐based products. Limitations of the Bostwick Consistometer are highlighted.

Steady shear rheology of rice-blackgram suspensions and suitability of rheological models

Rice-blackgram suspensions having different moisture contents (56–71%) were subjected to rheological testing up to a shear rate of 500 s −1using a concentric cylinder rheometer. The unfermented and fermented suspensions showed well pronounced shear-thinning behaviour and exhibited yield stress. The experimentally determined yield stresses were markedly higher in fermented suspensions than in unfermented suspensions. The latter also have a lower flow behaviour index, a lower apparent viscosity, but a higher consistency index. The rheological parameters were sensitive to moisture content in the suspensions, particularly at low moisture levels. Among the common rheological models, the Herschel-Bulkley model fitted the shear rate and shear stress data better (r = 0.992–0.999; p ≤ 0.001) than the power law model (0.985–0.994), or the Casson model (0.983–0.993). The measured values of the rheological parameters for the rice-blackgram suspensions used for making dosa, a traditional Indian fermented pancake, are reported.