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IMPROVEMENT OF THE QUALITY OF THE PRODUCTION OF RAW MILK CHEESES

Objectif

I. GENERAL CONTEXT

A. Advantages and benefits of the COST Action

For some years, specific research programmes have been emerging designed to improve the quality of the production of traditional sheep's cheese, in order to enhance the value of the product and to help to maintain the socio-economic fabric of the regions of production.

These research programmes, which are very few in number, in particular compared with those conducted on cheese from cow's milk, are currently confined to one production area and concern one particular type of cheese.

Moreover, despite the similarity between concerns and research topics, exchanges between the various teams of researchers are often extremely limited.

The latter two points mean that there is at present a dissipation of means and a lack of harmonization of analysis methods and results which might impede the possibility of establishing an overall European policy in this field.

The establishment of a COST programme should enable:

- initially, information networks to be set up which would make it possible, through a synergistic effect, to make national research programmes more effective and to exploit them better;

- later, through the setting up of a working party, research methods and results to be harmonized in order to produce technical development instruments at European level (in particular with regard to the production of cheese from raw milk and démarches in respect of registered designation of origin).

This harmonization of data and methods should make it possible, if appropriate, to set up a European research programme.

B. Description of the current situation

Research specific to milk and sheep's cheese has hitherto been conducted mainly by industrialists in the dairy field working on pasteurized milk. Research topics have therefore concentrated almost exclusively on the study of:

- the physical and chemical properties of milk and their consequences for cheese production technology;

- production problems associated with contamination by flora (problems of milking hygiene and the state of health of ewes), in particular heat-resistant flora.

The characterization of natural microflora in milk has been studied very little, but recent work on microfiltered milk (almost totally devoid of its flora) has shown that the flora has a decisive influence on the flavour of cheese from raw milk.

The progress of research in this field varies considerably between production regions:

France
Many teams, particularly at the INRA (National Institute for Agricultural Research), are working on sensory analysis, and on the microbiology of maturing and the mechanisms by which the taste and texture of cheese (soft or hard) made from cow's, goat's or ewe's milk are formed. Work is under way to identify the effect of non-lactic flora on the flavour of soft interior-ripened cheese and hard pressed cheese.

Spain
The Instituto del Frio and the University of Navarra, together with trade organizations (Consejo Regulador de la Denominación de Origen Queso Idiazabal and Queso Mahon) are carrying out work on isolating strains, sensory characterization and the study of maturing, in particular on goat's milk such as Majorero (Canary Islands) and cow's milk (Mahon).

Switzerland
The federal dairy research centre (Liebefeld-Bern) devotes itself to microbiological and physico-chemical work and sensory analysis in respect of hard pressed cheese.

Austria
Studies relate more particularly to the texture of pressed cheese. A new programme is under way to study the role of milk flora and heat treatment on a traditional cheese, Vorarlberg Käse.

Ireland
The food chemistry and microbiology departments, which have for some time been engaged on research into cheese-making technology, are more particularly specialized in the study of the proteolysis of maturing and the part played by the various enzymatic systems and, inter alia, the effect of lactic and non-lactic flora on proteolysis.

Sweden
The Research Laboratory of the Association of Swedish Dairies, involved in FLAIR and IDF work, is studying in particular the proteolysis of cheese.

Portugal
The dairy industry technology department (milk section) is taking part in European programmes, in particular on the characterization of lactic bacteria (Eclair programme) and is working with the trade on the study on improving the quality of traditional cheese from sheep's milk (Serra da Estrela) or from cow's milk (São Jorge, Azores).

Italy
In Sardinia, the Istituto e Caseario per la Sardegna has already isolated and characterized the strains of Pecorino Romano and Pecorino Fiore Sardo, two registered designation of origin cheeses.

Greece
The Universities of Athens and Salonika are actively engaged in European programmes (FLAIR, Eclair) designed either to develop biochemical sensory characterization methods for cheese, or to establish and characterize collections of strains of lactic bacteria.

With regard to the sensory descriptive analysis of registered designation of origin cheeses, Ossau Iraty, Pecorino Sardo, Idiazabal and Serra da Estrela have assessment grids. At the same time, work undertaken in the context of the Eclair programme on six registered designation of origin cheeses from cow's milk (Comté and Beaufort in France, Parmiggiano Reggiano and Fontina in Italy, Appenzell in Switzerland and Mahon in Spain) have made it possible to develop a guide to analyzing the texture of pressed cheeses [24].

The establishment of descriptors for cheese is under way in the context of the FLAIR programme "SENS" (025/COST 902), in which in particular France, Italy, Spain, Switzerland, Greece and the United Kingdom are taking part. An assessment guide for texture has already been published.

II. OBJECTIVES OF THE ACTION

The main objective of the Action is to establish a communications network enabling exchanges to take place between research teams in various countries working on two particular areas :

- the study of the dominant microflora in milk and traditional raw milk cheeses and its effect on the specific, particularly organoleptic, qualities of those cheeses;

- the sensory characterization of those cheeses.

Those exchanges will make it possible:

- for the various research teams to complement each other and work in synergy, which will facilitate progress in the research referred to earlier;

- a critical comparison of the various analysis methods used in microbiology which should result in harmonization of those methods;

- adaptation of a method of sensory analysis involving, inter alia, the drawing up of a common lexicon of sensory descriptors adapted to raw milk cheeses.

The establishment of the communications network will make it possible in the long term to set up a permanent network of European laboratories involved in the study of registered designation of origin/protected designation of origin cheeses.

The research areas associated with this COST Action relate directly to a quality objective.

Subsequent exploitation of the results will enable not only lactic fermentation agents, but also other bacterial strains, selected for their technological and organoleptic value, to be made available to farm-based or industrial processors. This will represent a significant technical improvement, as their use will make it possible not only to forestall production accidents, but also to preserve, or even affirm, the typical nature of the cheeses. The development of those fermentation agents will therefore make it easier to control the production quality of raw milk cheeses, as regards both the sensory and the hygiene aspects.

Furthermore, the establishment of sensory assessment grids specifically adapted to traditional cheeses, which are necessary for studying the organoleptic value of the strains, will constitute an effective instrument for quality control of the products.

Better control over quality, and a specific characterization of these traditional cheeses will certainly have repercussions from a socio-economic point of view. They will enable better exploitation of the products and a strengthening of the commercial policy governing registered designations of origin.

The possibility of controlling production quality by using selected strains will also help to organize processors on the basis of the collections of lactic bacteria they use. With regard to traditional sheep's cheeses, these various aspects will provide considerable support for production centres which are all situated in rural areas in difficulty (mountain, Mediterranean or island areas).

III. SCIENTIFIC CONTENT OF THE ACTION

The topics on which exchanges will take place may be divided into four largely interdependent areas:

- Study of microflora in raw milk and raw milk cheeses (isolation, identification and characterization);
- Work on the application and adaptation of a sensory analysis method specifically for traditional cheeses;
- Study of the connection between specific microflora and the particular sensory characteristics of those cheeses;
- Study of the possibilities for preparing and utilizing selected fermentation agents with a view to distributing them among processors.

The signatories will be committing themselves to conducting research projects which will enable them to play a constructive part in those exchanges.

As a preliminary to that action programme, and in order to provide a reference framework for the whole initiative, the various parties concerned expressed the wish that a document be drawn up describing the production technologies peculiar to each production area, explaining in particular the stages which, from milking to maturing, can influence the nature and activity of the flora.

A. Study of microflora

(a) Discussion of biochemical and technological methods of isolating, conserving, identifying and characterizing strains;

Isolation of microflora (bacteria, yeasts, fungi) could be carried out using either the milk or the cheese, and at different stages of production and maturing.

The objective being harmonization of the methods used, the working party concerned will compare the methods and techniques employed.

Comparison of isolation methods could be carried out on the basis not only of the nature of the matrices for enrichment and isolation or, where appropriate, of the carrier, but also of procedures for preparing samples, incubation.

With regard to methods of conservation, freeze-drying and deep-freezing (-80 C, -20 C) are currently used. Apart from comparing those methods, a comparison could also be made of the importance of the nature of the medium.

Identification and characterization of the strains can be carried out only by studying various characteristics. The presence or absence of certain characteristics enables the micro-organism to be identified by comparing it with a reference collection of strains.

The characteristics may be:

- phenotypic and biochemical in nature (morphology, colouring, spectrum of sugars utilized, growth, acid production, proteolysis, etc.);

- molecular in nature (study of the genome by methods such as DNA-DNA hybridization, comparison of restriction profiles by pulsed-field electrophoresis; study of the other cell components by methods such as electrophoresis for the characterization of soluble proteins, IR spectroscopy for the characterization of the other cell components, etc.). The large number of characteristics which could permit identification or assessment of the technological value is therefore obvious.

In order to harmonize the methods, the working party concerned will therefore first have to determine the various characteristics used for identification and technological characterization of the strains, and then compare the various methods used for determining those characteristics. In particular, for the technological characterization of the strains, one or more reference matrices will have to be selected.

For those methods of isolating, conserving, identifying and characterizing local strains, there are also plans to study, by means of inter-laboratory trials, the reproducibility of one or more of them by using a reference sample which could also serve as a standard sample.

The harmonization of culturing could be achieved by comparing not only culture matrices, but also incubation methods.

Work already carried out in the context of Eclair programme No 0190, on the isolation and sensory characterization of lactic bacteria from fermented cheese and milk, will serve as a methodological basis.

(b) Drawing up of a common inventory of strains according to their characteristics

The information collected by the participants on their collections of strains will be consolidated and entered in existing data bases available at European level (MINE network). The distribution of strains (free or restricted) will be left to the discretion of the participants.

B. Application and adaptation of a method of sensory analysis and drawing up of notation grids highlighting the particular characteristics of raw milk cheeses.

To attain this objective, a common lexicon of descriptors of the typical characteristics of the cheeses will be compiled and a common tasting method will be devised on the basis of work and results already obtained in the context of the FLAIR programme "SENS" (025/COST 902).

The selection of a term which is both descriptive and discriminant for sheep's cheese will necessitate a survey of the terms currently used in each region by producers, technicians and consumers.

C. Study of the link between specific microflora and the particular sensory characteristics of raw milk cheeses

In order to define the specific effect of raw milk flora on the sensory quality of cheese, two approaches are possible:

- Eliminating the flora by microfiltration and comparing the quality of the cheese obtained from raw milk and from microfiltered milk.

- Eliminating the flora by heat treatment and comparing the quality of the cheese obtained from raw milk and from pasteurized milk.

A combination of these treatments would also be possible.

The second option, however, has the disadvantage of also altering the milk's enzymatic system. Work on the effect of that system (activation of plasminogen, modification of redox enzymes, lipase inhibition) on the flavour of cheese should also be considered by a number of participants.

Test cheeses will be characterized from the sensory and chemical standpoints and compared with traditional cheese.

D. Study of the possibilities for preparing and utilizing selected fermentation agents with a view to distributing them among processors.

The ultimate objective of the programme will be to examine the possibility of developing fermentation agents which will make it possible to control production while still reproducing the particular characteristics of traditional cheeses.

The exchange programme is scheduled for a four-year period and could run as follows :I've used figure boxes for the diagram.
If there's a problem with the vertical spacing, either edit the figure boxes and adjust their vertical position or delete the instructions contained between this comments box and the next comments box.
3 years 1 year
Delete up to here. * : Existence of collection of strains
1 : Work on microbial strains
2 : Work on sensory analysis methods
3 : Study of influence of strains on sensory characteristics of cheese
4 : Work on the feasibility of developing fermentation agents made from selected strains.

IV. ORGANIZATION AND MANAGEMENT OF THE ACTION

The Management Committee, made up of one representative for each signatory country, will meet at least once a year. That representative should preferably be the scientific co-ordinator for the research projects undertaken by the various bodies taking part.

One of the permanent representatives will be responsible for co-ordination between the various countries and therefore for organizing and leading the meetings.

The Management Committee will carry out the tasks set out in Annex I, Section I, point 2 and, more specifically, will be responsible for organizing working parties, seminars, etc. (topic, date, venue, duration, speakers, etc.) on the basis initially of two meetings per year and two seminars for the Action.

As regards the working parties, it would be helpful to establish one specifically responsible for compiling sensory assessment grids enabling the particular features of traditional raw milk cheeses to be highlighted, with separate subgroups for the various types of cheese, in particular sheep's and goat's cheeses. The other working party or parties would concentrate more on the microbiological aspect of the problem.

Within each working party, one member would be made responsible for co-ordination and communication of the results.

These various points will be discussed in detail at the first Management Committee meeting.

Current status
Given that the scope of the project embraces a large diversity of scientific aspects, it was decided to organise six specialised working groups with the following programmes of work :

Microbial Taxonomy : to develop methodologies for the identification and characterisation of non starter micro-organisms growing in raw milk cheeses, with particular emphasis on facultatively heterofermentative lactobacilli.
Microbial Ecosystem : to study the development of micro-organisms during cheese ripening, and their possible influence on cheese quality with three specific items :
Behaviour of predominant groups of micro-organisms during ripening,
interaction between non starter and starter bacteria,
comparison between raw and pasteurised milk cheeses.
Biochemistry : to evaluate and develop methods for the measurement of lipolysis, proteolysis, fermentation products and production of volatile aroma compounds, arising from the activities of the natural milk flora in cheese and to investigate the activity of indigenous heat-sensitive milk enzymes during ripening.
Sensory : to develop a common methodology for cheese flavour analysis and to transfer expertise about cheese texture analysis (from a previous FLAIR/SENS project) to members.
Rheology : to evaluate and validate rheological methods for objective evaluation of texture, and to elaborate a procedure for the identification of cheese quality based on statistical treatment of rheological data and to transfer expertise to members.
Experimental design in cheese technology : to establish general guidelines for conducting experiments in cheese making, and to organise collaborative trials between members having pilot plants, to demonstrate the influence of raw milk flora on cheese characteristics.

Following a questionnaire made among members' countries, an inventory showed that at least 55 on-going or planned projects were relevant to COST 95 Action. Most of these projects were related to traditional raw milk cheeses (cow, goat, ewe) with emphasis on the characterisation of starter and non-starter micro-organisms and their influence on the quality of cheese. Among the different programmes, specific work will be carried out on 22 different varieties of traditional raw milk cheeses (not including cheddar).

Besides several documents already published or in preparation, an original experiment, consisting of making raw and pasteurised milk cheeses using a standardised cheese making protocol and using the same rennet, starter and packaging, was carried out by six different laboratories. The purpose of this trial was to demonstrate the influence of both the origin of milk and pasteurisation on the characteristics of the cheeses.

To date, 15 Short term scientific missions (STSMs) have been carried out. Successful applicants were from Italy (6), Spain (4), Ireland (2), France (1), Portugal (1), Greece (1) and host institutions were from France (5), Switzerland (3), Italy (3), Ireland (2), Scotland (1), Sweden (1). For all these missions, the objectives was to learn analytical techniques in microbiology, biochemistry, rheology and sensory analysis.

It is noteworthy to mention that a strong collaboration was established with the AIR 2039 Concerted Action, making possible the participation of a larger number of experts in the working groups. The acronym "FLORA" is used for the work carried out in collaboration between COST 95 and AIR 2039.
Work planned
Besides the two documents mentioned above, which should be completed in 1997, at least three documents will be produced by the two microbiology groups.
Considering the preliminary results obtained during the first experiment in making cheeses with a standardised protocol a second trial involving all the working groups is planned for 1997.
A final symposium of the Action will be organised in France. It is expected that, in addition to scientific information obtained during the various workshops and cheese making experiments, the results of the works carried in the various countries on the 22 traditional cheese varieties will be reported during this symposium.

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