The determining role of bolus rheology in triggering a swallowing

Swallowing is the final stage of an eating process. Even though individuals know exactly when and how to swallow, the controlling mechanisms and the determining criteria of bolus swallowing are still not yet clear. One hypothesis is that bolus rheology, i.e. its flow-ability and stretch-ability, determines the triggering of a swallowing and the main aim of this work was to test this hypothesis. A wide range of fluid foods, including 18 commercial products and 10 lab-constituted foods, were examined for easiness of swallowing by a panel of 19 subjects. Oral residence time, defined as the time from the ingestion till the completion of swallowing, was determined for each eating process. It was observed that the oral residence time had a linear relationship with the sensed difficulty of swallowing. That is a food sensed difficult-to-swallow tends to stay longer in the oral cavity. Rheological properties (both shear and stretching flow) of these foods and their simulated boluses (mixture of food and simulated saliva) have also been determined at body temperature. The apparent shear viscosity showed a positive correlation with the sensed difficult of swallowing. However, the stretching behaviour of a fluid food, characterised by the maximum stretching force and the work of stretching showed much improved correlation to the sensory perceived easiness of swallowing. It was concluded that bolus rheology, in particular its extensional stretch-ability, had the most important influence on the ease of swallowing.     

Evaluating chewing function: Expanding the dysphagia field using food oral processing and the IDDSI framework

The dysphagia field is still in relative infancy with a sophisticated knowledge base amassed since the early 1980's. The desire to identify aspiration and prevent life threatening pneumonia has resulted in a focus on the complexities of swallowing liquids. However, humans also ingest saliva, food, and oral medications, with the potential for these substances to incompletely clear the pharynx, be aspirated or block the airway. Safe swallowing of solid food in particular requires adequate chewing function, good oral control, and sufficient higher cortical function. Although screening and assessment for liquid swallowing safety is well established, the same cannot be said for the evaluation of safety to chew and swallow different food textures. While research into liquid swallowing physiology and its clinical application has largely come from the medical and allied health fields, our knowledge of chewing function for food textures comes from food texture research and food sensory science arenas. There is an exciting opportunity to bring the medical and food texture science fields together to expand our knowledge base on human chewing function, with clinical application to people with dysphagia. The development of the IDDSI Framework as an international standardized way of describing and labelling food texture and drink thickness allows the field to move toward management of texture modified food and thick liquids in a coordinated fashion, speaking the same language. This commentary will describe what we know of chewing function and how it is assessed clinically, proposing methods of assessment that utilize the IDDSI Framework.     

Swallowing profiles of food polysaccharide solutions with different flow behaviors

The relationship between physiological response and sensory perceived scores in swallowing was investigated using food polysaccharide solutions. Solutions from xanthan gum (0.3–0.9%) and locust bean gum (0.5–0.8%) were used as specimen with different flow behaviors identified by static and dynamic rheological methods. Acoustic analysis and sensory evaluation were carried out to investigate the swallowing profiles using the same human subjects. From acoustic analysis, time required for bolus to transfer through the pharyngeal phase t₂ decreased with increasing concentration of xanthan gum despite the viscosity increase. Also, the acoustic balance for the swallowing sound shifted to a higher frequency range with increasing concentration. The t₂ for locust bean gum was much less concentration-dependent and consistently larger than that for xanthan gum when compared at equivalent shear viscosity at 10 s⁻¹. Also, the acoustic balance for the swallowing sound was less concentration-dependent than that for xanthan gum. From sensory evaluation, 0.6% xanthan gum was scored the highest in perceived swallowing ease, while 0.75% locust bean gum was scored the lowest. Both t₂ and the acoustic balance correlated well with perceived swallowing ease. Results indicate that xanthan gum solutions flow as one coherent bolus through the pharyngeal phase with smaller variation of flow velocity than locust bean gum solutions, leading to a greater sensation of swallowing ease. “Structured fluid”, defined as fluid with yield stress such as xanthan gum solutions, is a rheological nature that allows bolus to be swallowed in one go, relating to perceived swallowing ease of liquid foods.     

NUMERICAL MODELING AND SIMULATION ON THE SWALLOWING OF JELLY

Studies of the swallowing process are especially important for the development of care foods for dysphagia. However, the effectiveness of experiments on human subjects is somewhat limited due to instrument resolution, stress to the subjects and the risk of aspiration. These problems may be resolved if numerical simulation of swallowing can be used as an alternative investigative tool. On this basis, a numerical model is proposed to simulate the swallowing of a simple jelly bolus. The structure of the pharynx was modeled using a finite element method, and the swallowing movements were defined by pharynx posterior wall shift, laryngeal elevation and epiglottis retroflexion. The rheological characteristics of the jelly were investigated using an oscillatory rheometer and a compression test. A Maxwell three-element model was applied to the rheological model of the jelly. The model constants were obtained from compression tests because the mode of deformation and the stress level of the compression tests were similar to those of the swallowed jelly. The frictional relationship between the organs and the jelly was estimated experimentally from some frictional measurements between the jelly and a wet sloping surface. The results of the simulations for the soft and hard jellies showed different patterns of swallowing that depended on their hardness, and the soft jelly produced faster swallowing because of its flexibility.

PRACTICAL APPLICATIONS

The object of this study is to develop a numerical simulation model of swallowing. Numerical modeling is suitable for the quantitative analysis of the swallowing process and may also be expected to enable a systematic study of care foods that are safe and offer some degree of comfort to patients suffering from swallowing disorders. The computer simulation can be used for evaluation without dangerous risks to the patient.     

Texture design for products using food hydrocolloids

Some in vivo measurements have been carried out using polysaccharide gels of different physical properties (i.e., elastic and plastic) and degrees of hardness. In vivo measurements tested included electromyography (EMG) and acoustic analysis of the swallowing sound to investigate the dynamic changes of food texture during oral processing. As a model of foods for dysphagia patients, the gels were soft enough to be eaten by compression between the tongue and the hard palate without biting by the teeth. From EMG, no significant differences were found between elastic gels and plastic gels in the duration of oral processing and the EMG activity of the suprahyoid musculature when compared at equivalent hardness. The EMG activity of the suprahyoid musculature correlated well with the compression load of gels at 95% strain. From the acoustic analysis, the plastic gels required shorter time to transfer through the pharynx and were scored higher in sensory cohesiveness than the elastic gels. Results indicate that oral processing of soft gels requires equivalent EMG activity of the suprahyoid musculature when the gel hardness is the same. Also, the plastic gels flow through the pharynx as one coherent bolus with smaller variation of the flow speed. Texture of foods for dysphagia patients should be optimized in terms of viscoelasticity so that they can easily transform to swallowable bolus during oral processing.     

Texture and texture assessment of thickened fluids and texture‐modified food for dysphagia management

Thickened fluids and texture‐modified foods are commonly used in the medical management of individuals who suffer from swallowing difficulty (known as dysphagia). However, how to reliably assess texture properties of such food systems is still a big challenge both to industry and to academic researchers. This article aims to identify key physical parameters that are important for objective assessment of such properties by reviewing the significance of rheological or textural properties of thickened fluids and texture‐modified foods for swallowing. Literature reviews have identified that dominating textural properties in relation to swallowing could be very different for thickened fluids and for texture‐modified foods. Important parameters of thickened fluids are generally related with the flow of the bolus in the pharyngeal stage, while important parameters of texture‐modified foods are generally related with the bolus preparation in the oral stage as well as the bolus flow in the pharyngeal stage. This review helps to identify key textural parameters of thickened fluids and texture‐modified foods in relation to eating and swallowing and to develop objective measuring techniques for quality control of thickened fluids and texture‐modified foods for dysphagia management.     

Sensory and instrumental analysis for slipperiness and compliance of food during swallowing

ABSTRACT:  In spite of its importance, there have been few attempts to evaluate the sensory attributes of the food bolus during swallowing. In the current study, the slipperiness, the degree of slide for the food bolus through the mucosal surface of the oro-pharynx, and the compliance, how easily the shape of a food bolus can be transformed for automatic and comfortable swallowing, were derived among several sensory attributes related to the swallowing. Therefore, the study aims were twofold: (1) to develop the methods of sensory and instrumental analyses for determining the slipperiness and compliance of the food bolus during swallowing and (2) to examine the appropriateness of the newly designed devices by correlating the data between the sensory and instrumental analyses. Six commercial food products were evaluated by 10 trained panelists for each attribute. The devices for assessing each attribute were developed in consideration of the oro-pharyngeal movements. The sensory and instrumental analyses showed high correlation and regression coefficients as well as intensity differences of the 6 samples for each attribute. In conclusion, the slipperiness and the compliance were suitable for acquiring a better understanding of the sensory attributes of the food bolus during swallowing, and the newly developed devices showed a high potential for determining those attributes.     

Next target for food hydrocolloid studies: Texture design of foods using hydrocolloid technology

Texture is important in terms of both food palatability and the safety of eating. Recently, the importance of texture has been emphasized for the development of nursing-care foods, including dysphagia foods, in recent aged society, where the number of patients with mastication and swallowing difficulties is increasing. Texture design of these food products is now one of the most important tasks in the food industry in Japan. Texture of these food products should be optimized by modulating viscoelasticity using hydrocolloids so that they can easily transform to ‘ready-to-swallow’ bolus during oral processing. This article reviews the importance of texture as an essential attribute of foods and also the usefulness of hydrocolloids as an ingredient to modify and control food texture. The article also covers recent trials by the author’s research team on bolus rheology and in vivo acoustic analysis. The trials are to find some objective parameters describing the mastication and swallowing eases as an alternative to conventional bulk rheology and subjective sensory analysis.     

Texture changes in bolus to the “point of swallow” - fracture toughness and back extrusion to test start and end points

The change in texture of a food bolus during chewing, from first bite to swallow, is dramatic for solid foods and a variety of analytical techniques are required to quantify the texture at any given point in the chewing cycle. The objective of the work presented in this paper is to develop mechanical and rheological tests relevant to a model food, allowing the texture of the bolus to be quantified at first bite, and when masticated to the point of swallowing. This paper presents one aspect of the “Food Structure Platform” programme, a multi-disciplinary New Zealand programme investigating the influence of structure on the textural attributes of solid foods. The programme team is developing model foods and novel techniques to test their mechanical and rheological properties.The first model food developed by the Food Structure Platform is a biscuit with a well defined range of hardness within one basic recipe. This was tested in 3-point bending to determine fracture stress and relate that to texture perceived on first bite. The biscuit samples were also masticated to the point immediately prior to where the subject would have normally swallowed then expectorated for rheological testing. Modified TPA and back extrusion, based on a cup and piston test piece, were used to test the rheological properties of the bolus from each of the biscuit models. Good correlations were found with fracture stress of the biscuit and sensory hardness for first bite. At the point of swallow the bolus had a consistent cohesiveness and saliva content irrespective of starting texture, whilst the hardness and adhesiveness was affected by starting texture/recipe.     

COMPARISON OF PHYSICAL PROPERTIES OF AGAR, LOW GEL STRENGTH AGAR AND GELATIN, AS SUPPLEMENTARY FOOD FOR PEOPLE WITH SWALLOWING DIFFICULTY

Low gel strength agar (LGSA), recently developed as a supplementary food for swallowing was compared with ordinary agar and gelatin. LGSA was developed to have physical properties close to that of gelatin, while keeping one property of agar, i. e. its setting temperature which can be controlled comparatively easier than gelatin. Each specimen was prepared with and without orange flavor. After determination of their basic properties, i. e. hardness, adhesiveness, cohesiveness and gumminess, three samples of two flavors, six in all, were studied for ease of swallowing using electromyography and sensory evaluation, on middle age (40 to 60 years old) and senior age (60 to 70 years old) subjects. Those experiments revealed nearly the same results with all samples, except for a slight difference in gumminess in LGSA and gelatin. No significant difference in electromyograms were noted in six samples or with age of subjects. It is feasible to employ agar materials together with gelatin in institutions whose members have swallowing disorders.     

FOOD TEXTURE AND ITS EFFECT ON INGESTION, MASTICATION AND SWALLOWING

The oral processing of most semisolid and solid foods can be summarized in terms of two opposing mechanical influences: forces that fracture food particles versus those that make them adhere to each other. During either the ingestion of food into the mouth or the early stages of mastication, the aim of processing solid food particles is usually to fracture them. However, later on towards swallowing, adhesion is desirable in order to try to form a sticky food bolus that could clear the mouth of isolated food fragments. Neither of these tendencies is actually a function of any particular force (or stress) or displacement (or strain) on food particles, but is instead controlled by energy. Food particles can adhere not only to each other but to the mouth's surfaces. This produces friction. While this is essential for the tongue to grip food particles and move them around the mouth, it also adds to the work that mouthparts must do during processing and may affect sensory perception of food quality. Successful processing of foods in the mouth requires a considerable amount of neural feedback from sensory receptors. We focus here on recent evidence about these sensory receptors with an attempt to reinterpret their role in terms of textural perception.     

STUDY OF FOOD TEXTURES BY RECORDING OF CHEWING AND SWALLOWING MOVEMENTS

Abstract Chewing and swallowing patterns were recorded in three subjects eating freely pieces of foods of various initial textures in an attempt to assess objectively these food textures as sensory stimuli in the mouth. In each phase of masticatory and swallowing movements corresponding to each piece of food, variations were noted differentiating the 16 textures tested. The number of masticatory movements, the time of mastication up to complete swallowing, the time course of the force of mastication and the number and distribution of swallowing movements were found to be the most discriminating parameters. In considering them, foods might be placed on a scale from hard and dry to soft and fluid textures. The results confirm the validity of recording chewing and swallowing movements as a new method for describing the true dimensions of oral sensory stimulations by food textures.     

RHYTHMIC AND IRREGULAR MOVEMENT OF THE FIRST MOLAR WHILE EATING FOODS WITH DIFFERENT TEXTURES

The three-dimensional movement of a tooth, any tooth, while naturally eating, was measured by an apparatus developed in our laboratory. The movement of the first molar on the usually used side is reported here. The mastication movements are divided into two parts, namely the rhythmical chewing period during which there are mastication pressure loads on the molar and the irregularly pulsated moving period in preparation for the swallowing followed by the rhythmical one during which there is no more pressure on it. The amplitudes of the up and down movements of the molar are 10–22mm for the rhythmical chewing period which are bigger than those for the irregularly moving period. The rhythmical chewing periods are distributed around 10–40 s depending on 14 kinds of food texture, and also on the size of the food, in a fairly similar manner for the participants. The period is longer for tough foods and bigger samples. The irregularly pulsated moving periods are widely distributed, 2–45s, and depend both on the food texture and on the participant. The irregular moving periods are longer for foods which scatter in the mouth or adhere to the teeth when chewing. The ingestion difficulty of the food was divided into two groups. One is where it is difficult to break down the food with the teeth and the other is where it is difficult to prepare for swallowing.     

QUALITY OF MEAT PRODUCTS DURING REFRIGERATED AND ULTRA-CHILLED STORAGE

Standard domestic refrigerators store food between 1 and 5C (33.8–41F). A manufacturer recently developed a refrigerator capable of storing food in the “ultra‐chilled region” (?3 to ?7C) and claimed that storage of fresh meat in this region better maintains quality. To understand quality in terms of chemical reaction rates, microbial growth and texture and flavor changes, three common consumer meat products – steak, ground beef patty and salmon – were stored for a selected period of time, as determined by microbial testing, in five refrigerator models with different environmental conditions (constant temperature and temperature fluctuation). At the end of the storage period, consumer panelists assessed the quality of the cooked samples by ranking them according to preference. In addition, instruments were used to measure the color and shear cutting force (for steak only) of each sample. Results from the consumer Ranking R‐Index Test indicate that panelists preferred samples stored under or near ultra‐chilled conditions rather than samples stored under standard refrigerated conditions. The ultra‐chilled samples not only had higher panelist rankings and more favorable comments, but also had lower microbial aerobic plate counts. The instrument readings, however, highly varied and did not correlate well with sensory data.     

Swallowing profiles of food polysaccharide gels in relation to bolus rheology

Swallowing profiles of food polysaccharide gels were investigated in relation to bolus rheology. Polysaccharide gel from either gellan gum or a mixture of gellan gum and psyllium seed gum was used as a model food. Acoustic analysis and sensory evaluation were carried out to investigate the swallowing profiles using the same human subjects. Model bolus was prepared through instrumental mastication using a mechanical simulator to mimic the action of the human jaw in the presence or absence of artificial saliva and was subjected to dynamic viscoelasticity measurements to investigate the rheological properties. Bolus from the binary gel was shorter in time required to transfer through the pharyngeal phase due to mass flow and was scored higher in sensory perceived cohesiveness (bolus forming) than that from gellan gum gel. Model bolus from the binary gel showed a rheologically weak gel (or structured fluid) behavior and was higher in structural homogeneity than that from gellan gum gel. Also, dynamic viscoelasticity parameters of the binary gel were less dependent on the addition level of saliva. Results indicate that the viscoelasticity balance is a key for texture design of dysphagia foods in relation to the saliva miscibility.     

INFLUENCE OF CHEWING EFFICIENCY ON TEXTURE AND FLAVOUR PERCEPTIONS OF FOOD

This study examined the effect of differences in chewing efficiency on selected panellists' perceptions of the stickiness and flavour of cooked pasta. Chewing efficiency was measured by the degree of breakdown of an almond, and weight loss of chewing gum after predetermined numbers of chews. Pasta was cooked for various lengths of time in tomato juice to provide a series of samples varying in texture and flavour. The attributes considered in this study were clearly understood and detected in all of the samples by all the subjects. Nevertheless the subjects differed in the time intensity representations of their perceptions of these attributes. Differences in the efficiencies with which subjects break down food in the mouth may account for the abilities of subjects to distinguish between samples in terms of texture and flavour.     

Texture,sensory and swallowing characteristics of high-pressure-heat-treated pork meat gel as a dysphagia diet

To develop a soft meat product for a dysphagia diet, high-pressure technology was applied. Pressure-heat-treated ground pork meat (PH) was prepared from ground pork mixed with water (ground meat: water, 1:0.5 or 1:1) and salt (1.5%). PH-gels were made from these meat homogenates by treatment at 400 MPa for 20 min, followed by heat treatment. Heat-treated pork meat homogenates (H) were also prepared. The hardness and adhesiveness of the 1:1PH-gel was lower than those of the 1:1H-gel. The PH-gel scored higher in sensory evaluations of elasticity, smoothness and ease of swallowing. Scanning electron micrographs indicated that the superior textural property of the 1:1PH-gel was caused by a network of myosin filaments. Videofluoroscopic examination of swallowing revealed that the 1:1PH-gel was easy to swallow and left little residue in the oropharynx. These results proved the utility of pressurization in creating a dysphagia meat diet.     

Using Sensory Properties of Food to Trigger Swallowing: A Review

The effect of food consistency on swallowing function has been widely studied, and it is well recognized that by delaying the flow of the food bolus, thickened liquids can help in the management of swallowing dysfunction. However, fewer studies have been carried out on the impact of food sensory properties and related liking on swallowing function. This paper reviews the role of taste, olfaction, and trigeminal perceptions on swallowing function and highlights the need for a deeper investigation of this aspect of patient diet modification.     

EFFECTS OF TYPES AND LEVELS OF FAT AND RATES AND TEMPERATURES OF COMMINUTION ON THE PROCESSING AND CHARACTERISTICS OF FRANKFURTERS

ABSTRACT— Frankfurter emulsions containing either 25% or 35% beef fat, pork fat, or cottonseed oil were prepared by comminuting at 1500, 2500, or 5000 rpm to temperatures ranging from 45°–85°F. Data were obtained on the viscosities of the emulsions; except for initially high viscosities for which unmelted fat was responsible, the viscosities of emulsions containing the fats, or oil, were similar: viscosities tended to decrease with increasing time and temperature of chopping. The frankfurters were stuffed, smoked, and cooked, and data were obtained on shrinkage, fat retention, ease of peeling, specific gravity, and texture. Shrinkage was inversely related to content of fat. Fat separation mainly occurred in processing frankfurters containing beef fat; the data suggest that emulsions containing beef fat should be comminuted to 65°–75°F to avoid possible under or overchopping: the results show that optimum conditions were time as well as temperature dependent. The air content of frankfurters varied inversely with the maximum temperature attained during communition. Frankfurter skin strength was lessened on increasing the temperatures to which emulsions were communited; elasticity, the equivalent of rubberiness, decreased under these conditions.