**5. Development of adapted texture-modified foods**

#### **5.1 Sensory evaluation**

Acceptance by consumers of food products is a main priority for the food industry. Development of new products is time consuming and costly. However, the formal study of sensory evaluation of foods is a science with a relatively recent history. As stated by M.A. Drake, sensory evaluation is a "collection of techniques that seek to differentiate between a range of products based on all of their sensory

Like extremely Like very much Like moderately Like slightly Neither like nor dislike Dislike slightly Dislike moderately Dislike very much Dislike extremely

#### **Table 3.**

*9-point hedonic scale [157].*

characteristics and to determine a quantitative description of all the sensory attributes that can be identified, not just the defects" [152]. Methods such as discrimination testing (Is there a difference between 2 formulations?), acceptability (Which food would you prefer? Rating scales of relative dislike and like), descriptive sensory evaluation (How can we discriminate between a range of products based on all of their sensory characteristics?) have provided additional tools for application in research, product development, and marketing [152, 153]. Important developments in the science of sensory evaluation were initially triggered in the U.S. by the desire to optimize food intake in U.S. armed forces [152, 154–156]. With the creation of the food acceptance program in 1945, the U.S. Army Quartermaster Food and Container Institute (Chicago) had four main divisions which were food habit studies, psycho-physiological studies, organoleptic studies and statistical theory. In 1949 and 1950, psychologists David Peryam and Norman Girardot were hired to lead the Food Acceptance Research Branch. As measurement is essential to building comparative datasets, the staple nine-point hedonic scale (**Table 3**) was developed to assess food acceptance and preference [157, 158]. This scale remains in use today to asses customers appreciation of assorted food products such as chips [159], beef sausage using pigeon pea as binding agent [160] or yoghurt [161].

In the past, food development for the treatment of dysphagia customarily stemmed from clinical settings [44, 72, 162]. Researchers state that TMF and TF are deemed to be at the core of the nutritional treatment for dysphagia diets [65, 163], therefore, it is essential to evaluate the sensory profile if optimal ingestion is to be achieved. Limited publications have assessed sensory characteristics of TMF or TF. Pureed peaches [164], pureed carrots [165–167], meats [166, 167], soups, pates and timbales [167] were assessed primarily by healthy young adult for sensory perception. Thickened fluids have been studied more extensively: water with and without barium, lemon flavored water, juices, milk and infant formula [63, 168, 169]. But, even fewer publications have included participants with impaired swallowing [164, 166]. Studies are mainly conducted with the participation of young healthy adults. To be fair, several neurological diseases affect oral expression or comprehension of instructions which could render consumer assessments difficult. However, when recommending approaches to improve nutritional intakes and adherence to a proposed dysphagia diet, customer appreciation—likes and aversions of patients—should be at the core of the plan. More sensory research should be done with TMF and TF to help in developing complete, nutritious, appetizing and varied menu plans.

### **5.2 Rheological evaluation**

Nutritional interventions for the treatment of dysphagia can take various forms and should progress with the medical conditions. Foods are molecularly and

#### *The Nutritional Challenges in Dysphagia: Not Only a Matter of Nutrients DOI: http://dx.doi.org/10.5772/intechopen.105167*

structurally elaborate and diverse. Oral nutritional supplements, texture-modified foods and thickened fluids often require the addition of the texture modifying agents which only adds to the complexity of these matrices. Comparing foods items is challenging in clinical trials. Over time, terminology and assessment methods have been proposed [170]. Two major milestones in the evolution of dysphagia diets development were the National Dysphagia Diet (NDD) [171] in 1999 and the International Dysphagia Diet Standardization Initiative (IDDSI) [39] in 2015.

Based on the work of food scientists Russell H. Mills [172] and Don Tymchuck [173], the NDD was the first diet to propose a quantifiable measure to assess flow of TF. Viscosity ranges were determine to discern different 3 different levels of consistency for fluids. Concepts of food texture such as adhesiveness, cohesiveness, firmness and springiness were also suggested to describe and classify TMF in 3 categories (**Table 4**).

After an extensive literature review and consultation among researchers, clinicians and industry leaders, the IDDSI group propose a more extensive descriptive framework and classification of the liquids with 5 levels to distinguish fluids and 5 levels for the MTF. A gravity flow test using a syringe is propose to measure liquid flow and 4 levels are recommended (**Table 4**). The syringe was preferred to other methods such as shear viscosity measurements or the use of empirical tests such as the Bostwick consistometer [174] or the line spread test due to the accessibility and ease of use of the syringe. But, velocity results obtained for various fluids using the IDDSI syringe and the Bostwick consistometer are unexpected and the discriminating capacity of the IDDSI levels remain to be demonstrated (**Figure 4**). The food texture descriptive parameters are still suggested to explain the MTF. However, other guidelines such as particle size, spoon-tilt test, drip test, fork pressure test and visual cues were added.

Both frameworks had important repercussions in the research and industrial arenas. By proposing a standardized terminology and food classification systems, these approaches helped researchers, clinicians, patients as well as the food industry to classify foods and allow better description of clinical protocols and comparison


*2 International dysphagia diet standardization initiative. 3*

*centiPoise.*

#### **Table 4.**

*Terminology and rheological parameters associated to various levels of dysphagia diets.*

**Figure 4.**

*Bostwick flow test and syringe flow test of common products (AAFC—Saint-Hyacinthe Research and Development Center (Canada)—unpublished data).*

of interventions. Still, clinical trials will be required to assess their impact on nutritional status of patients suffering from dysphagia. The main novelty of these proposed frameworks was the use of rheology.

Rheology is the science of deformation and flow of matter [175]. In the context of oropharyngeal dysphagia, fluids and semi-solid foods are the object of interest. Two (2) extensive reviews helped the understanding of the science of rheology specifically in the perspective of oropharyngeal dysphagia treatment [176, 177].

First, the review published by Gallegos et al. [176] focused on the rheology of fluids. Providing a short review of basic rheological concepts, they present fundamental parameters impacting the flow of fluids such as stress, strain and strain rate (**Table 5**), type of fluids Newtonian, non-Newtonian, viscoplastic fluids as well as time-dependent viscous flow behavior, shear viscosity and extensional viscosity. In light of their work, it becomes evident that a bolus will undergo major pressure and deformation before and during the course of deglutition. The various forces applied (i.e. shear rates) throughout swallowing are challenging to measure and have not been clearly established. For the moment, a shear rate of 50 s−1 is generally used in the


*These variables are temperature, pH, pressure and time dependent in Non-Newtonian fluids. Swallowing imposes a stress on the bolus and deformation of the fluid occurs. The composition of the bolus will influenced its rheological behavior.*

#### **Table 5.**

*Fundamental dynamic and kinematic variables of flow [176].*

*The Nutritional Challenges in Dysphagia: Not Only a Matter of Nutrients DOI: http://dx.doi.org/10.5772/intechopen.105167*

literature. Salivary alpha-amylase and the presence of contrast fluids (barium) are also addressed since their presence impacts the bolus texture parameters and rheological behavior as the bolus is being processed orally prior or during swallowing.

Raheem and colleagues proposed a comprehensive review of the publications addressing the TMF. They present the various tests, both sensory and instrumental, available to the food industry to measure textural characteristics of foods. Similarly to the work done with TF, the rheological assessment of TMF is scare in the literature. According to this review, a better understanding of the complex food matrices used in the nutritional treatment of dysphagia, by all stakeholders, must take place to improve TMF.

#### **5.3 Bridging the gaps**

As early as 1963, Dr. Alina Szczesniak [178, 179] led the food industry in bridging the gap between the emerging technologies of the times and the sensory evaluations of foods. By developing standard rating scale to describe the mechanical characteristics of foods that were now assessed by texturemeters, Dr. Szczesniak demonstrated that although more repeatable and quantifiable, the data obtained for instruments remained insignificant in product development if they were not linked to human assessment and ratings. This vision of correlating instrumental and sensory assessments should inspire more future research in nutritional treatment for dysphagia. The recent 'mouthfeel wheel' terminology should be a step in the right direction [180].
