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Summary -Using the same microfiltered milk, three 'raw milk' Swiss-type minicheeses were made after addition of three different retentates; one, remaining bacteria-free, was used as reference. The experiment was repeated three times at two different seasons. Factorial discriminant analyses were made on biochemical, physico-chemical and microbiological data at 12 weeks (end of warm storage, 18 "C) and 24 weeks (end of cold storage, 7 "C), At each ripening period, 'raw milk' cheeses were easily and significantly separated from the reference cheese. At 12 weeks, the three 'raw milk' cheeses were separated on the basis of propionic fermentation products, and to a lesser extent on proteolysis and levels of facultatively heterofermentative lactobacilli and starter lactic acid bacteria. At 24 weeks, differentiation was mainly based on proteolysis, since volatile fatty acids and lactate concentrations were nearly the same, irrespective of the cheeses. The same conclusions were drawn for win ter and autumn chee ses. Based on sensory evaluations made at the end of ripening, it was also possible to differentiate between the different 'raw milk' cheeses in winter and in autumn. Reference cheeses were always clearly separated from the other cheeses. The qualitative and quantitative importance of the indigenous microf1ora of milk on the biochemical and sensory characteristics of Swiss-type cheeses has been discussed.Swiss-type minicheese 1 microflora 1 proteolysis 1 volatile fatty acid 1 sensory analysis Résumé -Influence de la microflore du lait cru sur les caractéristiques des fromages à pâte pressée cuite: II. Caractéristiques biochimiques et sensorielles. Des minifromages à pâte pressée cuite ont été fabriqués à partir de lait cru microfi!tré, auquel étaient ajoutés des rétentats provenant de trois origines différentes. Chacun des trois rétentats issus de la microfiltration était réincorporé dans le lait microfiltré de mélange, pour obtenir trois fromages dits au «lait cru». Le lait microfiltré serOral communication at the IDF Symposium 'Ripening and Quality of Cheeses', Besançon, France, February 26-28, 1996. 152 y Demarigny el al vait de témoin. L'expérimentation a été répétée trois fois, en automne et en hiver. Une analyse factorielle discriminante a été effectuée, pour chaque saison, sur les données biochimiques, physico-chimiques et microbiologiques collectées à 12 semaines (sortie cave chaude, 18 "C) et à 24 semaines (sortie cave froide, 7 "C). À chaque stade, les fromages au «lait cru» se différenciaient significativement du témoin. De plus, à 12 semaines, il était déjà possible de caractériser les trois fromages au «lait cru», principalement à partir de leur profil fermentaire, et dans une moindre mesure sur les niveaux de protéolyse et de certaines populations microbiennes (lactobacilles hétérofermentaires facultatifs, bactéries lactiques du levain). À 24 semaines, la différenciation portait essentiellement sur les niveaux de certains paramètres de protéolyse, les concentrations en lactate, acétate et propion...

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Klila, an Algerian cheese produced in steppe and mountainous areas, is proving increasingly popular with consumers. It is traditionally made with ewe, goat or cow milk, leading to a product with high dry matter content (> 90%). In this work, we have characterized three different Klila cheeses made with the three different milks using physico-chemical and microbiological parameters. A triangle test was also performed on naïve consumers, and the three types of Klila were clearly distinguished by sensory analysis. They exhibited distinct features, in particular very low Aw (< 0.5) and pH values (< 4.5) preserving them from pathogens. Lactobacilli and enterococci were counted at low levels (< 4 log (cfu)/g) as well as some spore-forming bacteria (< 3 log (cfu)/g). Colonies were picked from MRS and BEA media. They were identified by sequencing and characterized on their ability to produce lactic acid and using REP-PCR. Lb plantarum was the main species isolated, followed by Pediococcus pentosaceus, Leuconostoc pseudomesenteroïdes and Lactobacillus fermentum. The Enterococcus genus was dominated by Ec durans, Ec faecium and Ec hirae. Among these two main populations, different subgroups were observed by means of the REP-PCR profiles and the lactic acid production of the isolates. Some strains were found in two and even three cheeses. We suppose that these microbes are representative of the environmental context in which Klila is produced.

The citrate metabolism has been extensively studied in lactic acid bacteria (LAB) for its aroma compound production. Among the 4-carbon (C4) by-products obtained from citrate fermentation, diacetyl is one of the better known products for its contribution to the buttery aroma of dairy products. A lot of documents deal with ways to improve diacetyl concentration in food matrices. Apart from these organoleptic advantages, in a microbial ecosystem, the citrate metabolism gives selective advantages to citrate positive microorganisms. Citrate metabolism allows the LAB to use another carbon source for their growth, withstand acidic conditions and generate a "proton motive force" (PMF). Moreover, the citrate/glucid co-metabolism leads to the fast release of organic compounds known for having bacteriostatic effects. Under specific conditions, the C4 pathway liberates diacetyl which is bacteriostatic. In this review we first describe the citrate metabolism and the enzymes involved in the two homo-and heterofermentative LAB Lc diacetylactis and Leuconostoc spp. Moreover, the way to shift the metabolic pathway toward the production of aromatic compounds is discussed for both of these fermentative types of bacteria. Finally, the selective advantages of citrate metabolism for LAB in complex microbial ecosystems are delineated.