Orientador: Glaucia Maria Pastore / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-03T14:23:04Z (GMT). No. of bitstreams: 1 Mamede_MariaEugeniadeOliveira_D.pdf: 3704106 bytes, checksum: 9f08fafe3f55058c6c5aa2d4ddd660c1 (MD5) Previous issue date: 2003 / Resumo: O vinho é uma bebida obtida pela completa ou parcial fermenta ção alcoólica do mosto de uva. A comercialização do vinho teve uma razoável evolução no Brasil. Os Champanhas/espumantes e espumantes "Asti" foram os vinhos que tiveram o maior consumo pela população brasileira nos últimos 10 anos. O Estado do Rio Grande do Sul (RG) é responsável por mais de 90 % da produção de uva para elaboração do vinho. A região da Serra Gaúcha (RG) produz uva com as melhores características para produção de vinho espumante. Durante a fermentação alcoólica, além de etanol, C02, glicerol são formados em paralelo compostos de sabor e aroma de diferentes classes de subst âncias tais como: ésteres, álcoois, ácidos, aldeídos, cetonas, lactonas, fenóis voláteis, terpenos, acetais, nitrilas, amidas entre outras. Estas classes de substâncias são provenientes da uva, da fermentação e também do envelhecimento ou amadurecimento. A análise sensorial permite a nós identificar as características ou propriedades que nos agradam em um alimento e tem sido utilizada intensamente para classificar vinhos com base na sua composição aromática. Os objetivos deste trabalho foram: a) isolar e selecionar microrganismos produtores de aroma de frutas em meio sintético; b) identificar os microrganismos produtores de aroma de frutas; c) estudar a composição de voláteis produzidos pelos microrganismos selecionados nos mostos de uvas Chardonnay e Pinot Noir; d) avaliar o grau de aceitação sensorial das amostras de mosto fermentado a 15°C em relação aos voláteis de aroma produzidos. A produção de aroma foi verificada em meio sintético contendo 5 % de glicose durante 72 horas a 30°C. A seleção dos microrganismos produtores de aroma foi realizada pela análise sensorial direta descritiva utilizando 10 provadores. A identificação das leveduras foi realizada pelo sistema automático e padronizado mini API/ID 32 C. Análises físico-químicas do mosto como densidade, álcool e açúcar foram realizados pelo densímetro Mustimetre DujardinSalleron (385200); as análises de acidez volátil, acidez total, S02 livre e total foram realizadas por titulação Os mostos Chardonnay e Pinot Noir foram fermentados com as leveduras selecionadas a 15°C e 20°C durante sete dias. Os compostos voláteis de aroma foram extraídos pela técnica de extração líquido-líquido com éter-etílico/hexano (1:1) e por ¿Dynamica Headspace¿ e identificados por cromatografia gasosa/espectrometria de massa (CG-EM) e índice de Kovats. A análise de aceitação do mosto fermentado a 15°C durante sete dias foi realizada por uma equipe composta por 25 provadores representativos do público alvo, utilizando escala hedônica não estruturada de nove centímetros. A intenção de compra foi registrada em uma escala de atitude de cinco pontos. As leveduras selecionadas foram Saccharomyces cerevisiae, Candida valida, Kloeckera apiculata e Pichia membranaefaciens. As leveduras apresentaram um maior cresicmento a 20°C do que a 15°C. Conseqüentemente a produção de compostos voláteis foi maior a 20°C do que a 15°C. Compostos formados durante a fermentação como acetaldeído, acetato de etila, etanol, isobutanol, acetato de amila, acetato de isoamila, álcool isoamflico, feniletanol, acetato de 2-feniletanol, ácido hexanóico, ácido propanóico, ácido butanóico, propanal, butanal entre outros foram detectados nos mostos e no caldo sintético em diferentes concentrações. Os resultados da análise de aceitação mostraram que oito amostras diferiram entre si na produção de aroma. Pelo teste de tukey apenas uma amostra diferiu significativamente em relação às outras amostras. Este resultado pode ser salientado pelos dados da concentração dos compostos majoritários, que mostrou ser muito similar na composição aromática das três amostras com maior aceitação / Abstract: Wine is an alcoholic drink obtained by the partial or complete alcoholic fermentation of grape must. The wine markets have evolved reasonably in Brazil. Champagne/sparkling and "Asti" sparkling core those most consumed by the population in the last 10 years. State of "Rio Grande do Sul" (RG) is responsible for more than 90 % the grape production for wine making. The "Serra Gaúcha"region produces grapes with the best characteristics for sparkling wine production. During the alcoholic fermentation in addition to ethanol, CO2 and glycerol are formed in parallel with flavor components derived from difterent groups of substances, such as esters, alcohols, acids, aldehydes, ketones, lactones, volatile phenols, tepenes, acetals, nitriles, etc. These groups of substances come from the grape or are formed during maturation/aging. Sensory analysis allows us to identify pleasant characteristics or properties of the food under study. It has been intensively uses to classify wines based on their aromatic composition. In this work we aimed: a) to isolate and select microorganisms that product fruit aroma in synthetic media, detectable by direct descriptive analysis; b) to identify the fruit aroma producing microorganisms; c) to study the composition of the volatiles produced by the selected microorganisms in Chardonnay and Pinot Noir grape musts; d) to evaluate the degree of sensory acceptance of must sample fermented at 15°C, with respect to the volatile aroma produced. The production of aroma was verified in synthetic media containing 5 % glucose during 72 hours at 30°C. Selection of aroma producing microorganisms in synthetic media was performed by direct descriptive sensorial analysis, using 10 testers. Yeast identification was carried out by the standard automatic system, mini APIIID 32 C. Physico-chemical analysis of the musts, such as and alcohol and sugar content, were eftected using the Mustimetre Dujardin-Salleron Densimeter (385200); the analyses of total volatile acidity, acidity, free and total S02, were carried out by titration. The Chardonnay and Pinot Noir musts were inoculated with the yeast at 15°C and 20°C incubated for 7 days. The volatile aroma compounds were extracted by the liquid ¿liquid incubated for 7 days. The volatile aroma compounds were extracted by the liquid-liquid exraction technique ethyl ether/hexane (1:1) and by the purge and trap extraction system and identified by GC;MS and by the kovats index. The acceptance fermeted must of the was determined by a team of 25 representative target consumers using a nine centimeter non-structured hedonic scale. The purchasing intention was registered on a five points attitude scale. The selected yeast were Saccharomyces cerevisiae, Candida valida, Kloeckera apiculata and Pichia membranaefaciens. The yeast grew more at 20°C than at 15°C. Consequently, they produced a higher concentration of volatiles at 20°C than at 15 oCo Compounds formed during fermentation, such as acetaldehyde, ethyl acetate, ethanol, isobuthyl alcohol, amyl acetate, isoamyl acetate, isoamyl alcohol, phenylethanol, 2-fenylethanol acetate, hexanoic acid, propanoic acid, butanoic aCid, propanal, butanal and others were detected in the must and the synthetic broth in different concentration. Results of the sensory analysis of the musts fermented at 15°C showed that the 8 samples tested differed between themselves with respect to the aromas produced. Using Tukey's test, only one sample was significant/y different in comparison with the others. This result is apparent from the data for the concentration of the major compounds, which were very similar for the three most accepted samples / Doutorado / Doutor em Ciência de Alimentos

Orientadores: Telma Teixeira Franco, Carlos Ricardo Soccol / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-03T19:30:30Z (GMT). No. of bitstreams: 1 Tagliari_CristianeVanessa_D.pdf: 4479697 bytes, checksum: 6be0c025bfea14b198b09f150c93d561 (MD5) Previous issue date: 2003 / Resumo: Avanços na biotecnologia, principalmente na área de tecnologia enzimática e de fragmentações, oferecem oportunidades para a utilização econômica de resíduos agroindustriais. A casca obtida durante o processamento do café por via seca tem sido pouco empregada quando comparada com volume em que é gerada. Este resíduo poderia ser mais utilizado se compostos tóxicos como cafeína e taninos fossem removidos. Fungos filamentosos são capazes de assimilar cafeína e taninos de um meio sintético líquido ou de resíduos de café. Existem poucos trabalhos sobre a detoxificação da casca de café e esta nunca foi relatada com cepas de Rhizopus delemar. A via de degradação da cafeína por este microrganismo e as enzimas envolvidas neste processo também não estão descritas na literatura. O objetivo deste trabaJho foi agregar valor a casca de café por fennentação no estado sólido com R. delemar, investigar a via de degradação da cafeína e caracterizar as enzimas envolvidas neste bioprocesso. As condições de fermentação da casca de café por R. delemar foram otimizadas e os melhores níveis de detoxificação (86% de redução da cafeína e 60% de taninos) foram obtidos em frascos de Erlenmeyer com 75% de umidade inicial, 1O6esporos/g substrato seco, pH 6,5 e 28°C. A cinética do processo fermentativo foi conduzida no biorreator de colunas com as condições otimizadas previamente e indicou que o desenvolvimento do fungo filamentoso e a sua respiração foram relacionados com a degradação de cafeína e de açúcares totais presentes na casca de café. A fase exponencial de crescimento microbiano foi encontrada entre 3 e 5 dias, quando foi detectado máximo consumo de 02 e após a máxima produção das enzimas e degradação da cafeína. Valores máximos de atividade enzimática, 1,8 e 3,3 U/g s.s. para a cafeína e a teofilina demetilase respectivamente, foram obtidos após 2 dias de fermentação em frascos de Erlenmeyer. O extrato enzimático foi estável após estocagem a 2°C e o Km estimado, a temperatura e o pH ótimos foram respectivamente 150J.1M, 30°C e pH 6,5 para a cafeína demetilase e 180J.µM, 30°C e pH 7,4 para a teofilina demetilase. Os resultados mostraram boas perspectivas para a utilização de Rhizopus sp. em processos de detoxificação da casca de café e novas oportunidades poderão surgir para a utilização deste bioproduto e para a aplicação do extrato enzimático obtido neste processo / Abstract: Advances in biotechnology, mainly in the area of enzymes and fermentation technology, offer potential opportunities for economic utilization of agro-industrial residues. The coffee husk obtained during dry processing of coffee has been poorly utilized when compared with the produced volume. Removing the toxics compound as caffeine and tannin, this residue could be more utilized. Filamentous fungi are able to assimilate caffeine and tannins from liquid synthetic media or coffee residue. There are few works about coffee husk detoxification and it was never described with strains of Rhizopus delemar. The caffeine degradation pathway and the enzymes involved in this process have not been described in the literature to. The aim of this work was to improve the nutritive value of coffee husk by solid-state fermentation with R. delemar, to investigate the caffeine degradation pathway and to charactecize enzymes involved in this bioprocess. The conditions of coffee husk fermentation by R. delemar were optimized and the best detoxification levels (86% of caffeine and 60% of tannin reduction) were obtained in Erlenmeyer t1asks with 75% initial moisture, 1O6spores/g dry substrate, at pH 6.5 and 28°C. The kinetic of fermentative process was carried out in packed bed column bioreactor using the conditions previously optimized and showed that the development of filamentous fungi and its respiration was related with caffeine degradation and total sugars presents in coffee husk. The exponential phase of microbial growth was achieved between 3 and 5 days, when was detected maximal 02 consumption and after the maximum production of enzymes and caffeine degradation. The maximum activities, 1.8 and 3.3 U/g d.s. for caffeine and the ophylline demethylase respectively, were achieved at 2 days of fermentation in Erlenrneyer :flasks. The enzymatic extracts were stable after storage at 2°C and the Km estimated, the optimum temperature and pH were respectively 150J.1M, 30°C and pH 6.5 for caffeine demethy1ase and 180J.µM, 30°C and pH 7.4 for theophylline demethy1ase. The results showed good prospects of using Rhizopus sp. for the coffee husk detoxification and would open new opportunities for the utilization of this byproduct and for enzymatic extract application / Doutorado / Desenvolvimento de Processos Químicos / Doutor em Engenharia Química

Orientador : Ahmed Athia El-Dash / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-03T23:17:14Z (GMT). No. of bitstreams: 1 Bianchini_MicheleCarolina_M.pdf: 1596733 bytes, checksum: cae6289c734fc3fd9db1acfae0c80c6d (MD5) Previous issue date: 2004 / Resumo: Um fermento natural desenvolvido para produção de panetone passou por uma secagem, visando obter um fermento natural em pó. Este trabalho investigou primeiramente os métodos de secagem viáveis para as leveduras e as bactérias lácticas presentes no fermento natural. Os métodos testados foram secagem em spray drier e secagem em estufa com ar forçado. O objetivo foi encontrar uma alternativa para a liofilização que é frequentemente usada em secagem de microorganismos. Após a seleção do método de secagem foram realizados 17 tratamentos referentes a um planejamento experimental 23 com três repetições no ponto central e seis pontos axiais. As variáveis independentes foram: temperatura de secagem (24, 32 e 40ºC), porcentagem de sorbitol (2, 6 e 10%) e porcentagem de sacarose (1, 3 e 5%). As variáveis respostas foram: tempo de secagem, contagem de bactérias lácticas e contagem de leveduras. As melhores condições encontradas foram 24ºC, 2% de sorbitol e 1% de sacarose. Durante as aplicações do fermento seco verificou-se que o antes e o pós da secagem têm uma influência muito grande na performance do fermento. A preparação do fermento para secagem ¿ que inclui a extrusão do fermento em extrusora de macarrão e os métodos de reidratação do fermento seco foram testados e analisados. O melhor crescimento dos microorganismos foi obtido com uma reidratação com 1,5% de leite em pó e 0,23% de nutriente de fermento. Com a reidratação definida, realizou-se os testes para o acerto da receita e do processo de fabricação de panetone com fermento seco. O panetone com fermento seco foi comparado tecnicamento com o panetone feito com fermento natural. Os parâmetros avaliados foram: volume específico, cor da crosta, características da crosta, cor do miolo, estrutura do miolo, umidade do miolo, aroma, gosto, pH e maciez em texturômetro. Na pontuação geral não houve diferença significativa entre o padrão e o teste. Na análise do pH, o panetone com fermento natural seco apresentou diferença significativa em relação ao panetone padrão, porém os valores atingidos os normais para o padrão de panetone. A análise da maciez em texturômetro mostrou uma ligeira superioridade do panetone padrão nos primeiros 30 dias. Na análise com 40 a 80 dias de fabricação os panetones tiveram uma maciez similar. O estudo mostrou que é possível eliminar a etapa de manutenção do fermento natural com a sua secagem e que fermento natural seco obtido é capaz de produzir panetones com bons resultados / Abstract: It has been developed a sourdough to produce panetone and it was dried. This work investigated firstly the practicable drying methods for yeasts and acid lactic bacterias presents in the sourdough. Spray drier and hot air. The object was to find an alternative to the freeze drying method, wich is often used to microorganisms. After the selection of the best method, an experimental design 23 with 17 treatments was planned ¿ with three central points and six axial points. Independent variables were: drying temperature (24, 32 and 40ºC), sorbitol dosage (2, 6 and 10%) and saccharose dosage (1, 3 and 5%). Dependents variables were: drying time, acid lactic bacteria counting and yeast counting. The best conditions were 24ºC, 2% of sorbitol and 1% of saccharose. During the dried sourdough aplications was verified that before and after drying conditions had a big influence in the sourdough performance. The sourdough drying preparation ¿ includes the sourdough extrusion and the sourdough rehidratation methods ¿ were analysed. The best microorganism development was obtained with 1,5% of powder milk and 0,23% of sourdough nutrient. Defined the rehidratation, tests to ajust the recipe and process were done. The panettone done with the dried sourdough was technically compared with the normal panetone with fresh sourdough. The considered parameters were: specific volum, color crust, crust caracteristics, color crumb, crumb struture, crumb moisture, flavour, taste, pH and softness. There was no significante diference at 5% in the total pontuation between standard and test. The tested panettones had significative diference compared with the standard in pH, although the obtained values were normal found in literature. In softness analysis the standard panettone had a little superiority in the first thirty days. In the analysis with 40 to 70 days after production all panettones had a similar softness. The study showed that it is possible to elimate the sourdough maintenance step and to obtain panettones with good results / Mestrado / Mestre em Engenharia de Alimentos

Food fermentation is a method widely used in the past to extend the storage life of food. Numerous studies on fermented food have revealed that they not only have biopreservative properties but also health benefits. Lactic acid bacteria are the major group of microorganisms involved in food fermentation and the properties that influence food are primarily due to the compounds released from microorganisms such as organic acids and bacteriocins. Their health benefits are exerted through several mechanisms including inhibiting the growth of pathogenic bacteria and modifying the host immune response. A number of strains that have been investigated show different properties even between the same species thus emphasizing the importance of strain identification. To determine if some traditional fermented Swedish foods contain lactic acid bacteria, bacteria from four fermented Swedish foods (two surströmming and two sausages) were isolated using MRS broth. Bacterial isolates were examined for their colony and cell morphology and Gram staining and were found to be predominantly Gram-positive cocci or rods. 16S rRNA PCR amplifications of selected isolates was performed using universal prokaryotic primers and sequenced. The sequencing results showed that the bacterial isolates from Oskars surströmming Filéer and Gognacs medvurst were Lactobacillus sakei and the isolate from Mannerströms surströmming was Enterococcus sp. This study showed that the traditional Swedish fermented food evaluated did contain lactic acid bacteria.

Ce travail consiste en l’étude de la faisabilité de l’application du chauffage ohmique aux opérations de fermentation et de cuisson de la pâte à pain, dans l’objectif d’une production de pain de mie sans croûte. Les caractéristiques de la pâte ont été étudiées, et principalement l’évolution de sa conductivité électrique – moteur de la génération de chaleur en chauffage ohmique. La conductivité électrique est très fortement dépendante des teneurs en sel et en eau de la pâte. Elle augmente également avec la température, mais diminue avec la porosité de la pâte et lors de la gélatinisation de l’amidon. Des équations simples ont pu être déterminées pour son calcul. Un premier modèle thermique a été développé afin de mieux comprendre la formation de gradients de température au sein du produit.Un prototype de four ohmique a été construit, permettant de réaliser à la fois la fermentation et la cuisson de pain de mie sans croûte. L’utilisation du chauffage ohmique permet une réduction significative de la phase de latence et donc du temps de fermentation. Une analyse d’images par tomographie rayons X a montré une porosité plusdéveloppée dans le produit fini, de même qu’une croissance des pores plus importante dans la partie supérieure du pain, contrairement à une cuisson conventionnelle.L’utilisation du chauffage ohmique en panification peut mener à des gains énergétiques potentiels d’un facteur 10. Les rendements énergétiques du procédé ont été évaluéssur gel de tylose, et sont comparables aux valeurs observées par de précédents auteurs. Enfin, un modèle numérique simplifié de transfert de chaleur et de matière a été développé, dans le but d’être employé comme outil prédictif lors d’une cuisson de pain par chauffage ohmique. / This work aims at studying the feasibility of applying ohmic heating to the proofing and baking steps of bread dough, for an objective of crustless bread production. The characteristics of the dough were studied, and mainly the evolution of its electrical conductivity – keyvariable of the heat generation in ohmic heating. The electrical conductivity is highly dependent on the salt and water contents of the dough. It also increases with the temperature, but decreases with the porosity of the dough and during the starch gelatinization step. Simple equations were used to calculate its evolution. A first thermal model was developed to understand better the formation of temperature gradients in the product.An ohmic oven prototype was built in order to realize proofing and baking of crustless bread in the same apparatus. The use of ohmic heating leads to a significant decrease of the lag time and therefore of the proofing time. An X-ray tomography image analysis showed a higher development of the porosity in the final product when using ohmic heating, as well as a more developed network in the upper part of the bread, contrary to a conventional baking.The use of ohmic heating may lead to potential energy savings of a factor of 10. The energy rates of the process were calculated using a gel of tylose, and were in the range of what could be observed by previous authors. Finally, a simplified numerical model of heat and mass transfer was developed, to be used as a predictive tool during the baking of bread by ohmic heating

This study was conducted in two trials. The aim was firstly to identify the qualitative characteristics of Atriplex nummularia (Hatfield Select). Goats and sheep were used to identify three palatability groups of plants in the A. nummularia (Hatfield Select) paddock. These palatability groups were compared in terms of quality to one another. Secondly, qualitative and quantitative intakes of A. nummularia (Hatfield Select) by goats and sheep were determined. This was done in a grazing trial lasting five days. A comparison was conducted between goats and sheep as well as between the different days of the grazing period. During the first trial, goats and sheep were used to identify the most-, medium- and least-palatable A. nummularia (Hatfield Select) plants. The regrowth on these plants were harvested and used for laboratory analysis to identify the qualitative differences between these three groups. These samples were also used to determine and compare degradability between the three groups as well as between goats and sheep. Goats and sheep preferred A. nummularia (Hatfield Select) plants with a significantly (p ¡Ü 0.05) higher crude protein (CP), phosphorus (P) and magnesium (Mg) content. The most preferred plants also had higher neutral detergent fibre (NDF), Ca, K, Na, Cl- and Cu content than the least preferred plants, but these were not significant (p > 0.05). A. nummularia (Hatfield Select) provides enough CP for maintenance and production in both goats and sheep. All mineral requirements for maintenance in goats and sheep can be satisfied on A. nummularia (Hatfield Select), except that of Cu. For production (growth and lactation) only P is deficient and needs to be supplemented. A. nummularia (Hatfield Select) makes an ideal drought fodder crop to support the natural veld during the dry season. An overall higher DM, N and NDF rumen degradability of Atriplex was recorded with goats than with sheep. Goats exhibited a significantly (p ¡Ü 0.05) higher DM and N degradation and although a higher NDF degradation was also recorded, this was not significant. The rate of DM, N and NDF rumen degradation was also higher in goats than in sheep. This means that goats have a more favorable rumen environment for the digestion of A. nummularia (Hatfield Select). DM and N degradation were also significantly (p ¡Ü 0.05) higher in the most palatable group than the least palatable group. NDF degradability decreased with palatability. This means that the most palatable plants have a higher digestibility and quality than the least palatable plants. In the second experiment, rumen and oesophageal fistulated sheep and goats were allowed to graze A. nummularia (Hatfield Select) for five days. Qualitative and quantitative intakes were determined. The quality and quantity of ingested material were compared between goats and sheep as well as between the different grazing days. There was a significant decline in the quality and quantity of intake over the grazing period. Some parameters were significant, for example CP. The CP concentration declined from 18% to 3.91 % for goats and from 19.88% to 6.61% for sheep. The cell wall constituents (NDF) increased by about 10% from the start to the end of the grazing period. IVDOM decreased by 14% and intakes were almost halved from the start to the end of the grazing period. Other authors have also observed this decrease in quality and quantity of intake over time. The lower quality and quantity in intake was because of a decline in the availability of high quality edible material. At the end of the grazing period, there was very little edible material left which caused an extremely low quality and quantity of intake. Rumen NH3-N concentrations also declined as the dietary CP declined, but it was still present in high enough concentrations to sustain the rumen micro flora population. Rumen VFA decreased over the grazing period. The acetic acid to propionic acid ratio increased towards the end of the grazing period. This caused a decline in the efficiency of utilization of ME for maintenance as acetic acid has an efficiency in utilization of ME of 59% and propionic acid of 86% (McDonald et al., 1995). This means that energy will have to be supplemented to sustain maintenance. / Dissertation (MSc (Agric) Animal Science, Nutrition)--University of Pretoria, 2007. / Animal and Wildlife Sciences / unrestricted

The production of biofuels and in particular bioethanol has increased rapidly since the early 1990’s. The advantages of biofuels include reduced CO2 production, a decrease in fuel importation for many nations (notably the US and Brazil), and comparatively simple blending with fossil fuels. The production of basic fuel ethanol (1st generation) involves the use of an energy crop feedstock (corn in US and sugar cane in Brazil). The feedstock is processed via simple mechanical methods to release the simple carbohydrates, mixed with water and fermented anaerobically via S. cerevisiae yeast into ethanol and CO2. Due to the low market value of fuel ethanol, profit margins are restrictive, and as a result sterilisation and aseptic techniques are not economically viable, and contamination by environmental organisms is commonplace. The current system of biocontrol involves the addition of antibiotics, primarily penicillin and virginiamycin, to the fermentation. While these antibiotics are broad spectrum and highly effective in reducing the impact of contamination, the negative environmental impacts of antibiotic usage are well known. In order to reduce the impact of contamination and reduce reliance on antibiotics an alternative system of biocontrol is required. In this thesis various biocontrol agents are assessed, including bacteriophage, hop acids, chitosan, onion oil extract, copper and silver ions. The effect of these agents on the growth of various contaminant bacteria and a strain of S. cerevisiae is assessed and fermentations are carried out under sterile and controlled contaminated conditions to generate data on the effect of the contaminant and the various methods of biocontrol. Other possibilities investigated include the insertion of plasmids containing heat shock proteins into S. cerevisiae to enhance thermo-tolerance.

Ting is a cooked fermented sorghum food that is popular amongst southern Africans for its sour taste and unique flavour. However, major challenges are associated with large-scale production and marketing of this spontaneously fermented food due to inconsistent microbiological and sensory quality. The use of starter cultures may circumvent these limitations. Prior to engaging starter cultures, detailed knowledge of the microbial diversity and dynamics during fermentation is important. Therefore, the aim of this study was to investigate microbial diversity and dynamics during sorghum fermentations, and to clarify the role of starter cultures regarding the microbiological safety and consumer acceptance of sensory characteristics of fermented ting. A culture-independent approach, based on the use of PCR-denaturing gradient gel electrophoresis (DGGE), revealed that Lactococcus lactis, Lactobacillus curvatus, Weissella cibaria and some Enterobacteriaceae were predominant at the end of spontaneous sorghum fermentations. Culture-dependent methods indicated that Lb. fermentum, Lb. plantarum, Lb. rhamnosus, E. faecalis, E. mundtii, W. cibaria and L. lactis were predominant at the end of fermentation. These results not only indicated the predominant bacteria during sorghum fermentation, but also indicated that a combined approach is required to reveal microbial diversity and dynamics during spontaneous sorghum fermentations. Based on the above results, L. lactis, Lb. fermentum, Lb. plantarum and Lb. rhamnosus were evaluated as starter cultures for production of ting. All the starter cultures were able to ferment sorghum, but the lowest pH and highest lactic acid was produced in naturally fermented sorghum inoculated with L. lactis. This fermentation showed an increase in the number of lactic acid bacteria and yeasts, whilst pathogen counts decreased. Ting from this fermented gruel, in contrast to naturally fermented sorghum, had sensory properties preferred by panelists. The results indicated that the use of L. lactis in starter cultures may result in ting with consistent and acceptable attributes. / Thesis (PhD)--University of Pretoria, 2011. / Microbiology and Plant Pathology / unrestricted

The methylotrophic yeast Pichia pastoris has become an efficient expression system for heterologous protein production. Different methods have been studied to enhance cell growth as well as the production of products of interest. Two of the major strategies for improving the product or biomass yields are optimizing bioprocess controls and cultivation conditions. In this work, the characteristics of this yeast system and of its different promoters are discussed, and the effect of operational strategies on cell growth and recombinant protein expression is also studied. The effect of different feeding strategies were studied and optimized for pGAP (glyceraldehyde-3-phosphate dehydrogenase)-regulated phytase production in P. pastoris. Alternative carbon sources were screened and the feasibility of using citric acid as a carbon source for recombinant protein production was also investigated. The effects of parameters such as the carbon source concentration and culture pH were studied using shake-flasks, and the effect of different feeding profiles on bioreactor performance was also investigated. Three feeding strategies, Stepwise feeding, Exponential feeding and DO-stat feeding were tested and DO-stat was found to be more efficient and led to a high phytase activity. A modified DO-stat method was investigated to overcome the oxygen limited condition in the standard DO-stat method. For the carbon source, citric acid showed promise in improving phytase expression. Further experiments in bioreactors performed with the presence of certain amount of citric acid showed that less glycerol could be used to achieve the same level of phytase activity.

Fermentation of sulfite spent liquor with Propionibacterium freudenreichii was done to produce volatile acids (acetic and propionic) and Vitamin B₁₂. It was found that in addition to producing these compounds some reduction in the pollution potential (COD) of this waste product was achieved. Better growth resulted if the spent liquor was first treated to remove lignin and calcium compounds. An existing spectrophotometry assay technique for measuring Vitamin B₁₂ content was modified for use in the presence of sulfite spent liquor. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate