RESUMEN
Ice cream is a complex product containing four different phases that affect its microstructure. Viscosity is a critical ice cream quality parameter that is typically measured using off-line methodologies, such as rheometry. In-line viscosity measurements allow continuous and instant analysis compared to off-line methodologies, yet they still constitute a challenge. This work focused on the preliminary study of the potential application of near-infrared (NIR) and Raman spectroscopy as analytical tools to assess the viscosity of ice cream mixes. Historically, partial least squares regression (PLSR) is a standard algorithm used for analysis of spectral data and in the development of predictive models. This methodology was implemented over a range of viscosity values, obtained by varying the ice cream fat content and homogenization conditions. Individual PLSR models showed some predictive ability and better performance compared to the integrated model obtained by data fusion. Lower prediction errors and higher coefficients of determination were obtained for NIR, making this technique more suitable based on model performance. However, other considerations should be accounted during the selection of the best method, such as implementation limitations. This study offers a preliminary comparison of the spectroscopic methods for quantitative analysis of viscosity of aged ice cream mixes and a starting point for an in-situ application study.
RESUMEN
We study the rheology of suspensions of ice crystals at moderate to high volume fractions in a sucrose solution in which they are partially soluble, a model system for a wide class of crystal mushes or slurries. Under step changes in shear rate, the viscosity changes to a relaxed value over several minutes, in a manner well fitted by a single exponential. The behavior of the relaxed viscosity is power-law shear thinning with shear rate, with an exponent of -1.76±0.25, so that shear stress falls with increasing shear rate. On longer time scales, the crystals ripen (leading to a falling viscosity) so that the mean radius increases with time to the power 0.14±0.07. We speculate that this unusually small exponent is due to the interaction of classical ripening dynamics with abrasion or breakup under flow. We compare the rheological behavior to mechanistic models based on flow-induced aggregation and breakup of crystal clusters, finding that the exponents can be predicted from liquid phase sintering and breakup by brittle fracture.
RESUMEN
Particle-tracking methods are used to study gelation in a colloidal suspension of Laponite clay particles. We track the motion of small fluorescent polystyrene spheres added to the suspension, and obtain the micron-scale viscous and elastic moduli of the material from their mean-squared displacement. The fluorescent spheres move subdiffusively due to the microstructure of the suspension, with the diffusive exponent decreasing from close to one at early times to near zero as the material gels. The particle-tracking data show that the system becomes more heterogeneous on the microscopic scale as gelation proceeds. We also determine the bulk-scale moduli using small-amplitude oscillatory shear rheometry. Both the macroscopic and microscopic moduli increase with time, and on both scales we observe a transition from a primarily viscous fluid to an elastic gel. We find that the gel point, determined as the time at which the viscous and elastic moduli are equal, is length-scale dependent--gelation occurs earlier on the bulk scale than on the microscopic scale.
RESUMEN
The small-scale rheology of Carbopol ETD 2050, a polymer gel with a yield stress, is studied as a function of polymer concentration by measuring the diffusion of submicron-sized spherical fluorescent particles suspended in gel. Dynamic light scattering is used to determine the mean-squared displacement