Thesis (M.S.) University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 21, 2007) Includes bibliographical references.

The total water uptake, rate of water uptake, extract release volume and maximum shear force were measured on a series of samples of irradiated freeze-dried beef. Forty seven pieces of round steak (2.5 cm x 2.5 cm x 10.4 cm or 1" x 1" x 4") were irradiated at one, three and five megarad. The control samples were not irradiated. Half of the samples were irradiated when fresh, and the other half were irradiated after freeze drying. This procedure has been defined as the "fresh-dry" irradiation sequence throughout the report. The samples were frozen in an air blast at two temperatures (-22.2°C and -56.1°C). Freeze-drying was carried out below 300 microns of Hg and a maximum shelf temperature of 15.6°C (60°F). There appears to be three phases of water uptake: 1) A very rapid, almost instantaneous, absorption. 2) A more gradual uptake (called Part.1 in the report). 3) A relatively slow asymptotic approach to an equilibrium condition (Part 2). These two last phases are shown to be straight lines when the logarithm of the water uptake is plotted against the logarithm of the immersion time. Irradiation level has no significant effect on the final water content or on the slow asymptotic absorption (Part 2) or the extract release volume, but has a significant effect on the gradual water uptake (Part 1) and on the shear press force. Fresh-dry irradiation sequence (and freezing rate) have a significant effect on the total water uptake and on the slow asymptotic water (Part 2) uptake, but not on the gradual water uptake (Part 1), or on the extract release volume or on the shear press forces. Freezing rates have a significant effect on the total water uptake, but not on the slow asymptotic water uptake (Part 2), on the gradual water uptake (Part 1), on the extract release volume or on the shear press forces. The highest total water uptake was found for the meat irradiated when fresh, and slow frozen at -2 2.2°C. The mechanism of the gradual absorption appears to follow a phenomena of water flow, as evidenced by the straight line relationship found in the plots of logarithm water uptake versus logarithm immersion time. / Land and Food Systems, Faculty of / Graduate

Thesis. 1975. M.S.--Massachusetts Institute of Technology. Dept. of Nutrition and Food Science. / Bibliography: leaves 109-112. / M.S.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Nutrition and Food Science, 1979. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaves 153-157. / Ph.D.

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Produtos desidratados em pó são amplamente consumidos por indústrias produtoras de alimentos prontos e pré-prontos, devido à facilidade de transporte, armazenamento, e vida de prateleira prolongada. É desejável que estes produtos sejam capazes de manter suas características o mais próximo possível do produto in natura quando são reidratados e, adicionalmente, que tragam vantagens econômicas para a indústria. O objetivo geral deste trabalho consistiu em produzir um sistema de secagem multi-estágio para frutas e hortaliças para manutenção de suas características e benefícios nutricionais, com custo de processamento reduzido. Para isso, foi necessário desenvolver e testar um protótipo do sistema de secagem hermeticamente fechado para permitir o processamento em baixa pressão e temperatura e fluxo de ar aquecido. A pesquisa se desenvolveu nas etapas de revisão da literatura, da escolha das matérias primas, da definição dos parâmetros de secagem, da obtenção e da caracterização dos pós de tomate e de pimentão. Foi aplicada uma ferramenta de tomada de decisão para escolha do método de secagem mais adequado. Foram avaliados no tomate os conteúdos de ácido ascórbico, compostos fenólicos totais, β-caroteno, licopeno, frutose, glicose, ácido cítrico, 5- hidroximetil-2-furfural (HMF) e as alterações causadas nos tecidos. No pimentão amarelo foram avaliados os conteúdos de glicose, frutose, sacarose, ácido ascórbico, HMF, proteínas, fibra alimentar, cor, índice de escurecimento e identificação do perfil dos carotenoides. De acordo com os resultados na avaliação do pó de tomate, o processo de secagem em dois estágios levou a menores perdas de açúcares, conteúdos mais elevados de carotenoides e compostos fenólicos totais, bem como formação de HMF e endurecimento da superfície. Nos tratamentos avaliados no processamento do pimentão amarelo, o processo de secagem em dois estágios resultou em perdas nos conteúdos de ácido ascórbico e açúcares, além do aumento do índice de escurecimento. Na escolha do processo de secagem, foram considerados diversos aspectos, visto que diferentes parâmetros podem implicar em diferentes custos de aquisição, consumo energético e qualidade do produto final. Neste contexto, o processo de secagem em fluxo de ar aquecido se mostrou vantajoso para a secagem de tomate. / Powdered dehydrated products are widely consumed by food industries of ready and pre-ready to eat products, due to its facility of transportation, storage and extended shelf life. It is desirable that these products can maintain its characteristics as closer as possible from fresh fruit when they are rehydrated and should bring economics advantages for the industry. The general objective of this work consists in producing a multi-stage drying system for fruits and vegetables for maintaining its characteristics and nutritional benefits, with lower processing costs. For this, it was necessary to develop and test a prototype of the drying system, hermetically closed for allowing the processing under low pressure and temperature and hot air flow. The research was developed in the steps of literature revision, raw materials choice, definition of drying parameters, obtaining and characterization of the tomato and sweet pepper powders. A decision-making tool was applied for the choice of the most proper drying method. In tomato were evaluated the contents of ascorbic acid, total phenolic compounds, β-carotene, lycopene, fructose, glucose, citric acid, 5-hydroxy-methyl-2-furfural (HMF) and tissue changes. In yellow sweet bell pepper were evaluated the contents of glucose, fructose, sucrose, HMF, protein, fibers, color, browning indices and the carotenoid profile identification. According to the results of the tomato powder evaluation, the drying process in two stages lead to lower losses of sugars, high contents of carotenoids, total phenolic compounds, HMF formation, surface hardening. In the evaluated treatments of processing of yellow sweet bell pepper, the drying process in two stages resulted in losses of ascorbic acid content, sugars, increase of browning indices. For the choice of drying process, several aspects were considered, since different parameters may imply in different acquisition costs, energy consumption, and the quality effects of the final product, in this context the drying process in hot air flow was pointed as advantageous for tomato drying.

En réponse à un stress nutritif, les espèces du genre Bacillus sont susceptibles de former desspores métaboliquement dormantes résistantes à d’autres formes de stress. Ces spores peuventse retrouver à forte concentration dans beaucoup d’aliments secs, ce qui peut provoquer desintoxications alimentaires ou dégrader les aliments lorsqu’ils sont réhydratés. Comme leurdestruction est très difficile, la plupart des méthodes couramment utilisées pour décontaminerles aliments secs sont peu efficaces. L’objectif de ce travail est de comprendre l’influence del’hydratation de la spore sur l’inactivation des spores sèches de B. subtilis. Une étudefondamentale a été menée en soumettant les spores placées dans les capsules d’AnalyseEnthalpique Différentielle à différent traitements thermiques et en associant simultanémentles thermogrammes obtenus à la viabilité des spores traitées. Les résultats montrent lapersistance d’une teneur en eau relativement élevée dans le protoplaste des spores équilibréesà faible aw (0,13). De plus, une relation forte a été mise en évidence entre la teneur en eau duprotoplaste de la spore et sa sensibilité thermique. La spectroscopie IR à transformée deFourier a montré que cette sensibilité est fortement reliée à la dénaturation/agrégation desprotéines et à la libération de l’acide dipicolinique. Ces résultats ont finalement permis dedévelopper un procédé d’inactivation thermique sous pression (entre 2 et 7 bar) des sporessèches. Le maintien d’une pression d’azote dans le réacteur chauffé permet d’empêcherl’évaporation de l’eau du protoplaste des spores et donc de favoriser leur inactivation. A termeet après développement, ce procédé peut être un moyen original de décontaminationd’aliments secs. / In response to starvation, species from the genre Bacillus are able to form metabolicallydormant spores which are very resistant to multiple forms of stress. They are found in quitehigh concentrations in some dried foods which, upon rehydration, may lead to food deterioration or food-borne diseases. Moreover, their destruction is rather difficult and mostof the techniques commonly used to treat dry foods result in a very low spore inactivation.The aim of this work is to better understand the role spore hydration in the inactivation ofdried Bacillus subtilis spores. A fundamental study was conducted using DifferentialScanning Calorimetry pans as reactors to perform a heat treatment in dried spores andsimultaneously relate the thermograms to spore viability. Results show the persistence of arelatively high water concentration in the core of extremely dry spores. Besides, a strongrelation between this core water concentration and spore thermal sensitivity wasdemonstrated. This destruction was found to be highly related to proteindenaturation/aggregation and dipicolinic acid release through Fourier Transform InfraredSpectroscopy analysis. From this fundamental study, a procedure for the inactivation of driedspores using low pressures (2-7 bar) and high temperature was developed. The systemconsisted of a heated reactor in which gaseous nitrogen was compressed to prevent theevaporation of water from the spores and so favor spore inactivation (> 5 log10). This methodof inactivation could be an interesting new way to optimize the decontamination of driedfoods.

Text in English / Fungal species and their mycotoxins are the most predorminant contaminants of dried agricultural products in sub-Saharan Africa (SSA) and the main species of fungi that can synthesize mycotoxins are Aspergillus, Fusarium and Penicillium. In Africa, aflatoxin is labelled as a great threat to human and animal health due to its high contamination levels reported of aflatoxins in foods. The aim of this study was to survey fungi and aflatoxin contamination of small-scale processed foodstuffs sold at informal retail outlets in the Johannesburg metropolis, South Africa. A total of 270 food samples (10 starch and legume based foods, 11 meat and fish based foods, 22 spices and local condiments, 14 dried fruits and vegetables) were collected from retailers; and analysed four (4) times in different seasons of spring, summer, autumn and winter. Out of the 270 samples analysed, only 27.8% were contaminated with fungal. Of all the six categories of foods analysed, roots and tubers (60.0%), nuts and seeds (40.0%), dried vegetables (37.1%), and the Meat and Insect foods (33.3%) respectively, had the most contaminated samples with fungal respectively. The least contaminated food groups were the fish foods (10.0%) and spices and local condiments (16.7%) respectively. Twenty percent of the 270 dried food analysed were contaminated by Aspergillus species out of which 61.1% of the contaminated samples had fungal counts above 103 cfu/g. Aspergillus niger was the most predominant Aspergillus species identified in all the categories of food samples analysed. Fruits and vegetables (24.4%) and the nuts and seeds (20.0%) food groups had the highest number of samples contaminated with aflatoxin. Peanut flour and Cardamom had the most incidence of aflatoxin. AFB1, AFB2 & AFG1 were the most prominent aflatoxin types recovered from the food samples. Almost all the food samples in which aflatoxin were identified had aflatoxin values above 10μg/ml. / Life and Consumer Sciences / M.Sc. (Life Science)