Bolus rheology of texture-modified food: Effect of degree of modification

Discrimination of cellulose microparticles in rats

Oral perception of food particles is important in mastication and swallowing. However, the mechanism underlying particle perception remains poorly understood because of the lack of suitable experimental systems. We evaluated microparticle perception in rats utilizing insoluble cellulose particles of varying diameters (20-170 μm). The cellulose additives have polycrystalline morphologies and contain smaller crushed particles. The filtrate containing 20 μm particles at a concentration of 1.6% was passed through 3 μm pore-size filter paper, and numerous small particles equivalent to a 0.25 mM soluble solution were observed. In two-bottle preference tests, rats showed no innate preference or avoidance of particles of any size at concentrations ranging from 0.05-1.6%. Next, conditioned preference learning tests employing 8% glucose and fructose solutions were performed. After being repeatedly presented with glucose and fructose solutions containing particles of different sizes (170 and 20 μm particles or 20 μm filtrate) at a concentration of 1.6%, the rats preferred particles in glucose solution even without glucose presentation. Intriguingly, rats preferred the filtrate following repeated presentations of glucose-containing filtrate and water containing fructose. These results suggest that rats can distinguish microparticles in water. The preference learning test is useful for analyzing particle perception mechanisms in mammals.

Bolus rheology of texture adjusted food-Effect of age

Swallowing disorders, or dysphagia, affect a large part of the population due to factors such as degenerative diseases, medication side effects or simply age-related impairment of physiological oropharyngeal function. The management of dysphagia is mainly handles through texture-modified foods of progressively softer, smoother, moister textures, depending on the severity of the disorder. Rheological and physiological-related properties of boluses were determined for a group of five older persons (average age, 74) for a set of texture-modified foods: bread, cheese and tomato and the combination into a sandwich. The softest class was gel food, after which came a smooth timbale; both were compared to boluses of regular food. The subjects chewed until ready to swallow, at which point the bolus was expectorated and measured regarding saliva content, linear viscoelasticity and shear viscosity. The results were compared to those of a previously studied younger group (average age, 38). The general physiological status of the subjects was determined by hand and tongue strength, diadochokinesis and one-legged standing and showed that all subjects were as healthy and fit as the younger group. Age-related properties such as one-legged standing with closed eyes and salivary flow plus bolus saliva content were lower for the older group, but the average chews-until-swallow was surprisingly also lower. Consequently, bolus modulus and viscosity were higher than for the younger group. Overall, the intended texture modification was reflected in bolus rheological and physiological-related properties. Bolus modulus, viscosity, saliva content and chews-until-swallowed all decreased from regular food to timbale food to gel food.

Correlations of sensations of hardness and springiness of agar and gelatin gels with mechanical properties in human participants

OBJECTIVES

It is unclear which mechanical properties of foods cause the texture sensation in humans. This study aimed to investigate the relationship between unilateral compression measurements and the sensations of hardness and springiness in gels.

METHODS

Three different concentrations of agar and gelatin gels were prepared by the addition of agar (1%, 2%, and 3%) and gelatin (4%, 8%, and 16%) to water or apple juice. In a stress-rupture test, stress-strain curves were obtained by the application of uniaxial compression with a disc plunger at a compression rate of 10 mm/s. The hardness, springiness, and palatability of the gels were evaluated by 12 healthy volunteers using a visual analog scale.

RESULTS

The sensation of hardness was positively correlated with the sensation of springiness for the agar and gelatin gels. Palatability decreased as hardness increased for both gels. In terms of mechanical properties, the sensation of hardness was only significantly correlated with the initial elastic modulus, while the sensation of springiness was correlated with the late elastic modulus and other mechanical properties such as fracture strain, time, and stress.

CONCLUSIONS

These results suggest that sensations of hardness and springiness are produced in the initial and late stages, respectively, during the food-crushing process using the tongue, palate, and teeth.

Quantitative Textural and Rheological Data on Different Levels of Texture-Modified Food and Thickened Liquids Classified Using the International Dysphagia Diet Standardisation Initiative (IDDSI) Guideline

Diet modification is a common compensation strategy to promote swallowing safety in patients with swallowing difficulties. The International Dysphagia Diet Standardisation Initiative (IDDSI) guideline provides qualitative descriptions on texture-modified food and thickened liquid. This study aimed to establish quantitative textural and rheological data on different IDDSI levels based on common Chinese ingredients and dishes. Textural and rheological properties of 226 samples of various food textures and 93 samples of various liquid consistencies were obtained using a texture profile analysis (TPA) and viscometer, respectively. The establishment of such quantitative data can be used for future texture-modified food product development and research purposes.

Differentiation of Bolus Texture During Deglutition via High-Density Surface Electromyography: A Pilot Study

OBJECTIVE

Swallowing is a complex neuromuscular task. There is limited spatiotemporal data on normative surface electromyographic signal during swallow, particularly across standard textures. We hypothesize the pattern of electromyographic signal of the anterior neck varies cranio-caudally, that laterality can be evaluated, and categorization of bolus texture can be differentiated by high-density surface electromyography (HDsEMG) through signal analysis.

METHODS

An HDsEMG grid of 20 electrodes captured electromyographic activity in eight healthy adult subjects across 240 total swallows. Participants swallowed five standard textures: saliva, thin liquid, puree, mixed consistency, and dry solid. Data were bandpass filtered, underwent functional alignment of signal, and then placed into binary classifier receiver operating characteristic (ROC) curves. Muscular activity was visualized by creating two-dimensional EMG heat maps.

RESULTS

Signal analysis results demonstrated a positive correlation between signal amplitude and bolus texture. Greater differences of amplitude in the cranial most region of the array when compared to the caudal most region were noted in all subjects. Lateral comparison of the array revealed symmetric power levels across all subjects and textures. ROC curves demonstrated the ability to correctly classify textures within subjects in 6 of 10 texture comparisons.

CONCLUSION

This pilot study suggests that utilizing HDsEMG during deglutition can noninvasively differentiate swallows of varying texture noninvasively. This may prove useful in future diagnostic and behavioral swallow applications.

LEVEL OF EVIDENCE

4 Laryngoscope, 133:2695-2703, 2023.

Rheology and tribology of chitosan/Acacia gum complex coacervates

Acacia gum (Gum Arabic; GA) and chitosan (CTS) form complex coacervates in acidic environments, providing a polymer-rich aqueous material with interesting bio-lubricant properties. We investigate the interplay of the tribology and rheology of these coacervates, demonstrating that they dramatically reduce the friction coefficient between lubricated soft model surfaces as compared to solutions of the individual polymers. We characterize the phase separation behavior using microscopy, electrophoretic mobility and thermogravimetric analysis. The macroscopic rheological behaviour is predominantly viscous and ranges from weakly to strongly shear thinning: viscosity levels and strength of shear thinning increase with decreasing ionic strength, but no apparent yield stress or predominant elasticity were observed even in the absence of salt. Conversely, friction coefficients measured between soft and rough surfaces increase with a rise in ionic strength and can be scaled onto a Stribeck-type master curve across varying ionic strength and pH in the mixed and hydrodynamic lubrication regimes.

Novel approaches to the study of viscosity discrimination in rodents

Texture has enormous effects on food preferences. The materials used to study texture discrimination also have tastes that experimental animal can detect; therefore, such studies must be designed to exclude taste differences. In this study, to minimize the effects of material tastes, we utilized high- and low-viscosity forms of carboxymethyl cellulose (CMC-H and CMC-L, respectively) at the same concentrations (0.1-3%) for viscosity discrimination tests in rats. In two-bottle preference tests of water and CMC, rats avoided CMC-H solutions above 1% (63 mPa·s) but did not avoid less viscous CMC-L solutions with equivalent taste magnitudes, suggesting that rats spontaneously avoided high viscosity. To evaluate low-viscosity discrimination, we performed conditioned aversion tests to 0.1% CMC, which initially showed a comparable preference ratio to water in the two-bottle preference tests. Conditioning with 0.1% CMC-L (1.5 mPa·s) did not induce aversion to 0.1% CMC-L or CMC-H. However, rats acquired a conditioned aversion to 0.1% CMC-H (3.6 mPa·s) even after latent inhibition to CMC taste by pre-exposure to 0.1% CMC-L. These results suggest that rats can discriminate considerably low viscosity independent of CMC taste. This novel approach for viscosity discrimination can be used to investigate the mechanisms of texture perception in mammals.

Instrumental and sensory techniques to characterize the texture of foods suitable for dysphagic people: A systematic review

The interest to characterize texture-modified foods (TMFs) intended for people with oropharyngeal dysphagia (OD) has grown significantly since 2011. Several instrumental and sensory techniques have been applied in the analysis of these foods. The objective of the present systematic review was to identify the most appropriate techniques, especially for the food industry and clinical setting. The search was carried out in three online databases according to the "Preferred Reporting Items for Systematic Reviews and Meta-Analyses" (PRISMA). Across the multiple trials reviewed, Texture Profile Analysis and the Uniaxial Compression Test were most used as the instrumental technique for solid foods, and the Back Extrusion Test for fluid and semisolid foods. All trials used descriptive analysis as the sensory technique. However, the experimental conditions of the trials lacked standardization. Consequently, the results of the trials were not comparable. To properly characterize the texture of TMFs intended for OD by each technique, an international consensus is needed to establish standardized experimental conditions. Methods based on these techniques should also be validated by collaborative studies to verify repeatability, replicability, and reproducibility.

Understanding relations between rheology, tribology, and sensory perception of modified texture foods

The aim of this work was to examine relations between instrumental and sensory parameters in a texture modified food matrix, with and without saliva. Nine pureed carrot samples (eight thickened and a control) were developed with starch (0.4 and 0.8% wt/wt), xanthan (0.2 and 0.4% wt/wt) or starch-xanthan blends that met International Dysphagia Diet Standardisation Initiative (IDDSI) Level 4 guidelines using fork and spoon tests. Rheological and tribological tests were conducted on the food and simulated bolus prepared by adding fresh stimulated saliva to the food (1:5, saliva:food) to mimic oral processing. Perceived sensory properties were identified using a temporal dominance of sensations (TDS) test (n = 16) where panelists were given a list of nine attributes. The area under the curve was extracted from TDS curves for each attribute/sample and this was correlated with rheological (viscosity at 10 s^-1 , G', G″, and tan δ at 1 Hz) and tribological (friction coefficient in three regimes) data. The viscosity of the control sample decreased after adding hydrocolloids (except Starch_0.8%) and with saliva incorporation. G' and G″ either increased or were similar for xanthan and blends and decreased for starch-thickened samples. Hydrocolloid addition increased friction for all samples and was higher with saliva addition. Sensory results showed that samples with starch were perceived as thick and grainy while xanthan was perceived as smooth and slippery. A greater number of sensory attributes correlated with viscoelastic parameters compared to friction coefficients. Correlations were highest with the saliva added samples, further highlighting the importance of including saliva during instrumental testing.