Band 22, Heft 6

Dynamic oscillatory and creep tests are two common rheological methods used to determine viscoelastic properties. In the food industry, these tests are generally performed in the linear viscoelastic region, providing information on food structure and behavior over a range of timescales. However, this small-strain testing gives an incomplete picture of structural deformation and breakdown. Nonlinear oscillatory and creep testing, on the other hand, may yield a more complete fingerprint of food structural behavior. In this study, whey protein isolate (WPI)/κ-carrageenan gels with different structures were studied under large amplitude oscillatory shear (LAOS) and creep tests to determine the impact of structure on nonlinear oscillatory and creep behavior, and to examine correlations between nonlinear oscillatory and creep parameters. Evaluated structural types comprised a homogeneous protein gel, a bicontinuous gel, in which both WPI and κ-carrageenan exhibited a continuous network, and a carrageenan continuous gel. Creep data were fit to 4-element Burgers models for further analysis, and the predicted compliance values were found to be in agreement with experimental data (R 2 ≥ 0.90). Carrageenan continuous gels showed the greatest degree of nonlinearity under LAOS (25 % strain), while homogeneous gels displayed the least. Nonlinear oscillatory data was found to correlate (R 2 > 0.7, p < 0.05) with parameters used in the 4-element Burgers model. Hence, nonlinear viscoelastic behavior among materials may be evaluated by both creep data and nonlinear oscillatory data. However, nonlinear oscillatory data gives a quantitative measure of the type and extent of nonlinear behavior, while creep data indicates only the presence of nonlinear behavior. By combining information on structural behavior derived from nonlinear oscillatory and creep data, it is possible to determine nonlinear behavior over a wide range of timescales, yielding insight into structural deformation and breakdown under application of stress or strain at different rates.

This paper discusses the influence of fat type in the structure of ice cream, during its production by means of rheo-optical analysis. Fat plays an important part in the ice cream structure formation. It's responsible for the air stabilization, flavor release, texture and melting properties. The objective of this study was to use a rheological method to predict the fat network formation in ice cream with three types of fats (hydrogenated, low trans and palm fat). The three formulations were produced using the same methodology and ratio of ingredients. Rheo-optical measurements were taken before and after the ageing process, and the maximum compression force, overrun and melting profile were calculated in the finished product. The rheological analysis showed a better response from the ageing process from the hydrogenated fat, followed by the low trans fat. The formulation with palm fat showed greater differences between the three, where through the rheological tests a weaker destabilization of the fat globule membrane by the emulsifier was suggested. The overrun, texture measurements and meltdown profile has shown the distinction on the structure formation by the hydrogenated fat from the other fats.

Simulations are performed to investigate the flow of a shear-thinning, non-Newtonian fluid in a collapsed elastic tube and comparisons are made with experimental data. The fluid is modeled by means of the Bird- Carreau viscosity law. The computational domain of the deformed tube is constructed from data obtained via computer tomography imaging. Comparison of the computed velocity fields with the ultrasound Doppler velocity profile measurements show good agreement, as does the adjusted pressure drop along the tube’s axis. Analysis of the shear rates show that the shear-thinning effect of the fluid becomes relevant in the crosssections with the biggest deformation. In fact, the maximum shear rate is about a factor of thirty larger than its corresponding maximum value in the undeformed tube, and the viscosity is reduced by a factor of two. The effect of the shearthinning behavior has also been compared with identical simulations carried out for a Newtonian fluid.

An adaptive neuro-fuzzy inference system (ANFIS) was used to accurately model the effect of gum concentration (GC) and shear rate (SR) on the apparent viscosity (h) of the ice-cream mixes stabilized with different concentrations of xanthan gum. ANFIS with different types of input membership functions (MFs) was developed. Membership function “the gauss2” generally gave the most desired results with respect to MAE, RMSE and R2 statistical performance testing tools. The ANFIS model was compared with artificial neural network (ANN) and multiple linear regression (MLR) models. The estimation by ANFIS was superior to those obtained by ANN and MLR models. The ANFIS and ANN model resulted in a good fit with the observed data, indicating that the apparent viscosity values of the ice-cream can be estimated using the ANFIS and ANN models. Comparison of the constructed models indicated that the ANFIS model exhibited better performance with high accuracy for the prediction of unmeasured values of apparent viscosity h parameter as compared to ANN although the performance of ANFIS and ANN were similar to each other. Comparison of the constructed models indicated that the ANFIS model exhibited better performance with high accuracy for the prediction of unmeasured values of apparent viscosity ɳ parameter as compared to ANN although the performance of ANFIS and ANN were similar to each other.

This paper describes the development of a rapid rheological method for the characterization of functionalized citrus pulp fibers by high pressure homogenization. The suspension rheology of the fibers differ significantly depending on the applied processing conditions, making it critical to have quick and robust quality control tools in place. The weak polyelectrolyte nature of the fibers was considered in order to define the adequate solvent conditions for the rheological evaluation of the suspensions. Secondly, an improved dispersion method using ethylene glycol was developed in order to ensure optimal hydration of the dry fiber. The effect of fiber concentration was then studied both under steady-shear and oscillation tests. The dry matter concentration for the rapid rheological method was set at 4 w/w% above the experimental critical concentration or percolation threshold.