MODELLING SOLID FOOD ORAL PROCESSING USING QUALITY FUNCTION DEPLOYMENT

: This paper shows a model for food oral processing using quality function deployment. Modelling consists of two phases. In the first phase, authors constructed a generic flow chart of solid foods oral processing, based on which five oral processing quality demands were derived. These five characteristics were inputs in the second phase where a house of quality has been constructed translating oral processing characteristics into useful information for research and development of solid food. As a conclusion, authors suggest methods to validate this model with the aid of a qualified sensory panel and results of a consumers’ survey. When validated, this method can be of interest in the product development process, especially for developing special purpose products such as food for denture wearers, food for healthy aging or food for sportsmen.


INTRODUCTION
Epidemic health problems such as obesity, diabetes, and dyspepsia are becoming highly important. Limitations of masticatory performance and food choices may influence nutrient intake and gastrointestinal disorders in the elderly population (Brodeur et al., 1993). It is obvious that the elderly population may have difficulties with oral processing of hard solid foods. The cause of such a situation may be seen in the lack of jaw muscle strength and health of oral apparatus (Kohyama et al., 2003). Veyrune and Mioche (2000) showed that dental status roles the oral processing of meat. Masticatory performance influence gastric emptying rates, and digestion efficiency (Pera et al., 2002). On the other hand, consumer's demands for healthier, yet tasteful food, are growing. Regarding that, food product design and quality modelling should be reconsidered from the customer's viewpoint and newly gained knowledge in food oral processing.
Quality Function Deployment (QFD) dates from the second half of the 20 th century. It was developed in post-WWII Japan, with the aim of better product design and production. In the early years, it was limited only to heavy industry (Costa et al., 2012). QFD is present in the food industry since 1987 (Charteris, 1993). It translates customer requirements throughout different phases of the product's life cycle, ensuring the achievement of quality target values. Akao (2004) saw the QFD as a method that serves to develop a design quality, which aims to translate the customers' requirements into the final quality characteristics. In this way, major quality assurance points should be determined and used in the production process. Thereby, customers' quality demands should be satisfied. In order to transform customer's quality demands, QFD uses matrices, known as houses of quality (HOQ), where the method itself may consist of several matrices. The first idea of the QFD method included four matrices (product planning, product design, production planning and quality planning). The purpose of each HOQ is to translate technical parameters from the previous one into further measurable parameters. Because of the food complexity, QFD application for food product development, in most of the cases included construction of the first HOQ (Benner et al., 2003;de Fátima Cardoso et al., 2015). Main elements of the HOQ are: (i) customer quality demands -WHATs, (ii) quality characteristics affecting customer requirements or technical parameters -HOWs, (iii) relationship between WHAT and HOW, and (iv) target values -HOW MUCH (Djekic et al., 2017). In recent years, QFD has been applied in many cases of food development, such as rice noodle ( On the other hand, food oral processing represents a relatively new field of research in the domain of food science and technology. According to Chen (2009Chen ( , 2014, food oral processing involves a series of actions, including first bite, chewing and mastication, food oral transportation, etc., with the aim of swallowable bolus formation. During this process, ingested food undergoes numerous changes, such as food structure failure, chemical changes related to oral enzymatic digestion, temperature-associated transitions (melting), saliva incorporation and particle agglomeration (Pascua et al., 2013;Stokes et al., 2013). Even though continuous efforts are made by scientists from food, psychology, physiology, dental and clinical studies, and other disciplines, exact mechanisms and governing principles of these oral operations are still not fully understood (Chen, 2009).
Oral processing is important for numerous aspects. Influence of different textures on the oral processing parameters has been shown by Zijlstra et al. Although there is an interest in oral processing consideration within product development, to the best of authors' knowledge, there is no structured method for food quality modelling which includes oral processing parameters.
According to the above mentioned, this paper deals with possible application of QFD. The aim of it is to include oral processing parameters into food product development. Such a solution in the process of quality modelling could contribute to better product design, especially in the case of products intended to special dietary patterns. HOQ provided by this research intends to translate customer's demands on the oral processing parameters of solid (chewable) foods.

Construction of the solid foods oral processing flowchart
Authors of this paper with the experience in the fields of food science, food quality, sensory analysis, and oral processing, took a part in the construction of a solid foods oral processing flowchart. Its construction was based on the following cri-

RESULTS AND DISCUSSION
The first outcome of this paper is a solid food oral processing flowchart (Figure 1). Actions taken by solid food mastication are shown as rectangulars. Hardness perception occurs with the first bite (Duizer and Winger, 2006). The first bite is followed by the first deformation of the food material, after which it extends to the fracture (shown in rhombus). Oral processing continues with the acceptation of a broken piece of food into the oral cavity, after which comminution and bolus formation are taking place. Swallowing thresholds are determined by particle size and saliva incorporation (Engelen, et al., 2005). During all phases of oral processing, complex sensory perception sequences occur.
The second outcome is HOQ (Figure 2). The first room of the presented HOQ (WHATs) has five oral processing quality demands extracted from the oral processing flowchart (Figure 1) bearing in mind work of Costa et al. (2000), who defined these inputs as loose, vague, quantitative statements in the customer's own words, which indicate benefits that customers expect to be fulfilled by the product. Quality characteristics mentioned here were defined based on the previous experimental experience in oral processsing, literature findings and in accordance with solid food oral processing flowchart presented in this paper. However, fine tuning of selected characteristics should be considered depending on product specificities, the intended use of the product and customer's needs.
Rankings of five quality characteristics (product breaks easily with the first bite; it's easy to chew the product; product doesn't require strong strokes; product doesn't require too much time to swallow, and product doesn't require a lot of saliva) are used as inputs for defining weight importance. W i is the weight importance of the 'i' demanded oral processing quality characteristics and should be identified by the customers, mainly through consumers' survey. Relative weight is the percentage of the weight importance divided by the sum of all weight importance, equation 1.

CONCLUSIONS
Application of the proposed method for oral processing modelling remains to be investigated in the future. Due to the food complexity, this flowchart should be validated for all solid (chewable) types of food. Demanded oral processing quality characteristics, or WHATs, need to be adjusted for the product specificities, the intended use of the product and customer's needs. Weight importance of oral processing quality characteristics should be defined through a consumers' survey. R&D oral processing parameters -HOWs presented in this paper should be the same for all types of solid foods. Relationship between demanded quality characterristics and oral processing parameters should be defined using an expert panel with experience in quality modelling, product development (food technologists), and with the understanding of oral processing.

АCKNOWLEDGEMENTS
This paper is a result of the research within the National project TR31034 "Odabrane biološke opasnosti za bezbednost i kvalitet hrane animalnog porekla i kontrolne mere od farme do potrošača" (Selected biological hazards for safety of food of animal origin and control measures from farm to consumer), financed by the Ministry of Education, Science and Technological Development, Republic of Serbia.