Objective
A. BACKGROUND
Flavour perception is related to the way aroma is released (or inversely retained) from food systems. Flavour release depends on the nature and concentration of flavour compounds present in the food, as well as on their availability for perception as a result of interactions between the major components and the flavour compounds in the food. Food compositional and structural factors, e.g. as a result of the presence of macromolecules, and eating behaviour determine perception and the extent of flavour release. Knowledge of binding behaviour of flavour compounds in relation to the major food components, their rates of partitioning between different phases, and the structural organisation of food matrices is of great practical importance for the flavouring of foods, in determining the relative retention of flavours during processing or the selective release of specific compounds during processing, storage and mastication.
The major mechanisms likely to occur in flavour release, are (i) specific binding of aroma molecules and (ii) entrapment of these molecules within a matrix. Specific binding can occur for some aroma molecules with proteins (covalent linkage?) or with amylose (complexation). On the other hand, entrapment would mostly affect transport phenomena and hence aroma diffusion throughout the matrix. Additionally, proteins and polysaccharides affect the kinetics of aroma release as they influence the transport of aroma through the food into the air phase. Therefore, the way a food matrix is structured is of great importance to flavour release and flavour perception. In order to understand the phenomena occurring in complex food systems, studies on more simplified systems are required, e.g. homogeneous systems (a macromolecular solution or a gel) or biphasic systems. In the case of a biphasic system, the composition of each phase and particularly a difference in polarity may yield the partition of aroma in the system between the two phases.
Depending upon the nature of these phases, partitioning will make aroma molecules to be preferentially located either in the dispersed phase or in the continuous one. It appears therefore that flavour release should result from a combination of these different events and it is the object of the present programme to understand these overall phenomena in complex aqueous systems by taking into account these mechanisms.
In aqueous food systems polysaccharides and proteins are generally the major components determining the structure of food products. The examination of these macromolecular components is of primary importance in order to follow up the consequences when other smaller molecules, such as aroma compounds, are present. The way these volatile compounds are trapped in food systems will determine flavour release and thus, flavour perception and the appearance of a product to the consumer.
Different mechanisms controlling flavour release are likely to occur in food systems. Diffusion phenomena influenced by the viscosity of the system, unspecific binding or specific bindings to one of the macromolecular components are possibilities for the interactions of flavour molecules within the food matrix. A good knowledge of the matrix is required to understand the flavour release phenomena. The oral processing of food and the evolution of its structure during this phase is an important step to understand the role of the structure in flavour release and perception.
More knowledge in this field is necessary to help the European industry to formulate better food products by choosing the most appropriate flavours, non-volatile ingredients, and processing conditions. This COST Action will be particularly useful to generate knowledge that will allow industry to influence flavour release and retention. This is a very difficult task, which cannot be achieved by simply choosing a different flavour, but is particularly important for low calorie products.
The majority of the studies dealing with this topic takes place in Europe. The study of food structure and its impact on flavour release and perception needs a multidimensional approach that cannot be achieved by isolated teams. Several activities are already going on, which can easily be co-ordinated and integrated to give considerable synergy. So there is a need to organise trans-
institutional activities to co-ordinate the choice of model systems, and to stimulate the integration of now uncoordinated but related activities. The Action would also give more insight into the physical and structural aspects of flavour-texture interactions.
Finally COST seems to offer the best framework for the proposed co-operation because we need above all to improve communication between teams, to allow integration of individual activities/projects, and hence achieve synergy.
B. OBJECTIVES AND BENEFITS
The main objective of the Action is to understand the impact of the structural organisation of food matrices as well as their changes during mastication on flavour release and flavour perception.
This objective can be sub-divided as follows:
- To understand the perception of flavour and texture as a function of composition, structure and physiology.
- To develop appropriate methods to follow the aroma release and perception during oral processing.
- To extrapolate results obtained with simple model systems to food-like models.
- To develop mathematical models which predict the relationship between the structural organisation of food matrices at molecular and meso-structure level, rheology and transport phenomena, flavour release and sensory perception.
- To establish a European network in this area and develop a European project on the relationships between structure, composition and perception in food products.
Secondary objectives can be defined as follows :
- To generate scientific data on the structural organisation of food matrices and interactions with flavour compounds at molecular level.
- To generate scientific data on the structural organisation of food matrices and interactions with flavour compounds at meso-structure level.
- To relate the structural organisation of food matrices to rheology and transport phenomena of flavour compounds.
- To relate the influence of structural organisation of food matrices to flavour release.
- To relate the influence of structural organisation of food matrices to sensory perception
- To develop mathematical models which predict the relationship between the structural organisation of food matrices at molecular and meso-structure level, rheology and transport phenomena, flavour release and sensory perception.
Benefits for the Food industry
- Understanding the relationships between structure, composition and perception will allow industry to make its product development activities much more efficient and effective.
- Methodologies will be developed which industry can apply to its own product development R&D.
C. SCIENTIFIC PROGRAMME
Research efforts in the participating countries will be co-ordinated through this COST co-operation to ensure that duplication of effort is avoided. The COST Action will define a programme of collaboration between the participating scientists, provide guidelines for research and permit the elaboration of an integrated model through studies on complementary model systems and comparison of results.
To reach the objectives, common and complementary model systems have to be defined. The model systems will be polysaccharide-based and/or protein-based, with or without lipids.
After this first phase of the action, different scientific aspects have to be understood and controlled :
1. Molecular level
From all the mechanisms involved in the flavour release and perception phenomena, molecular interactions have a major effect. Examples currently reported in the literature concern specific bindings of aroma compounds with proteins and aroma/amylose complexation. From this consideration, the physicochemical interactions between volatile substances and their environment at the molecular level have to be studied. The main objective of such a molecular level approach would be to contribute to a better understanding of the mechanisms taking place at molecular level controlling the overall release and perception phenomena in complex food systems. Different types of molecular interactions would therefore have to be considered: physical and/or chemical bonding, complexation, lipophilic/hydrophilic interactions, hydrogen bonding, electrostatic effects.
Task 1 : Characterisation of aroma/matrix interactions
After a report on existing data, the determination of the nature of aroma/matrix interactions at molecular scale will be achieved using proven experimental techniques such as spectroscopic methods (Infra Red with Fourier Transform, Nuclear Magnetic Resonance ...) and microscopy techniques (Transmission Electronic Microscopy ; Atomic Force Microscopy).
Task 2 : Molecular modelling of ligand/matrix interactions
Molecular modelling of ligand/matrix interactions using molecular dynamics approach will be developed as a basis for the other levels of the programme.
2. Meso-structure level
Food matrices are mostly multi-components and multi-phasic systems. But they are often defined only by their composition and by macroscopic properties. There is a need to fully understand and control their mesostructure level. The objective of such a mesostructure level approach would be to contribute to a better understanding of the transfer and diffusion phenomena. Different model
systems will be studied taking into account the following aspects : dispersion state and phase distribution of components, supramolecular structures, thermodynamic immiscibility between polymers and interfacial properties. Biopolymers are often used to realise microencapsulation of active substances such as aroma compounds and some structures specific to this application could be of interest for this part of the programme.
Task 1. Characterisation of the key structural elements and the nature of various interfaces
In this task, methodologies will be defined to describe the structural organisation and the interfaces at different levels of organisation. This would allow participants to the different groups of the programme to understand and better control the matrices. The obtained data are to be linked with the rheology data as mesostructure contributes to the rheological behaviour of a matrix. Meso-structure will be studied through various experimental techniques such as rheology, microscopy, calorimetry, laser granulometry, spectroscopic methods, zeta metry, mercury porosimetry, various adsorption techniques, contact angle measurements, specific surface area determination.
Task 2 : Study of the structural changes in food systems as induced by food preparation and food intake
In this task, the structural changes induced by food preparation and food intake (mastication, etc...) will be studied. Links will be established with rheology and sensory perception.
3. Rheology and transport phenomena
Rheological characterisation of the matrices is essential to the programme with different respects: (i) from viscoelastic measurements, it is possible to gain information related to the structure of the matrix (link with meso-stucture level) particularly when dealing with multiphasic systems, (ii) in some cases, changes in the rheological properties may result from interactions between aroma compounds and biopolymers; this is an indirect way for finding evidence for interactions at the molecular level (link with molecular level) and (iii) this will provide a means to control the mechanical characteristics, and hence the texture, of the systems under investigation for flavour release and sensory perception.
Task 1. Rheology.
In this task, common methodologies will be defined to describe the rheological properties of the matrix. This would allow participants to the different groups of the programme to prepare the matrices in a reproducible way. This task can be divided in two sub-tasks : (i) Description of the viscoelastic behaviour of the different matrices that will be chosen (link with the meso-structure level). (ii) Definition of procedures for studying the large deformation (and rupture) behaviour of the matrices (particularly the solid ones)(link with the sensory perception).
Task 2. Transport phenomena.
It is necessary to understand how diffusion of flavour compounds within the matrix is influenced by its structural organisation. From the diffusion coefficient of aroma compounds, it is expected to gain information on their mass transfer in the matrix, an essential information for the understanding of flavour release (link with flavour release). The project aims at improving available techniques to quantify the transport properties of flavour compounds in such systems.
4. Flavour release
Flavour release is controlled by thermodynamic and kinetic components. Macromolecules, such as proteins and polysaccharides containing matrices, can have an influence on both components. The studies in this WG will be focused on the effect of structural organisation of food matrices on flavour release in general, but the effects on the thermodynamic and kinetic component of flavour release will be discriminated.
Task 1. Influence of structural organisation of food matrices on the thermodynamics of flavour release.
The influence of various food structures as a function of polysaccharide and protein type and content on the thermodynamics of flavour release will be determined. The concentrations in the food phase and in the vapour phase of the foods will be analysed under equilibrium conditions. Static headspace gas chromatography and exponential dilution techniques will be applied. With the same techniques, the influence of oral physiological factors (saliva) on the equilibrium concentrations will be studied.
Task 2. Influence of structural organisation of food matrices on the kinetics of flavour release.
In this task the influence of various food structures, as a function of polysaccharide and protein type and content, on the kinetics of flavour release is determined. For in-depth knowledge of the complex kinetics of flavour release from the food systems, various analysis techniques will be used. Analysis techniques directly employed on the food will be used such as dynamic headspace systems combined with gas chromatography, model mouth systems combined with gas chromatography, mass transfer coefficient measurements and diffusion techniques. Furthermore, in-mouth and in-nose analysis will be conducted using atmospheric pressure chemical ionisation mass spectrometry (APcI-MS) and proton transfer reaction mass spectrometry (PTR-MS), buccal headspace gas chromatography, as well as Spit-Off Odorant Measurements (SOOM) and Exhaled Odorant Measurement (EXOM) techniques. Mastication and swallowing behaviour will be studied by electromyography, videofluoroscopy and real-time magnetic resonance imaging. The work will include studies on the interaction of consumers and the food systems, especially the influence of mastication rate and force, saliva flow rate and composition, and breathing patterns. Links will be necessary with the other parts of the scientific programme upstream of this task to control the structure of the studied models and downstream from this task to rely data with sensory perception.
5. Sensory perception
The overall sensory impression of a food is the result of the integrated input of all senses. The sensory work package of this COST Action will focus on the tactile, taste and olfactory contributions to this overall sensory impression. Especially olfactory and texture sensations are complex, and so are their interactions. Nevertheless some general principles are beginning to emerge, among others resulting from COST Action 96 on interactions between food matrices and small molecules. This COST Action will focus on the textural and structural properties of foods, and their interactions with flavour release and flavour, taste and texture perception. This is an important area for the food industry, as a good understanding in this area will allow better and easier translation of consumer wishes into product characteristics, and make the development of new food products more efficient and effective.
The link with the other parts of the scientific programme is evident because sensory measurements allow the translation of physical chemical information in information which is directly linked to consumer perception and appreciation, and vice versa.
Task 1. Development of dynamic sensory methods.
Several methods will be used or developed : Static sensory profiling and quantitation, Time intensity studies, Reaction time measurements, Olfactometry, Sensometrics, modelling.
A great part of the work will be to develop methods concerning the mastication process.
Task 2. Sensory aspects of the structural organisation of food matrices.
Specific questions need to be solved concerning : (i) the relationship between sensory perception and intra-nasal measurements of concentrations of flavour substances (ii) the interaction between volatile and non volatile flavour compounds (iii) interactions between flavour sensations and texture sensations.
The final aim is to answer to the following questions : How can sensory information on flavour-texture interactions best be collected and processed? How do specific structural elements effect texture and flavour sensations and perception?
D. ORGANISATION
The organisation and co-ordination of the COST Action will be assumed by a Management Committee (MC). At the first meeting the MC will appoint the chair and the deputy chair of the MC and the five WGs.
The WGs could cover the different scientific levels previously defined :
Working group
Key words
Molecular level
Molecular modelling - Chemical interactions -
Starch inclusion complexation
Meso structure
Structural elements - dispersions - emulsions - aggregates - interfaces
Rheology and transport phenomena
Viscoelastic properties
Diffusion - Distribution -Mass transfer
Kinetic / thermodynamic
Flavour release
Static and dynamic measurements
- Volatiles / non volatiles
- Oral / nasal
- Headspace
artificial mouth / mouth model
Sensory perception
Retronasal / orthonasal
Dynamic
Oral physiology
Interaction between senses (Texture / Taste / Aroma )
The final goal of this COST Action is to propose an integrated model (help for formulation in the food industry).
F. ECONOMIC DIMENSION
The following COST countries have actively participated in the preparation of the Action or otherwise indicated their interest :
AUSTRIA
BELGIUM
CZECH REPUBLIK
DENMARK
FRANCE
GERMANY
IRELAND
ITALY
NETHERLANDS
NORWAY
POLAND
SWEDEN
SWITZERLAND
UNITED KINGDOM
At least these 14 countries in Europe have ongoing work in the research area described, and are interested by this Action.
On the basis of national estimates provided by the representatives of these countries, the economic dimension of the activities to be carried out under the Action has been estimated, in 2001 prices, at roughly Euro 66 million.
This estimate is valid under the assumption that all the countries mentioned above, but no other countries, will participate in the Action. Any departure from this will change the total cost accordingly.
G. DISSEMINATION PLAN
The aim of this COST Action is clearly to produce a tool for the food industry to develop new products. Then, the target audience for the dissemination of the results of the Action is, first of all, the companies that expressed their interest to this Action.
An e-mail network will be established at the very beginning of the Action to collect data and then will be used to exchange information.
An effort will be done to disseminate information concerning both extensively used methods and new methodologies.
During the Action, all the reports (meetings, workshops, seminars and conferences) will be available through the e-mail network. The establishment of a web-page is also envisaged. Following the obtained results, scientific articles will be published.
Other researchers working in the field will be invited for seminars and conferences.
It is the intention to submit the scientific results to peer reviewed journals and to present them at European and other international meetings.
Also are envisaged
- a layman advisory brochure in 3 languages (English, French and German), to inform food, cosmetic and pharmacology industries and transfer the knowledge acquired during the Action
- Open industrial meetings or seminars for European industry personals (to be arranged in each participating country)
The interested parties will disseminate regular information to the industry through distribution of scientific reports, courses, net-work groups, industrial seminars etc.
Several of the scientists are linked to the FLAIR-FLOW EUROPE Programme. This allows dissemination of scientific work to industry and the establishment of links between research and industry.
Moreover, the interested parties of this programme are involved in higher education institutes or are giving lectures to students from the technician level to the post-doctoral level and so participate to the dissemination of the results of the COST Action. The aim of this COST Action is clearly to produce a tool for the food industry to develop new products. Then, the target audience for the dissemination of the results of the Action is, first of all, the companies that expressed their interest to this project.