Cheese ripening room in the Mandailles valley
In the production of raw milk cheeses of designated origin, the manufacturing and ripening stages involve a wide range of microbial flora provided by the natural inoculation of the milk and the surface of the cheese. The Cheese Research Laboratory (URF) at the Clermont-Theix Research Centre in Aurillac conducts research aimed at guaranteeing the safety of cheese while preserving the diversity of flavours and textures. One of its priorities is to examine all types of bacterial communities, from the farm to ripened cheese, using a microbial ecology approach. To achieve this objective, URF places great emphasis on the conservation of the microbial resources of raw milk cheeses both ex situ, through a collection of microbial consortia or pure strains, and in situ, via the maintenance of biodiversity throughout the production chain. Far from being in conflict, these two strategies work together to achieve the URF’s goal.
©INRA, AH. CainCheese of designated origin from the Massif Central region: Saint-Nectaire and Salers. Ripening of Cantal cheese in a ripening room in Auvergne.
Ex situ conservationThe URF ex-situ collection was set up in 1973 in response to a concern expressed by producers of cheeses with PDO (Protected Designation of Origin) status from the Massif Central region of France: the potential disappearance of microbial diversity due to required hygiene measures. The collection aims at preserving the maximum number of individual microorganisms that make up the microbial community of a given cheese ecosystem, including the actual cheese and rinds of such PDO cheeses as Salers, Cantal, Saint-Nectaire, Bleu d’Auvergne and Roquefort. These microbial communities are preserved as microbial consortia or as pure strains after isolation and characterisation of a number of culturable microorganisms in the community. Certain species appear to deal with the stress of conservation methods better as multi-species microbial consortia rather than as pure cultures.
The collections of microbial strains include the following:
- Lactic acid bacteria of the genera Lactobacillus, Leuconostoc, Enterococcus, Lactococcus, Pediococcus and Streptococcus thermophilus; Staphylococcus and coryneform bacteria (Corynebacterium flavescens, Brevibacterium linens, Brachybacterium tyrofermentans, etc.);
- Yeast of the genera Kluyveromyces, Debaryomyces, Saccharomyces, Yarrowia, Candida, Pichia and Geotrichum;
- Moulds of the Penicillium genus or less common species of the Cylindrocarpon genus (characteristic of Saint-Nectaire cheese) or Gymnoascus genus (mould responsible for the uneven aspect of the rinds of Cantal, Salers and Laguiole cheeses).
The strains are identified using a combination of molecular methods. Their capabilities of technological interest, both individual and associated (e.g. in determining flavour or inhibiting pathogens), are also characterised.
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Cheese of designated origin from the Massif Central region: Roquefort.
Penicillium roquefortii: Developed on agar medium and observed under an optical microscope | © INRA, N. Mansion, AH. Cain
and MC. Le Tarnec |
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Putting microbial biodiversity to optimum use
The strains in the collection are selected in order to comply with the need to regulate cheesemaking procedures whilst preserving the specific characteristics of PDO cheeses from the Massif Central region. In 1983, to ensure optimum use of the collections, URF helped set up an interprofessional production laboratory (LIP) for primarily fungal starters in the heart of the Massif Central. The laboratory isolates and reproduces strains to meet the specific requirements of certain cheese manufacturers. In situ conservation
In situ conservation of microbial diversity throughout the chain of production ensures the rich, diverse flavours of traditional PDO raw milk cheeses. It is based on a streamlined approach to implementing production and milk processing practices that favour flora of interest rather than pathogens. Nowadays, molecular biology technology is used to manage microbial diversity from the milk stage to the ripening of cheese. Tools such as Single Strand Conformation Polymorphism (SSCP) allow for in situ characterisation (i.e. characterisation directly in milk or cheese) of microbial communities specific to each product. Bacteria other than lactic acid have thus been identified in raw milk. As yet, little is known of the role they play in cheese. Pooling knowledge within the RESOMIL network
This collection forms an integral part of the network of microorganisms of dairy interest (RESOMIL). It thus benefits from the pooling of scientific knowledge for preserving and managing strains and ensuring they remain harmless.
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Written by :
Marie-Christine Montel, Céline Delbès, Cécile Callon, Catherine Foucaud-Scheunemann
Contacts :
Marie-Christine Montel
Unit :
Cheese Research Unit
Department :
Microbiology and the Food Chain
Label for the news :
Research example
Date of creation : 25/10/2005
Date of last update : 27/10/2005
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