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Four Gram-positive, aerobic, non-sporulating, rod-shaped bacteria isolated from the surface microflora of Reblochon cheese at the late stage of ripening had chemotaxonomic properties characteristic of members of the family Microbacteriaceae. The isolates had virtually identical SDS-PAGE whole-organism protein patterns, shared many chemical and phenotypic characteristics and formed an independent branch in the Microbacteriaceae 16S rRNA gene tree that was most closely related to the type strains of Mycetocola species. The new isolates had chemotaxonomic properties consistent with their classification in the genus Mycetocola but were readily distinguished from recognized members of this taxon based on DNA-DNA relatedness, whole-organism protein and phenotypic data. The combined genotypic and phenotypic data indicate that the isolates should be classified in the genus Mycetocola as members of a novel species, for which the name Mycetocola reblochoni sp. nov. is proposed. The type strain is LMG 22367(T) (=R-20377(T) =BRB-1L41(T) =DSM 18580(T)).

De facon a etudier la relation entre les conditions de production du lait et les teneurs en composes d'interet nutritionnel dans le fromage, il est necessaire de savoir dans quelle mesure la variabilite de composition du fromage depend de celle du lait d'origine. Les effets respectifs de la composition du lait et de la transformation fromagere sur la variabilite de composition du fromage en composes d'interet nutritionnel ont donc ete etudies en conditions reelles de production du fromage et en considerant quatre technologies fromageres differentes. Les caracteristiques nutritionnelles du lait a l'origine du fromage sont soumises a de grandes variations en partie dues a l'espece animale (vache vs. chevre). Mis a part les aspects lies a la teneur en matiere seche du fromage, la variabilite de composition du fromage en acides gras, en β-carotene, en xanthophylles et en vitamine E depend principalement de la composition du lait d'origine, alors que pour la vitamine A celle-ci est influencee a la fois par la composition du lait d'origine et par la transformation fromagere. Par contre, la composition en folates et en mineraux du fromage, ainsi que son potentiel antioxydant total, varient principalement avec la transformation fromagere. Par ailleurs, le type de technologie fromagere exerce un effet important sur la composition du fromage en mineraux et en folates, mais n'a aucun effet sur les autres composes influences par la transformation fromagere. En consequence, la teneur du fromage en composes liposolubles, contrairement aux composes hydrosolubles, depend directement des conditions de production du lait. Le potentiel antioxydant total des fromages a pâte pressee, a la difference de leur lait d'origine, est positivement correle avec certains composes antioxydants liposolubles. Il pourrait par consequent etre influence par les conditions de production du lait.

Certain strains of Staphylococcus aureus (S. aureus) are capable of producing enterotoxins. In dairy products, these enterotoxins are the second major cause of foodborne disease in France. The main objective of this study was to type a selection of enterotoxigenic and non-enterotoxigenic strains of S. aureus using a reliable method, pulsed-field gel electrophoresis (PFGE), to explore the genetic relationships between enterotoxin producing strains in vitro and non-enterotoxigenic strains. Ninety-one enterotoxigenic strains of S. aureus, and 20 non-enterotoxigenic strains, were typed by pulsed-field gel electrophoresis after digestion using SmaI endonuclease. This study revealed a specific profile for the enterotoxin D producing S. aureus strains. Enterotoxin D is one of the enterotoxins most frequently isolated in food-poisoning outbreaks, after enterotoxin A, implicating dairy products. Of the 29 PFGE profiles observed, the enterotoxin producing strains of S. aureus were represented by 24 of these profiles. However, no link was found between the different biotypes and the PFGE profiles. Interestingly, all the in vitro enterotoxin D producing strains were clustered in one pulsotype.

Streptococcus thermophilus is a lactic acid bacterium widely used for manufacturing milk products. The protein composition of three strains of S. thermophilus grown in either M17 me- dium or milk was investigated. These conditions were chosen on the basis of the observed technologi- cal differences between these strains. Protein extracts prepared from cells harvested at the same pH (5.2 ± 0.1), were analyzed by two-dimensional gel electrophoresis. Gel comparison revealed qualita- tive and quantitative differences between the two growth media and between the strains. Some pro- teins with quantitative variation were partially identified. The most significant medium-related differences concerned the number of spots detected and the heat shock protein (GroEL, HSP70) levels which were higher in milk than in M17. On the contrary, the levels of enzymes (proton translocating ATPase, pyruvate kinase, tributyrin esterase, phospho-glycerate kinase, glyceraldehyde-3-phosphate dehydrogenase, fructose diphosphate aldolase, superoxide dismutase) and of a putative penicillin binding protein were lower in milk than in M17. Strain-related differences were accentuated in milk for heat shock proteins, tributryrine esterase and dinitrogenase reductase. Streptococcus thermophilus / milk / proteome / 2D-PAGE electrophoresis

La fabrication des fromages a pâte cuite tel que l'emmental, implique le chauffage du caille entre 51 °C et 54 °C conduisant au developpement exclusif de Streptococus thermophilus. L'electrophorese bidimensionnelle a ete utilisee pour comparer la composition proteique d'une souche de S. thermophilus cultivee dans le lait a sa temperature optimum de croissance (42 °C) et dans les conditions thermiques de fabrication de l'emmental. La souche ITGST82 choisie pour cette etude presente des caracteres technologiques stables et une vitesse d'acidification rapide. Dans les conditions de fabrication de l'emmental, le nombre de spots proteiques detectes est plus eleve (680) qu'a 42 °C (610) et les niveaux d'expression sont significativement differents pour certaines proteines identifiees : la tributyrine esterase (+ 6 fois), la proteine de transport de la glutamine (+ 2 fois), GroEL (+ 5 fois), Hsp70 (+ 2 fois), la phosphoglycerate kinase (- 3 fois), la glycosyl transferase (- 3 fois), la dinitrogenase reductase (- 2 fois). Cette etude a permis d'observer la reponse globale d'adaptation de S. thermophilus aux conditions de fabrication de l'emmental et de reconnaitre des biomarqueurs (proteines) specifiques correspondant a cet etat.

Compared to many cheeses, lipolysis of Emmental is generally low. It concerns about 1-2% of cheese fat and the amount of free fatty acids (FFAs) varies from 2 to 7 g.kg -1 of ripened cheese. In this work, we studied the extent of lipolysis due to propionic acid bacteria (PAB). The re- lease of FFAs during the ripening of Emmental cheeses made from microfiltered milk, with or with- out propionic acid bacteria (PAB) was followed. The usual cooking step in the cheese process (up to 50 o C and 30 min) inactivated the lipoprotein lipase (EC 3.1.1.34) and the main factor in the lipolysis of Emmental cheese was shown to be the lipolytic activity of PAB. This activity was strain-dependent and not related to the production of propionic acid in cheese. The most abundant FFAs were palmitic acid, oleic acid, myristic acid and stearic acid as in milk fat and it was concluded that lipolytic activity of PAB is non-specific. Lastly, an interaction still not elucidated was evidenced between certain PAB strains and thermophilic lactobacilli strains regarding lipolysis extent in Emmental cheese. propionic acid bacteria / lipolysis / free fatty acid / Emmental cheese

Comprehensive collaborative studies from our laboratories reveal the extensive biodiversity of the microflora of the surfaces of smear-ripened cheeses. Two thousand five hundred ninety-seven strains of bacteria and 2,446 strains of yeasts from the surface of the smear-ripened cheeses Limburger, Reblochon, Livarot, Tilsit, and Gubbeen, isolated at three or four times during ripening, were identified; 55 species of bacteria and 30 species of yeast were found. The microfloras of the five cheeses showed many similarities but also many differences and interbatch variation. Very few of the commercial smear microorganisms, deliberately inoculated onto the cheese surface, were reisolated and then mainly from the initial stages of ripening, implying that smear cheese production units must have an adventitious “house” flora. Limburger cheese had the simplest microflora, containing two yeasts, Debaryomyces hansenii and Geotrichum candidum , and two bacteria, Arthrobacter arilaitensis and Brevibacterium aurantiacum . The microflora of Livarot was the most complicated, comprising 10 yeasts and 38 bacteria, including many gram-negative organisms. Reblochon also had a very diverse microflora containing 8 yeasts and 13 bacteria (excluding gram-negative organisms which were not identified), while Gubbeen had 7 yeasts and 18 bacteria and Tilsit had 5 yeasts and 9 bacteria. D. hansenii was by far the dominant yeast, followed in order by G. candidum , Candida catenulata , and Kluyveromyces lactis . B. aurantiacum was the dominant bacterium and was found in every batch of the 5 cheeses. The next most common bacteria, in order, were Staphylococcus saprophyticus , A. arilaitensis , Corynebacterium casei , Corynebacterium variabile , and Microbacterium gubbeenense . S. saprophyticus was mainly found in Gubbeen, and A. arilaitensis was found in all cheeses but not in every batch. C. casei was found in most batches of Reblochon, Livarot, Tilsit, and Gubbeen. C. variabile was found in all batches of Gubbeen and Reblochon but in only one batch of Tilsit and in no batch of Limburger or Livarot. Other bacteria were isolated in low numbers from each of the cheeses, suggesting that each of the 5 cheeses has a unique microflora. In Gubbeen cheese, several different strains of the dominant bacteria were present, as determined by pulsed-field gel electrophoresis, and many of the less common bacteria were present as single clones. The culture-independent method, denaturing gradient gel electrophoresis, resulted in identification of several bacteria which were not found by the culture-dependent (isolation and rep -PCR identification) method. It was thus a useful complementary technique to identify other bacteria in the cheeses. The gross composition, the rate of increase in pH, and the indices of proteolysis were different in most of the cheeses.

La composition microbiologique de 158 echantillons de laits crus de vache preleves a la fin de la traite chez 27 producteurs des departements de Savoie et Haute-Savoie a ete etudiee. Seize groupes microbiens ont ete choisis parmi les groupes d'interet technologique (flore acidifiante mesophile, flore halotolerante, bacteries propioniques…), les groupes d'alteration (Pseudomonas, enterobacteries, Clostridium spp.) ou certains groupes potentiellement pathogenes (staphylocoques a coagulase positive, Escherichia coli). Si en moyenne les laits analyses renferment tres peu de germes (moyenne inferieure a 10 000 ufc.mL -1 ), il est possible de distinguer 5 classes de laits qui different par leur teneur en flore mesophile aerobie revivifiable (de 1 200 a 15 000 ufc.mL -1 en moyenne) et par leur proportion en flore d'interet technologique et en flore d'alteration. Les laits des differentes classes ne possedent pas les memes capacites intrinseques a l'acidification spontanee et a la coagulation. De meme, l'aspect des coagulums obtenus varie. Une enquete realisee chez tous les producteurs lors du prelevement des laits montre que leurs pratiques different pour le lavage du materiel de traite et les soins apportes aux mamelles avant et apres la traite. Ces pratiques et leur combinaison influencent le niveau des populations microbiennes et la proportion entre les flores d'interet technologique et les flores d'alteration.

Qualitative aspect of proteolytic activity of thermophilic lactobacilli using in Swiss cheeses. The average peptidic pattern was established from 253 French Emmental cheeses sampled in 50 factories. It contained 53 peptidic peaks, 4 of which were the most important in quantity. Two Lactobacillus helveticus strains and five Lactobacillus delbrueckii ssp. lactis strains were tested in Emmental experimental cheesemaking in association with three different propionic strains (21 cheeses). The Propionibacterium freudenreichii strains did not affect the peptidic pattern of ripened Emmental cheese. On the other hand, 13 peptidic peaks were significantly influenced by the thermophilic lactobacilli strain. The two species of thermophilic lactobacilli were discriminated by three peptidic peaks. Seven peptidic peaks were correlated with the ammonia amount in ripened Emmental cheese. No significant correlation was found between peptidic peaks and SN/TN and NPN/TN. At the same time, the peptidic pattern produced by the seven lactobacilli strains were stud- ied in laboratory. The most specific peptidic peak of the French Emmental cheese were not found by using the Hammarsten casein as substrate. Another substrate, similar to hard cooked cheeses, lyophilized and sterilized by ionisation was tested. This substrate was obtained with microfiltered milk and Streptococcus thermophilusstrains only. This substrate digested by thermophilic lactobacilli allowed to find the specific peptidic peaks of the French Emmental cheese. For example, the 14th peak obtained in laboratory was significantly different according to lactobacilli species, as it was observed in the Emmental cheese experiments. This peak distinguished the strains inside the Lb. delbrueckii ssp. lactis too. peptidic pattern / proteolysis / thermophilic lactobacilli / Emmental

This work aimed to improve the knowledge and the control of interactions between lactic acid bacteria (LAB) and propionibacteria (PAB) in order to control the propionic acid fermentation in European hard cheeses, and therefore their quality. Among more than 50 couples of strains LAB/PAB used in cheese making, some pairs of strains were chosen in function of quality results on cheeses (sensorial analysis). A whey model system and an alternative conductimetric method, with good reproducibility were used to study interactions. The lipolytic activity of PAB strains varied by a factor 4 to 5. The aroma of ripened Emmental cheese was linked to the level and the type of lipolysis in the cheese, correlated with lipolytic activity of PAB. The main pathways of the utilisation of lactate by PAB, studied by 13 C RMN, were useful to understand the balance between final products: acetic, propionic acid, CO 2 .

Dans l'emmental, deux fermentations se succedent habituellement : la fermentation lactique, puis la fermentation propionique. Parfois, une fermentation indesirable se manifeste : la fermentation butyrique. De multiples micro-organismes concourent a ces fermentations et interagissent : lactocoques, streptocoques et lactobacilles thermophiles, lactobacilles heterofermentaires et pediocoques, bacteries propioniques. Il s'agit donc d'un ecosysteme microbien qui, avec les bacteriophages, possede ses parasites. Les proprietes de chaque groupe microbien, leurs interactions et leurs participations aux caracteristiques finales de l'emmental sont decrites. Elles doivent etre prises en compte pour leur selection et leur emploi comme ferment.

Les aptitudes technologiques des bacteries lactiques thermophiles evoluent au cours des generations. Pour etudier ce phenomene, vingt et une souches ont ete repiquees dans differentes conditions de culture ou l'on a fait varier la nature du milieu et la temperature d'incubation jusqu'a obtenir environ 250 generations. L'activite acidifiante, la resistance au lysozyme, l'activite aminopeptidasique, la sensibilite aux phages et le caractere lysogene des souches ont ete evalues avant, pendant et apres chaque serie de repiquages. L'activite acidifiante est l'aptitude la plus instable : les repiquages a 44 °C entrainent surtout une variation de cette activite mesuree a cette meme temperature lorsque les souches sont cultivees sur bouillon ; les repiquages en cycle thermique type emmental entrainent generalement une augmentation de l'activite acidifiante lorsque les souches sont cultivees sur lait et une diminution lorsqu'elles sont cultivees sur bouillon. Trois origines de variation ont pu etre identifiees : l'heterogeneite clonale des souches, une adaptation transitoire aux conditions de culture et une adaptation par selection de populations stables presentant de nouvelles proprietes par rapport a la souche originelle.

Cheeses were made with Lactobacillus helveticus strain L1, which has high aminopeptidase activity, and two clones (L2, L3), selected for their lack of aminopeptidase activity. Strains L2 and L3 were obtained from L1 by mutagenesis. The differences observed in cheese were essentially due to the variation of the aminopeptidase activity, the only parameter varying according to treatments. The physicochemical analyses of cheeses showed no differences in acidification, moisture of curd, and casein degradation. Differences between ripened cheeses were observed only by sensorial analysis; cheeses made with aminopeptidase-deficient lactobacilli (L2, L3) were more stiff and more bitter than those made with L1. The mutants should not be considered as bitter peptide-producing clones, but rather as allowing an accumulation of this kind of peptides in cheeses. These results explain the bitterness in ripened cheeses made with some strains or species of Lactobacillus (e.g., Lactobacillus delbrueckii ssp. lactis ) that have a very low aminopeptidase activity. Therefore, the aminopeptidase activity must be controlled when strains of lactic acid bacteria are intended for manufacture of cheese.

International audience; Prevalence of enterococci and antibiotic resistance profiles of Enterococcus faecalis was analyzed in 126 French cheeses from retail stores. Forty-four percent of pasteurized or thermised-milk cheeses, and up to 92% of raw-milk cheeses contained detectable enterococci. A total of 337 antibiotic resistant enterococci were isolated in 29% and 60% of pasteurized-milk and raw-milk cheeses, respectively. E. faecalis was the predominant antibiotic resistant species recovered (81%), followed by Enterococcus faecium (13%), and Enterococcus durans (6%). The most prevalent antibiotic resistances were tetracycline (Tet) and minocycline (Min), followed by erythromycin (Ery), kanamycin (Kan) and chloramphenicol (Cm). The most common multiple antibiotic resistance phenotype was Cm Ery Kan Min Tet. The occurrence of antibiotic genes, as searched by PCR, was 100 % for aph3'IIIa, 96 % for ermB, 90 % for tetM and 80 % for catA in isolates resistant to Kan, Ery, Tet or Cm, respectively. MLST analysis of 30 multidrug resistant E. faecalis revealed that ST19, CC21, CC25 and CC55 isolates were the most common in cheeses. In conclusion, as in many other European countries, French cheeses do contain enterococci with multiple antibiotics resistances. However, low occurrence of high-level gentamicin resistant or sulfamethoxazole/trimethoprim-resistant enterococci and absence of vancomycin- or ampicillin- resistant enterococci indicate that cheeses cannot be considered as a major reservoir for nosocomial multi-drug resistant enterococci.

The purpose of the present study was to characterize the development of Listeria monocytogenes on wooden shelves used for cheese ripening. The fate of two L monocytogenes strains was analysed over time as a function of the presence of a native biofilm, the farmhouse origin of cheeses, and the wooden shelves properties. In presence of a native microbial flora on the shelves, deposited populations of L monocytogenes remained stable or even decreased by up to 2 log(10)(CFU/cm(2)) after 12 days of incubation at 15 degrees C in all tested conditions. By contrast, L monocytogenes populations increased by up to 4 log(10)(CFU/cm(2)) when the resident biofilm was thermally inactivated, suggesting a microbial origin of the observed inhibitory effect. All together, our results suggest that the biocontrol of pathogens multiplication on wooden shelves by resident biofilms should be considered for the microbiological safety of traditional ripened cheeses. (C) 2011 Elsevier Ltd. All rights reserved.

International audience; Little work has been carried out on the microbiology of wooden shelves supporting cheese during ripening, and the safety of their use during cheese ripening has frequently been asked. Microbial characterization (enumerations on specific growth media) and description of their physicochemical conditions (pH, water activity, and salt concentration) were determined on 50 wooden shelves of 3 different ages at the end of the cheese-ripening process, using cheeses from 8 farm producers. The experiments were performed during 2 different seasons (summer and autumn). Micrococci-corynebacteria and yeasts and molds were found to be the dominant microflora on the shelves. Leuconostocs, facultative heterofermentative lactobacilli, enterococci, staphylococci, and pseudomonads were also found but at lower levels. There was no statistical difference in the major microflora between shelves of different ages. Moreover, the total counts and the predominant microflora showed a surprising homogeneity between origins of cheeses. For most of the microflora enumerated, no seasonal variation was observed. Regardless of the age of the shelves, the wood had high water activity values (0.94 to 0.97), neutral pH values (7.1 to 8.3), and low salt contents (0.11 to 0.17 mg/cm2). The origins of the cheese had a statistically significant impact on water activity, pH, and salt concentration, whereas the age of the shelves did not influence these parameters. This study demonstrated the stability of the technological biofilm present on wooden shelves and will serve to enlarge the debate on the use of wood in cheese ripening.

International audience

Congélation de micro-organismes d'intérêt laitier : optimisation des conditions d'adaptation des souches avant congélation et des conditions de remise en culture après congélation

International audience; Conjugated linoleic acid (CLA), and especially rumenic acid, are isomers of linoleic acid which have a great potential in human nutrition for their beneficial properties. The most important sources of natural CLA are milk and dairy products such as cheese. This study was delineated to assess the effects of sampling according to the cheese wheel, the seasonal and regional influence on CLA content in French Emmental cheese and, finally, the effects of culinary preparation of three different dishes (gratin, béchamel sauce and cheese fondue) and processed cheese. The rumenic acid content of Emmental cheese varied between 0.6% and 1.5% of total fatty acids according to the season and region of production, and appeared homogeneous through the cheese wheel. The culinary utilization and processing did not change the rumenic acid content of Emmental cheese.; Les isomères conjugués de l'acide linoléique (CLA) et, en particulier, l'acide ruménique (C18:2 9 cis 11 trans) possèdent des effets bénéfiques d'un grand intérêt en nutrition humaine. Le lait et les produits laitiers, tels que les fromages, sont d'importantes sources naturelles d'acide ruménique. Ce travail avait pour but d'en établir la répartition au sein de la meule de fromage, d'étudier l'influence de la saison et de l'origine régionale sur la teneur en CLA de l'Emmental français et enfin, de mesurer les effets de son utilisation, soit en cuisine dans la préparation de sauce béchamel, de gratin et de fondue, soit dans la fabrication de fromage fondu. La teneur de l'Emmental français en acide ruménique varie de 0,6 % à 1,5 % de la teneur totale en acide gras selon la saison et la région de production, elle est homogène au sein de la meule de fromage. Aucune modification significative de la teneur en CLA n'est observée lors de l'utilisation de l'Emmental, aussi bien pour les trois préparations culinaires que pour la fabrication de fromage fondu.

Les relations entre les conditions de production du lait et les teneurs en composés d'intérêt nutritionnel de fromages fermiers au lait de vache ou de chèvre ont été étudiées en conditions réelles de production au sein de 4 filières fromagères (Abondance, Tomme de Savoie, Salers/Cantal et Rocamadour). Au total, 432 fromages, dont 306 au lait de vache et 126 au lait de chèvre, produits tout au long de l'année par 74 producteurs fermiers ont été analysés. Dans un premier temps, les effets respectifs des conditions de production du lait et de la transformation fromagère sur la variabilité de composition du fromage ont été quantifiés. Dans un second temps, les relations entre la composition du fromage et les conditions de production du lait, préalablement identifiées au moyen d'enquêtes, ont été étudiées. Le fromage fermier se caractérise par une grande variabilité de composition qui dépend majoritairement de la transformation fromagère pour la vitamine B9 et les minéraux et des conditions de production du lait pour les acides gras (AG), les vitamines A et E et les caroténoïdes. L'espèce animale explique une grande partie de la variabilité en certains AG et en b-carotène dans le fromage. Les teneurs en micronutriments liposolubles et le potentiel antioxydant du fromage dépendent principalement de la nature de la ration fourragère (pâturage vs fourrages conservés) quelle que soit l'espèce animale. Les rations à base de pâturage sont associées à des teneurs en caroténoïdes et en vitamines A et E et à un potentiel antioxydant dans le fromage plus importants. En revanche, les facteurs de variation du profil en AG du fromage ont différé dans cette étude entre les vaches et les chèvres. Pour les fromages au lait de vache, il dépend principalement de la nature de la ration fourragère (pâturage vs fourrages conservés). Les fromages associés au pâturage sont plus riches en AG saturés et insaturés à longue chaîne (³ C18) et plus pauvres en AG saturés à courte et moyenne chaîne (C6:0 à C16:0). Le profil en AG du fromage au lait de chèvre dépend principalement de la proportion de matières grasses apportées par les concentrés dans la ration, du stade de lactation des animaux et dans une moindre mesure de la présence ou non de lin dans les concentrés. Ce fromage est plus riche en AG à longue chaîne et plus pauvre en AG saturés à courte et moyenne chaîne lorsque la proportion de matières grasses apportées par les concentrés est plus importante, les concentrés contiennent du lin et les animaux sont en début de lactation. En conclusion, ce travail a permis de collecter des données représentatives et détaillées sur les caractéristiques nutritionnelles de différentes variétés fromagères et de hiérarchiser les effets des principaux facteurs de production responsables de la variabilité de composition du fromage., The relationships between the conditions of milk production and the contents of components of nutritional interest in cow's or goat's milk farmhouse cheeses have been studied under real conditions of production in four cheese chains (Abondance, Tomme de Savoie, Salers/Cantal and Rocamadour). In total, 432 cheeses, including 306 cow's milk ones and 126 goat's milk ones, produced throughout the year by 74 farmhouse producers, were analysed. First, the respective effects of the conditions of milk production and the cheese-making process on the compositional variability in cheese were quantified. Subsequently, the relationships between the cheese composition and the conditions of milk production, beforehand identified by means of surveys, were studied. Farmhouse cheese was characterized by a great compositional variability which mainly depended on the cheese-making process for vitamin B9 and minerals and on the conditions of milk production for fatty acids (FA), vitamins A and E and carotenoids. The animal species explained a great part of the variability in some FA and b-carotene contents in cheese. The contents of fat-soluble micronutrients and the antioxidant capacity in cheese mainly depended on the nature of the fodder ration (pasture vs. preserved forages) whatever the animal species. The pasture-based rations were associated with higher levels of carotenoids, vitamins A and E and antioxidant capacity in cheese. On the other hand, the influencing factors of the FA profile in cheese differed in this study between cows and goats. As regards cow's milk cheeses, it mainly depended on the nature of the fodder ration (pasture vs preserved forages). Cheeses associated with pasture were richer in long length saturated and unsaturated FA (³ C18) and poorer in short and medium length saturated FA (C6:0 à C16:0). The FA profile of goat's milk cheese mainly depended on the percentage of fat from the concentrates in the ration, the stage of lactation of animals and to a lesser extent the presence or not of linseed in the concentrates. This cheese was richer in long length FA and poorer in short and medium length saturated FA when the percentage of fat from the concentrates was higher, the concentrates contained linseed and the animals were in early lactation. In conclusion, this work allowed to collect representative and detailed data on the nutritional characteristics of various cheese varieties and to hierarchy the main production factors responsible for the compositional variability in cheese.

The relationship between C. tyrobutyricum, C. sporogenes and C. beijerinckii in experimental cheese conditions, and their influences on late-blowing and butyric fermentation, have been investigated. A molecular approach using a PCR-TTGE method in combination with conventional methods, such as microbiological and physico-chemical analysis, was performed to monitor the evolution of these clostridial species, simultaneously with the occurrence of cheese defects. Sixteen Emmental type cheeses were produced from milk inoculated with different clostridial spore associations. In all cheeses inoculated with C. tyrobutyricum, obvious signs of late blowing were detected. In cheeses inoculated with C. beijerinckii or C. sporogenes, a formation of holes in cheese body was observed, with a concomitant slight amount of butyric acid production. Even though C. beijerinckii and C. sporogenes were less metabolically active and less numerically important than C. tyrobutyricum in cheese as shown by TTGE profiles, the association of these species to C. tyrobutyricum enhanced the butyric fermentation and the cheese defects. The level of butyric content in ripened cheese increased to 268 mg 100 g− 1 in presence of C. tyrobutyricum, and reached a maximum of 414 mg 100 g− 1 in presence of the C. beijerinckii–C. tyrobutyricum (1:10) association. The propionic fermentation was also higher in cheese inoculated with C. tyrobutyricum, and was slowed down in presence of C. beijerinckii and C. sporogenes. From 30 days of ripening, a strong correlation between the chemical contents and the intensity of cheese defects was demonstrated. A chemical analysis of cheese associated with a molecular method for microbial spoilage investigation allows the prediction of the level of late blowing at early stages of ripening, and the understanding of the origin of the defect.

A nested-PCR temporal temperature gradient gel electrophoresis (TTGE) approach was developed for the detection of bacteria belonging to phylogenetic cluster I of the genus Clostridium (the largest clostridial group, which represents 25% of the currently cultured clostridial species) in cheese suspected of late blowing. Primers were designed based on the 16S rRNA gene sequence, and the specificity was confirmed in PCRs performed with DNAs from cluster I and non-cluster I species as the templates. TTGE profiles of the PCR products, comprising the V5-V6 region of the 16S rRNA gene, allowed us to distinguish the majority of cluster I species. PCR-TTGE was applied to analyze commercial cheeses with defects. All cheeses gave a signal after nested PCR, and on the basis of band comigration with TTGE profiles of reference strains, all the bands could be assigned to a clostridial species. The direct identification of Clostridium spp. was confirmed by sequencing of excised bands. C. tyrobutyricum and C. beijerinckii contaminated 15 and 14 of the 20 cheese samples tested, respectively, and C. butyricum and C. sporogenes were detected in one cheese sample. Most-probable-number counts and volatile fatty acid were determined for comparison purposes. Results obtained were in agreement, but only two species, C. tyrobutyricum and C. sporogenes , could be isolated by the plating method. In all cheeses with a high amount of butyric acid (>100 mg/100 g), the presence of C. tyrobutyricum DNA was confirmed by PCR-TTGE, suggesting the involvement of this species in butyric acid fermentation. These results demonstrated the efficacy of the PCR-TTGE method to identify Clostridium in cheeses. The sensitivity of the method was estimated to be 100 CFU/g.

International audience; The relationships between the texture and composition of Abondance cheese (Haute-Savoie, France) and the milk used for its production, were investigated under real conditions of cheese production. Ten different types of pasture, exploited by three producers, were involved. Milk characteristics, linked to the type of pasture, affected cheese texture, as did the cheesemaking process. Cheeses from milk produced on mountain pastures (M, n = 5, 1 500-1 850 m) exhibited different rheological properties from those produced with milk from valley pastures (V, n = 5, 850-1 100 m): they were less elastic and less deformable. Rheological characteristics were mainly linked to the proportion of 18 atoms of carbon unsaturated fatty acids, which was higher in M milks, and to the proteolysis of cheese. Plasmin activity, which was higher in M milks, could enhance primary proteolysis in the corresponding cheeses. Differences in sensory texture, which were greater between M cheeses than between V cheeses, were attributed to variations in moisture and salt content. These differences could be linked to the cheesemaking process and also to the characteristics of milks, such as their pH-value and acidifying ability.; Relations entre la texture de fromages d'Abondance, leur composition, et celle des laits produits par des vaches pâturant différents types de pelouse. Les relations entre la texture du fromage d'Abondance (Haute-Savoie, France), sa composition et celle du lait utilisé pour sa fabrication ont été étudiées dans des conditions réelles de production du fromage. Dix pâturages différents, exploités par 3 producteurs, ont été étudiés. Les caractéristiques du lait, liées aux types de pâturage ont joué un rôle dans l'élaboration de la texture, de même que les paramètres de fabrication. Les fromages fabriqués à partir de laits produits sur des pâturages de montagne (M, n = 5, 1 500-1 850 m) étaient moins élastiques et moins déformables que les fromages issus de laits produits sur des pâturages de vallée (V, n = 5, 850-1 100 m). Ces caractéristiques rhéologiques étaient liées principalement à la teneur en acides gras insaturés à 18 atomes de carbone des laits, plus élevée dans les laits M, et à la protéolyse des fromages. La plasmine, plus active dans les laits M, contribuerait à une protéolyse primaire plus importante dans ces fromages. Les fromages M présentaient une plus grande diversité de texture que les fromages V, en partie associée à des différences de teneurs en eau et en sel. Ces différences seraient liées à la technologie mise en oeuvre et à certaines caractéristiques du lait comme son pH et son aptitude à s'acidifier.

Success in making a cheese acceptable in both flavour and texture depends partly on curd properties which determine the retention of fat and moisture and, thus, cheese yield and composition (Green & Grandison, 1993). When considering farmhouse and/or Appelation d'Origine Contrôlée cheese where milk treatments are not allowed, curd properties depend only on milk composition and clotting characteristics, which are subject to wide fluctuations over the year owing to the cow's stage of lactation and nutritional factors (O'Keeffe, 1984; Macheboeuf et al. 1993). These variations often result in seasonal differences in the chemical or sensory properties of the cheese (Kefford et al. 1995) which are sometimes difficult to understand (Grandison et al. 1985). Only a few studies have assessed the cheesemaking quality of milk by actually making ripened cheese; most studies report milk coagulation properties and curd firmness.The object of this work was to study the influence of the chemical composition and clotting characteristics of the milk on the chemical and sensory properties of ripened cheeses when milk characteristics vary widely.

La methode est basee sur la mesure de l'evolution du pH dans un lait ecreme reconstitue. Le lait est inocule a 1% avec une suspension bacterienne. L'incubation a lieu dans un bain-marie dont la temperature reproduit l'evolution de celle du caille pendant les 24 premieres heures d'une fabrication standard de fromage a pâte cuite. Les mesures effectuees sur 52 cultures commerciales et 80 souches pures de bacteries lactiques thermophiles montrent qu'il existe une tres grande diversite d'activite acidifiante. La methode mise au point peut etre utilisee aussi bien pour selectionner des souches que pour controler des cultures commerciales

In a study of the evolution of conjugated linoleic acid (CLA) during cheese production, the influence of Emmental cheese processing on the CLA content and the CLA isomer composition was evaluated. The use of raw and thermised milk, changes of processing temperature and the effect of propionic acid bacteria (PAB) were investigated. The content of CLA in raw milk was 8·6±1·9 mg/g fat and in the ripened cheese at 70 d was 8·6±1·6 mg/g fat, under normal processing conditions. No changes in the CLA content and CLA isomer composition were observed during Emmental cheese manufacturing process. Changes in cooking and moulding temperatures did not influence the CLA content. CLA content of cheese made from microfiltered milk with two different Propionibacterium freudenreichii strains was very close to cheeses made without PAB. CLA levels seem to be stable in this type of dairy product under the conditions examined.