Orientadores: Vivaldo Silveira Junior, Javier Telis Romero / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-09T22:31:56Z (GMT). No. of bitstreams: 1 Bernardi_Marina_M.pdf: 337845 bytes, checksum: b22d2f1ecde63498948bfd0748a26993 (MD5) Previous issue date: 2008 / Resumo: Neste trabalho são apresentadas a hidrodinâmica e a transferência de calor no escoamento de ovo líquido integral através de dutos com paredes corrugadas, simulando trocadores de calor a placas. A condição de contorno admitida foi a de temperatura da parede constante durante o aquecimento do fluido. A reologia do ovo integral foi determinada experimentalmente em uma ampla faixa de temperaturas (289 ¿ 335K). O ovo apresentou comportamento reológico dependente do tempo, o qual foi explorado neste trabalho. Para os estudos da perda de carga e transferência de calor objetivando o dimensionamento correto de tubulações e equipamentos destinados ao transporte e processamento de fluidos tixotrópicos os parâmetros reológicos independentes do tempo foram empregados. O modelo de Ostwald-De Waelle foi ajustado às curvas reológicas experimentais desconsiderando a dependência do tempo. Foram realizadas medidas experimentais de perda de carga para a determinação do fator de atrito em função de um número de Reynolds generalizado, cujos resultados foram empregados para determinação dos parâmetros geométricos x e u para o regime laminar e dos parâmetros P1 e P2 para o regime turbulento. Esses parâmetros geométricos foram utilizados para correlacionar os coeficientes de transferência de calor convectivos experimentais com as propriedades físicas do fluido, resultando em equações formato clássico, Nusselt=Nu(Reg,Prg) / Abstract: At this work are showed the heat transference and hydrodynamics of liquid egg flow between ducts with corrugated walls, simulating plate heat exchangers. The contour conditions admitted was the constant temperature in the walls during the fluid heating. The whole egg rheology was experimentally determinated in a extend temperature range (289 ¿ 335K). The egg rheology behavior was time dependent, which was explored at the present work. However, to study the loss of load and heat transference this time dependence behavior was not considerated, because, according to Skelland, the correct sizing of equipments and tubings used to tixotropic fluid transport and processing must be done using time independent rheologic parameters. The Ostwald-De Waelle model was adjusted at the experimental rheologycal curves disrespecting the time dependence. It was realized experimental determinations of loss of load to determination of Fanning factor in function of Reynolds generalized number, and the results was used to determination of x and u geometrics parameters to laminar flow and P1 and P2 to turbulent flow. These geometrics parameters were used to correlated the experimental heat transference coefficient with the fluid physic properties resulting in equations on the classic format, Nusselt=Nu(Reg,Prg) / Mestrado / Mestre em Engenharia de Alimentos

Parmi les desserts à base d’ovoproduits, l’île flottante est reconnue comme particulièrement sensible d’un point de vue microbiologique car sa commercialisation souffre de la survenue intempestive d’altérations que les industriels souhaitent maîtriser. Les travaux réalisés au cours de cette thèse avaient pour objectif de mieux appréhender ces phénomènes afin de mieux les contrôler. Nous avons montré que l’altération de l’île flottante concernait principalement la crème anglaise et qu’elle s’accompagnait d’un développement bactérien conséquent, d’une fréquente diminution du pH et de modifications sensorielles liées à l’aspect et à l’odeur. Les principales bactéries détectées ont été identifiées comme appartenant au groupe Bacillus cereus et aux genres Staphylococcus et Enterococcus. Le blanc d’œuf pasteurisé, utilisé pour la fabrication des œufs en neige, s’est avéré être une source de contamination possible.Cependant, l’implication de bactéries installées sous forme de biofilms dans l’environnement de production ou véhiculées par d’autres ingrédients a aussi été fortement envisagée. La ré-inoculation, en culture pure, d’une collection bactérienne représentative dans de la crème anglaise stérile a montré que différents types de modifications sensorielles et physico-chimiques s’exprimaient d’un genre bactérien à l’autre et qu’ils étaient notamment corrélés à la capacité des bactéries à consommer les sucres et les protéines de la crème anglaise et à produire des métabolites dont des composés volatils odorants. Ces résultats à l’appui, différents tests ont pu être proposés, p / Among the chilled egg products-based desserts, the French dessert “île flottante” is recognized as particularly sensitive from a microbiological point of view, because marketing is suffering from untimely spoilage occurrence that manufacturers wish to control. The work done in this thesis aimed to better understand these phenomena in order to better control them. We have shown that the dessert spoilage mainly concerned the custard cream and it was characterized by high bacterial count, frequent pH decreasing and sensory changes of appearance and smell. The main bacteria detected were identified as belonging to the Bacillus cereus group and Staphylococcus and Enterococcus genera. The possible involvement of bacteria from the pasteurized egg white, used for the egg white foaming, in the dessert spoilage issue was established.However, the involvement of bacteria from biofilms installed in the production environment or provided by other ingredients was also strongly suspected. The spoilage potential assessment of pure culture of a representative bacterial collection in sterile custard cream has shown that different types of sensory and physicochemical changes were expressed according to bacterial genus and that these changes were particularly correlated with the ability of bacteria to consume sugars and proteins of custard and to produce various volatile compounds with specific odorous. With these results, various tests have been proposed for a better control of the white egg batches orientation according to their microbiological quality and so to guarantee their safety with