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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Estabilidade da carne de cordeiro em diferentes condições de armazenamento / Stability of lamb meat at different storage conditions

Rafaella de Paula Paseto Fernandes 15 April 2011 (has links)
Atualmente no Brasil a carne ovina é comercializada quase exclusivamente congelada. No entanto, praticamente não existem estudos no país sobre alterações na qualidade desta carne durante seu armazenamento. Com a crescente demanda do consumidor por produtos de maior conveniência, surge a necessidade de maiores estudos em relação à estabilidade de cortes cárneos ovinos estocados sob refrigeração, principalmente em decorrência de sua curta vida útil. Os objetivos deste trabalho foram avaliar a estabilidade da carne ovina quando estocada sob refrigeração e congelamento e se diferentes sistemas de acondicionamento em atmosfera modificada poderiam aumentar a estabilidade desta carne quando armazenada sob refrigeração. Foram realizados dois experimentos. No primeiro, lombos ovinos foram embalados a vácuo e armazenados sob refrigeração (4±1ºC) por 28 dias e congelamento (-18±1ºC) por 12 meses. No segundo, os cortes foram acondicionados individualmente em 3 diferentes sistemas de embalagem com atmosfera modificada: 1) Á vácuo (sistema tradicional); 2) Com injeção de gases na proporção 75% O2 e 25% CO2 e 3) Com injeção de 100% de CO2). Neste segundo experimento as carnes foram armazenadas sob refrigeração (1±1ºC) por um período de 28 dias. A estabilidade dos cortes foi avaliada por meio de análises físicas, químicas, microbiológicas e sensoriais, sendo que no segundo estudo, além destas análises também foi acompanhada a composição gasosa no espaço-livre. Foram realizadas três repetições de cada um dos estudos. A carne de cordeiro, nas diferentes temperaturas de estocagem e nos três sistemas de embalagens, apresentou-se estável ou com índices aceitáveis em relação à maioria dos parâmetros físicos e químicos avaliados e dentro dos padrões estabelecidos pela legislação brasileira para microrganismos patogênicos durante todo o período. No primeiro estudo, mesmo com uma redução significativa da maciez (de 3 para 8 Kg), a carne congelada continuou sensorialmente aceitável, com todos os atributos, inclusive a textura, recebendo notas em torno de 7 (\"gostei moderamente\"). Portanto, é possível afirmar que a carne de cordeiro apresenta vida de prateleira de no mínimo 12 meses quando armazenada à -18ºC. Em relação à avaliação da estabilidade do lombo ovino refrigerado, detectou-se um aumento elevado das contagens de psicrotróficos anaeróbios, atingindo valores da ordem de 107 UFC/g amostra já aos 14 dias. Esta carne foi avaliada sensorialmente apenas em relação aos atributos cor, aparência geral e aroma. Mesmo considerando as elevadas contagens de microrganismos psicrotróficos, os consumidores não detectaram alterações significativas nos atributos avaliados durante os 28 dias de armazenamento refrigerado. No segundo trabalho, os sistemas de embalagem com injeção de gases foram eficientes em reduzir a proliferação de microrganismos deterioradores quando comparados com o sistema tradicional de embalagem à vácuo. Em relação às diferentes composições gasosas, o sistema com 100% de CO2 apresentou menores contagens microbiológicas do que aquele com 75% O2 e 25% CO2, sendo possível concluir que o sistema de embalagem contendo 100% CO2 garantiu uma maior estabilidade durante 28 dias de armazenamento. No entanto, o lombo de cordeiro acondicionado nesta condição apresentou uma menor preferência sensorial da aparência em relação aos demais tratamentos durante todo o período avaliado. / Nowadays, in Brazil, sheep meat is mainly commercialized as frozen meat. However, in the country studies on possible quality meat changes during frozen storage are scarce. In addition, the increasing consumer demand for higher convenience products supports the need of more studies on of sheep meat cuts stability stored under refrigeration, mainly due to its short shelf life. The objectives of this work were to evaluate the stability of sheep meat when stored under refrigeration and freezing as well as to evaluate different packaging systems under modified atmosphere and the effect of this technology on the meat stability when stored under refrigeration. In order to achieve these objectives, two experiments were performed. In the first study, sheep loins were vacuum packaged and stored under refrigeration (4±1ºC) for 28 days and freezing (-18±1ºC) for 12 months. For the second study, cuts were individually packed in three different atmospheres: 1) vacuum (traditional system), 2) With 75% O2 and 25% CO2 and 3) With 100% CO2. For second experiment, meat was stored under refrigeration (1±1ºC) for a period of 28 days. Stability of the cuts was evaluated by means of physical, chemical, microbiological and sensory analysis, while for the second study, there were also performed headspace gas composition along the storage. Three replications of each study were carried out. The lamb meat at different storage temperatures and the three packaging systems, presented good stability or acceptable indexes in relation to most physical and chemical parameters evaluated. Samples showed good microbiological stability according to standards established by Brazilian legislation for pathogenic microorganisms throughout the storage period. In the first study, there was a significant reduction in tenderness (3 to 8 kg), nevertheless, the frozen meat continued sensory acceptable, showing texture scores around 7 (like moderately). Therefore, it is clear that the lamb meat has a shelf life of at least 12 months when stored at -18ºC. In relation to evaluation of the stability of chilled lamb loin, it was detect a high increase counts of anaerobic psychrotrophic, reaching around 107 CFU/g at 14 days storage. For thies reason, this meat was sensory evaluated only in relation to attributes color, overall appearance and flavor. Even considering the high counts of psychrotrophic, the consumers did not detect significant changes in the attributes evaluated during the 28 days of refrigerated storage. For he second work, it was verified that the gas compositions applied were more effective in reducing the proliferation of deteriorative microorganisms when compared with the traditional vacuum packaging. The system with 100% CO2 presented lower microbiological counts than that with 75% O2 and 25% CO2. Thus the packaging system containing 100% CO2 assured greater stability during 28 days storage. However, the lamb loin packed in this condition presented a lower preference sensory appearance compared to other treatments during the evaluated period.
2

Estabilidade da carne de cordeiro em diferentes condições de armazenamento / Stability of lamb meat at different storage conditions

Fernandes, Rafaella de Paula Paseto 15 April 2011 (has links)
Atualmente no Brasil a carne ovina é comercializada quase exclusivamente congelada. No entanto, praticamente não existem estudos no país sobre alterações na qualidade desta carne durante seu armazenamento. Com a crescente demanda do consumidor por produtos de maior conveniência, surge a necessidade de maiores estudos em relação à estabilidade de cortes cárneos ovinos estocados sob refrigeração, principalmente em decorrência de sua curta vida útil. Os objetivos deste trabalho foram avaliar a estabilidade da carne ovina quando estocada sob refrigeração e congelamento e se diferentes sistemas de acondicionamento em atmosfera modificada poderiam aumentar a estabilidade desta carne quando armazenada sob refrigeração. Foram realizados dois experimentos. No primeiro, lombos ovinos foram embalados a vácuo e armazenados sob refrigeração (4±1ºC) por 28 dias e congelamento (-18±1ºC) por 12 meses. No segundo, os cortes foram acondicionados individualmente em 3 diferentes sistemas de embalagem com atmosfera modificada: 1) Á vácuo (sistema tradicional); 2) Com injeção de gases na proporção 75% O2 e 25% CO2 e 3) Com injeção de 100% de CO2). Neste segundo experimento as carnes foram armazenadas sob refrigeração (1±1ºC) por um período de 28 dias. A estabilidade dos cortes foi avaliada por meio de análises físicas, químicas, microbiológicas e sensoriais, sendo que no segundo estudo, além destas análises também foi acompanhada a composição gasosa no espaço-livre. Foram realizadas três repetições de cada um dos estudos. A carne de cordeiro, nas diferentes temperaturas de estocagem e nos três sistemas de embalagens, apresentou-se estável ou com índices aceitáveis em relação à maioria dos parâmetros físicos e químicos avaliados e dentro dos padrões estabelecidos pela legislação brasileira para microrganismos patogênicos durante todo o período. No primeiro estudo, mesmo com uma redução significativa da maciez (de 3 para 8 Kg), a carne congelada continuou sensorialmente aceitável, com todos os atributos, inclusive a textura, recebendo notas em torno de 7 (\"gostei moderamente\"). Portanto, é possível afirmar que a carne de cordeiro apresenta vida de prateleira de no mínimo 12 meses quando armazenada à -18ºC. Em relação à avaliação da estabilidade do lombo ovino refrigerado, detectou-se um aumento elevado das contagens de psicrotróficos anaeróbios, atingindo valores da ordem de 107 UFC/g amostra já aos 14 dias. Esta carne foi avaliada sensorialmente apenas em relação aos atributos cor, aparência geral e aroma. Mesmo considerando as elevadas contagens de microrganismos psicrotróficos, os consumidores não detectaram alterações significativas nos atributos avaliados durante os 28 dias de armazenamento refrigerado. No segundo trabalho, os sistemas de embalagem com injeção de gases foram eficientes em reduzir a proliferação de microrganismos deterioradores quando comparados com o sistema tradicional de embalagem à vácuo. Em relação às diferentes composições gasosas, o sistema com 100% de CO2 apresentou menores contagens microbiológicas do que aquele com 75% O2 e 25% CO2, sendo possível concluir que o sistema de embalagem contendo 100% CO2 garantiu uma maior estabilidade durante 28 dias de armazenamento. No entanto, o lombo de cordeiro acondicionado nesta condição apresentou uma menor preferência sensorial da aparência em relação aos demais tratamentos durante todo o período avaliado. / Nowadays, in Brazil, sheep meat is mainly commercialized as frozen meat. However, in the country studies on possible quality meat changes during frozen storage are scarce. In addition, the increasing consumer demand for higher convenience products supports the need of more studies on of sheep meat cuts stability stored under refrigeration, mainly due to its short shelf life. The objectives of this work were to evaluate the stability of sheep meat when stored under refrigeration and freezing as well as to evaluate different packaging systems under modified atmosphere and the effect of this technology on the meat stability when stored under refrigeration. In order to achieve these objectives, two experiments were performed. In the first study, sheep loins were vacuum packaged and stored under refrigeration (4±1ºC) for 28 days and freezing (-18±1ºC) for 12 months. For the second study, cuts were individually packed in three different atmospheres: 1) vacuum (traditional system), 2) With 75% O2 and 25% CO2 and 3) With 100% CO2. For second experiment, meat was stored under refrigeration (1±1ºC) for a period of 28 days. Stability of the cuts was evaluated by means of physical, chemical, microbiological and sensory analysis, while for the second study, there were also performed headspace gas composition along the storage. Three replications of each study were carried out. The lamb meat at different storage temperatures and the three packaging systems, presented good stability or acceptable indexes in relation to most physical and chemical parameters evaluated. Samples showed good microbiological stability according to standards established by Brazilian legislation for pathogenic microorganisms throughout the storage period. In the first study, there was a significant reduction in tenderness (3 to 8 kg), nevertheless, the frozen meat continued sensory acceptable, showing texture scores around 7 (like moderately). Therefore, it is clear that the lamb meat has a shelf life of at least 12 months when stored at -18ºC. In relation to evaluation of the stability of chilled lamb loin, it was detect a high increase counts of anaerobic psychrotrophic, reaching around 107 CFU/g at 14 days storage. For thies reason, this meat was sensory evaluated only in relation to attributes color, overall appearance and flavor. Even considering the high counts of psychrotrophic, the consumers did not detect significant changes in the attributes evaluated during the 28 days of refrigerated storage. For he second work, it was verified that the gas compositions applied were more effective in reducing the proliferation of deteriorative microorganisms when compared with the traditional vacuum packaging. The system with 100% CO2 presented lower microbiological counts than that with 75% O2 and 25% CO2. Thus the packaging system containing 100% CO2 assured greater stability during 28 days storage. However, the lamb loin packed in this condition presented a lower preference sensory appearance compared to other treatments during the evaluated period.
3

A study of the high speed diesel engine exhaust with respect to gas composition and smoke density

Akduman, Hasim January 1951 (has links)
A study of exhaust gas composition at various engine speeds, loads, and cooling water temperatures was made on an International Harvester UD-6 Diesel Engine. Simultaneously, smoke density was measured with a smokemeter, the principle of which was based on the obstruction of light. Exhaust gases were analyzed with a Fisher Precision Gas Analyzer. The components analyzed were carbon dioxide, oxygen, illuminants, carbon monoxide, hydrogen, and methane. The results of this study have led the investigators to the following conclusions. 1. The exhaust gas composition was chiefly a function of fuel-air ratio. 2. The effect of cooling water temperature on exhaust gas composition was not conclusive over the range of temperature investigated. (120 to 160 degrees Fahrenheit) 3. The so-called “chilling of direct oxidation reactions” were experienced at maximum brake horsepower check. 4. Smoke density increased with an increase in fuel-air ratio at ratios above .04. The cooling temperature effect was negligible. 5. There was a relationship between smoke density and free, or unburned carbon in the exhaust. 6. A higher precision method of gas analysis would be required for any study of the mechanics of combustion inside the combustion chamber. / Master of Science
4

Physical and biogeochemical controls on the DMS/P/O cycle in Antarctic sea ice / Contrôles physiques et biogéochimiques sur le cycle du DMS/P/O dans la glace de mer Antarctique

Brabant, Frédéric 14 September 2012 (has links)
Il a récemment été démontré que la glace de mer antarctique pouvait jouer un rôle significatif dans la dynamique des gaz à effet climatique (dont le dimethylsulfure ou DMS) dans les régions polaires. Ce travail s’est d’abord attaché à la mise au point d’une méthode de mesure fiable du diméthylsulfoxyde (DMSO) dans la glace de mer, supprimant les interférences générées par la production de DMS au sein de l’échantillon en réponse au choc osmotique subi lors de la fonte de l’échantillon de glace. Une procédure de détermination séquentielle du DMS, par broyage à sec, puis du dimethylsulfoniopropionate (DMSP) et du DMSO sur le même échantillon de glace a été développée et utilisée à large échelle dans ce travail. Les données du présent travail ont été acquises dans le cadre de deux programmes d’observation intégrés menés sur la glace de mer antarctique à des saisons différentes mais avec une méthodologie commune :1) choix de sites d’étude homogènes afin de minimiser l’impact de la variabilité spatiale sur l’interprétation des résultats dans une optique d’évolution temporelle et 2) priorité à la caractérisation du cadre physico-chimique (texture, température, salinité, couvert de neige, susceptibilité au drainage des saumures,….) avant toute autre analyse. L’étude menée dans le cadre du programme ISPOL (nov.–dec. 2004) a permis d’observer que la stratification des saumures a un impact positif sur la conversion du DMSP en DMS au sein de la glace mais ralentit les flux de DMS et DMSP vers l’océan. Le couvert de glace est caractérisé à cette période de l’année par une perte nette de DMSP et génère des flux combiné de DMS et DMSP du même ordre de grandeur que les flux de DMS atmosphériques mesurés dans le cadre d’autres études. L’étude menée dans le cadre du programme SIMBA (sept.–oct. 2007) a permis de mettre en évidence l’importance du forçage atmosphérique sur le régime thermique et la dynamique du DMS/P/O dans la glace. Les communautés d’algues de surface produisent de fortes concentrations de DMS/P/O en réponse au stress thermique, osmotique et potentiellement radiatif durant les périodes de refroidissement et la mise en place d’un régime soutenu de drainage des saumures contribue à évacuer périodiquement les hautes concentrations de DMS/P/O produites dans la glace vers l’océan sous-jacent. Le couvert de glace affichant une production nette de DMS/P/O à cette période de l’année génère des flux combinés de DMS et DMSP plus de dix fois supérieurs à ceux observés pour la glace estivale. L’étude menée sur de la glace artificielle a permis de mettre en évidence l’impact des processus physico-chimiques sur la signature en gaz de la glace en croissance constituant un premier pas vers la modélisation des transports de gaz dans la glace de mer et leurs échanges au travers des interfaces glace-océan et glace-atmosphère. <p><p><p>SUMMARY - It has recently been demonstrated that Antarctic sea ice recently demonstrated plays a potentially significant role in the dynamics of climatically significant gases (amongst which dimethylsulphide or DMS) in Polar Regions. This research work has initially focused on the development of a reliable method for the determination of dimethylsulphoxide (DMSO) within sea ice, avoiding interferences generated by DMS production within the sample in response to the osmotic shock caused by melting. A sequential determination procedure of DMS, dimethlsulphoniopropionate (DMSP) and DMSO on the same ice sample has been developed and used on a large amount of samples in the present work. Data presented in this research project have been collected in the framework of two integrated sea ice observation programs focused on Antarctic sea ice at different seasons but following a common approach: 1) choice of homogeneous study sites to minimize the impact of spatial variability on the interpretation of the results in a time series perspective and 2) priority given to the characterization of the physicochemical framework (texture, temperature, salinity, snow cover, susceptibility to brine drainage,…) prior to any other study. The study conducted in the framework of the ISPOL experiment (Nov.–Dec. 2004) demonstrated that stratification of the brine inclusions network positively influenced the conversion of DMSP into DMS but decreased fluxes of DMS and DMSP towards the ocean. The ice cover at that time of the year is characterised by a net DMSP loss and generates combined DMS and DMSP fluxes whose values fall in the range of atmospheric DMS flux from sea ice measured in the frame of other studies. The study conducted in the framework of the SIMBA experiment (sept.–oct. 2007) emphasized the importance of atmospheric thermal forcing on the sea ice thermal regime and DMS/P/O dynamics. The surface community of algae produced elevated levels of DMS/P/O in response to thermal, osmotic and potentially radiative stress during periods of atmospheric cooling while the development of an intense brine drainage regime contributed to periodically release the elevated levels of DMS/P/O produced in the sea ice towards the underlying ocean. The ice cover exhibited at that time of the year a net production of DMS/P/O and produced combined DMS and DMSP fluxes more than ten times higher than those observed for summer sea ice. The study conducted on laboratory prepared growing sea ice emphasised the impact of physicochemical processes on the gas signature of growing sea ice and represents a first step towards modelling gas exchanges within sea ice and across its interfaces with the ocean and the atmosphere.<p> / Doctorat en Sciences agronomiques et ingénierie biologique / info:eu-repo/semantics/nonPublished

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