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Links to deliverables and publications from FP7 projects, as well as links to some specific result types such as dataset and software, are dynamically retrieved from OpenAIRE .
Exploitable results
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.
In vivo 13c Nuclear Magnetic Resonance (NMR) spectroscopy was used to elucidate the pathways and the regulation of lactate metabolism non-invaively, in living cell suspensions of Propionibacterium freudenreichii subsp. shermanii. Shermanii cells respond to changes in rich medium osmolarity by varying the concentrations specific solutes, and especially glycone-betine, in order to maintain their constant turgor pressure. Implications of such behaviour in cheese technology are discussed.
Forty-two PAB-LAB (propionibacteria/lactobacilli) associations were tested by ITFF-ITG in Emmental cheese making following the make procedure : ripening of partially skimmed milk for 1h at 32 C with Streptococcus thermophilus ITG ST82/87 (ITTFF, La Roche sur Foron, France), 30 min total clotting time, cooking the mixed whey and curd particles for 35 min at 53 C, pressing for 6 h at a temperature decreasing to 30 C, salting for 48h at 12 C, ripening for 15 days at 12 C, followed by 15 days at 15 C and then at least 30 days in the delbrueckii subsp, lactis ITG LL51 and P. freudenreichii ITG P23 were used as reference pair. Pairs from the following list were used in different experiments :Lb helveticus ITG LH41, LH56, LH192, LH1 (from ITFF La Roche sur Foron, France), LHB230 (Valio, Helsinki, Finland), Lb delbruecki subsp, lactis ITG LL51, LL57, LL69, LL205, LL229, LL230, and P freudenreichii ITG P1, P14, P18, P23 from (ITFF Rennes, France) and P131 from Valio. Cheeses were judged by a group of ten experts, normally used by ITFF-ITG in it quality control framework, for odour, smell and texture characteristics.
This study of the quality of 150 Emmental cheeses made with 42 different pairs of LAB/PAB allowed the partners to build a technical typology of pairs PAB/LAB as a function of the level of propionic acid fermentation obtained in cheese. The statistical interpretation of quality data by multifactorial analysis (automatic hierarchical classification, factorial analysis) led to the constitution of statically homogenous groups of cheeses. For example on taste : the multifactorial sensorial analysis allowed us to identify 5 groups of cheeses according to their taste. For example : group 5 with piquant and acid tastes (gathering the cheeses made with the strains ITG LH 56 and ITG P14 or ITG P18); group 1 with cheeses without piquant or a bitter taste made (VALIO P131 and ITG LL51). About texture : the interpretation of the texture score showed that the cheeses are grouped essentially according to the lactobacilli species used. The clearest results were obtained with the odour patterns where cheeses are well grouped according to PAB
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