Effect of barium sulfate, thickener type, and saline solution on the rheological properties of liquids used for instrumental swallowing assessment.

Shear and extensional rheological characterization of thickened fluid for dysphagia management

The swallowing process can be visualized using videoradiography, by mixing food with contrast medium, e.g., barium sulfate (BaSO(4)), making it radiopaque. The sensory properties of foods may be affected by adding this medium. To evaluate if and to what extent sensory and rheological characteristics of mango purée were altered by adding barium sulfate to the food. This study evaluated four food samples based on mango purée, with no or added barium sulfate contrast medium (0%, 12.5%, 25.0%, and 37.5%), by a radiographic method, and measured sensory texture properties and rheological characteristics. The sensory evaluation was performed by an external trained panel using quantitative descriptive analysis. The ease of swallowing the foods was also evaluated. The sensory texture properties of mango purée were significantly affected by the added barium in all evaluated attributes, as was the perception of particles. Moreover, ease of swallowing was significantly higher in the sample without added contrast medium. All samples decreased in extensional viscosity with increasing extension rate, i.e., all samples were tension thinning. Shear viscosity was not as dependent on the concentration of BaSO(4) as extensional viscosity. Addition of barium sulfate to a model food of mango purée has a major impact on perceived sensory texture attributes as well as on rheological parameters.

Shear and extensional deformation are two basic rheological properties which occur during food manipulation, mastication, deglutition executed during oral consumption and also in the processing and packaging of foods. Fluid resistance against shear and extensional deformation differ widely and whilst this has been confirmed theoretically and experimentally, a clear understanding of human perception of these properties will have beneficial returns to the food industry in designing and manufacturing of high quality, nutritious food to suit consumers' need (Laguna, Aktar, Ettelaie, Holmes, & Chen, 2016).

Development of an online rheometer for simultaneous measurement of shear and extensional viscosity during the polymer extrusion process

Okra is a vegetable that is widely grown around the world. Okra mucilage contains a high mucus concentration that can be useful for supporting the swallowing process. Although the extensional rheology of okra mucilage is essential to its flow, its extensional viscosity has not received much attention. Using a filament stretching rheometer, the extensional viscosity of the mucilage in okra was examined. The Giesekus model was used to predict this parameter. The okra mucilage with different concentrations was extracted from fresh okra. The extensional viscosity was measured using a filament breakup apparatus. The diameter of the liquid bridge was measured by a laser micrometer and it was also observed by a high-speed camera. A rotational rheometer was used to measure the shear viscosity. In addition, the master curves for the shear viscosity were plotted to eliminate the influence of solvent and shear rate and evaluate the influence of concentration on the elasticity of okra mucilage. The okra mucilage shear and extensional viscosity were predicted using the Giesekus model. Every sample of okra mucilage exhibited shear thinning behavior. In addition to having a high extensional viscosity that is hundreds of times higher than its shear viscosity, okra mucilage also exhibited stretching phenomena. The master curves demonstrated that the pseudoplasticity of the okra mucilage increased along with the concentration. The rheological behavior of the mucilage in okra can be explained by the Giesekus model. Okra mucilage's shear viscosity exhibited shear thinning behavior and a strong extensional viscosity that was significantly higher than its shear viscosity. The shear and extensional viscosity of okra mucilage can be described and predicted using the Giesekus model.

Field data from polymer flooding operations sometimes indicate a better-than-expected polymer injectivity below fracturing pressure. Current interpretations for this unexpected phenomenon are based either on geomechanical considerations (for unconsolidated sand formations) or on polymer mechanical degradation, potentially occurring in the injection facilities and the near wellbore area. In this paper, a new approach of polymer injectivity is suggested. It is based on the study of polymer mechanical degradation with respect to both shear and extensional viscosities. In the first part of this work, we have investigated the onset of mechanical degradation by submitting semi-dilute solutions of high molecular weight partially hydrolyzed polyacrylamide (HPAM) to extensional laminar flow created by an API capillary system. We have then measured both shear and extensional viscosity of the native and the degraded HPAM solutions. We consider the onset of mechanical degradation to be reached when shear viscosity loss is equal to 10%. At low degradation rate, shear viscosity is unaffected while extensional viscosity decreases up to 30%, whereas, at higher degradation rates, shear viscosity drops by 10% (onset) while extensional viscosity is reduced up to 60%. This means that degraded HPAM with weakly affected shear viscosity can develop much less resistance to extensional flow. In the second part, we have explored the influence of mechanical degradation on injectivity by determining resistance factors of native and degraded HPAM solutions. Solutions have been injected in reproducible unconsolidated sand packs. At low velocities, resistance factors were similar for both kinds of solutions, as expected from their comparable shear viscosities. However, at high velocities, namely where flow in porous media implies high extensional deformations in the vicinities of the pore throats, apparent rheo-thickening was much less marked for solutions degraded at high extensional rate. These results allow understanding why polymers which do not seem to be mechanically degraded according to their shear viscosity can show a very good injectivity, thanks to the reduction of extensional resistance in porous media. They could also lead to establish guidelines for designing new polymer pre-treatment methods aimed at improving injectivity while retaining the mobility control ability of polymers.

The extensional viscosity is an important rheological characteristic of polymer melts. It is however not as frequently reported on as the shear viscosity. The extensional viscosity is of special interest when considering polymeric materials for foaming and film blowing processes. Here, the extensional (and shear) viscosity along with the melt strength and the tensile properties of the corresponding solid film of a β-glucan concentrate are reported on. A capillary viscometer equipped with a hyperbolic die, yielding a contraction flow, was used to assess the extensional viscosity of the aqueous β-glucan compound at room temperature and at elevated temperatures (110 and 130 °C). In general, the extensional viscosity as well as the shear viscosity decreased with increasing deformation rate. The influence of two different amounts of added water (40 and 50%) was also examined. As expected, both types of viscosities decreased with increasing temperature. It is suggested that gelatinization of the starch fraction in the concentrate at 110 and 130 °C contributes to temperature dependence of the viscosity. To some extent, this is supported by light microscopy and confocal scanning laser microscopy studies of the microstructure of the materials. The results reported here indicate that the β-glucan concentrate might, after some modifications, be used as a complement to fossil-based polymers and processed by conventional manufacturing techniques.

Microfibrillated cellulose (MFC) is obtained by high-shear treatment of cellulose. MFC is suitable for use as clean-label, low-calorie thickener in semi-solid foods such as mayonnaises due to its high water holding capacity. The aim of this study was to determine the effect of type and concentration of thickener on rheological, tribological and sensory properties of low-fat mayonnaises. Low-fat mayonnaises were prepared with four types of thickeners (MFC, chemically modified starch, native waxy corn starch, xanthan gum) at three concentrations. Higher biopolymer concentrations resulted in increased shear viscosities, G′ and G″, yield stress and enhanced lubrication (i.e. lower friction coefficients). Mayonnaises with modified starch and xanthan gum generally had higher shear viscosity and yield stress compared to mayonnaises with comparable concentrations of MFC and waxy corn starch. MFC-thickened mayonnaises had highest G’, G” and boundary friction coefficients. Sensory properties of mayonnaises were determined using the Rate-All-That-Apply (RATA) method (n = 80). Addition of xanthan gum induced high sliminess and pulpiness, and low melting, creaminess and smoothness. Sensory properties of mayonnaises with MFC were generally similar to those with modified and waxy corn starch, despite differences in appearance (increased yellowness and slightly lower glossiness). Multiple Factor Analysis revealed that more shear-thinning mayonnaises were perceived as slimy. Boundary friction was negatively correlated with stickiness, while friction at the start of the hydrodynamic regime was positively correlated with melting sensations. We conclude that microfibrillated cellulose can be used as a thickener in low-fat mayonnaise as an alternative to commercially used chemically modified starch without considerably affecting its sensory texture properties.

Recent studies show that understanding the rheological properties of thickened fluids, such as viscosity and yield stress, is advantageous in designing optimal thickened fluids for the treatment of dysphagia. To date, these studies have focused on the rheological behavior of thickened fluids in shear deformation, while limited information is available on the surface tension of thickened fluids or their rheological behavior in extensional deformation. Knowledge of the extensional properties of thickened fluids (extensional viscosity and cohesiveness) is important to fully understand the behavior of such fluids while swallowing. Our aim in this work, therefore, was to characterize water and skim milk thickened with a commercial thickener (xanthan gumbased) to determine extensional deformation and surface tension properties. It was observed that the surface tension decreases as the thickener concentration increases due to the accumulation of the biopolymer at the surface of the fluid when it dissolves in water. In addition, the extensional viscosity of the fluid increased over time as the filament thinned (i.e., as the Hencky strain increased) until it reached a plateau. It was observed that the maximum extensional viscosity, which is related to the cohesiveness of the fluid, increases with the higher concentrations of thickener. However, the cohesiveness of thickened skim milk was lower than that of the thickened water at a given thickener concentration due to lower surface tension. This study confirms that by increasing the concentration of thickener, it will not only increase the shear viscosity (i.e., bolus thickness) of the fluid, but also the extensional viscosity (i.e., bolus cohesiveness).

Field data from polymer flooding operations sometimes indicate a better-than-expected polymer injectivity below fracturing pressure. Current interpretations for this unexpected phenomenon are based either on geomechanical considerations (for unconsolidated sand formations) or on polymer mechanical degradation, potentially occurring in the injection facilities and the near wellbore area. In this paper, a new approach of polymer injectivity is suggested. It is based on the study of polymer mechanical degradation with respect to both shear and extensional viscosities. In the first part of this work, we have investigated the onset of mechanical degradation by submitting semi-dilute solutions of high molecular weight partially hydrolyzed polyacrylamide (HPAM) to extensional laminar flow created by an API capillary system. We have then measured both shear and extensional viscosity of the native and the degraded HPAM solutions. We consider the onset of mechanical degradation to be reached when shear viscosity loss is equal to 10%. At low degradation extensional rate, extensional viscosity decreases to the same extent as shear viscosity (10%), whereas, at high degradation extensional rates, the decrease reaches up to 60%. This means that degraded HPAM with weakly affected shear viscosity can develop much less resistance to extensional flow. In the second part, we have explored the influence of mechanical degradation on injectivity by determining resistance factors of native and degraded HPAM solutions. Solutions have been injected in reproducible unconsolidated sand packs. At low velocities, resistance factors were similar for both kind of solutions, as expected from their comparable shear viscosities. However, at high velocities, namely where flow in porous media implies high extensional deformations in the vicinities of the pore throats, rheo-thickening was much less marked for solutions degraded at high extensional rate. These results allow understanding why polymers which do not seem to be mechanically degraded according to their shear viscosity can show a very good injectivity, thanks to the reduction of extensional resistance in porous media. They could also lead to establish guidelines for designing new polymer pre-treatment methods aimed at improving injectivity while retaining the mobility control ability of polymers.

Emulsification is an inherent problem of silicone oil used in vitreoretinal surgery. It has been shown that silicone oil can be made more resistant to emulsification and easier to inject by adding high-molecular-weight components (5% or 10% 423-kDa polydimethylsiloxane [PDMS]) to normal 1000 mPa · s silicone oil. The authors hypothesize that this might also reduce the movement of oil within an eye. A model eye chamber made of surface-modified poly(methyl methacrylate) was driven by a computer and a stepper motor to mimic saccadic eye movement. Seven silicone oils with different shear and extensional viscosities were tested. Two sets of eye movements were used: (amplitude 9°, angular velocity 390°/s, duration 50 ms) and (amplitude 90 °, angular velocity 360°/s, duration 300 ms). The movements were captured and analyzed by video recording. The angular velocity of an oil bubble relative to the eye chamber appears to form an exponential relationship with its shear viscosity. Depending on the thickness of the film of aqueous between the eye wall and the oil bubble, the shear rate was estimated to be between 6 and 14 × 10(4) s(-1). The addition of 10% of 423-kDa PDMS to 1000 mPa · s silicone oil significantly reduced the peak relative velocity compared with the base oil of 1000 mPa · s but not 5000 mPa · s. The addition of high molecular components to a base oil increases its extensional and shear viscosity. Although the extensional viscosity affected the ease with which the oil could be injected, the results showed that it was the shear viscosity that determined the relative velocity between the oil and the wall of the vitreous cavity, and thus the propensity to emulsify.

Formation of internal cake due to the invasion of reservoir rock by drilling, completion, and fracturing fluids is known to be one of the major causes of productivity reduction. Although the causes of internal cake formation are relatively well identified, the actual physical mechanisms involved in internal cake formation are yet to be understood. In particular, a quantitative means of relating physical properties of fluids to the degree of productivity reduction are not well established. A detailed investigation on the role of the rheology of viscoelastic fluids on the formation of "internal filter cakes" is, therefore, needed. The extensional viscosity for pure liquids without any structure is 3 times the shear viscosity. For these liquids, contribution of the extensional viscosity to the pressure loss is, therefore, constant and often neglected. However, for viscoelastic fluids, such as polymer based drilling and completion fluids, the extensional viscosity may be several orders of magnitude larger than the shear viscosity. This will lead to a significant increase in pressure loss, which is very often attributed to the development of internal cake. A series of core flow experiments have been conducted to investigate the possible relationship among the polymer concentration, fluid extensional viscosity, shear viscosity, filtration loss characteristics, and pressure drop across the core samples and hence, any change in the original rock permeability. Results of extensional and shear viscosity measurements, API filtration loss tests, and formation damage tests conducted by using two different Partially Hydrolized Polyacrylamide (PHPA) solutions (1.5 and 3.0 lb/bbl) are shown in this paper. Comparison of the PHPA test results with the previously published Xanthan Gum (XG) test results are also provided.

Rheological investigations of beta glucan functionality: Interactions with mucin

The importance of shear and extensional rheology and tribology as the design tools for developing food thickeners for dysphagia management

The sensory perceptions of sweetened, flavoured and thickened solutions prepared from xanthan, dextran, sucrose and banana flavour were evaluated and correlated to rheological parameters. The primary aim of this research was to evaluate the relevance of viscosity measured at low shear or at high shear for predicting sensory perceptions. Additionally considered were extensional viscosity estimated from filament thinning experiments and complex shear viscosity. The design of experiments included two groups of 5 samples matched at low shear rate and high shear rate, respectively. Mouthfeel perceptions were well correlated to low shear viscosity, however, including high shear viscosity or extensional viscosity as an additional model parameter improved the predictive quality of the models for thickness, stickiness and mouth coating. Stickiness and mouth coating were better correlated to extensional viscosity than low shear viscosity, although a model including both parameters predicted stickiness and mouth coating best. The complex viscosity at 100 rad/s was also highly correlated to the perception of thickness. Since correlations were not improved over steady shear parameters, complex viscosity was not considered in models based on more than one rheological parameter. Flavour was also scored during sensory evaluation and sweetness and overall flavour were highly correlated. The results of this study have highlighted that there is no single rheological parameter that will ultimately correlate to a range of mouthfeel perceptions. For certain mouth feel perceptions a model comprising shear and extensional rheological parameters will have higher predictive power than a model solely based on shear rheological parameters.