Summary -The seasonal variations in milk fat composition, especially du ring the grazing period, often lead to poor eye formation in Swiss-type cheese. The influence of free fatty acids on the grow1h and metabolism of the dairy propionibacteria has been studied in this work. Linoleic (C 1B : 2 ), laurie (C 12 : 0 ), myristic (C14:0) and oleic acids (C1B:1) inhibited the growth and acid production of P treudenreichii subsp shermanii in the reference medium. The antibacterial activity of Iinoleic acid can be overcome by additions of cholesterol and soya lecithin to the medium. The four species and !WO subspecies of dairy Propionibacterium could be divided into !WO groups according to their high susceptibility to unsaturated fatty acids (P freudenreichii subsp shermanii and subsp freudenreichit) or low susceptibility (P acidipropionici, P jensenii and P thoeniJ). Nevertheless, this inhibitory action of free fatty acids was not observed in milk, retentate media or lactic curd. A total extraction of the milk lipids led to the recovery of this inhibitory effect on Propionibacterium. The possible modes of action of these molecules are discussed on the basis of the observed potassium effluxes and disturbances in the cell membranes.

Summary -This paper reports results on the esterolytic activity of dairy Propionibacterium. Ali the species present an active esterolytic system on naphthyl substrates for fatty acids which contain < 10 carbons. Setween 1 to 4 activities of different specificities were revealed on non-denaturing polyacrylamide gel electrophoresis for each species. These activity patterns could be very useful in differentiating between a few Propionibacterium species. lon-exchange chromatography allowed 3 main esterase activities to be separated on a concentrated intracellular extract of P freudenreichii subsp freudenreichii. These activities have very different substrate specificities which agree closely with those determined by electrophoresis.esterase 1Propionlbacterium 1fatty acid llipolysis 1cheese Résumé -Activités estérasiques des bactéries proploniques. Les activités estérasiques des bactéries propioniques laitières ont été étudiées. Toutes les espèces possèdent des activités estéra-siques significatives sur des dérivés naphtyl d'acides gras contenant jusqu

The lipase and esterase activities of eight strains of dairy Propionibacteriumfreudenreichii subsp. freudenreichii were studied. A lipase activity was detected on whole cells and in the culture supernatant. The highest activity was expressed at 45°C and pH 6.8. An esterase activity was also detected in the culture medium. The electrophoresis of the intracellular fractions of the cells revealed from three to six different esterase activities. Two esterases were common to all the strains. The substrate specificity was dependent on each esterase, but no activity was revealed, in our experimental conditions, on ester substrates with a chain length longer than that of butyrate.

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-L'emploi des bactéries propioniques lors de la fabrication des fromages à pâtes pressées cuites est actuellement mal maitrisé. Les exigences grandissantes de l'industrie fromagère (en matière de standardisation des procédés) soulèvent d'intéressantes questions concemant l'identification et les réelles propriétés technologiques (modes d'intervention dans l'affinage) des levains propioniques. Cette revue, non exhaustive, présente les résultats obtenus récemment sur l'identification phénotypique et génotypique des espèces ainsi que sur la différenciation des souches. Certaines avancées significatives dans des domaines susceptibles d'avoir des répercussions technologiques sont présentées: activités protéolytiques et autolytiques des bactéries propioniques, production en fermenteur d'acide propionique, mise en évidence de bactériophages infectant P freudenreichii (principale espèce utilisée comme levain en fromagerie). Propionibacterium spp 1 identification 1 taxonomie 1 protéolyse 1 autolyse 1 bactériophage 1 fromage 1acide propionique Summary-Dairy propionic acid bacteria. Propionic acid bacteria are used in Swiss type cheese technology without real control. The increasing demands of the cheese industry as regards standardisation of processes raise interesting questions about the identification and the accurate technological properties of propionic starters. The results obtained recently on phenotypical and genotypical identification of dairy propionic species as weil as a means of differentiation between strains are presented in this non exhaustive review. Moreover, sorne observations relating to the technological use of propionic acid bacteria have been summarized: proteolytic activity, autolysis, propionic acid production and first observation of a bacteriophage infecting P freudenreichii.