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Control of interactions between lactic acid bacteria and propionibacteria in hard cheese making

The Control of propionic acid fermentation is the key point for improving the quality of hard cheeses including eyes and flavour, but also nutritional qualities, some compounds good for health being produced by propionibacteria during ripening. As cheese-makers control accurately the choice of propionibacteria, the main objective of this project is to improve knowledge and control of interactions between lactic acid bacteria and propionibacteria.

The main results at the end of the second period are:
a model for the test of interactions was built, improved and used at a large scale;
more than 50 pairs of strains of lactic acid bacteria/propionibacteria were used in cheese making;
an alternative conductimetric method, that is rapid and flexible, could be used to test interactions;
inhibitor and activator compounds have been isolated;
the lipolytic activity of propionibacteria strains has been studied in detail;
genetic characterisation techniques (RAPD, PFE) were used to give a better knowledge of the propionibacteria collection;
main pathways of the utilisation of lactates by propionibacteria were studied by 13C RMN;
the accumulation of threalose and glycine-betaine by different strains is a condition for the resistance to high levels of salt in cheeses.

As strong interactions between propionibacteria and lactic acid bacteria are validated, companies which produce cheese starters could be interested in selecting pairs of propionic/lactic starters for cheese makers. These coupled starters could be of great interest as the quality of some emmental cheeses produced with these starters is now well known. Propionibacteria producers are interested in the measure of accumulation of glycine-betaine by propionibacteria as a predictive assay of their resistance to high salt levels in cheeses.

For consumers, it is important to emphasise that the protective influence of propionic acid and the probiotic activities of propionibacteria are two current issues of microbiological research. These bacteria are considered as good for health.


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Biotechnology - Food