Dissertations / Theses on the topic 'Meat Nitrites'

Dietary nitrite intake has been implicated in numerous gastrointestinal cancers in humans due to the formation of a group of carcinogens called N-nitroso compounds. The need to estimate their intake is vital in establishing at risk population and to monitor and perhaps one day manage their dietary intake. This is the first study to estimate nitrate and nitrite in selected vegetables, cured and fresh meat in Australian food supply using ion-paired reversed-phased HPLC. Nitrite content in meat products analysed ranged from 0 to 83.9 mg/kg in medallion beef and Frankfurt, respectively; nitrate content ranged from 18.7 mg/kg in minced beef to 142.5 mg/kg in salami. The nitrite content was below the maximum limit set by the Food Standards Australia and New Zealand. Nitrate content in selected vegetables ranged from 123 to 4850 mg/kg in Iceberg lettuce and English spinach, respectively; only minimal nitrite at 20 mg/kg was present in Gai choy, which was most likely due to bacterial contamination during storage. Based on the food consumption pattern of Australians, the dietary nitrite and nitrate intake from bacon were 1.51 and 3.42 mg per capita per day, which was below the Adequate Daily Intake set by the European Union Scientific Committee for food in 1995. Taking into considerations of oral nitrate reduction to nitrite and the endogenous nitrate formation, the upper extreme of dietary nitrite and nitrate intake in Australians were 44 and 2.4 times over the ADI, respectively. However, this does not take into effect of other dietary promoters and inhibitors. Eighteen healthy human volunteers were put on a low nitrate, nitrite and antioxidant diet for three days during which they were fed one serving of cured meat with and without 500 mg of vitamin C. Using GC-MS, N-nitrosodimethylamine was not detected in the urine before or after vitamin C supplementation, suggested that a diet low on nitrate and nitrite cannot produce NDMA and thus may reduce the risk of developing gastrointestinal cancers. Different extraction methods and combination of herbs and spices were demonstrated in vitro to show inhibition against B. cereus, Escherichia coli, Listeria monocytogenes, Salmonella Enteritidis and Staphylococcus aureus. In addition, autoclaved turmeric powder at 0.3 % (w/v), hot water extracted turmeric with ginger at 0.5 % and rosemary at 1.0 % showed growth inhibition against Clostridium sporogenes, which was used as a surrogate for Clostridium botulinum. The use of these combinations of herbs and spices may replace or at least reduce the use of nitrite as a preservative in cured meat products to prevent botulism and reduce dietary nitrite intake.

Sporadic problems with pink color defect, or pinking, has occurred in cooked meat products for decades. Pink color can be due to the presence of undenatured myoglobin, denatured globin hemochromes, or nitrosylhemochrome. This research documented the level of added nitrite that produced nitrosylhemochrome in processed meat rolls from fabricated beef round, pork shoulder, turkey breast, and chicken breast. For each meat type, preliminary studies were conducted to narrow the range at which added nitrite caused pinking. Subsequently, the nitrite levels were increased incrementally by 1-ppm, and pink color was measured by trained panelists and by a Hunter color meter. Nitrosylhemochrome content was determined by acetone extraction. Panel and instrumental measurements identified pink color in beef samples formulated with 14-ppm nitrite; nitrosohemochrome extracts detected pigment at 12- ppm. Nitrite levels that caused pinking in pork shoulder were much lower than in beef. Panelists identified pink color at 4-ppm nitrite, and Hunter color meter values showed increased redness at 6-ppm. Pigment extraction detected nitrosylhemochrome at 4- ppm added nitrite. The trained panel and Hunter color meter detected pink color in turkey breast at 2-ppm added nitrite; nitrosohemochrome extraction detected pink pigment at 3-ppm added nitrite. In chicken breast, pink color was detected visually and instrumentally at 1-ppm added nitrite. Pigment extraction detected nitrosylhemochrome at 2-ppm added nitrite. Lower levels of nitrite (1-3-ppm) caused pinking in light-colored meats (turkey and chicken breast, meats with total pigment between 19-ppm and 27-ppm). Higher levels of nitrite (5-14-ppm) caused pink color defect in dark pigmented meat (beef round and pork shoulder, meats with total pigment levels between 56-ppm and 147-ppm). Regression analysis was used to relate total pigment and the minimum level of nitrite causing pinking. The minimum nitrite level causing pinking was the lowest level of nitrite at which the trained panel, acetone extraction, and instrumental results detected pink color or nitrosyl pigment. The formula obtained from the model was as follows: Y = 0.092X + 0.53, where "Y" is the minimum level of added nitrite to cause pinking and "X" is the total pigment of the meat. This formula can be used to estimate the level of nitrite that can be expected to cause pinking in a wide range of pigmented meats.

Dissertação de Mestrado em Segurança Alimentar
O salpicão é um enchido curado tradicional português, que pertence a um vasto grupo de produtos cárneos. Para além de representarem parte da dieta mediterrânica, estes produtos são importantes para as economias rurais e para a preservação da herança. No entanto, em 2015, a IARC avaliou a carcinogenicidade do consumo de carne processada. Como resultado, a carne processada foi classificada como carcinogénica para humanos (Grupo 1), com base em evidência suficiente de que o consumo de carne processada causa cancro colorretal. As N-nitrosaminas inserem-se no grupo das substâncias responsáveis por este efeito carcinogénico. Desta forma, é importante saber se estes compostos estão presentes nos produtos cárneos, particularmente no salpicão. Mais ainda, é importante perceber se estão reunidas as condições para a sua formação, nomeadamente precursores e ambiente ácido. Por estes motivos, analisaram-se amostras de salpicão, de três unidades fabris distintas, quanto aos teores de nitratos, nitritos, aminas secundárias e N-nitrosaminas. Também o pH das amostras foi analisado. As análises químicas foram efetuadas nos seguintes pontos temporais: carne (T0), pré-enchimento (T1), meia cura (T2), produto final (T3), meio do prazo de validade (T4) e final do prazo de validade (T5). Os valores de pH variaram entre 5,6 e 5,8 na carne (T0) e mantiveram-se dentro da gama esperada para produtos fermentados. Não se detetaram nitratos (acima do Limite de Quantificação). Quanto à determinação de nitrito residual, apenas se detetaram (acima do Limite de Quantificação) nas amostras da unidade fabril C, mas sempre em teores muito inferiores ao permitido na legislação da EU (100 mg NaNO2/kg). Não se detetaram aminas secundárias nas amostras da unidade fabril B. Detetaram-se aminas secundárias em algumas amostras da unidade fabril A (T1 e T5) e da unidade fabril C (T0, T1 e T5), sendo que os valores médios mais elevados foram: 7,4 mg de Piperdina/kg, 11,0 mg de Di-n-propilamina/kg, 20,9 mg de Pirrolidina/kg, 22,6 mg de Morfolina/kg e 26,2 mg de Dimetilamina/kg. Não se detetaram nitrosaminas nas amostras analisadas. Apesar de existir uma válida preocupação em torno das N-nitrosaminas, estes compostos não foram detetados nos produtos em estudo, nem os seus precursores em concentrações suficientes, para a sua formação. É necessário continuar a estudar este assunto para que se consiga compreender a relação entre o consumo de diferentes tipos de carne processada e o verdadeiro risco para a saúde do Homem.
ABSTRACT - Characterization of chemical hazards in traditional cured meat sausages: nitrosamines and precursors - “Salpicão” is a traditional Portuguese cured sausage, and it belongs to a wide group of meat products. These products not only represent part of the Mediterranean diet, but also have great value for the economy of rural areas and for the preservation of heritage. However, in 2015, IARC has evaluated the carcinogenicity associated to the consumption of processed meat. As a result, processed meat was classified as carcinogenic to humans (Group 1), based on sufficient evidence that the consumption of processed meat causes colorectal cancer. N-nitrosamines are among the responsible substances for the assessed carcinogenic effect. Therefore, there is a need to understand if these compounds are present in meat products, particularly in “salpicão”. Moreover, it is also important to know if the combination of precursors and acidic environment are gathered, to generate N-nitrosamines. For this purpose, samples of “salpicão”, from three distinct factories, were analysed for the quantification of nitrate, nitrite, secondary amines, and N-nitrosamines levels. The pH levels were also evaluated. The chemical analyses and pH evaluation were performed at the following time points: raw meat (T0), before stuffing (T1), middle of curing process (T2), finished product (T3), middle of shelf-life (T4), and end of shelf-life (T5). The pH values of all meat samples ranged between 5,6 and 5,8 and remained within the expected for fermented products. No residual nitrate levels were found to be above the Limit of Quantification. As for residual nitrite levels, those were only detected (above Limit of Quantification) in the samples from factory C, but always considerably under the legal EU limit (100 mg NaNO2/kg). No secondary amines were detected in the samples from factory B. Secondary amines were detected in few samples of the factory A (T1 and T5) and factory C (T0, T1 and T5), with the highest mean values of 7,4 mg of Piperdine/kg, 11,0 mg of Dipropylamine/kg, 20,9 mg of Pyrrolidine/kg, 22,6 mg of Morpholine/kg and 26,2 mg of Dimethylamine/kg. No nitrosamines were detected in the analysed samples. Although nitrosamines may be substances of great concern, they were not found in these meat products, nor their precursors, in sufficient concentrations. Further studies are required to fully understand the link between the consumption of different kinds of processed meat and the actual risk that they represent to human health.
N/A

Dissertação de Mestrado Integrado em Medicina Veterinária
Atualmente, existe uma procura crescente por conservantes naturais, sobretudo de origem vegetal, para reduzir o conteúdo de nitrito e/ou nitrato (aditivos químicos) em produtos curados à base de carne. Com este trabalho pretendeu-se estudar formas de substituir o uso destes aditivos químicos por infusões de quatro ervas aromáticas (Manjericão Rubra, Tomilho Limão, Orégãos vulgar e Sálvia Ananás), como fonte natural de nitrato, avaliando a evolução da microbiota tecnológica, características físico-químicas e sensoriais (baseado numa escala Just about right), num modelo cárneo armazenado em refrigeração durante quatro dias. Foram realizadas seis formulações, com diferentes concentrações de nitrato de sódio (mg) por quilograma de produto cárneo, correspondentes a: (C) Controlo com 0 ppm; (T1) Manjericão rubra com 70 ppm; (T2) Tomilho limão com 70 ppm; (T3) Manjericão rubra com 100 ppm; (T4) Sálvia ananás com 100 ppm; (T5) Orégãos com 100 ppm. Os modelos cárneos foram analisados realizando-se contagens de Aeróbios totais a 30 ºC, Enterobacteriaceae, Bactérias Ácido Lácticas (BAL) e Staphylococcus coagulase negativa (SCN). Foram ainda determinados os teores de nitratos, nitritos, cloretos, a cor e o pH. As infusões com sálvia ananás mostraram ter um maior conteúdo de nitrato (63.124 mg/100ml) em comparação com infusões de tomilho limão e orégãos. O modelo cárneo T4 apresentou uma maior quantidade de nitratos (média 16.91 mg/kg). Este produto modelo após um período de 2 para 4 dias de armazenamento a 4 ºC, apresentou valores de nitrito de 3.93 mg/kg, onde se observou que a cor após cozedura teve um aumento da coordenada a* no dia 4, demonstrando uma cor mais rosada/avermelhada, indicativo do desenvolvimento do nitrosohemocromogénio. Além disso na caracterização sensorial do produto modelo não se notou nenhum aroma a ervas ou especiarias, exibindo sabores e cheiros neutros. Estes resultados indicam que os ingredientes naturais, como a infusão de sálvia ananás, podem ser possivelmente utilizados como alternativa a aditivos químicos na cura tradicional. Contudo, é necessária mais investigação para avaliar o impacto sensorial e microbiológico deste ingrediente quando utilizado em produtos curados à base de carne com novas formulações e com a adição de novos condimentos.
ABSTRACT - Application of aromatic plants infusions to replace chemical additives in a fermented meat model - Currently, there is an increasing demand for natural preservatives, mainly of vegetable origin, to reduce the content of nitrite and/or nitrate (chemical additives) in cured meat products. This work aimed to study ways to replace the use of these chemical additives by infusions of four aromatic plants (Red Basil, Lemon Thyme, Common Oregano and Pineapple Sage), as a natural source of nitrate, evaluating the evolution of technological microbiota, physical-chemical and sensory characteristics (based on a Just about right scale), in a meat model stored in refrigeration for four days. Six formulations were performed, with different concentrations of sodium nitrate (mg) per kilogram of meat product, corresponding to (C) 0 ppm control; (T1) 70 ppm red basil; (T2) 70 ppm lemon thyme; (T3) 100 ppm red basil; (T4) 100 ppm pineapple sage; (T5) 100 ppm common oregano. The meat models were analysed by performing total Aerobic counts at 30 ºC, Enterobacteriaceae, Lactic Acid Bacteria (BAL) and Staphylococcus coagulase negative (SCN). The levels of nitrates, nitrites, chlorides, colour and pH were also determined. Pineapple Sage infusions showed a higher nitrate content (63,124 mg/100ml) compared to lemon thyme and common oregano infusions. The T4 meat model showed a higher nitrate content (mean 16.91 mg/kg). This model product after a period of 2 to 4 days of storage at 4 ºC, showed nitrite values of 3.93 mg/kg, where it was observed that the colour after cooking had an increase of the a* coordinate on day 4, showing a pinker/redder colour, indicative of the development of nitrosohemochromogen. In addition, the sensory characterization of the model product did not show any herbs or spices aroma, presenting neutral flavours and smells. These results indicate that natural ingredients, such as pineapple sage infusion, can possibly be used as an alternative to chemical additives in traditional curing. However, further research is needed to assess the sensory and microbiological impact of this ingredient when used in cured meat products with new formulations and the addition of new condiments.
N/A

Os peitos de galinhas matrizes pesadas de corte, poedeiras comerciais brancas e frangos foram desossados manualmente, com o objetivo de avaliar e comparar as propriedades tecnológicas – capacidade de retenção de água e de emulsificação – bem como pH e composição centesimal, além de elaborar e avaliar sensorialmente um produto reestruturado empanado, tipo nugget. Os resultados das análises indicaram que não houve diferença significativa entre as carnes analisadas, nem entre produtos processados, implicando utilização regular desse tipo de matéria-prima na indústria de alimentos. O restante das carcaças das galinhas foi utilizado para extração de carne mecanicamente separada (CMS) para avaliação da estabilidade microbiológica. As CMSs foram submetidas a dois tratamentos: I) com 150ppm de nitrito, embaladas em saco de polietileno; e II) com 150ppm de nitrito e 500ppm de eritorbato, embaladas em saco de polietileno. Como controle, as amostras de CMS foram apenas acondicionadas em sacos de polietileno. Todas as embalagens foram estocadas e congeladas a –18ºC por 99 dias. Os resultados da análise de caracterização microbiológica indicaram que tanto as amostras de CMS de galinha matriz quanto de galinha poedeira atenderam os padrões de contagem requeridos pela legislação Brasileira. A avaliação da estabilidade microbiológica das CMSs no primeiro e no último dia para mesófilos, Escherichia coli, Staphylococcus aureus, Clostridium perfringens e Pseudomonas, bem como as análises quinzenais de microrganismos psicrotróficos, indicaram que não houve uma redução significativa nas contagens, independentemente do tratamento aplicado. Não foi detectada Salmonella em nenhuma das amostras analisadas. Tais resultados apontaram o tempo de estocagem como o principal fator na redução da carga bacteriana.
The breasts of heavy fowls, white commercial egg-layers and chickens were manually deboned in order to evaluate and compare technological properties—water hold and emulsifying capacity—and pH and centesimal composition, as well as to prepare and assess a restructured coated product. The results of the analyses indicated that there was not a significant difference between the meats analyzed, nor among the processed products, implying the regular use of such meat in the food industry. The remaining parts of the hens’ carcasses were mechanically deboned for the evaluation of microbiological stability. The mechanically deboned meat (MDM) was submitted to two treatments: I) 150ppm of nitrite, packed in polyethylene bags; II) 150ppm of nitrite and 500ppm of erythorbate, packed in polyethylene bags. The control meats were just packed in polyethylene bags. All samples were frozen-stored at –18ºC for 99 days. The results of microbiological characterization indicated that both samples from heavy fowls and egg-layers were in accordance with the Brazilian legislation. MDM microbiological stability evaluation on the first and last days for fecal coliforms, mesophiles, Staphylococcus aureus, Clostridium perfringens and Pseudomonas, as well as the analyses carried out every fifteen days for psychrotrophics bacteria indicated that there was not a significant reduction in the presence of the above, irrespective of the treatment applied. Salmonella was not detected in any of the samples. Such results indicated that freezing storage period was the main factor responsible for the reduction of the bacterial count in MDM.

In the first section of the thesis graphitic carbon nitride was for the first time synthesised using the high-temperature condensation of dicyandiamide (DCDA) – a simple molecular precursor – in a eutectic salt melt of lithium chloride and potassium chloride. The extent of condensation, namely next to complete conversion of all reactive end groups, was verified by elemental microanalysis and vibrational spectroscopy. TEM- and SEM-measurements gave detailed insight into the well-defined morphology of these organic crystals, which are not based on 0D or 1D constituents like known molecular or short-chain polymeric crystals but on the packing motif of extended 2D frameworks. The proposed crystal structure of this g-C3N4 species was derived in analogy to graphite by means of extensive powder XRD studies, indexing and refinement. It is based on sheets of hexagonally arranged s-heptazine (C6N7) units that are held together by covalent bonds between C and N atoms. These sheets stack in a graphitic, staggered fashion adopting an AB-motif, as corroborated by powder X-ray diffractometry and high-resolution transmission electron microscopy. This study was contrasted with one of many popular – yet unsuccessful – approaches in the last 30 years of scientific literature to perform the condensation of an extended carbon nitride species through synthesis in the bulk. The second section expands the repertoire of available salt melts introducing the lithium bromide and potassium bromide eutectic as an excellent medium to obtain a new phase of graphitic carbon nitride. The combination of SEM, TEM, PXRD and electron diffraction reveals that the new graphitic carbon nitride phase stacks in an ABA’ motif forming unprecedentedly large crystals. This section seizes the notion of the preceding chapter, that condensation in a eutectic salt melt is the key to obtain a high degree of conversion mainly through a solvatory effect. At the close of this chapter ionothermal synthesis is seen established as a powerful tool to overcome the inherent kinetic problems of solid state reactions such as incomplete polymerisation and condensation in the bulk especially when the temperature requirement of the reaction in question falls into the proverbial “no man’s land” of classical solvents, i.e. above 250 to 300 °C. The following section puts the claim to the test, that the crystalline carbon nitrides obtained from a salt melt are indeed graphitic. A typical property of graphite – namely the accessibility of its interplanar space for guest molecules – is transferred to the graphitic carbon nitride system. Metallic potassium and graphitic carbon nitride are converted to give the potassium intercalation compound, K(C6N8)3 designated according to its stoichiometry and proposed crystal structure. Reaction of the intercalate with aqueous solvents triggers the exfoliation of the graphitic carbon nitride material and – for the first time – enables the access of singular (or multiple) carbon nitride sheets analogous to graphene as seen in the formation of sheets, bundles and scrolls of carbon nitride in TEM imaging. The thus exfoliated sheets form a stable, strongly fluorescent solution in aqueous media, which shows no sign in UV/Vis spectroscopy that the aromaticity of individual sheets was subject to degradation. The final section expands on the mechanism underlying the formation of graphitic carbon nitride by literally expanding the distance between the covalently linked heptazine units which constitute these materials. A close examination of all proposed reaction mechanisms to-date in the light of exhaustive DSC/MS experiments highlights the possibility that the heptazine unit can be formed from smaller molecules, even if some of the designated leaving groups (such as ammonia) are substituted by an element, R, which later on remains linked to the nascent heptazine. Furthermore, it is suggested that the key functional groups in the process are the triazine- (Tz) and the carbonitrile- (CN) group. On the basis of these assumptions, molecular precursors are tailored which encompass all necessary functional groups to form a central heptazine unit of threefold, planar symmetry and then still retain outward functionalities for self-propagated condensation in all three directions. Two model systems based on a para-aryl (ArCNTz) and para-biphenyl (BiPhCNTz) precursors are devised via a facile synthetic procedure and then condensed in an ionothermal process to yield the heptazine based frameworks, HBF-1 and HBF-2. Due to the structural motifs of their molecular precursors, individual sheets of HBF-1 and HBF-2 span cavities of 14.2 Å and 23.0 Å respectively which makes both materials attractive as potential organic zeolites. Crystallographic analysis confirms the formation of ABA’ layered, graphitic systems, and the extent of condensation is confirmed as next-to-perfect by elemental analysis and vibrational spectroscopy.
Die vorliegende Arbeit befasst sich mit der Synthese und Charakterisierung neuer Allotropen und Nanostrukturen von Karbonitriden und berührt einige ihrer möglichen Anwendungen. Alle gezeigten, ausgedehnten, kovalent verbundenen Karbonitridgerüste wurden in einem ionothermalen Syntheseprozess – einer Hochtemperaturbehandlung in einem eutektischen Salzgemisch als ungewöhnlichem Lösungsmittel – aus einfachen Präkursormolkülen erzeugt. Der Kondensationsmechanismus folgt einer temperaturinduzierten Deaminierung und Bildung einer ausgedehnten, aromatischen Einheit; des dreifach substituierten Heptazines. Die Dissertation folgt vier übergreifenden Themen, beginnend mit der Einleitung in Karbonitridsysteme und der Suche nach einem Material, welches einzig aus Kohlenstoff und Stickstoff aufgebaut ist – einer Suche, die 1834 mit den Beobachtungen Justus von Liebigs „über einige Stickstoffverbindungen“ begann. Der erste Abschnitt zeigt die erfolgreiche Synthese von graphitischem Karbonitrid (g-C3N4); einer Spezies, welche auf Schichten hexagonal angeordneter s-Heptazineinheiten beruht, die durch kovalente Bindungen zwischen C- und N-Atomen zusammengehalten werden, und welche in einer graphitischen, verschobenen Art und Weise gestapelt sind. Der zweite Abschnitt berührt die Vielfalt von Salzschmelzensystemen, die für die Ionothermalsynthese geeignet sind und zeigt auf, dass die bloße Veränderung der Salzschmelze eine andere Kristallphase des graphitischen Karbonitrides ergibt – das g-C3N4-mod2. Im dritten Abschnitt wird vom Graphit bekannte Interkallationschemie auf das g-C3N4 angewendet, um eine Kalliuminterkallationsverbindung des graphitischen Karbonitirdes zu erhalten (K(C6N8)3). Diese Verbindung kann in Analogie zum graphitischen System leicht exfoliiert werden, um Bündel von Karbonitridnanoschichten zu erhalten, und weist darüberhinaus interessante optische Eigenschaften auf. Der vierte und letzte Abschnitt handelt von der Einführung von Aryl- und Biphenylbrücken in das Karbonitridmaterial durch rationale Synthese der Präkursormoleküle. Diese ergeben die heptazinbasierten Frameworks, HBF-1 und HBF-2 – zwei kovalente, organische Gerüste.

Pediococcus acidilactici as a lactic acid producer, and sucrose were added to breakfast strip products in order to reduce added levels of sodium nitrite and sodium chloride and yet limit the growth of Clostridium botulinum and inhibit toxin production. Sucrose at 0.4 or 0.9% with P. acidilactici at 1.0 x 10 cells/g were added during preparation of breakfast strip products prepared with combinations of 40 or 80 ppm sodium nitrite and 1.0 or 2.0% sodium chloride. Other ingredients were added at levels normally used in cured meat products. C. botulinum types A and B at 1,000 spores/g were inoculated during product preparation. The finished products were sliced, vacuum packed, double bagged, vacuum sealed again, and incubated at 27 C. Samples were analyzed before incubation and every week for 4 weeks for anaerobic plate counts, pH, residual nitrite, Most Probable Number counts, and botulinal toxin. The results revealed that 0.9% sucrose increased the acid production, thus inhibiting the botulinal growth and toxin formation in the products. Lactic acid bacteria and sucrose at 0.4% did not produce enough acid to inhibit toxin formation. Sodium nitrite at 40 ppm and sodium chloride at 1.0% permitted increased growth rate and toxin development of C. botulinum. Addition of 0.9% sucrose and P. acidilactici was necessary to provide antibotulinal properties to breakfast strip products prepared with 40 ppm sodium nitrite and 1.0% sodium chloride.

Experiments were carried out to measure the surface energy of boron nitride (BN) powders. A reliable procedure has been developed for measurement of surface energy of powders using the capillary rise technique based on Washburn's equation. It is measured by finding the contact angle from liquid penetration experiments with polar and non-polar liquids. Both the dispersive and non-dispersive components of surface energy are determined. The results of the surface energy of BN powders has been found to correlate well with the critical shear rate for the onset of melt fracture, indicating the importance of surface energy in the procedure of selecting an effective processing aid. In addition, experiments were carried out in both an Instron capillary rheometer equipped with a special annular die (Nokia Maillefer wire coating cross-head) and a parallel-plate rheometer to investigate the effect of a new processing additive (boron nitride powder in combination with a fluoroelastomer) on the rheology and processability of molten polymers. Metallocene polyethylenes with and without boron nitride (BN) and fluoroelastomer are tested in extrusion. First, it is demonstrated that BN is a superior processing aid compared to conventional fluoropolymer ones. Secondly, it is found that the combination of BN powders with a small amount of a fluoroelastomer improves even further the processability of molten polymers. They can essentially be processed at higher shear rates without exhibiting gross melt fracture. DSC and TGA experiments using polymer specimens with and without BN were also carried out to investigate the mechanism by which gross melt fracture is being eliminated in the presence of boron nitride.
Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate

Submitted by Ana Hilda Fonseca (anahilda@ufba.br) on 2016-09-14T16:34:31Z No. of bitstreams: 1 Tese Mariangela V Lopes.pdf: 3032469 bytes, checksum: 36404d46d79768ab384fb49c544f496e (MD5)
Approved for entry into archive by NUBIA OLIVEIRA (nubia.marilia@ufba.br) on 2016-09-14T20:43:57Z (GMT) No. of bitstreams: 1 Tese Mariangela V Lopes.pdf: 3032469 bytes, checksum: 36404d46d79768ab384fb49c544f496e (MD5)
Made available in DSpace on 2016-09-14T20:43:57Z (GMT). No. of bitstreams: 1 Tese Mariangela V Lopes.pdf: 3032469 bytes, checksum: 36404d46d79768ab384fb49c544f496e (MD5)
Neste trabalho, foram desenvolvidos procedimentos e sistemas automatizados para o controle de qualidade de carnes e produtos cárneos quanto à presença de aditivos (NO2- e NO3-), degradação (evolução de H2S), presença de adulterante (SO3-) e riscos de contaminação pela capacidade sortiva de metais. O desenvolvimento destes procedimentos vem contrapor as metodologias clássicas recomendadas pelos órgãos oficiais brasileiros. Os métodos e procedimentos aqui desenvolvidos obedecem às recomendações da Química Analítica moderna, as quais priorizam precisão, exatidão, sensibilidade, custos operacionais, versatilidade, robustez, rastreabilidade, minimização de resíduos e produtividade analítica. O sistema de analise por injeção em fluxo (FIA), para análise seletora e discriminatória de H2S evoluído pela carne, foi desenvolvido baseado no método do azul de metileno. O emprego da multicomutação, associado à câmara de pervaporação, conferiu versatilidade ao sistema com produtividade analítica de 30 determinações h-1. Paralelo a isto, foi realizada uma avaliação da degradação de carnes empregando a espectroscopia no infravermelho próximo (NIR) para averiguação das condições de conservação de carnes. Os resultados foram concordantes para as duas metodologias (NIR e FIA), sendo possível detectar indícios de deterioração após 30 min de exposição da carne à atmosfera em temperatura ambiente. O desenvolvimento de sistema em fluxo para análise seqüencial de NO2- e NO3-, em produtos cárneos, utilizando câmara de tubos concêntricos (CTC) foi baseado no método de Greiss. A CTC proporcionou a divisão da zona da amostra, facilitando as determinações seqüenciais de NO2- e NO3-. A subzona da amostra que passava pelo tubo central da CTC resultava apenas na determinação do NO2-. A amostra que passava pelo tubo externo (coroa) da CTC, percolava grãos de cádmio coperizado, resultando na redução do NO3- existente à NO2-. Este sistema ofereceu boa sensibilidade para a quantificação dos analitos, apresentando limites de detecção de 0,018 e 0,036 mg L-1 para NO2- e NO3-, respectivamente. O procedimento proposto atingiu produtividade analítica de 120 determinações h-1. O desenvolvimento de sistema automatizado em fluxo para análise discriminatória de sulfito em carnes foi baseado no método da p-rosanilina. Foi empregado câmara de permeação gasosa, onde o SO3- presente na amostra, permeava através de membrana de PTFE para a reação com o reagente cromogênico. O sistema foi satisfatório para screening analysis, com produtividade analítica de 12 determinações h-1. A capacidade sortiva de metais pela carne bovina foi também avaliada. Foi avaliado o contato estático da carne com soluções de referência de Cd e Pb, preparadas com água de torneira, a pH 6. Foi empregada válvula multiportas, com oito canais para execução dos experimentos, enquanto que metais foram determinados por ICP OES. Os resultados indicaram um elevado poder sortivo, cerca de 80% para ambos os metais, evidenciando risco potencial de contaminação para as carnes submetidas a práticas inadequadas de abate e comercialização
In the present work automated systems and procedures to control the quality of meats and meat products had been developed, in concern to the additive presence (NO2- and NO3-), degradation (H2S evolution) and presence of adulterating species (SO32-). Also the metal sorption capacity on meat was evaluated. The development of these methods comes to oppose classical methods recommended by brazilian official agencies. The developed procedures follow the recommendations of the modern Analytical Chemical, which prioritizes the precision, exactness, sensitivity, traceability, robustness, reduced operational costs, lesser production of residue and raised analytical productivity. The flow analysis (FIA) procedure to discriminate H2S in meat sample was developed based on methylene blue method. Multicommutation, associated to gas permeation conferred versatility to the system with analytical throughput of 30 determinations h-1. Parallel to this, the spectroscopy in the near infrared region (NIR) was carried out to evaluate meat degradation. A flow system for sequential NO2- and NO3- analysis in meat products, using concentric tubes chamber (CTC) was based on the Greiss method. The CTC provides the division of sample zone, permitting the sequential analysis. The sample sub zone that passed for the central pipe of the CTC resulted in the determination of the NO2-. The sample that passed through external CCP pipe, percolated the cadmium column, allowing the reduction of the NO3- to NO2-. This system offers sensitivity in the quantification of anilities with detection limits of 0.036 for NO3- and 0.018 mg L-1 for NO2-, reaching 120 determinations h-1. The flow system for the screening analysis of SO32- in meat sample was based on p-rosanilne method. Chamber for gas permeation was employed. The system revealed efficient for screening analysis with analytical throughput of 12 determination h-1. The metal sorption capacity on meat was evaluated. The investigated species comprised Cd and Pb from solutions prepared with tap water at pH 6. In the experimental set, it was employed an eight channels multiport valve in order to prepare part of the samples, while the metal determinations was carried out by using ICP OES technique. The results obtained demonstrated an expressive retention capacity of meat for Cd2+ and Pb2+ ions with percentages ca. 80% (m/m) for both metals, indicating the potential risks related to the consumption of meat submitted to inappropriate conditions of abattoir, handling, storage and commercialization.

Orientador: Marise Aparecida Rodrigues Pollonio
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos
Made available in DSpace on 2018-08-16T12:31:59Z (GMT). No. of bitstreams: 1 Nascimento_Renatado_M.pdf: 1842864 bytes, checksum: ff48ba117e4d598457a6c594bc8eefaf (MD5) Previous issue date: 2010
Resumo: No desenvolvimento de produtos cárneos com apelos saudáveis, a redução de sódio e a substituição de nitrito de sódio são relevantes estratégias a serem implementadas pela indústria de processamento. Embora, já seja possível encontrar em alguns mercados produtos cárneos com redução de sódio, a produção desses itens com aceitação sensorial e desempenho tecnológico ainda é um grande desafio. Este trabalho tem o objetivo de avaliar a influência da redução de cloreto de sódio e a substituição do nitrito de sódio por extrato vegetal em embutidos cozidos de peru. Cloreto de potássio foi utilizado para substituir total ou parcialmente cloreto de sódio combinado com um mascarador comercial de sabor amargo nas formulações estudadas. Na pesquisa de substituição de nitrito de sódio em embutido cozido de peito de peru, extrato vegetal de aipo foi aplicado como fonte de nitrato e cultura starter como fonte redutora. Os níveis de substituição de cloreto de sódio por cloreto de potássio avaliados foram: 25%, 50% e 75%. Na primeira etapa do trabalho avaliou-se a redução de cloreto de sódio com foco nos atributos sensoriais. De acordo com testes afetivos de Diferença do Controle e de Aceitação, foi possível concluir que a redução de 25% de NaCl é possível de ser realizada sem afetar a aceitação do produto. Na segunda etapa, avaliou-se o processo de fabricação mais indicado para aplicação do extrato de aipo e cultura starter como substitutos do nitrito de sódio. Finalmente, na terceira etapa foram elaboradas formulações com substituição de NaCl por KCl e mascarador de sabor amargo (25%, 50% e 75% de substituição) com adição de nitrito de sódio e com substituição de nitrito de sódio por extrato de aipo, como fonte de nitrato, e cultura starter, como fonte redutora. Estudou-se a estabilidade dessas formulações ao longo de 60 dias de armazenagem à temperatura de 4°C, através de determinações físico-químicas, instrumentais, sensoriais e microbiológicas. Observou-se que todas as formulações mantiveram-se estáveis ao longo dos 60 dias em relação aos parâmetros físicos e oxidação lipídica. Os produtos com substituição de nitrito de sódio mostraram um tendência de aumento de intensidade de coloração amarela mais acentuada do que os produtos com adição de cloreto de sódio. A análise sensorial demonstrou que não houve efeito significativo da redução do NaCl sobre atributos gosto salgado e sabor. Em relação à estabilidade microbiológica, todas as formulações apresentaram resultados similares e considerados aceitáveis em relação às normas de legislação. A condução desse trabalho permitiu a elaboração de um embutido cozido de peru com redução de sódio e substituição de nitrito de sódio por uma fonte natural de nitrato com resultados que garantem a viabilidade tecnológica dessa reformulação promovendo apelos mais saudáveis para essa categoria de produto cárneo
Abstract: During developing meat products with healthy appeal, sodium reduction and replacement of sodium nitrite are important strategies to be implemented by the processing industry. Products with reduced sodium can be found in markets stores, although, the production of these goods with sensory acceptance and technological performance is still a great challenge. This study aims to evaluate the effect of reducing sodium chloride and the replacing sodium nitrite by celery extract in cooked turkey breast. Potassium chloride and a bitter taste masking were selected as a sodium chloride replacer, and celery extract and starter culture as substitute of sodium nitrite and reduction agent respectively. The replacement levels of sodium chloride by potassium chloride were evaluated at: 25%, 50% and 75%. At first stage of the study sodium reduction was evaluated with a focus on sensory attributes. According to sensory evaluation, it was concluded that the reduction of 25% NaCl can be accomplished without affecting product acceptance. In the second step, manufacturing process was asset for application of the extract of celery and starter culture as substitutes for sodium nitrite. Finally, the third phase were prepared formulations with replacement of NaCl by KCl and bitter mask taste (25%, 50% and 75% replacement) with the addition of sodium nitrite and sodium nitrite substitution for celery extract, as a source of nitrate and starter culture, such as source reduction. The stability of formulations were evaluated over 60 days of storage at 4 ° C, through physical-chemical determinations, instrumental, sensory and microbiological. Through the analytic determinations showed that all formulations were stable over the 60 days. The instrumental analysis (determination of color throughout the period of shelf-life of sliced and products exposed to light) showed a trend of replacing products with sodium nitrite present intensity of yellowish sharper than the products with added sodium chloride, and the sensory analysis showed that the effect of reduction of NaCl did not alter this sensory attribute. Regarding microbiological stability, all formulations showed similar results and considered acceptable. The conduct of this work allowed the preparation of a built-cooked turkey with sodium reduction and replacement of sodium nitrite by a natural source of nitrate with results that promote healthier appeals to this category of meat product
Mestrado
Mestre em Tecnologia de Alimentos

Dans le cadre de la fabrication de pièces structurales pour l’industrie aéronautique, de nouveaux matériaux composites à matrice céramique sont envisagés par le motoriste Safran. Lors de l’utilisation dans des environnements sévères de combustion, et sous chargement mécanique, la matrice pourra s’endommager par fissuration et la capacité du matériau à s’auto-protéger sera réduite. Les travaux présentés dans cette thèse ont pour but d'identifier les mécanismes prépondérants de ruine de ce type de matériaux composites en fonction de différentes sollicitations thermiques, mécaniques et environnementales. Une démarche multi-échelle a été adoptée, de manière à considérer les phénomènes à une échelle microscopique (chaque constituant) et macroscopique (synergie entre les constituants au sein du matériau). Le comportement en oxydation/corrosion du matériau composite et de chacun de ses constituants a été caractérisé puis modélisé pour être extrapolé à des environnements de combustion. Différents domaines de protection du matériau ont ainsi été mis en évidence. Dans cette même optique, le comportement thermomécanique des constituants matriciels et du composite a fait l’objet d’essais de fluage pour déterminer les paramètres d’une première modélisation, et analyser les dégradations associées. En couplant les différents résultats obtenus, il est ainsi possible d’évaluer la criticité des différents phénomènes de ruine. Des scenarii de ruine sont donc présentés
To design and manufacture CMC structural components for aeronautics, Safran develops a new CMC grade, provided to resist severe combustion environments. Understanding this new composite material damaging and failure mechanisms is essential: environmental conditions, mechanical loading, and matrix damages, can lead to a decrease in its self-protective properties. The aim of this work is to identify prevailing high temperature degradation mechanisms of those MI SiC/SiC CMCs, depending of different thermal, mechanical and environmental stresses. To fulfill that outcome, a multi-scale approach was considered, by examining phenomena from single constituents to complex composite architecture (effects of constituents’ synergy). High temperature oxidation/corrosion behaviors of the composite material and each of its constituents were characterized, and modeled to meet representative combustion environment. Different operating areas of efficient self-protection of the composite material were therefore highlighted. In the same perspective, themomechanical behaviors of both matrix constituents and composite were experimentally explored, enabling the determination of behavior laws. Related degradations in the composite material were also analyzed. Crossing all results, it was thereby possible to evaluate kinetics and criticality of failure mechanisms: different damaging scenarios are thus proposed, depending on environmental conditions

The incorporation of Gallium Nitride (GaN) Power Amplifiers (PAs) into future high power aperture radar systems is certain; however, the introduction of this technology into multifunction radar systems will present new challenges to radar engineers. This dissertation describes a broad investigation into amplitude and phase transients produced by GaN PAs when they are excited with multifunction radar waveforms. These transients are the result of self-heating electrothermal memory effects and are manifested as interpulse instabilities that can negatively impact the coherent processing of multiple pulses. A behavioral model based on a Foster network topology has been developed to replicate the measured amplitude and phase transients accurately. This model has been used to develop a digital predistortion technique that successfully mitigates the impact of the transients. The Moving Target Indicator (MTI) Improvement Factor and the Root Mean Square (RMS) Pulse-to-Pulse Stability are used as metrics to assess the impact of the transients on radar system performance and to test the effectiveness of a novel digital predistortion concept.
Ph. D.

Today, thermophilic Campylobacter spp. (besides Salmonella) represent one of the most common sources of human bacterial gastrointestinal infection. The main source of human C. jejuni infections is the consumption of insufficient heated chicken meat. Quantitative data on the occurrence of thermophilic Campylobacter spp. on poultry carcasses and poultry meat are needed to perform quantitative risk assessments and to verify the effect of different intervention strategies. The aims of the investigations presented here were (i) to generate accurate qualitative and quantitative data on the occurrence of Campylobacter spp. on within the primary production stage in at the abattoir and food, (ii) to study the behaviour of nine genotypically different C. jejuni strains in chicken meat juice supplemented with different concentrations of sodium chloride, curing salt and sodium nitrite, (iii) to detect the Campylobacter genotype distribution in poultry flocks by applying AFLP analysis and to describe a potential carry-over of Campylobacter strains among sequential and adjacent poultry flocks. For the above mentioned purposes, a number of samples (171 neck skin samples, 1047 samples of different turkey meat products and 112 turkey minced meat samples from an abattoir) were investigated in accordance with themethod of ISO / TS 10272-2: 2006 and ISO10272-1: 2006 to the quantitative and qualitative presence of Campylobacter spp.. The Campylobacter-strains were inoculated in chicken juice at initial concentrations of 102 and 104 CFU/ml and incubated for 24h at 42°C. Furthermore, 18 flocks of four poultry species were monitored to investigate the distribution and spread of Campylobacter genotypes between sequential and adjacent flocks. Caecal and liver samples were obtained at frequent intervals from birds of all flocks and these samples were examined for Campylobacter. The amplified fragment length polymorphism (AFLP) analysis was performed to genotype Campylobacter isolates. The prevalence of Campylobacter on neck skin was 83.0 % and the mean number was 2.00 log10 cfu/g. For turkey meat samples with skin (wings and thighs) the detected prevalence was 68.2 % and mean number 1.73 log10 cfu/g, respectively. Turkey meat samples without skin (breast filet) showed a prevalence of 79.0 % and a mean number of 1.58 log10 cfu/g. No Campylobacters were detectable in the turkey minced meat samples. Large variations between the detectable numbers of Campylobacter spp. were observed (maximum number up to 3.98 log10 cfu/g for turkey meat with skin) and confirm the importance of an early detection (before or during slaughter and processing) of these heavily contaminated slaughter lots. Whereas the strains multiplied in the media supplemented without additional of NaCl or with 1% NaCl, the bacterial population was significantly reduced when 2% NaCl was added. Growth did not occur and the cell number gradually decreased in chicken meat juice containing 3% NaCl. Significant differences in the survival potential among the different strains were only visible in the extreme condition of 3% NaCl supplementation. There was no different behaviour of the strains under the influence of NaCl compared with the behaviour in meat juice containing curing salt. The addition of sodium nitrite did not alter the survival. Of the 1643 caecal and liver samples investigated, 452 (27.5%) caecal samples and 11 (0.7%) liver samples contained Campylobacter. Of the caecal isolates 76.3% were identified as C. jejuni and 23.7% were identified as C. coli. Poultry flocks were largely colonized by more than one AFLP type and an intense exchange of Campylobacter genotypes between different poultry flocks occurred. The results show clearly that poultry and poultry meat are regarded as one of the main sources of thermophilic Campylobacter spp. infection in humans in the food chain. This is evident not only from the high rate of occurrence of these pathogens, but also from the often-high quantitative exposure samples. The risk of a foodborne infection is also enhanced by the comparatively very low minimum infectious dose for humans. At present, a complete elimination of thermophilic Campylobacter spp. from the food chain appears practically unreachable. This difficulty is reduced by the results of genetic strain diversity, because they suggest the existence of a variety of input sources
hermophile Campylobacter (C.) spp. stellen heute neben den Salmonellen eine der häufigsten Ursachen für bakteriell bedingte Magen-Darm-Erkrankungen beim Menschen dar. Unzureichend erhitztes Geflügelfleisch und Geflügelfleischprodukte stellen eine der Hauptinfektionsquellen für humane C. jejuni-Infektionen dar. Quantitative Daten über die Belastung von Geflügelkarkassen und Geflügelfleisch mit thermophilen Campylobacter spp. werden benötigt, um einerseits quantitative Risikobewertungen durchführen zu können, andererseits aber auch den Erfolg verschiedener Interventionsmaßnahmen messen zu können. Zur Minderung der Zahl alimentär bedingter humaner Campylobacter-Infektionen spielt neben der Senkung der Campylobacter-Belastung von Nutztieren und der Vermeidung von Kreuzkontaminationen auch die Reduktion des Vorkommens des Erregers in der Lebensmittelkette durch technologische Prozesse eine große Rolle. Campylobacter spp. sind während der Be- und Verarbeitung von Lebensmitteln verschiedensten Stressoren ausgesetzt. Ziele der hier vorgestellten Untersuchungen waren, (i) Exakte qualitative und quantitative Daten zum Vorkommen von Campylobacter spp. in der Primärproduktion, auf dem Schlachthof und in Lebensmitteln zu ermitteln. (ii) Die Tenazität ausgewählter, genetisch unterschiedlicher C. jejuni-Stämme gegenüber verschiedenen Natriumchlorid-, Pökelsalz- und Natriumnitrit-Konzentrationen im Geflügelfleischsaftmodell zu untersuchen. (iii) Die Verwandtschaftsgrade der isolierten Stämme mit Hilfe einer molekularbiologischen Fingerprintingmethode (AFLP-Typisierung) darzustellen sowie das Vorkommen von thermophilen Campylobacter in verschiedenen Geflügelarten in einem Betrieb zu ermitteln. Dazu wurden 171 Halshautproben, 783 Proben verschiedener Putenfleischerzeugnisse und 233 Putenhackfleischproben aus einem Schlacht- und Zerlegebetrieb in Anlehnung an die Methode ISO/TS 10272-2: 2006 und ISO10272-1:2006 auf das quantitative und qualitative Vorkommen von Campylobacter spp. untersucht. Der Keimzahlverlauf wurde in experimentell kontaminiertem Geflügelfleischsaft (Zusatz von C. jejuni: 102 und 104 KbE/ml) über einen Zeitraum von 24 h (Bebrütungstemperatur 37°C) untersucht. 19 verschiedene Wirtschaftsgeflügel-Herden wurden untersucht, um die Verteilung und Ausbreitung von Campylobater-Genotypen zwischen sequentiellen und angrenzenden Herden festzustellen. Blinddarm- und Leber-Proben wurden in kurzen Abständen von Vögeln aller Herden gewonnen und untersucht . Für die Genotypisierung von Campylobacter spp. wurde die AFLP-Methode eingesetzt. Im Ergebnis wurden auf 83,0 % der Halshautproben Campylobacter spp. nachgewiesen, wobei der Mittelwert der quantitativen Belastung von Putenhalshautproben bei 2,00 log10 KbE/g lag. Putenfleischproben mit Haut waren zu 54,8 % Campylobacter positiv. Hier betrug die quantitative Belastung 1,79 log10 KbE/g. Bei Putenfleisch ohne Haut lagen die Nachweisraten bei 52,2,% bzw. 2,03 log10 KbE/g. In keiner der Putenhackfleischproben war Campylobacter nachweisbar. Große Schwankungen in der quantitativen Belastung (Maximalwerte bis 4,0 log10 KbE/g bei Putenfleisch mit Haut) bestätigen die Notwendigkeit, vor allem die stark belasteten Schlachtpartien schon vor bzw. während der Schlachtung und Verarbeitung identifizieren zu können. In Geflügelfleischsaft ohne bzw. mit Zusatz von 1% NaCl konnten sich alle Stämme vermehren, während das Wachstum bei 2% NaCl-Zusatz gehemmt wurde. Darüber hinaus konnte bei höherer NaCl-Konzentration (3%) eine Reduktion der Keimzahl nach 6 h Bebrütung bzw. ein Absterben von C.jejuni nach 24 h festgestellt werden. Dabei zeigten die Stämme im Geflügelfleischsaft mit 3% NaCl-Zusatz signifikante Unterschiede in ihrer Absterberate. Es konnte gezeigt werden, dass unterschiedlich ausgeprägte Salztoleranzen innerhalb der untersuchten Stämme mit unterschiedlichem Genotyp existieren, diese jedoch nur unter Extremsituationen signifikant ausgeprägt waren. Durch die Zugabe von praxisüblichen Pökelsalzkonzentrationen anstelle von Kochsalz und von Natriumnitrit konnte das Verhalten von C. jejuni in keinem Versuchsansatz beeinflusst werden. 452 Caecalproben (27,5%) und 11 Leberproben (0,7%) von insgesamt 1643 Caecal- und Leberproben wurden positiv auf Campylobacter spp. getestet. Von den 1643 aus dem Caecum stammenden getesteten Isolaten wurden 76,3% der Isolate als C. jejuni und (23,7%) der Isolate als C. coli identifiziert. Die AFLP- Analyse zeigte einen signifikanten Unterschied in der Diversität der AFLP-Typen aus den individuellen Herden und Proben aus unterschiedlichen Herden. Dies deutet auf eine große Zahl von Infektionsquellen hin. Die Ergebnisse belegen insgesamt sehr deutlich, dass Geflügel- Geflügelfleisch eine bedeutsame Quelle des Eintrags von Campylobacter-Keimen in die Nahrungskette ist. Das geht nicht nur aus der hohen Rate des Vorkommens dieser Erreger hervor, sondern auch aus der oftmals hohen quantitativen Belastung der Proben. Das Risiko einer Lebensmittelinfektion wird zudem durch die vergleichsweise sehr geringe minimale Infektionsdosis für den Menschen erhöht. Eine vollständige Elimination von thermophilen Campylobacter spp. aus der Lebensmittelkette erscheint derzeit praktisch nicht erreichbar. Diese Schwierigkeit wird durch die Ergebnisse zur genetischen Stammdiversität untersetzt, denn sie legen die Existenz einer Vielzahl unterschiedlicher Eintragsquellen nahe

Made available in DSpace on 2014-12-17T14:07:04Z (GMT). No. of bitstreams: 1 JulianaPN_DISSERT.pdf: 2953662 bytes, checksum: 47355bc7fed206f60c6c6b5d8565099b (MD5) Previous issue date: 2012-06-06
Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior
Nickel alloys are frequently used in applications that require resistance at high temperatures associated with resistance to corrosion. Alloys of Ni-Si-C can be obtained by means of powder metallurgy in which powder mixtures are made of metallic nickel powders with additions of various alloying carriers for such were used in this study SiC, Si3N4 or Si metal with graphite. Carbonyl Ni powder with mean particle size of 11 mM were mixed with 3 wt% of SiC powders with an average particle size of 15, 30 and 50 μm and further samples were obtained containing 4 to 5% by mass of SiC with average particle size of 15 μm. Samples were also obtained by varying the carrier alloy, these being Si3N4 powder with graphite, with average particle size of 1.5 and 5 μm, respectively. As a metallic Si graphite with average particle size of 12.5 and 5 μm, respectively. The reference material used was nickel carbonyl sintered without adding carriers. Microstructural characterization of the alloys was made by optical microscopy and scanning electron microscopy with semi-quantitative chemical analysis. We determined the densities of the samples and measurement of microhardness. We studied the dissociation of carriers alloy after sintering at 1200 ? C for 60 minutes. Was evaluated also in the same sintering conditions, the influence of the variation of average particle size of the SiC carrier to the proportion of 3% by mass. Finally, we studied the influence of variation of the temperatures of sintering at 950, 1080 and 1200 ? C without landing and also with heights of 30, 60, 120 and 240 minutes for sintering where the temperature was 950 ?C. Dilatometry curves showed that the SiC sintered Ni favors more effectively than other carriers alloy analyzed. SiC with average particle size of 15 μm active sintering the alloy more effectively than other SiC used. However, with the chemical and morphological analyzes for all leagues, it was observed that there was dissociation of SiC and Si3N4, as well as diffusion of Si in Ni matrix and carbon cluster and dispersed in the matrix, which also occurred for the alloys with Si carriers and metallic graphite. So the league that was presented better results containing Si Ni with graphite metallic alloy as carriers, since this had dispersed graphite best in the league, reaching the microstructural model proposed, which is necessary for material characteristic of solid lubricant, so how we got the best results when the density and hardness of the alloy
Ligas de N?quel s?o freq?entemente utilizadas em aplica??es que requerem resist?ncia mec?nica a elevadas temperaturas associada ? resist?ncia ? corros?o. Ligas de Ni-Si-C podem ser obtidas por meio de metalurgia do p? em que s?o realizadas misturas de p?s de n?quel met?lico com adi??es de p?s de diferentes portadores de liga, para tal foram utilizados neste trabalho SiC, Si3N4 ou Si met?lico com grafita. P?s de Ni carbonila com tamanho m?dio de part?culas de 11 μm foram misturados a 3% em massa de p?s de SiC com tamanho m?dio de part?culas de 15, 30 e 50 μm e foram obtidas ainda amostras contendo 4 e 5% em massa de SiC com tamanho m?dio de part?culas de 15 μm. Tamb?m foram obtidas amostras variando-se o portador de liga, sendo estes p?s de Si3N4 com grafita, com tamanho m?dio de part?culas de 1,5 e 5 μm, respectivamente. Assim como Si met?lico com grafita, com tamanho m?dio de part?culas de 12,5 e 5 μm, respectivamente. O material de refer?ncia adotado foi n?quel carbonila sinterizado sem adi??o de portadores. A caracteriza??o microestrutural das ligas foi feita por microscopia ?ptica e eletr?nica de varredura com an?lise qu?mica semi-quantitativa. Foram determinadas as densidades das amostras e obtidas medidas de microdureza Vickers. Foi estudada a dissocia??o dos portadores de liga ap?s sinteriza??o em 1200 ?C durante 60 minutos. Foi avaliada, ainda, para as mesmas condi??es de sinteriza??o, a influencia da varia??o do tamanho m?dio de part?culas do portador SiC, para a propor??o de 3% em massa. Por fim, foi estudo a influencia da varia??o das temperaturas de sinteriza??o em 950, 1080 e 1200 ?C sem patamar e, ainda, com patamares de 30, 60, 120 e 240 minutos para sinteriza??o cuja temperatura foi de 950 ?C. As curvas de dilatometria mostraram que o SiC favorece a sinteriza??o do Ni de forma mais eficaz que os demais portadores de liga analisados. O SiC com tamanho m?dio de part?culas de 15 μm ativa a sinteriza??o da liga de forma mais eficaz que os demais SiC utilizados. Por?m, com as an?lises qu?mica e morfol?gica para todas as ligas, foi poss?vel observar que houve dissocia??o do SiC e do Si3N4, assim como difus?o do Si na matriz de Ni e carbono aglomerado e disperso na matriz, o que tamb?m ocorreu para as ligas com portadores Si met?lico e grafita. Portanto, a liga que apresentou melhores resultados foi de Ni contendo Si met?lico com grafita como portadores de liga, j? que esta apresentou grafita melhor dispersa na liga, atingindo o modelo microestrutural proposto, do qual ? necess?rio para material com caracter?stica de lubrificante s?lido, assim como obteve os melhores resultados quando a densidade e dureza da liga

Au cours de ce travail, nous avons étudié deux types de défauts interfaciaux: domaines d’inversion (DI) et joints de grains (JG) dans des semiconducteurs de structure wurtzite (nitrures- d’éléments III, ZnO et l’hétérostructure ZnO/GaN) en utilisant le MET haute résolution et la modélisation ab initio. Dans le cas des DI, nos analyses théoriques montrent qu'une configuration tête-à-tête avec une séquence d'empilement à l’interface AaBbAa-AcCaA (H4) est la structure la plus stable dans les composés binaires (nitrures et ZnO wurtzites). De plus, un gaz d’électrons (2DEG) ou de trous (2DHG) à 2 dimensions est formé pour les configurations « tête-à-tête » ou queue-à-queue. A l’interface ZnO/GaN, l'observation de MET très haute résolution a confirmé la configuration H4 avec une interface -Zn-O-Ga-N. Notre modélisation théorique a mis en évidence la formation d’un gas de trous à 2 dimensions à cette hétérointerface. Nous avons aussi réalisé l’étude topologique, théorique et par MET des joints de grains de rotation autour de l’axe [0001] dans ces matériaux. Dans le GaN, nous avons trouvé que les plans du joint sont simplement formés par des dislocations de type a déjà connues pour le matériau en couche mince. Par contre, dans ZnO, la théorie topologique est complétement démontrée, et la dislocation [101 ̅0] est une brique de base dans la constitution des joints de grains avec des cycles d’atomes 6-8-4-
In this work, we investigated two kinds of interfacial defects: inversion domain boundaries (IDBs) and grain boundaries (GB) in wurtzite semiconductors (III-nitrides, ZnO and ZnO/GaN heterostructure) using high-resolution TEM and first-principle calculations. For IDBs, theoretical calculation indicated that a head-to-head IDB with an interfacial stacking sequence of AaBbAa-AcCaA (H4) is the most stable structure in wurtzite compounds. Moreover, 2-dimensional electron gas (2DEG) and 2-dimensional hole gas (2DHG) build up in head-to-head and tail-to-tail IDBs, respectively. Considering the IDB at the ZnO/GaN heterointerface, TEM observations unveiled the H4 configuration with a -Zn-O-Ga-N interface. Moreover the theoretical investigation also confirmed stability of this interface along with the corresponding formation of a 2DHG. A detailed topological, TEM and theoretical investigation of [0001] tilt Grain Boundaries (GBs) in wurtzite symmetry has also been carried out. In GaN, it is shown that the GBs are only made of separated a edge dislocations with 4, 5/7 and 8 atoms rings. For ZnO, a new structural unit: the [101 ̅0] edge dislocation made of connected 6-8-4-atom rings is reported for the first time, in agreement with an early theoretical report on dislocations and jogs in the wurtzite symmetry

Depuis de récentes années de nouveaux composants optiques ont fait leur apparition. Ces composants connus sous les noms de « Méta-optiques » ou encore « Métasurfaces », rendent possible le contrôle et la mise en forme du front d’onde de la lumière permettant alors de mettre en forme n’importe quel faisceau incident et ainsi créer des fonctionnalités optiques classiques telles que focaliser ou dévier la lumière, ou alors des fonctionnalités aux propriétés surprenantes telle que la réalisation de métahologramme dépendant en polarisation. En effet, grâce à l’arrangement périodique de résonateurs de dimensions géométriques sous-longueur d’onde, il est alors possible d’obtenir un contrôle local arbitraire du faisceau incident. Néanmoins, même si de nombreuses applications ont pu être démontré dans la communauté, seuls quelques matériaux se retrouvent être compatibles pour le développement industriel de ces composants. De plus, afin de passer de composant passif à actif, pour la réalisation de composant dynamique, il est nécessaire de passer de matériau diélectrique à matériau semi-conducteur. C’est pourquoi dans ces travaux, nous nous sommes intéressés à l’utilisation d’un matériau semi-conducteur qui est le Nitrure de Gallium pour la réalisation de composants métasurfaciques. Nous présentons alors dans un premier temps une étude numérique des nanostructures utilisées lors de ces travaux. Puis nous montrons comment est réalisée la conception de nos méta-optiques en présentant la méthode de design et les procédés de nanofabrications employés, notamment une nouvelle technique de gravure, compatible uniquement avec les matériaux cristallins et préservant leurs propriétés optiques. Nous exposons ensuite différentes applications où nos composants sont utilisés telles que : la réalisation de métalentilles de large ouverture numérique et de large surface, l’optimisation de réseaux métasurfaciques permettant d’atteindre des efficacités de diffraction supérieur à 80% ou encore la réalisation expérimentale de méta-hologramme permettant de conserver l’information du moment angulaire orbitale du faisceau incident
In the past years, new optical components have appeared. These components, known as "meta-optics" or "metasurfaces", made it possible to control and to shape the wavefront of the light. This allows the control of any incident beam and the creation of conventional optical functionalities, such as focusing or deflecting the light, or functionalities with additional features such as the possibility of creating polarization-dependent meta-holograms. Indeed, thanks to the periodic arrangement of resonators with sub-wavelength geometric dimensions, it is possible to obtain an arbitrary local control of the incident beam. Nevertheless, even though many applications have been demonstrated in the community, only a few materials are found to be compatible for the industrial development of these components. In addition, in order to pass from passive to active components for the fabrication of dynamic devices, it is necessary to switch from dielectric materials to semiconductor materials. For these reasons, we are interested in the use of a semiconductor material, Gallium Nitride, for the development of metasurface components. We first present a numerical study of the nanostructures used during this work. Then, we show how the design of our meta-optics is done by presenting the numerical conception method and nanofabrication processes used, which includes a new etching technique compatible only with crystalline materials while preserving their optical properties. Finally, we suggest different applications where our components can be used, such as: the development of metalenses with high numerical aperture and large surface; the optimization of metasurface high contrast gratings allowing to reach diffraction efficiencies higher than 80%; or the fabrication of meta-holograms preserving the information of the orbital angular momentum of the incident beam

碩士
中興大學
食品暨應用生物科技學系所
99
Red mold rice (RMR) is a kind of fermented rice by growing Monascus on the cooked rice. The Japanese named it beni koji or aka koji, while the European called it Chinese red rice. RMR is used to make wine and fermented soybean curd in Taiwan and southeast area. In addition, it can be as a coloring agent and seasoning for foods, meat preservative and traditional Chinese medicine as well. It is reported that RMR is considerably rich in nutrition. In this study, RMR was prepared by inoculating a strain of Monascus purpureus BCRC 33327 into cooked rice, and semi-solid state fermentation was performed. Finally, the fermentation broth was pressed and dehydrated by freeze-drying. The dehydrated RMR was then used as one of food additives in preparing the salted and cured meat (SCM) to partially replace sodium nitrite. Changes in components of RMR and SCM were investigated during fermentation of RMR and curing of SCM. Results showed that the total soluble solid content increased with the fermentation time, and the Hunter’s L value appeared going down, but Hunter’s a and b values showed increase. The total soluble content reached to 28.1~28.8±0.2 oBrix after pressing of RMR, which was found hard to be dried completely. The crude protein content increased from 0.32±0.03% to 1.46±0.08%; while crude fat increased from 5.91±0.30% to 7.93±0.83% during lyophilization of RMR. Five different ratios of nitrite to RMR at 0.075%: 0%; 0.0375%: 1%; 0%: 1%; 0%: 2%; and 0%: 3%, were used to make SCM. The curing time was 42 hours. Negative relationship between Hunter’s L value of SCM and amount of RMR added was found; however, those Hunter’s a and b values of SCM appeared positive relationship. Regarding changes of antioxidant activity, the DPPH scavenging ability was 14.31±0.93% for SCM with nitrite alone; but it was 25.19±0.91% if 3% RMR was used. The reducing power was 0.572±0.001 for SCM with only nitrite being added, while it was 0.903±0.006 for that of adding 3% RMR. Similarly, the total antioxidant capacity increased from 0.04±0.00 mM to 0.13±0.00 mM as trolox. In general, the antioxidant activities of SCM were increased with amount of RMR added. Content of γ-aminobutyric acid (GABA) of RMR was 0.019±0.001%, while citrin was unable to be detected in SCM. Results of sensory evaluation by Preference test revealed that SCM prepared by adding nitrite and RMR at ratio of 0.0375% to 1% won the highest score.