Batches of fromage blanc, a soft white cheese were prepared from whole pasteurized cow's milk. Processing and formulation methods were used in cheese making to reduce Listeria monocytogenes in artificially contaminated cheese. Treatments implemented included use of additional starter culture in formulation (25% more starter culture than original formulation), use of a higher temperature draining process (at 45oC instead of 22oC), addition of the anti-listerial bacteriocin nisin (Danisco Nisaplin) in formulation at different levels (125 ppm, 250 ppm, 400 ppm), and combinations of these treatments. Characteristics including pH, fat content, protein content, and color were evaluated for each treatment cheese. Statistically significant differences (p<0.0001) were found between the population (log CFU/g) values of L. monocytogenes in the different treatment cheeses and control cheese. Treatments using additional starter culture or higher temperature draining alone were not successful in significantly reducing numbers of L. monocytogenes, but when combined, a 1 log reduction resulted. Of the different concentrations of nisin used in cheese formulation, the level of 250 ppm nisin was used in combination treatments. The treatments using 250 ppm nisin were able to reduce numbers of L. monocytogenes by 2 log 24h after addition. Combination treatments with 250 ppm nisin and additional starter culture in formulation reduced the level of L. monocytogenes by only 1 log, while combination treatments coupling 250 ppm nisin with a higher temperature draining and treatments with 250 ppm nisin, additional starter culture, and a higher temperature draining were able to reduce the pathogen by 2 log. There were statistically significant (p<0.0001) differences found between cheese treatments for values of pH, fat content, and protein content. This soft cheese could be standardized for each of these parameters by the processor before packaging and sale of cheese. There were no statistically significant (p>0.05) differences found between colorimetric values for different cheese treatments. / Master of Science

This diploma thesis deals with the changes in content of fatty acids in long-lasting stored sterilized processed cheeses. Cheeses were stored under different temperatures 6 ± 2 °C, 23 ± 2 °C and 40 ± 2 °C during 23 months. Measurements was made in 16th and 23rd month of storage. The samples of sterilized processed cheeses were extracted by using mixture of solvents (ethanol, diethylether and petrolether). The obtained fat was then saponified by methanolic solution of potassium hydroxide. The methylesthers were analyzed by gas chromatography with flame ionization detection. Lauric, myristic, palmitic, oleic and stearic acids were the most abundant in cheeses. The yield was measured in these main acids. To summarize the content of fatty acids decreased during time of storage and also by influence of storage temperature higher than in refrigerator.

Les fromages d’«Appellation d’Origine Protégée» (AOP) présentant un cahier des charges précis sont garants d’un savoir-faire, d’une tradition et d’un lien avec le terroir et sont également reconnus pour leurs qualités organoleptiques. Malgré une bonne implantation au niveau du marché et une consommation non négligeable, certains fromages AOP voient leurs ventes baisser. Pour dynamiser certains de ces fromages, notamment les fromages à pâte persillée, leur utilisation comme « fromages ingrédients » s’avérerait pertinente. Ce nouveau segment, très porteur pour les fromagesindustriels, consiste à les utiliser dans des préparations culinaires aussi bien à chaud qu’à froid. L’objectif des travaux de cette thèse est de réaliser d’une part un focus sur les propriétés sensorielles des fromages à pâte persillée AOP du Massif central, induites par le chauffage et plus particulièrement de la Fourme d’Ambert, en étudiant les fractions solubles de ces fromages, d’un point de vue biochimique et sensoriel, et d’autre part de connaître les préférences des consommateurs vis-à-vis des fromages à chaud. Dans un premier temps, un screening sur le comportement à chaud de différentes catégories de fromages à pâte persillée a conduit à identifier des différences texturales et gustatives et de ce fait, à catégoriser les fromages selon leurs aptitudes culinaires. Ce positionnement sensoriel a ainsi permis de sélectionner un « fromage modèle » : la Fourme d’Ambert. Dans une seconde phase, l’étude des fractions solubles a confirmé sa contribution relative dans la perception gustative des fromages à pâte persillée. Toutefois, aucune différence sensorielle n’est observée sur les fractions suite au traitement thermique malgré quelques différences sur la teneur de certains composés sapides. Enfin, la dernière phase a consisté à identifier les préférences des consommateurs vis-à-vis de la Fourme d’Ambert à froid et à chaud. Quelle que soit la température, le fromage est bien apprécié par les consommateurs. La segmentation des consommateurs révèle des perceptions différentes selon trois groupes : un groupe avec des préférences pour des fromages très typés, à l’inverse, un groupe ayant une attirance pour les fromages ayant des flaveurs moins prononcées et un dernier, axé sur les préférences des fromages à chaud. Corrélées aux profils sensoriels, aux commentaires libres des consommateurs et à leurs attentes, certaines variables sensorielles ou comportementales ont pu expliquer ces différences de préférences. Ces résultats montrent l’intérêt de l’usage de certains fromages à pâte persillée AOP en tant que « fromages ingrédients » présentant de bonnes aptitudes culinaires, par leurs propriétés fonctionnelles et gustatives. L’acceptation des fromages à chaud par les consommateurs renforce le fait que les fromages AOP peuvent être utilisés aussi bien à froid qu’à chaud, permettant ainsi l’innovation dans la filière. / PDO cheeses through their specifications are recognized for a quality in relation to a geographical origin, technical know-how, and a typical gustative quality. Despite a good consumption of PDO cheeses, the marketed volumes decreased for most of them. In order to make them more attractive, some cheeses as Blue cheeses could be used as “cheeses ingredient”. Cheeses are usually consumed at the end of a meal but a new trend is emerging: cheeses are more and more used in culinary preparations, both hot (pizza, gratin, sauce) and cold (sandwiches, salads). The main objective of this study was to firstly highlight the impact of heating on sensory properties of French PDO Blue cheeses and more particularly Fourme d’Ambert. The water-soluble fraction which plays an important role in the favour of cheeses was secondly studied in order to evaluate the impact of heating on this extract. The last objective consisted in measuring the consumers liking towards cold and heated cheeses. Therefore, sensory and biochemical methods were performed to describe crude cheeses and liking. The first study highlighted the impact of heating on both textural properties and flavour of four PDO blue-type cheeses. The main results showed that PDO cheeses present different culinary properties and thus are compatible with a use into hot preparations. The first step allowed to select a model cheese: Fourme d’Ambert. The second step consisted in studying the impact of heating on the crude cheeses and on the water-soluble fraction. In parallel, the gross composition was performed on soluble fractions and cheeses according to heating treatment. Although no treatment difference was observed on the water-soluble fraction gustatory profile, a slight difference was showed on certain chemical constituents between the water-soluble extracts. The last step was focused on the consumers liking towards cold and heated cheeses. The results showed that cheeses were much appreciated whatever heating treatments highlighting a slightly preference towards heated cheeses. Moreover, 3 groups of consumers were formed based on different preferences. One group preferred heated cheeses while two others groups preferred cold cheeses. Consumers’ group preferences were explained by means of sensory profiles and open-ended questions responses.Finally, this study shows the opportunities of new culinary uses for Blue cheeses. Sensory methods application had allowed to provide detailed information on heating properties of blue cheeses. In addition, consumers’ acceptance reinforce that PDO cheeses can be used in cold or heated preparations.

Les Escherichia coli producteurs de Shiga-toxines (STEC) sont des bactéries pathogènes originaires du tractus digestif des ruminants qui peuvent contaminer certains aliments. Une fois ingérés, ils peuvent provoquer des pathologies graves. Le comportement des STEC n’appartenant pas au sérotype O157:H7 dans les fromages était mal connu. Par ailleurs, en dépit d’une forte prévalence des STEC dans les fromages, cet aliment est moins impliqué dans les épidémies que la viande. C’est pourquoi nous avons étudié dans un premier temps le devenir de ces STEC au cours de la fabrication de 5 schémas technologiques de fromages différents. Dans un deuxième temps, nous avons analysé le comportement et la survie de STEC ayant survécu à la fabrication d’un fromage au cours d’une digestion artificielle. Nos résultats ont montré que certaines technologies sont favorables à la croissance des STEC. Seul un affinage de plus de 60 jours a permis une réduction du taux des STEC. Les étapes de cuisson du caillé ou de coagulation longue de certaines technologies semblent inhiber la croissance des STEC. De plus, la croissance et la survie observées pour les souches E. coli O157:H7 étaient plus faibles que pour les souches E. coli non-O157:H7. L’étude de la survie des souches STEC au cours de la digestion artificielle a montré une différence de comportement entre les 2 souches STEC testées : la souche E. coli O157:H7 a survécu à la digestion tandis que celle de sérotype O26:H11 s’est fortement développée en fin de digestion. / Shiga-toxin producing Escherichia coli (STEC) are an important cause of foodborne illness. They are originated from the digestive tract of the ruminants and can contaminate certain food. Once ingested, they can be responsible for a variety of clinical outcomes. To date, most authors have focused their work on the behavior of E. coli O157:H7 during cheese manufacturing: little is known about the behavior of non-O157:H7 STEC. Furthermore, the presence of STEC strains has been found in raw milk cheeses but dairy products remain less implicated in outbreaks than meat. Consequently, we chose to study the behavior of O157:H7 and non-O157:H7 STEC strains during the manufacturing of 5 different cheese technologies. Then, secondly, it appeared interesting to evaluate the survival of STEC isolated from cheeses during artificial digestion. Our results showed that certain technologies are favorable to the growth of the STEC. Only a long ripening step (>60 days) could then allow a reduction of the STEC rate. In contrast, the cooking step of the curd or the long coagulation of certain technologies inhibited their growth. Our results also showed that the growth and the survival of the E. coli O157:H7 strains were lower than those of the non-O157:H7 E. coli strains. The study of the survival of STEC strains during the artificial digestion highlighted an important difference of behavior for the 2 strains tested: the E. coli O157:H7 strain was able only to survive whereas the E. coli O26:H11 strain knew an important growth at the end of digestion.

O objetivo deste estudo foi avaliar o efeito inibitório de Lactobacillus rhamnosus sobre as contagens de Staphylococcus aureus e Listeria monocytogenes, aspergidos isoladamente ou em combinação sobre a superfície de queijo Minas Frescal, durante armazenamento por 21 dias a 7ºC. O delineamento consistiu em esquema fatorial 2x2x2, sendo 8 tratamentos com 4 repetições. As características físico-químicas (pH, atividade de água, umidade, teor de gordura, proteína e perfil de textura) foram determinadas nos queijos dos tratamentos sem adição de L. rhamnosus ou contendo este probiótico (T1 e T2, respectivamente). Verificaramse as contagens de L. rhamnosus, S. aureus e L. monocytogenes nos queijos de todos os tratamentos nos dias 1, 7, 14 e 21 de armazenamento. Foram também analisados os percentuais de sobrevivência dos microrganismos submetidos a condições de simulação do trato gastrointestinal (TGI) utilizando ensaios in vitro. Não houve efeito significativo (P&gt;0,05) entre os parâmetros físico-químicos dos queijos dos tratamentos T1 e T2. As contagens de L. rhamnosus aumentaram (P&lt;0,05) em todos os tratamentos a partir do dia 7 de armazenamento, estabilizando ao redor de 108 UFC/g, sendo que a presença concomitante de L. monocytogenes e/ou S. aureus nos queijos não influenciou a contagem de L. rhamnosus. L. rhamnosus diminuiu em cerca de 1 ciclo log as contagens de L. monocytogenes, e não exerceu efeito inibitório sobre S. aureus após 21 dias. S. aureus não sobreviveu ao teste de simulação ao TGI. No entanto, L. rhamnosus e L. monocytogenes apresentaram percentuais de sobrevivência entre 74,6% a 86,4%, e entre 75,8% a 94,1%, respectivamente. Os resultados demonstraram que a adição de L. rhamnosus não alterou as características físico-químicas dos queijos Minas frescal, porém exerceu efeito inibitório sobre L. monocytogenes, mas nenhum efeito sobre S. aureus. A utilização de L. rhamnosus como probiótico apresenta um potencial para inibição de L. monocytogenes na fabricação de queijos Minas frescal. São necessários estudos sobre os mecanismos envolvidos na competição entre as bactérias por substratos no alimento, bem como sua sobrevivência nas condições do TGI em ensaios in vivo. / The aim of this study was to evaluate the effects of Lactobacillus rhamnosus on growth of Staphylococcus aureus and Listeria monocytogenes in Minas frescal cheese during 21 days of storage at 7ºC. The experimental design was totally randomized, in a 2x2x2 factorial arrangement with 8 treatments and 4 replicates per treatment. Physical chemical parameters such as pH, moisture, water activity, fat, protein and texture profile analysis were carried out in cheeses where no microorganism were inoculated (T1) and in the cheeses inoculated with the probiotic bacteria, L. rhamnosus (T2). The counts of L. rhamnosus, S. aureus and L. monocytogenes were examined on days 1, 7, 14, 21 of storage. Survival percentage of the bacteria after exposure to simulated gastrointestinal conditions was studied in vitro. Statistical analysis indicated that there were no significant differences (P&gt;0,05) among the means of the physical chemical parameters analyzed in treatments 1 and 2. From day 7 on, the counts of L. rhamnosus increased (P&lt;0,05) in all treatments, stabilizing and reaching up to 108 CFU/g. It was noticed that the concurring presence of L. monocytogenes and/or S. aureus in the cheese samples did not show influence in the counts of the probiotic bacteria. The L. rhamnosus caused about 1 log cycle reduction in the counts of L. monocytogenes, but showed no inhibitory effect on S. aureus at the end of the period of storage. S. aureus did not survive the exposure to simulated gastrointestinal conditions. However, L. rhamnosus and L. monocytogenes showed survival percentages varying from 74,6% to 86,4%, and from 75,8% to 94,1%, respectively. The results showed that the addition of L. rhamnosus had no influence on the physical chemical characteristics of the Minas frescal cheese and no inhibitory effect on S. aureus, nevertheless demonstrated inhibitory effect on L. monocytogenes. The addition of probiotic strains of L. rhamnosus in Minas frescal cheese represents potential for L. monocytogenes inhibition. It is essential to carry out studies on the mechanisms involved in the competition for substrate by bacteria, as well as their survival to simulated gastrointestinal conditions in in vivo experiments.

Os queijos artesanais, elaborados com leite cru, são apreciados por suas características sensoriais peculiares. Com objetivo de assegurar a inocuidade destes produtos, a legislação brasileira estabeleceu padrões microbiológicos sanitários para estes alimentos. Microorganismos probióticos são conhecidos por sua capacidade de modular favoravelmente a microbiota do hospedeiro por meio da produção de substâncias antimicrobianas, em especial, os ácidos orgânicos e bacteriocinas. Assim, o presente estudo buscou avaliar a utilização de micro-organismos probióticos como alternativa para melhorar a qualidade microbiológica de queijos artesanais usando o Queijo Artesanal da Serra da Mantiqueira como modelo. Para tanto, foi incorporada à microbiota do leite uma preparação composta de 16 cepas de micro-organismos probióticos, obtendo-se uma concentração final de 3x106 UFC/ml de leite. A estratégia adotada consistiu em comparar os queijos inoculados com micro-organismos probióticos em relação aos queijos não inoculados (controle), durante o período de maturação de 45 dias, em três estações do ano (inverno, verão e outono). As amostras foram coletadas nos dias 1, 15, 30 e 45 para a determinação dos parâmetros: umidade, pH, concentrações de carboidratos, ácidos orgânicos e análises microbiológicas. Avaliou-se também a composição da microbiota dos queijos pela técnica do pirossequenciamento dos genes do rRNA 16S. Os resultados permitiram verificar que os gêneros predominantes na microbiota dos queijos foram Streptococcus, Lactobacillus e Lactococcus , em diferentes níveis nas três estações do ano. Foi possível observar que a incorporação das culturas probióticas resultou em diferentes efeitos nas estações avaliadas no que se refere às concentrações de carboidratos e ácido cítrico, bem como de ácidos orgânicos ao final dos 45 dias de maturação, possivelmente devido à variabilidade da microbiota verificada nas diferentes estações. No tocante às características microbiológicas, observou-se que, durante o período de maturação, 95% dos queijos confeccionados nas diferentes condições apresentaram padrões de qualidade em conformidade com o estabelecido na legislação, no que se refere às concentrações de coliformes termotolerantes, estafilococos coagulase positivos, Salmonella sp e Listeria sp independentemente da incorporação das culturas probióticas. Entretanto, a adição das culturas probióticas reduziu a carga microbiana de gêneros da família Enterobacter iaceae , em especial Enterobacter , Citrobacter , Klebsiella , Kluyvera e Obesumbacterium durante processo de maturação. Especificamente, o emprego das culturas probióticas resultou em redução do percentual total de Enterobacter iaceae na microbiota dos queijos de 0,41% para 0,17% no verão, e de 12,42% para 6,71% no outono. Neste contexto, a adição de culturas probióticas pode constituir alternativa viável para melhoria da qualidade microbiológica de queijos elaborados com leite cru por meio do incremento do potencial antagônico da microbiota sobre espécies de micro-organismos potencialmente patogênicos, toxigênicos e deteriorantes, além de agregar valor ao produto final. / Artisanal cheeses, made with raw milk, are appreciated for their sensorial profiles, which differentiates them from industrialized cheeses. In order to ensure safety to consumers, Brazilian legislation established microbiological standards for these products. Probiotics are well known for their ability to favorably modulate the host\'s microbiota by producing antimicrobial compounds, mainly organic acids and bacteriocins. Therefore, this study aimed to evaluate the use of probiotic microorganisms as an alternative to improve the microbiological quality of artisanal cheeses through inhibition of contaminating microorganisms, using Mantiqueira Highlands Artisanal Cheese as a model. To do so, a preparation consisting of 16 probiotic strains was added to the milk, at a final concentration of 3x106 CFU/ml. Additionally, the effects of this practice on pH, carbohydrates and organic acids concentrations over a 45 day ripening period were evaluated. Analyses of cheese bacterial community composition were also undertaken by means of 16S rRNA gene pyrosequencing. The strategy consisted of comparing cheeses made with probiotic cultures with a control group, to which no probiotic culture was added. Over a 45 day ripening period, in three seasons (winter, summer and autumn), samples were collected at days 1, 15, 30 and 45 in order to conduct pH, moisture, carbohydrate, organic acids, microbiological and pyrosequencing analyses. The results showed that the addition of probiotic cultures resulted in distinct effects in the different seasons regarding carbohydrate and organic acids concentrations, possibly due to variability in bacterial community composition. The results also demonstrated that 95% of cheeses were deemed acceptable according to Brazilian law regarding coliforms, positive coagulase staphylococci, Salmonella sp. and Listeria sp, regardless of adding probiotics. However, the incorporation of probiotic microorganisms resulted in reduced populations of genera belonging to Enterobacteriaceae family, especially Enterobacter, Citrobacter, Klebsiella, Kluyvera and Obesumbacterium, throughout the whole ripening process. Specifically, the addition of probiotic cultures reduced the total percentage of Entercobacteriaceae from 0,41% to 0,17% in the summer, and from 12,42% to 6,71% in the fall. In this context, the use of probiotic microorganisms may represent a viable alternative for improving microbiological quality of raw milk cheeses by means of incrementing the antagonistic potential of cheese microbiota towards potentially pathogenic and toxigenic microorganisms.

Os queijos artesanais, elaborados com leite cru, são apreciados por suas características sensoriais peculiares. Com objetivo de assegurar a inocuidade destes produtos, a legislação brasileira estabeleceu padrões microbiológicos sanitários para estes alimentos. Microorganismos probióticos são conhecidos por sua capacidade de modular favoravelmente a microbiota do hospedeiro por meio da produção de substâncias antimicrobianas, em especial, os ácidos orgânicos e bacteriocinas. Assim, o presente estudo buscou avaliar a utilização de micro-organismos probióticos como alternativa para melhorar a qualidade microbiológica de queijos artesanais usando o Queijo Artesanal da Serra da Mantiqueira como modelo. Para tanto, foi incorporada à microbiota do leite uma preparação composta de 16 cepas de micro-organismos probióticos, obtendo-se uma concentração final de 3x106 UFC/ml de leite. A estratégia adotada consistiu em comparar os queijos inoculados com micro-organismos probióticos em relação aos queijos não inoculados (controle), durante o período de maturação de 45 dias, em três estações do ano (inverno, verão e outono). As amostras foram coletadas nos dias 1, 15, 30 e 45 para a determinação dos parâmetros: umidade, pH, concentrações de carboidratos, ácidos orgânicos e análises microbiológicas. Avaliou-se também a composição da microbiota dos queijos pela técnica do pirossequenciamento dos genes do rRNA 16S. Os resultados permitiram verificar que os gêneros predominantes na microbiota dos queijos foram Streptococcus, Lactobacillus e Lactococcus , em diferentes níveis nas três estações do ano. Foi possível observar que a incorporação das culturas probióticas resultou em diferentes efeitos nas estações avaliadas no que se refere às concentrações de carboidratos e ácido cítrico, bem como de ácidos orgânicos ao final dos 45 dias de maturação, possivelmente devido à variabilidade da microbiota verificada nas diferentes estações. No tocante às características microbiológicas, observou-se que, durante o período de maturação, 95% dos queijos confeccionados nas diferentes condições apresentaram padrões de qualidade em conformidade com o estabelecido na legislação, no que se refere às concentrações de coliformes termotolerantes, estafilococos coagulase positivos, Salmonella sp e Listeria sp independentemente da incorporação das culturas probióticas. Entretanto, a adição das culturas probióticas reduziu a carga microbiana de gêneros da família Enterobacter iaceae , em especial Enterobacter , Citrobacter , Klebsiella , Kluyvera e Obesumbacterium durante processo de maturação. Especificamente, o emprego das culturas probióticas resultou em redução do percentual total de Enterobacter iaceae na microbiota dos queijos de 0,41% para 0,17% no verão, e de 12,42% para 6,71% no outono. Neste contexto, a adição de culturas probióticas pode constituir alternativa viável para melhoria da qualidade microbiológica de queijos elaborados com leite cru por meio do incremento do potencial antagônico da microbiota sobre espécies de micro-organismos potencialmente patogênicos, toxigênicos e deteriorantes, além de agregar valor ao produto final. / Artisanal cheeses, made with raw milk, are appreciated for their sensorial profiles, which differentiates them from industrialized cheeses. In order to ensure safety to consumers, Brazilian legislation established microbiological standards for these products. Probiotics are well known for their ability to favorably modulate the host\'s microbiota by producing antimicrobial compounds, mainly organic acids and bacteriocins. Therefore, this study aimed to evaluate the use of probiotic microorganisms as an alternative to improve the microbiological quality of artisanal cheeses through inhibition of contaminating microorganisms, using Mantiqueira Highlands Artisanal Cheese as a model. To do so, a preparation consisting of 16 probiotic strains was added to the milk, at a final concentration of 3x106 CFU/ml. Additionally, the effects of this practice on pH, carbohydrates and organic acids concentrations over a 45 day ripening period were evaluated. Analyses of cheese bacterial community composition were also undertaken by means of 16S rRNA gene pyrosequencing. The strategy consisted of comparing cheeses made with probiotic cultures with a control group, to which no probiotic culture was added. Over a 45 day ripening period, in three seasons (winter, summer and autumn), samples were collected at days 1, 15, 30 and 45 in order to conduct pH, moisture, carbohydrate, organic acids, microbiological and pyrosequencing analyses. The results showed that the addition of probiotic cultures resulted in distinct effects in the different seasons regarding carbohydrate and organic acids concentrations, possibly due to variability in bacterial community composition. The results also demonstrated that 95% of cheeses were deemed acceptable according to Brazilian law regarding coliforms, positive coagulase staphylococci, Salmonella sp. and Listeria sp, regardless of adding probiotics. However, the incorporation of probiotic microorganisms resulted in reduced populations of genera belonging to Enterobacteriaceae family, especially Enterobacter, Citrobacter, Klebsiella, Kluyvera and Obesumbacterium, throughout the whole ripening process. Specifically, the addition of probiotic cultures reduced the total percentage of Entercobacteriaceae from 0,41% to 0,17% in the summer, and from 12,42% to 6,71% in the fall. In this context, the use of probiotic microorganisms may represent a viable alternative for improving microbiological quality of raw milk cheeses by means of incrementing the antagonistic potential of cheese microbiota towards potentially pathogenic and toxigenic microorganisms.

Le conditionnement, opération unitaire clé du processus industriel de fabrication des produits fromagers, consiste à remplir par un jet de façon homogène des emballages de formes variées par des produits à propriétés rhéologiques complexes tout en assurant des cadences optimisées. L’objectif de cette étude est de prédire le remplissage d’un emballage, à partir de la connaissance de la rhéologie des produits et des paramètres opératoires pour le dimensionnement de nouveaux procédés de conditionnement ou l’optimisation de procédés existants.Nécessaire à la poursuite de l’étude, le comportement rhéologique des produits fromagers dans les domaines de sollicitation du procédé à 80°C a été caractérisé comme rhéofluidifiant, à seuil de contrainte, élastique en-dessous et au-dessus du seuil d’écoulement.L’hydrodynamique des jets et du remplissage lors du conditionnement a été étudiée avec trois types de produits grâce au pilote à l’échelle laboratoire du procédé, dimensionné pour reproduire les conditions opératoires industrielles. Après avoir vérifié la cohérence des résultats obtenus avec le dispositif expérimental avec ceux de la littérature pour un fluide newtonien, l’étude s’est portée sur des fluides modèles viscoplastiques, gels de Carbopol®, et sur des produits fromagers.Cinq régimes d’écoulement ont été observés et caractérisés à partir des évolutions du diamètre de jet et de la vitesse d’atteinte des bords pendant le remplissage et de la hauteur de motte finale du dépôt après le remplissage, paramètre décisif de la qualité du conditionnement. Des diagrammes de fonctionnement adimensionnels d’observation des régimes ont été déterminés à partir des forces en jeu dans le système. Ainsi, le régime d’écoulement peut être prédit par ces diagrammes à partir des propriétés rhéologiques du produit et des paramètres géométriques et opératoires du procédé. / Packaging is a key step of cheese products industrial manufacturing process. It consists in filling containers of various shapes with non-Newtonian products while ensuring optimized rates. The aim of the present work is to describe the influence of cheese rheological properties as well as process parameters onto packaging, thereby contributing towards its optimization.Necessary for the study, the rheological behavior of cheese products on the process stress range at 80°C has been identified as shear-thinning with a yield stress, with elasticity both below and above the yield stress.Jets and filling hydrodynamics during packaging have been studied with three types of products by the means of the laboratory-scale process pilot, which is able to reproduce the industrial process conditions. After checking for consistency between experimental and litterature results for Newtonian products, the study focused on viscoplastic model fluids, Carbopol® hydrogels, and on cheeses.Five flow patterns have been observed and characterized through jet diameter, spread velocity during filling and final mound height after filling, which is a key factor of the packaging quality. Flow patterns dimensionless distributions have been determined from the forces involved in the system. Thus, the flow pattern can be predicted thanks to theses distributions from product rheological properties and geometrical and process parameters.

Made available in DSpace on 2014-08-20T13:42:06Z (GMT). No. of bitstreams: 1 Denise da Fontoura Prates.pdf: 535436 bytes, checksum: c3acb08e8f12a05440096b13c688b6f2 (MD5) Previous issue date: 2010-12-17 / Listeria monocytogenes is a Gram-positive of ubiquitous natural, psychrotropic pathogen which colonizes the surfaces of equipment and utensils in food processing industries. Milk and dairy products, especially cheeses with medium and high humidity have been implicated in listeriosis cases and outbreaks. Microbial contamination could be originated in raw material or be incorporated during the development stages of the product, coupled with inadequate hygiene practices. The general aim of this study was to evaluate the occurrence of Listeria spp. along the processing line of cheese with middle and high humidity, in three dairy subjected to different levels of sanitary survey located in Southern Brazil. From 208 samples tested Listeria spp. were isolated 7.69%, being isolated 43.75%, 25%, 31.25%, respectively, in dairy products A, B and C. From these isolates, 25% were found in raw milk, 18.75% in contact surfaces with the product, 50% in areas without contact with the product and 6.25% in the final product. L. innocua and L. monocytogenes were the only species identified between the isolates being L. innocua the prevalent species (68.7%). Among the serotypes of L. innocua, the serotype 6a was prevalent (72.7%) and between L. monocytogenes serotype 4b was prevalent (55.6%). All Listeria strains isolated from raw material and final product showed multiresistance to five antibiotics (penicillin, amoxicillin, chloramphenicol, cefaclor and clindamycin) of the fifteen antibiotics tested. Among the samples of raw material assessed microbiologically, the raw milk showed the highest levels of contamination and the highest levels found between them were > 1.1x106 MPN/mL for fecal Overall, 1.1x105 MPN/mL for fecal coliform, 4x105 CFU/ml for coagulase-positive staphylococci and Salmonella spp. in one of the samples. Among six samples of the final product, only one showed himself at odds with the existing regulatory standard, exceeding the allowed limit for ECP. Listeria spp. and L. monocytogenes were present along the lines of the three dairy processing plants, regardless of the size of the industry, highlighting the risk of contamination during food manufacturing. Therefore, it becomes necessary to introduce effective measures to reduce such contamination or improvements in the practices already adopted by the industry, because of the risks to public health. / Listeria monocytogenes é uma bactéria Gram-positiva de natureza ubíqua, psicrotrófica, que coloniza superfícies de equipamentos e utensílios dentro de indústrias processadoras de alimentos. Leites e derivados lácteos, em especial queijos com média e alta umidade, têm sido incriminados em casos e surtos de listeriose, por serem alimentos que favorecem o desenvolvimento microbiano, além de serem prontos para o consumo. A contaminação microbiana pode ter origem na matéria-prima, ou ser incorporada durante as etapas de elaboração do produto, associada a práticas inadequadas de higiene. O objetivo geral neste trabalho foi avaliar a ocorrência de Listeria spp., em especial de L. monocytogenes, ao longo da linha de processamento de queijos de média e alta umidade, em três laticínios, localizados na região sul do Rio Grande do Sul, submetidos a diferentes níveis de inspeção sanitária. Das 208 amostras avaliadas 7,69% apresentaram Listeria spp., sendo isoladas, 43,75%, 25%, 31,25%, respectivamente, nos laticínios A, B e C. Destes isolados, 25% foram encontrados no leite cru, 18,75% em superfícies de contato com o produto, 50% em superfícies sem contato com o produto e 6,25% no produto final. L. innocua e L. monocytogenes foram as únicas espécies identificadas entre os isolados, sendo L. innocua a espécie prevalente (68,7%). Entre os sorotipos de L. innocua, o prevalente foi 6a (72,7%) e entre L. monocytogenes o sorotipo prevalente foi 4b (55,6%). Todas as cepas de Listeria isoladas da matéria-prima e do produto final apresentaram multirresistência a cinco (penicilina, amoxilina, cloranfenicol, cefaclor e clindamicina) dos 15 antibióticos testados. Dentre as amostras de matéria-prima avaliadas microbiologicamente, as de leite cru, foram as que apresentaram os maiores níveis de contaminação, sendo que, os níveis mais elevados encontrados entre as amostras de leite cru foram: >1,1x106 NMP.mL-1 para coliformes totais, 1,1x105 NMP.mL-1 para coliformes termotolerantes, 4x105 UFC.mL-1 para estafilococos coagulase positiva (ECP) e a presença de Salmonella spp. em uma das amostras avaliadas. Entre as seis amostras de produto final, apenas uma apresentou-se em desacordo com o padrão regulamentar vigente, excedendo o limite permitido para ECP. Listeria spp. e L. monocytogenes foram isoladas ao longo das linhas de processamentos nos três laticínios, independente do porte da indústria, evidenciando risco de contaminação durante a fabricação dos dois tipos de queijo, os quais são produtos prontos para o consumo. Dessa forma, torna-se necessária a implantação de medidas eficazes para redução dessas contaminações, ou melhorias nas práticas já adotadas pelas indústrias, em virtude dos riscos à saúde pública.

L'objectif de cette thèse était de caractériser, de modéliser et de hiérarchiser les mécanismes acteurs de la croissance de bulles dans un fromage à pâte pressée non-cuite à l'échelle de la bulle. Pour cela, trois étapes majeures ont été envisagées. Une première étape de mise au point d’une méthode de détermination des paramètres du modèle mécanique (modèle de Maxwell généralisé) par ajustement de courbes expérimentales de compression-relaxation a été effectuée. Une deuxième étape de validation a consisté en la réalisation d'un dispositif expérimental permettant de soumettre une bulle isolée dans un cylindre de fromage à diverses sollicitations mécaniques, à suivre l'évolution du dispositif en temps réel et de façon non invasive par IRM, et à confronter ces résultats à des simulations reproduisant les conditions d'acquisition. Une dernière étape a consisté à rajouter la prise en compte du transport de matière (CO2) au sein du fromage dans la modélisation. Les résultats de simulation ont dans un premier temps été confrontés au comportement moyen des bulles au sein d'un bloc de fromage, et dans un deuxième temps un dispositif expérimental de validation similaire à celui de l'étape précédente a été développé. La caractérisation mécanique du fromage a montré que les propriétés rhéologiques n'évoluent pas au cours de l'affinage, mais qu'elles sont soumises à un fort gradient spatial. Le modèle de Maxwell a été validé expérimentalement dans des conditions de sollicitations mécaniques uniquement et une étude de sensibilité a permis de montrer la forte influence des temps de relaxation les plus longs (plusieurs heures) et de la position de la bulle sur la croissance. L'étude du couplage entre transport de quantité de mouvement et transport de matière dans un contexte de croissance d'une seule bulle a permis de montrer la grande influence des paramètres de transport de matière sur la croissance de bulle, en particulier pour le coefficient de diffusion et le taux de production de CO2. Dans un contexte où deux cavités gazeuses sont mobilisées, les paramètres géométriques (position, dimensions, forme des cavités) se sont montrés aussi importants que les paramètres de transport de matière. / The objective of this PhD thesis was to characterise, model and rank the mechanisms involved in the growth of bubbles in semi-hard cheeses, at the bubble scale. Three steps were considered. First, a mechanical characterisation of the material enabled to define a rheological model to describe the behaviour of the material (generalised Maxwell model), and to set-up a method to determine the model parameters by fitting of compression-relaxation data. Secondly, the Maxwell model consisted in setting up an experimental validation procedure allowing studying different loads on a single bubble surrounded by a cheese cylinder. Experiments were monitored in real-time in a non-invasive manner by MRI imaging and were compared to simulations reproducing the experimental conditions. Finally, mass transport (CO2) was also taken into account in the model. Simulation results were first compared to the average bubble growth in cheese blocks, and then a dedicated experimental set-up similar to that used previously was used. Mechanical characterisation of semi-hard cheese showed the rheological properties did not evolve during ripening, but presented a steep spatial gradient. Despite its simplicity, the Maxwell model showed good agreement with the experimental results. A sensitivity study demonstrated that the highest relaxation time (about several hours) and the bubble position were the most influent parameters over bubble growth, when only the mechanical model was involved. Coupling between mass and momentum transport in a single bubble case demonstrated the great influence of the mass transport parameters on bubble growth, especially diffusivity and CO2 production rate. In the case where two gaseous cavities are involved, geometric parameters (cavities positions, dimensions and shape) proved to be as important as the mass transport parameters on the bubble growth.