| Rheological properties of confectionary products, chocolate syrup, peanut butter, and chocolate, were studies using conventional tube viscometry, rotational viscometry, or Magnetic Resonance Imaging (MRI)-based tube viscometry (tomographic viscometry).; Like other food suspensions, the products' flow behaviors followed a shear-thinning pattern. The flow behaviors of chocolate syrup at ∼20°C was well described by the power law model. The Casson model and Bingham plastic model were used to describe the flow behavior of peanut butter at 30--50°C. Using ANOVA, the yield stress of peanut butter was not temperature dependent, but the viscosity, which followed the Arrhenius relationship, decreased as the temperature increased. The flow behavior of chocolate was well characterized by the Casson model. The first part of the study was conducted using rotational rheometry to characterize commercial chocolates; thixotropy was observed and its degree varied with different chocolates. The second part was conducted using MRI-based tube viscometry on molten milk chocolate (wall slip was observed in the flow profiles and it affected the difference in Casson parameters obtained from different viscometers).; The observed rheological results are useful for control of product processing, characterization of product quality, and for equipment design. Moreover, the agreement in results observed from the tube flow studies proves the reliability and reproducibility of the tomographic viscometric method and its possible use as an in-line viscometer. |
