Rheological,tribological and sensory attributes of texture-modified foods for dysphagia patients and the elderly: A review

Texture-modified foods (TMFs) and thickened fluids have been used as a therapeutic strategy in the management of food intake in the elderly and people with dysphagia. Despite recent advances in describing rheological features of TMFs for dysphagia management, there is still paucity of research regarding the sensory attributes, therapeutic thickness levels and swallowing safety of these foods. Additionally, the relationship between mechanical and structural properties of TMFs throughout the oral processing is not yet fully understood. The present review discusses several properties of food boluses that are important during oral processing to allow for safe swallowing. Dynamic changes that occur during oral processing of TMFs will be reviewed. The use of hydrocolloids to improve the cohesiveness of TMFs and how this impacts the sensory properties of TMFs will be also discussed. Additionally, this review will suggest potential new research directions to improve textural and sensory properties of TMFs.     

甘薯泥作为吞咽障碍食品的研究进展

质构改良食品作为吞咽障碍患者的安全食品,具有质地柔软、吞咽安全及满足患者营养需求的特点,不同国家对吞咽障碍食品的分级各不相同,大多都聚焦于食品本身的质构特性。近些年,吞咽障碍患者的饮食安全备受关注,开发吞咽障碍食品的研究逐渐增加。甘薯泥是新鲜甘薯经过一系列加工制成的泥状食品,保留了甘薯中绝大多数营养物质,具有柔软、营养成分高的特点,是适合吞咽障碍患者食用的质构改良食品的优质原料。但甘薯泥的质构特性受到多方面因素的影响,例如加工原料、加工工艺以及贮藏条件等,限制甘薯泥作为吞咽障碍食品在食品领域的应用。该文将对质构改良食品的分类、甘薯泥加工工艺及影响甘薯泥质构特性的研究进行综述,旨在为适合吞咽障碍患者食用的甘薯泥产品的研发及应用提供理论依据。     

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.     

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.     

The impact of modification techniques on the rheological properties of dysphagia foods and liquids

Modifying food and the textures of food has been done for decades within the food science and technology field. More recently, modifying the texture of foods has been used to manage swallowing disabilities (dysphagia). Swallowing disabilities are often associated with dehydration and malnutrition, thus nutritional intervention has formed part of serving texture-modified diets. The question remains whether these modification techniques are viable for individuals with swallowing disabilities living in majority world countries. This study used two modification methods on a widely used specialized nutritious food (SNF) to determine whether it may be modified and used in dysphagia management. The techniques had to be ergonomic and economically appropriate for individuals with swallowing disabilities living in majority world countries. The International Dysphagia Diet Standardization Initiative's (IDDSI) standards were used to determine whether the texturally modified SNF is safe for swallowing. Rheological measurements were performed to determine apparent viscosity and structure recovery of each sample. The effects of two modification techniques, aeration and particle separation, on the rheological properties of the SNF were also measured and analyzed. It was determined that both milk and water could be used with this SNF to create a dysphagia diet, but only under certain conditions. The overall results indicated that heating the samples increased the apparent viscosity and exacerbated lumping. Room temperature samples had less lumps and could be classified to the desired levels of the IDDSI (Level 2 and Level 4). Using a whisk to aerate the samples reduced lumps significantly and using a sieve to separate particles of liquid samples eliminated lumps. This study provides new data on how texture modification techniques and the IDDSI framework could be adapted to individuals living in majority world countries. By using modification techniques that are ergonomic and economically viable and an SNF with longevity, this study could be useful in guiding future training of nursing staff and caregivers of individuals living in poverty or resource-constrained communities. This study also adds to the data on the rheological properties of dysphagia foods, although this study did not make use of commercial thickeners generally used in the modification of diets.     

Clinical applications of IDDSI framework for texture recommendation for dysphagia patients

Dysphagia is a highly prevalent eating and swallowing disorder among elderly people, impacting negatively on the health and well‐being of those afflicted. With increasing populations of elderly people, food industries are under growing pressure to produce appropriately texture‐modified food for safe consumption by these vulnerable populations. Recently published International Dysphagia Diet Standardisation Initiative (IDDSI) framework provides a new global guideline on texture modification and standardization for dysphagia patients. This work was designed to test the feasibility of IDDSI framework for clinical applications by assessing the correlation between swallowing capability of dysphagia patients and the IDDSI texture levels. Altogether 26 elderly subjects were recruited and assessed for their dysphagia grades using the Water Drinking Test. Subjects were provided with fluid samples constituted at different consistencies from a commercial product and swallowing performance (time of swallowing, number of swallows, and number of coughs) was monitored and recorded. Correlations among swallowing capability parameters were observed. Most importantly, results from this work clearly demonstrated that the severity of dysphagia by water‐based swallow tests correlates positively with the IDDSI fluid thickness aimed at reducing dysphagia symptoms in those patients, confirming the reliability and feasibility of IDDSI framework for clinical applications.

Practical applications

Swallowing disorder or dysphagia occurs commonly among many elderly people and imposes negative impacts on their health and well‐being. Medical professionals can diagnose eating and swallowing capability in a qualitative manner, but have difficulty in making diet recommendation because of the lack of texture guidance. This work confirmed the feasibility of IDDSI framework for clinical and bedside applications. The correlation between the capability grades of swallowing and IDDSI texture levels established in this work provides a useful measure for such applications.     

Food polysaccharides and roles of rheology and tribology in rational design of thickened liquids for oropharyngeal dysphagia: A review

In today's market environment, an aging society is recognized as one of the megatrends in the world. The demographic change in the world population age structure has driven a huge demand in healthcare products as well as services that include the technological innovation for the health and wellness of the elderly. Dysphagia or swallowing difficulty is a common problem in the elderly as many changes in swallowing function come with aging. The presence of a strong relationship between swallowing ability, nutritional status, and health outcomes in the elderly leads to the importance of dysphagia management in the population group. Modification of solid food and/or liquid is a mainstay of compensatory intervention for dysphagia patients. In this regard, texture-modified foods are generally provided to reduce risks associated with choking, while thickened liquids are recommended for mitigating risks associated with aspiration. In this review, we discuss thickened liquids and other issues including the importance of their rheological and tribological properties for oropharyngeal dysphagia management in the elderly. The review focuses on both commercial thickeners that are either based on modified starch or xanthan gum and other potential polysaccharide alternatives, which have been documented in the literature in order to help researchers develop or improve the characteristic properties of thickened liquids required for safe swallowing. Furthermore, some research gaps and future perspectives, particularly from the nutrition aspect related to the interaction between thickeners and other food ingredients, are suggested as such interaction may considerably control the rate of nutrient absorption and release within our body.     

Sensory properties of thickened and protein-enriched plant-based frozen desserts

The number of consumers following plant-based diets has increased and in turn, the variety of plant-based foods available on the market has also increased. Many plant-based foods aim to mimic the functionality and sensory properties of conventional dairy products; however, they may not be suitable for specific populations. Dysphagia, for example, is a swallowing condition requiring texture-modified foods that meet specific criteria. While many conventional thickened products exist that are safe for individuals with dysphagia, the growing interest in plant-based eating alongside the increasing prevalence of dysphagia prompts a need for research on the use and safety of thickened plant-based alternatives. This study investigated the sensory properties of a thickened protein-enhanced ice cream (dairy and whey) compared to thickened protein-enhanced plant-based frozen desserts (cashew and pea, and coconut and pea). The formulations were evaluated using the International Dysphagia Diet Standardization (IDDSI) Spoon Tilt Test and a sensory trial (n = 104 participants, 47 flexitarians and 57 typical consumers) using static (hedonic scales and check-all-that-apply [CATA]), and dynamic (temporal check-all-that-apply (TCATA)) methods. The dairy and whey sample consistently passed the IDDSI test, while the plant-based samples did not. TCATA identified that the plant-based samples had an increased cohesiveness and adhesiveness, and decreased slipperiness when compared to the dairy and whey sample. The differences in textural properties may explain why the plant-based samples did not pass the IDDSI test. The study identified that although plant-based foods strive to mimic conventional dairy products, they have different textural and flavor properties.     

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.     

Food oral processing—A review

Food oral processing is an essential procedure not only for the consumption and digestion of foods but also for the appreciation and pleasure of food texture and food flavour. The consumption of a food inside mouth involves various oral operations, including first bite, chewing and mastication, transportation, bolus formation, swallowing, etc. Exact mechanisms and governing principles of these oral operations are still not fully understood, despite of continuous efforts made by scientists from food, psychology, physiology, dental and clinical studies, and other disciplines. This article reviews recent progresses and literature findings about food processing and transformation in mouth, with particular attention on the physiology and rheology aspects of oral operations. The physiological behaviour of human's oral device is discussed in terms of biting capability, tongue movement, saliva production and incorporation, and swallowing. The complexity of oral processing is analysed in relation to the rheology and mechanical properties of foods. The swallowing and oral clearing process is also examined for its criteria, triggering mechanism, bolus deformation, and the rheology of swallowing.     

Texture Modification Technologies and Their Opportunities for the Production of Dysphagia Foods: A Review

Dysphagia or swallowing difficulty is a common morbidity experienced by those who have suffered a stroke or those undergone such treatments as head and neck surgeries. Dysphagic patients require special foods that are easier to swallow. Various technologies, including high‐pressure processing, high‐hydrodynamic pressure processing, pulsed electric field treatment, plasma processing, ultrasound‐assisted processing, and irradiation have been applied to modify food texture to make it more suitable for such patients. This review surveys the applications of these technologies for food texture modification of products made of meat, rice, starch, and carbohydrates, as well as fruits and vegetables. The review also attempts to categorize, via the use of such key characteristics as hardness and viscosity, texture‐modified foods into various dysphagia diet levels. Current and future trends of dysphagia food production, including the use of three‐dimensional food printing to reduce the design and fabrication time, to enhance the sensory characteristics, as well as to create visually attractive foods, are also mentioned.     

透明质酸多糖增稠适用于吞咽困难的肠内营养制剂及其流变学性质

胶体增稠的食物流体黏度是吞咽困难饮食护理中的关键参数。这类流体需有较高的黏度和较强的非牛顿流体行为。本研究采用流变学方法表征了透明质酸多糖对含豌豆蛋白和大豆油的营养制剂的增稠效果,研究了增稠营养制剂的流动性质、黏弹性和黏度的剪切时间依赖性。结果表明：未经增稠的营养制剂是表观黏度很低（仅约为0.010 Pa·s）的牛顿流体,不能满足安全吞咽的要求;而透明质酸具有良好的增稠效果,当透明质酸质量分数为0.5%时,营养制剂的初始黏度可达8 Pa·s,增稠后营养制剂具有方便可调节的表观黏度、剪切变稀性质以及良好的黏弹性,流变学性质能满足安全吞咽的要求。     

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.     

Temperature controlled cryoprinting of food for dysphagia patients

Temperature Controlled Cryoprinting (TCC), employs temperature-controlled freezing to generate a desired ice crystal microstructures in each printed voxel, to yield a 3D printed bioproduct with intended microstructure. We introduce the use of TCC, originally developed for tissue engineering, for food manufacturing. TCC was used to make a beef product with anisotropic texture, for people with dysphagia (food swallowing difficulties). The effects of printing, cross-linking order, and directional freezing rates on the microstructure, viscoelastic and textural properties of TCC beef, were examined. Scanning electron microscopy shows that when directional freezing occurred before cross-linking, the microstructure consists of anisotropic alternating ridges of beef material with elongated pores parallel to the freezing direction. Shear stress tests confirmed that the meat had solid-like behavior and textural anisotropy, a desirable property lacking in conventional isotropic dysphagia foods. International Dysphagia Diet Standardization Initiative tests categorize the TCC beef as level 6 (soft and bite-sized) food.Industrial relevanceThe TCC technology can be used to provide texture and anisotropic microstructure to a variety of isotropic food products, such as ground meat, alternative meat or synthetic meat. The TCC technology could be also used for one-step process that combines manufacturing and freezing of foods.     

基于TPA和Vis/NIR的番茄货架期的品质检测

针对番茄货架期的质地变化特点,采用质地多面分析方法(TPA)对番茄货架期的质构参数的变化进行了分析,通过TPA测试方法测得的典型的质构特性曲线,由该曲线计算出番茄的硬度,粘附性,内聚性,弹性,胶粘性,咀嚼性等质构参数,通过对各质构参数间的相关分析得出了相关矩阵表。结果表明,随着贮藏时间的延长,番茄各质构参数都有不同程度的降低,番茄的硬度和内聚性相关关系显著(P0.01),番茄的咀嚼性和其它的质构特性都存在相关关系(P0.05)。根据番茄货架期的质构参数变化规律,将番茄货架期分为货架前期(1~3 d),货架中期(4~6 d)和货架后期(7~9 d)。应用可见/近红外光谱(Vis/NIR)结合主成分分析方法(PCA)对不同货架期的番茄进行了检测分析,基于PC1和PC2的番茄货架期分类率为97%,为今后进一步分析建立水果和蔬菜货架期品质预测模型奠定了理论基础。     

EFFECT OF ADDED SALT ON TEXTURAL PROPERTIES OF HEAT-INDUCED GELS MADE FROM GUM–PROTEIN MIXTURES

Large deformation rheological tests were employed to determine the textural differences in heat‐induced gel systems. Three different large deformation rheological methods (viscosity index and apparent elasticity, texture profile analysis (TPA) and torsional fracture) were employed to study the dependence of the ion type on the textural properties of heat‐induced mixed protein–gum gels. Protein–gum mixed solutions were prepared with bovine serum albumin (BSA) or egg white albumin (EWA) (20% w/v) with κ‐carrageenan (KCG), gellan (GLN) or xanthan gums (XNT) (0.5% w/v) at 0.1 M sodium chloride (NaCl), potassium chloride (KCl) or no added salt. Despite inherent differences in protein type, the main effect on the textural properties evaluated was for the kind of salt added, since potassium ions, with a strong influence on KCG and GLN gelation, affected the parameters related to the structure or hardness of the samples. There was no significant effect on parameters associated with sample ductility or elasticity. GLN formed stronger gels than KCG, whereas XNT did not perform as well in gel formation since it does not contribute to protein matrix formation. The results indicated that potassium may be substituted for sodium ions at low ionic strengths in foods where the incorporation of KCG or GLN helps to improve texture and related features.     

增稠组件在老年吞咽功能障碍患者中的使用

随着我国特殊消费者人群数量的不断增加,市场对增稠组件类产品的需求也在迅速增长。如何对这类产品进行科学有效的规范和管理,引导企业研究开发出满足特殊人群特定营养需求的个性化产品,不仅是生产企业和消费者十分关注的问题,也是监管部门十分紧迫的任务。本文阐述了老年吞咽功能障碍的流行病学、吞咽困难评估方法、增稠组件类产品在老年吞咽功能障碍患者中的使用、增稠流体黏稠程度影响因素、食物质构等级的分类标准和评价方法,提出生产企业依据食物的质构特性,以及不同质构特性产品与不同吞咽困难严重程度患者之间的对应关系,研究设计符合或匹配于目标人群饮食能力的产品,有望成为增稠组件类产品未来的研究方向。     

Effect of saliva on physical food properties in fat texture perception

Sensory properties of food drive our food choices and it is generally accepted that lipids greatly contribute to the sensory properties of many foods and consequently to eating pleasure. Many studies have investigated the mechanisms of the fat perception. Unfortunately they used a variety of methods and products, thereby making generalization very difficult. The mechanism of fat perception in oral cavity is combined of several processes. Lipid composition and its properties strongly influence food structure. During consumption food is exposed to a range of in-mouth processing steps. Oral sensation of fat texture changes with time, from a first bite to chewing, while mixing with saliva, up to swallowing and even after swallowing. The present work reviews many aspects of fat texture perception from physical chemistry to physiology. Understanding the underlying mechanisms of in-mouth lipid processing would provide new concepts to produce low-fat food products with full-fat perception.     

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.