A TRIZ-based Creativity Tool for Food Processing Equipment Design

A TRIZ-based Creativity Tool for Food Processing Equipment Design

M. Totobesola-Barbier, C. Marouz�, F. Giroux
CIRAD-AMIS-PAA¹, Equipment and Process Design Laboratory
73, avenue J.-F. Breton
34398 Montpellier CEDEX 5, France
Tel: 33 (0)4 67 61 65 97
Fax: 33 (0)4 67 61 44 15
francois.giroux@cirad.fr

Abstract

This article presents the customizing of TRIZ concepts for the development of a methodology to systematically improve creativity for the search for appropriate engineering principles for food equipment in the context of developing countries. Such methodology is necessary to help generate equipment that are adapted to the socio-economic and technical environment, as often demanded in these countries. The bases of this specific methodology are the TRIZ ideas of using predefined standard or general problems and solutions coupled with the creation and utilization of a structured capitalization of knowledge. They facilitate and lead the search towards a wider panel of potential solutions by nurturing creativity and favoring the transfer, modifications and/or combination of pertinent existing solutions (engineering principles). This tool meets the methodological needs of designers working in a context characterized by scarce investment, lack of knowledge, insufficient scientific information and referential. In this methodology, the standard problem is based on the main function of the equipment to be designed and the specification of the products to be processed. A previous inventory, analysis and classification of existing unit operations in the food industries permitted the predetermination of the categories of main functions and the potential associated principles involved in agro-food processing. The identification of the corresponding standard solutions is facilitated by the use of the same data (function/product specification) in a database purposely created on these principle. This database is a structured referential that orientates and facilitates the search. It also contains additional information on existing applications of the principles. Two examples of application of this methodology are given. This method has been developed in a particular context but it can be used also by SMEs in industrial countries, in order to re-organize TRIZ databases in relation with specific industrial sector.

Key words: creativity, design, developing countries, equipment, food processing, function, TRIZ, unit operations

Introduction

In many developing countries there is an increasing demand for small and medium-scale agro-food equipment for post harvest handling and processing. The necessity to guarantee a good quality and conservation for trade is the main reason to this demand. The offer has been often limited to imported, copied, and adapted equipment designed mainly in developed countries. This offer has been inadequate to the socio-economic and technological context because of its high investment, operating and maintenance costs, high technological level, inappropriate scales and/or its technological features that are not appropriate to products specific to tropical and sub-tropical countries (Odey� Finzi, Berot Inard et al., 1996). To better respond to this need, universities, research centers and development organizations have made efforts at promoting local innovation, but they were insufficient. Small teams of designers were set up to work on design projects, but most members had a background only in mechanics while they should also possess skills in finance, management, agronomy, agro-food process engineering, marketing, and sociology. Consequently, they tended to rapidly generate prototypes based on the engineering principles that they know of (Ndiaye, Marouz� et al., 2001). These prototypes often failed because of insufficient consideration of the other factors that need to be taken into account in design process, and lack of knowledge of the specificity of agro-food products (i.e. biochemical and biological properties, high sensitivity to changes in physical and chemical parameters such as temperature, pH). In addition, the scarcity of investment, the lack of communication in scientific and industrial information, and the absence of appropriate design method have also affected these efforts.

In order to support the local design of agro-food equipment, CIRAD and its partners have developed and validated during the last five years, a specific methodology called CESAM² (Giroux and Marouz�, 1997). The development of the CESAM methodology was based on the study of the traditional design process of equipment in developing countries. This study has allowed the definition of the weaknesses of the traditional approach, the identification of the improvements needed, and that of compulsory stopping-off points for the design trajectory to be successful. The CESAM methodology is based on a multidisciplinary approach and a �concurrent engineering�-type organization of its different phases. It helps in the definition of the objectives, the tools, and the required resources of design projects (Marouz�, 1999). The eight concurrent phases of CESAM are:

Launching of the design project (identification of general objectives, users, team, leader, budget, schedule�)
Analysis of users� needs and state-of-the-art (functional expression of needs, list of relevant existing equipment, state of competition, cost objectives, risk evaluation�)
Searching of engineering principles for the equipment to be designed (use of creativity, functional analysis, knowledge capitalization)
Selection of technical solutions based on predetermined socio-economic, technical and environmental criteria
Equipment definition (definition of parts, assembly�)
Manufacture of prototype
Prototype validation
Equipment distribution (popularization) and project evaluation

Whereas phase 3 (searching of principles) is one of the most important phases, its implementation presented difficulties during the validation of the CESAM methodology by design projects in different countries (Ndiaye, Marouz� et al., 2001). It is indeed a key phase of the design process since it is the transition phase between the statement of the problem and the finding of a solution (Cavalucci and No�l, 2001) -the problems tackled in this article is of the type: �What is the most appropriate engineering principle for an equipment to be designed for a given purpose?�. The phase 3 of CESAM is where ideas of solutions, i.e. potential principles, should sparkle from design teams. Therefore it depends on their creativity. Since creativity is nurtured by knowledge (Ngassa, Bary et al., 2002), the understanding of the basic scientific principles involved in food processing -chemistry, biology, and engineering- helps the generation of new processes and modify existing ones (Earle, 1983). The fact is, design teams� lack of basic knowledge makes difficult the identification and generation of potential principles; hence the need for a design methodology that takes into account these limitations.

This article describes our contribution to facilitate the stage of principle search of the design of agro-food equipment in the context of developing countries. It consists of the development of a TRIZ-based creativity tool focused on engineering principles utilized in food technology. This tool is meant mostly to facilitate the identification and transfer of potential principles from the processing of a product (existing ) to that of another product (versus a transfer from an industrial sector to another as favored in classical TRIZ). The TRIZ approach have been chosen because unlike most creativity tools based on the psychology of the users (e.g. brainstorming, synectics, etc.), TRIZ techniques present the advantage of guiding and facilitating the search for potential solutions (Zusman and Zlotin, 1997). Considering the constraints mentioned and the type of problems to be treated, TRIZ knowledge-based tools such as predefined standard patterns of problems, standard solutions, and scientific effects database (Altshuller, 1984) have been selected and adapted because they are more useful. Besides, the TRIZ method is appropriate to the solving of complex problem. Consequently, it is also helpful in overcoming a complexity that is rather caused by the many limitations than a high technological level (In developing countries, equipment design mostly concerns intermediate level technology.).

This article presents the development and the functioning of a TRIZ-based creativity tool for the search of engineering principles in agro-food equipment design. It includes the following parts:

The formulation of �standard problems³� based on the definition of the principal function of the equipment to be designed and the characterization of the products to be processed to facilitate the identification of all potential solutions (in this case, the potential principles)
The definition of �standard solutions� to lead the search toward pertinent principles that can be directly applied, or modified or combined to generate new ones
The setting up of a database on scientific principles applied in agro-food processing, and existing applications to be used as a reference
The functioning of the methodology for the search of principles in agro-food equipment design

For the development of these components, a collection of relevant information was necessary. For this purpose we undertook an inventory of existing unit operations⁴ in food industries, followed by their functional classification and the statement of the principles involved, as defined in Food Engineering Science (Earle, 1983).

1. Definition of standard problems based on process function and product characterization

For the development of a methodology for principle search, we adapted the first phase of the general TRIZ model (figure 1). This phase consists of analyzing and reformulating specific problems into standard or general problems by replacing all specific terms with generic ones. The use of standard problems facilitates the identification potential solutions by two ways (Salamatov, 1999):

It helps identify a wider range of potential solutions that exist in different scientific fields or industrial sectors, therefore favoring intra- and interdisciplinary transfer of solutions.
It guides the search towards potential specific technical solutions through to the use of predefined standard solutions.

Figure 1: TRIZ general model (Domb, 2001)

Instead of the TRIZ standards (Substance-field models, contradicting technical parameters, and physical contradictions), we propose standard problems that are based on the combination of the main function of the equipment to be designed and a characterization of the raw material to be processed as shown by arrow 1 of figure 2.

Figure 2: Standard problems in the methodology for the search of engineering principles in agro-food equipment design

For example, �How to separate particulate substances of specified sizes and densities from a liquid of a certain characteristics (e.g. density and/or viscosity�)� is the standard problem that corresponds to the specific problems �How to clarify a juice� or �How to stop yeast activity in brewery�. As will be shown in part 2 of this article, the standard solutions that correspond to this standard problem can be the principles of separation based on the difference in nature of the substances to be treated (solid/liquid) and/or the difference in size (among all particulate solids in suspension and molecular substances dissolved in the liquid). These standard solutions will lead to specific technical solutions such as a filtration or centrifugation techniques. The knowledge of these techniques helps generate new technical solutions by their modification or combination

1.1 The functional approach

The functional approach used in this new tool for the definition of the standard problems is the same as in design methodologies such as the value analysis: the function allows the definition of each task in a process or one of its activities in terms of goals and not solutions (CSVA, 2002). It is used to specify the purpose or intended use of a product to be designed (CCE, 1990). Only the principal function is considered. It is defined as the Main Useful Function (MUF) in TRIZ techniques such as function mapping and trimming in comparison to other definitions of function⁵. A system possesses a MUF and any system component which does not contribute towards the achievement of this function is ultimately harmful (e.g. in heat exchanger, the MUF is to transfer heat to the product; everything else in the system is there solely because we don�t know yet how to achieve the MUF without the support of ancillary components) (Winkless, Mann et al., 2002). The other main reason for the use of functionality is because it is a universal concept. It is easier to understand than the TRIZ standards which require learning, more reflection on their meaning, and sufficient knowledge for their interpretation into specific technical solutions (Beaufils, 2000). The advantage of researching and clearly defining the main and necessary functions is to permit greater scope within the creative research field. The more �open� the definition, the better it is. An expression of the functions that suggests solutions reduces this scope (CCE, 1990).

Furthermore, the definition of the function facilitates the sharing and application of scientific knowledge for the processing of a product to that of another within the same industrial sector (the case of food processing industries), and also between widely different industries such as biology and engineering (Vincent and Mann, 2002). The use of our tool aims mainly at facilitating the first type of transfer by creating and using in a logical way a structured referential on existing principles applied in food processing industries. For instance, the principles of membrane filtration are used in dairy products processes for the separation of milk components, in winery and brewery to stop microbial activity by separation of microorganisms. They are also used in chemical engineering for the production of acids and bases by using membrane selectivity to separate and combine the right chemical elements. Examples of interdisciplinary transfer of scientific principles that recently generated several novel food technologies called minimal processing methods include pulsed electric fields, high hydrostatic pressure, pulsed lights or ultrasound, etc. (Fellows, 2000). These new processes that preserve the flavors, colors and nutrients of the products making them closer to fresh products.

The inventory and functional classification of about 160 unit operations mainly used in agro-food processing showed that the functions can be categorized into five main functions presented in table 1.

Table 1: The main functions of unit operations in food processing

Main functionsg⁶	Examples of unit operations
1. Separation	Sorting, cleaning, grading, sieving or screening, peeling, centrifugation, filtration, membrane technologies (microfiltration, ultrafiltration, nanofiltration, reverse osmosis), expression, extraction using solvents, membrane concentration, dehydration (drying), evaporation, distillation, concentration, freeze-concentration, freeze drying
2. Mixing	Solids mixing, liquid mixing (or emulsification using mixers and emulsifiers), liquid and solid mixing
3. Preservation	Dehydration (drying), osmotic dehydration, pasteurization, sterilization, irradiation, blanching, packaging, controlled and modified atmosphere packaging, freezing, chilling, freeze-drying, coating, enrobing, fermentation, pulsed electric fields, high hydrostatic pressure, pulsed light, ultrasound, ohmic heating (direct electrical heating of foods)
4. Transformation with changes in composition	Enzyme technology and fermentation, cooking, baking, roasting, frying
5. Transformation without changes in composition	Size reduction (for fibrous foods: slicing, flaking, shredding, dicing; for dry foods: milling; for liquid foods: homogenization), forming (or moulding)

1.2 Characterization of the products to be processed

The characterization of the products to be processed is also important in leading the search toward pertinent principles, making it more effective and rapid. This characterization can be done by using parameters that are preferably measurable. These parameters can be classified into different categories to specify the properties of foods as shown in table 2.

Table 2: Categories of properties and measurement parameters for food products

Categories of properties	Examples of commonly used parameters
Geometrical	Shape, size, length, volume, etc.
Physical	Density, specific gravity, temperature and pressure of phase changing (e.g. evaporation, freezing, sublimation), color, water activity⁷, rate of heat penetration, etc.
Chemical	pH, redox potential⁸, HLB value⁹, miscibility, molecular composition, moisture content, concentration in components, surface activity, weight average molecular weight distribution, etc.
Rheological	Viscosity, shear rate, flow rate, slip velocity, strain amplitude, relaxation time, etc.
Biological	Enzymatic activity, specific growth rate of microorganisms, etc.

It is recommended to use a limited number of parameters for the search to be manageable. In general, the size and the state (fundamental states such as solid, liquid, gas; and intermediate states such as semi-solids such as colloid, gel, emulsion, foam, and fluids other than liquids¹⁰) are commonly used. Nevertheless, it is recommended to complement these data with pertinent parameters such as density, shape, viscosity, pH, phase transition parameters (temperature, pressure) that specify further the products because a wide panel of engineering principles are based on them. The characteristics of the final product may also be specified to give additional hints for the search of the most appropriate principles. For example, in the case of oil extraction, the principles of separation to be adopted are different according to the quality of the targeted final product (e.g. crude vs. refined oil).

2. The standard solutions and the database on principles involved in food processing

The concept of using standard solutions is used as a link that leads the search towards pertinent principles which can be directly applied, or modified or combined to generate new ones. Actually the standard solutions is based on the same concepts of equipment function and product characterization as shown on figure 3. The search for the standard solution that corresponds to the standard problem at hands is facilitated by the use of the database that has been created to gather in a structured way as much as possible of the principles applied in agro-food processing. This structure starts with the same data on equipment function and product characteristics in order to lead the user to the pertinent existing principles and their applications (figure 3).

3. The database on principles applied in food processing

This database is an integral part of the principle search methodology. It is a referential that gathers and structures information on existing agro-food engineering principles. It contains additional information on existing technical solutions (physical equipment) involving the principles. Thanks to its content and structure, it increases design teams� knowledge and creativity, and it guides their search. It helps the identification of pertinent principles and the generation of new ones by bringing modifications or by combination (Earle, 1983), it also promotes the generation of suitable technical solutions (equipment) by thinking by analogy (Domb, 2001),

This database has also been created to provide a more accessible tool in terms of cost (The TRIZ-based software that include much larger scientific effects databases are still too expensive considering the limiting investment capacities of targeted users). It focuses only on agro-food engineering processes; therefore, it does not favor new transfers of principles from other scientific and industrial areas. Nevertheless, it can be perfectly integrated in multidisciplinary effects databases with a structure based on functions and substance specifications such as that of the software TechOptimizerTM. This possibility of integration will improve the efficiency of our tool when these software will become less costly. At present this integration is only possible for research & development centers, and big companies provided with such software.

Figure 3: Logical use of the database on food processing for the search for principles

The main components of this database are:

a) Main functions of equipment in food processing

As developed in part 1.1 of this article, the main functions define the principal purpose of the equipment to be designed. These main function, therefore, constitute the first component of the database. They are complemented by additional information on specific functions. These specific functions consist of the actions upon specific physical, chemical, geometrical, or biological parameters to realize the principal function. To preserve food for example, these actions can be increasing the temperature of the product at a certain level and maintaining it to for a certain time to ensure the lethality¹¹ on microorganisms, increasing the concentration in preserving agents such as free radicals compounds (such as in irradiation); decreasing pH or temperature, etc.

b) Characterization of substances

As shown in part 1.2 this component of the database contains the second most important information used in this methodology for it permit the location of the standard solution within the database; therefore it is the pointer for the identification of pertinent principles.

c) General principles

These are principles that are common to a group of specific principles. For instance, reduction of water activity include evaporation of water (a phase transfer) and mass transfer as in salting and in osmotic dehydration techniques. Each one of these two general principles regroup a certain number of specific principles. This information is given to indicate that specific principles can be grouped into general principles.

d) Specific principles

These are specific physical, chemical, geometrical, or biological principles that can be applied to realize a function. For example, the specific principles for preservation by reduction of water activity by evaporation include the following:

Energy transfer by contact with heated air or heated surfaces
Energy transfer from light waves (as in sun drying),
Energy transfer from ultrasound waves,
Difference in pressure as in vacuum dryers (pressure below atmospheric pressure),
a combination principles as in freeze-drying and indirect solar drying (the food product is in contact with air heated by solar energy)

e) Existing unit operations and equipment

For each function and principles of realization, a list of existing unit operations and equipment that apply them is given.

f) Operating principle, parameters of control, advantages and disadvantages of the equipment

All unit operations and equipment that realize the same function and use the same principles are grouped together. Then their operating principles, parameter(s) of control, advantages and disadvantages are listed. For example, the function of preservation by reduction of water activity by evaporation, different dryers having different operating principles exist. They include the following:

Hot air dryers which functioning is based on the type of air flow (parallel or co-current flow, counter-current, cross-flow, center-exhaust flow): Bin dryers, cabinet dryers (tray dryers), tunnel dryers, conveyor dryers (belt dryers), fluidized-bed dryers, kiln dryers, pneumatic dryers (pneumatic ring dryers and flash dryers), rotary dryers, spray dryers, and solar dryers
Heated surface or contact dryers which functioning principle is based on conduction: drum or roller dryers, vacuum band and vacuum shelf dryers
Other types of dryers based on other principles: microwave dryers, ultrasonic dryers, freeze dryers, etc

Information on advantages and disadvantages of the different technical solutions are also provided. It consists mostly of a comparison in energy consumption, rapidity, simplicity, flexibility, controllability, processing temperature, pressure, which define feasibility, general energy consumption and effects on foods.

4. The methodology for the search of principles in agro-food equipment design

The sequence of the actions to be realized in this methodology is given in figure 4.

Figure 4: Scheme of the methodology for the search of principles in food processing

Compared to the general scheme of TRIZ, the differences are located in the following points:

The tests 2.1 and 2.2 lead the search either exclusively within the agro-food processing sector by using the database on principles applied in food engineering, or in the other sectors if inter-disciplinary transfer of principles is sought. This can be facilitated by the use of multidisciplinary databases such as in TRIZ-based software when they are available. The two search paths can also be undertaken simultaneously.
Action 4 provides an alternative by reformulating the standard problem in the case that previously defined standards have not led to pertinent principles. This reformulation can be done, for example, by proposing a change in the nature of the product to be processed. This change supposes the necessity of intermediate or ancillary functions.
Action 5 proposes an evaluation of all principles directly identified by using the database and generated by their modification and/or combination. This evaluation is proposed in order to eliminate the principles that are not feasible and to classify the feasible ones taking in account predefined technical, economical and social criteria. The selected principle(s) is then considered for further precision in the following step of the design process (definition of the equipment). Undertaking the evaluation step at the end of this methodology is a way to free users� mind of the feasibility issue during the creativity phase.

Examples of application of the methodology

To illustrate the use of this methodology an example on the search for appropriate principles for an equipment for coconut oil extraction, and an example on the production of starch from cassava are given. Both examples deal with the search of the best potential principles for the main function of separation considering given criteria. At the beginning, we do the hypothesis that ancillary functions in traditional processes are not necessarily useful (e.g. cutting, rasping, etc.), and that other principles still unknown in the coconut oil and cassava industries may improve the traditional processes. We also suppose that only the database on principles applied in food processing is available. The results show that the differences in the characteristics of the products in these examples lead to the identification of some different principles.

Table 2: Examples of application of the methodology

Steps of the methodology	Starch extraction from cassava	Oil extraction from coconut
Standard problem	Separation of molecular size solid that is hydrophilic and sensitive to high temperature (starch), contained in a matrix of fibrous solid substance containing water (the cassava root)	Separation of a hydrophobic liquid (oil) from a matrix of fibrous solid containing water (the coconut meat). The final product desired is crude oil (not refined)
Standard solution (Components a and b of the database)	For both examples, the database on food processing principles does not contain a standard solution leading to principle(s) that directly allows the realization f the main function. There is a need to reformulate the standard problem.
Reformulation of the standard problem (Components a and , b of the database)	The nature of the substances to be separated can be modified in both case in order to identify existing standard solutions; and therefore, identify pertinent principles in the database. In the case of starch extraction, the tuber which is solid, can be transformed into a dry particulate solid (by a rasping or blending or crushing operation, followed by a drying process, and finally a separation by size such as sieving, or by density such as in cyclone), or into a pulp or a suspension which is a mix of particulate solid and a specified water content by rasping, blending and adding water (dilution) followed by all liquid/solid separation techniques. In the case of coconut oil extraction, an existing standard solution which consists of separating two liquids (the emulsion made of oil and water also called coconut milk) that are not miscible is pertinent. However, it requires the realization of a first separation function to eliminate the solid matrix that contains these liquids. Once the emulsion extracted, the water is separated from the oil.
Standard solutions and pertinent principles (Components a,b,c,d of the database)	a) Separation of particulate solid of a certain size contained in another particulate solid of a bigger size (this supposes a first ancillary function of transformation without change in composition (a size reduction by cutting the solid for example) b) separation of particulate solids of a molecular size, hydrophilic, from a mix of particulate solid and liquid (the pulp obtained by ancillary functions of size reduction such as blending, shredding , rasping or crushing for example) c) separation of particulate solids of molecular size, hydrophilic in suspension in an important volume of water (suspension)		a) Separation of an hydrophobic liquid contained in a particulate solid with a given moisture content (this supposes a first ancillary function of transformation without change in composition: a size reduction by cutting the solid for example) b) Separation of a hydrophobic liquid from a mix of immiscible liquids and particulate solid (the pulp of coconut meat obtained by blending, shredding or rasping for example )
Existing, pertinent principles (Components c and d of the database)	a.1) Combination of pressure, difference in nature, size, and weight to separate the starch from the fiber and the water (expression by presses, expellers followed by filtration, sedimentation and weight) as in classical processes a.2) Principle of pectinolytic enzymes and cellulase to degrade the walls of the cells that contains the starch followed by separation by size (filtration) or by weight (sedimentation, centrifugation) a.3) principles of application of high pressure to degrade the structure of the cell walls, followed by principle of filtration b.1) principle of separation by size (screening) preceded by drying to separate the water as in classical dry process b.2) principle of separation by density using air (cyclone) preceded by drying to separate the water b.3) Principle of separation by size of the fibrous solid part by size density or weight (settling) preceded by dilution (adding water) b.4) Principle of separation by settling accelerated by electromagnetic field preceded by an ionization of starch molecules b.5) principle of separation using difference in weight and acceleration (particulate solid/liquid centrifugation)		a.1) Principles of pressure (classical mechanical expression) combined with principle of separation by difference in nature (hydrophobicity) and in density (sedimentation): classical process a.2) Principles in a.1 followed by separation by difference in nature, combined with difference in density and acceleration (centrifugation) a.3) Principle of release of the oil based on the degradation of the cells of the coconut meat by high temperature (boiling) combined with principle of separation by difference in nature (hydrophobicity) and in density (sedimentation): classical process a.4) Principle of release of the oil based on the degradation of the cell walls of the coconut meat by high pressure followed by principle of separation by difference in nature (hydrophobicity) and in density (sedimentation) b.1) Principle of dissolution based on difference in nature (hydrophobicity) such as in extraction by solvent (e.g. hexane), followed by principle of difference in temperature of phase transition to separate the solvent (distillation): classical process b.2) Enzymatic attack of the walls of the cells to release the oil followed by the separation of the residues by difference in nature (filtration) or in weight (centrifugation).
Evaluation and selection of the most feasible principles using socio-economical, technological, and environmental criteria)	Transferable principles: - Principles involved in a.2 can be interesting economically; however, biological principles are more difficult to control than the other principles. - Principle in b.2 is interesting but it has to be preceded by an appropriate drying principle of the pulp which may increase its cost. - Principle in b.5 seems to be the most feasible but it has to be preceded by filtration to separate the fiber.		The principles which transfer seems to be viable are the ones used in a.2, a4 and b.2. The same observations as in the application of these principles for starch extraction are valid

Conclusion and prospective

A TRIZ-based methodology is developed to help the search for engineering principles for the design of food equipment adapted to the technical and socio-economic context of countries where designers are lacking scientific knowledge in food processing, and limited in investment capacities. The development of the methodology is based on the adaptation and integration of the most accessible TRIZ techniques considering the constraints mentioned and the inherent complexity of some TRIZ concepts which will not be used. The selected TRIZ concepts are coupled with the collect and rational use of relevant scientific agro-food processing information. The approach of the methodology combines the reformulation of a specific problem of principle search into a standard problem based on the statement of the main function of the equipment to be designed and the scientific characterization of the product to be processed. This standard problem simultaneously guide and widen the field of the search to all potential principles that can be used to realize a given function (e.g. separation) for the processing of all kinds of products as long as they have the same characteristics (e.g. particulate solids of given sizes or shapes, or liquids of specified densities). The standard solution that corresponds to the standard problem identified is located in the database set up on all principles involved in agro-food processing. The root of this database is indeed made of the same data on equipment main functions and products characterization, which guide the users toward the most pertinent principles and existing applications. The main functions and categories of food products by geometrical, physical, chemical and biological properties have been identified in previous study of unit operations in food industries. The identification of pertinent principles encourages their transfer from the processing of a product to that of another one, and their modification or combination to create new ones for the design of appropriate new equipment considering the predefined technical, socio-economical and environmental criteria. The development of this methodology is at its early stage. The integration of more scientific information such as the principles of hurdle technologies¹² into this methodology is believed to further nurture creativity and the generation of new principles.

This method has been developed in the particular context of food-processing equipment design, made by multidisciplinary design teams in developing countries, but it can be used also by SMEs in industrial countries, in order to re-organize TRIZ databases in relation with their specific industrial sector. Indeed the working conditions of the design teams are often the same ones in the SMEs as in the developing countries: a direct utilization of TRIZ databases is generally to heavy and must be adapted to each industrial sector. The specific needs of developing countries in terms of low cost, limited power, availability of raw materials, etc., are only specific constraints having to be taken into account in the final step of selection of solution.

About the authors

Mireille Totobesola-Barbier, engineer in Agro-food Industries from ENSIA-SIARC¹³ in Montpellier, holds a Master�s degree in Food Sciences from the University of Sciences and Techniques (2002), and in Economics and Management of Agro-food enterprises from the University of Law and Economics in Montpellier (1994). She worked as a research associate at Conservation International in Washington, D.C. (USA) from 1995 to 1997, and at the international research center for tropical agriculture (CIAT) in Latin America from 1998 to 2000.

Claude Marouz�, Ph.D., is a researcher at CIRAD. Dr. Marouz� holds a Ph. D. in �G�nie Industriel� from the Ecole Sup�rieure d�Arts et M�tiers (ENSAM) in Paris.

Fran�ois Giroux , Professor at the ENSIA-SIARC, is a research Associate at CIRAD. Pr. Giroux is also the Director of ENSIA-SIARC11 in Montpellier since 1988.

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Footnotes

French acronyms for � Centre de coop�ration Internationale en Recherche Agronomique pour le D�veloppement, D�partement Am�lioration des M�thodes pour l'Innovation Scientifique, Programme Agro-alimentaire � meaning centre for international cooperation in agricultural research for the tropics and subtropics, department of Advanced Methods for Innovation in Science (AMIS), Agrifood Systems Programme
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French acronym for �Conception d' Equipements dans les pays du Sud pour l'agriculture et l'agroalimentaire, M�thode �
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The technical term � standard problem � is sometimes substituted by � problem model � or � general problem � (Domb, 2001). The same is done with � standard solutions �.
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Food processes are very diverse, but careful analysis shows that they can be broken down into a small number of a series of basic or unit operations (Earle, 1983). These operations are performed by different equipment having the required functions. Some equipment can do various operations or en entire process, they are multifunctional.
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Two function types can be distinguished (Commission, 1990) :

The product�s service functions (those which directly satisfy the users� requirements) : the use functions, the esteem functions, and to explicitly define the benefits that is to be brought to the market.

The technical functions of the product�s elements to describe an existing or envisaged solution.
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Some unit operations may perform combination of two or more useful functions. In these cases, it is recommended to select the most important and relevant function for the formulation of standard problem. The more careful the definition of the main function, the more efficient the search of appropriate principles and definition of specific technical solutions. For instance, the principles of membrane technology in clarification (separation of impurities), concentration (separation of water), and preservation of liquid foods (separation of microorganisms) involve in general a difference in molecular weight and in pressure. However other principles may be combined to these two to achieve more efficiently the main function (e.g. for the membrane separation of microbial cells, spores and/ enzymes, difference in charge between the particulate substances and the membrane are also used to enhance the efficiency of the separation by electrostatic repulsion).
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Water activity is the ratio of vapour pressure of water in a solid to that of pure water at the same temperature (Fellows, 2000).
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Oxidation/reduction potential of food or microbial substrate (Fellows, 2000).
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Hydrophile-lipophile balance : The ratio of hydrophilic to hydrophobic groups on the molecules used to characterize emulsifiers (Fellows, 2000).
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Some solids (for example powders and particulate materials) are termed � fluids � and can flow without desintegration when pressure is applied to them. In contrast, solids deform when pressure is applied to them (Fellows, 2000).
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Lethality is the integrated killing effect of heating temperature and time on microorganisms (Fellows, 2000)
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Hurdle technologies also known as �combined processes�, �combination preservation� or �combination techniques� is the concept of combining several factors to preserve foods. An understanding of the complex interaction of temperature, water activity, pH, chemical preservtives, etc. is used to design a series of hurdles (barriers ) that ensure microbial safety of processed foods (Fellows 2000).
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French Acronym for � Ecole Nationale Sup�rieure des Industries Agro-alimentaires - Section Industries Alimentaires des R�gions Chaudes �. ENSIA-SIARC is a training and research Department of the ENSIA based in Paris. This department focuses on helping food companies in the developing countries, in the mediterranean and the tropical areas.
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