The main subject of this diploma thesis is the study of the effect of humidity on the total sterilization effect of the dielectric barrier discharge. Sterilization is a process which can eliminate all forms of life. The plasma sterilization is one of the methods that are suitable for sterilization of temperature and chemical sensitive materials. This sterilization method was proved to be effective on the wide spectrum of procaryotic and eucaryotic microorganisms. Basically, the main inactivation factors for cells exposed to plasma are heat, UV radiation and various reactive species. Dielectric barrier discharge (DBD) operating at atmospheric pressure was used for the sterilization of the samples. The discharge was generated in dry air and in humid air. The plasma power densities were 2 160 mW.cm-3, 2 279 mW.cm-3 and 2 760 mW.cm-3 (dry air) or 2 326 mW.cm-3 and 2 850 mW.cm-3 (humid air). Humidity of air was achieved using a wash bottle filled with water through which air flowed into the DBD reactor. Fungi spores of Aspergillus niger were used as model microorganisms. Whatman paper No. 1 was used as the carrying medium. When comparing sterilization efficiency of humid and dry air operating at the same conditions, the higher sterilization effect was observed in humid air. The sterilization effect of the DBD generated in air was compared with results obtained during plasma generation in argon and nitrogen. At the same conditions, the highest sterilization effect was observed in argon, followed by humid air, nitrogen and dry air. It was found out that in our experimental setup the active species are probably the main inactivation mechanism. The influence of temperature on the inactivation of microorganisms was completely negligible. The discharge parameters were studied by means of the optical emission spectroscopy (OES). Plasma treated samples were analyzed employing scanning electron microscopy (SEM). Damage of the microorganisms due to the effect of plasma as well as plasma effect on the structure of the carrying medium was evaluated.

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La décontamination microbienne est sujet majeur de préoccupation du secteur agroalimentaire. Des nouvelles technologies physiques de décontamination, dites athermiques, sont d'un emploi croissant. La Lumière Pulsée, utilisée pour décontaminer les surfaces et les liquides clairs, en fait partie. Elle utilise des flashes de lumière blanche riches en UV, et délivrés en moins d'une milliseconde. La plupart des traitements par lumière pulsée sont définis dans la littérature par des paramètres spécifiques à l'équipement utilisé. Le but de cette étude a été dans un premier temps de caractériser le traitement par lumière pulsée par les grandeurs physiques appropriées (fluence, tension aux bornes de la lampe, etc...), en reliant une dose de lumière à niveau de décontamination microbienne. L'équipement pilote de la société CLARANOR a révélé des réduction logarithmiques allant jusqu'à plus de 5 unités sur des spores de B. subtilis, et de plusieurs autres espèces de bactéries sporulées, avec des fluences inférieures à 1,5 J/cm², appliquée en un seul flash La mise au point d'une méthode d'inoculation par spray à permis d'évaluer l'efficacité décontaminante de la lumière sur différentes surfaces, y compris des hydrophobes, par pulvérisation des microorganismes en couches formées d'une seule épaisseur de cellules. L'application de la technologie sur des surfaces inertes comme le polystyrène a montré une décontamination notamment sur des spores de B. subtilis, et d'A. niger, supérieures à 4 cycles logarithmiques en utilisant des fluences inférieures à 1 J/cm². L'influence des facteurs liés au système d'éclairage a montré une importance capitale des longueurs d'onde UV, mais ne permettent pas de réduire l'efficacité à la seule action de la dose UV-C. L'efficacité de la technologie a permis de réaliser une étude concernant la décontamination de sirop de sucre dans une optique d'application industrielle. Une réduction supérieure à 3 cycles logarithmiques de spores d'A. acidoterrestris dans du sirop de saccharose a été obtenue en flux continu, sur une épaisseur de 10 mm de liquide

Made available in DSpace on 2017-07-10T18:08:12Z (GMT). No. of bitstreams: 1 Caroline Mariana de Aguiar.pdf: 5014872 bytes, checksum: 64beb98ea03bbb601831a3ce234b8c31 (MD5) Previous issue date: 2010-02-11 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Lignocellulosic materials are the most abundant residues in the world and there is a worldwide concern to use them as raw material for bioethanol production. This is possible because these materials are rich in cellulose. Cellulose is a biopolymer composed of glucose molecules linked by ß-1-4 glycosidic bonds. Glucose can be converted into ethanol by fermentation and can be obtained from cellulose by enzymatic hydrolysis using cellulases. The cellulases can be produced by several microorganisms under appropriate environmental conditions. Amongst these microorganisms is the fungus Aspergillus niger. In this work, cellulases were obtained by fermentation cultivating A. niger in broth containing pretreated lignocellulosic materials such as sugarcane bagasse, corn straw or wheat straw as the only carbon source. The fermentation kinetic was observed when the pretreated sugarcane bagasse was used as the carbon source. Several variables that affect the enzymatic hydrolysis were analyzed using the three pretreated lignocellulosic materials as hydrolysis substrate. The variables analyzed were: pH, temperature, time of the hydrolysis, mass fraction of the substrate and dilution of the enzymatic broth. The pretreatment of the lignocellulosic materials is paramount for exposing the cellulose chain. Pretreatment consisted of using 4%w/w NaOH solution or 1%w/w H2O2 and their efficiency for removing the lignin from the residues were evaluated. The enzymatic activity also was evaluated by submeting the lignocellulosic materials to successive enzymatic hydrolysis. The enzyme deactivation was evaluated by cooling or freezing the enzymatic broth. It was concluded that Aspergillus niger produces cellulases when grown on medium with pretreated lignocellulosic materials as carbon source. Considering the fermentation kinetic, the ideal time to collect the enzymatic broth with maximum productivity was about 7 days. The cellulase complex does not suffer considerable deactivation when stored at -18°C (freezer) for 43 days, however, the broth activity drops by 43% after 48 hours when stored at 4°C (fridge). The corn straw showed better results as carbon source in fermentation and as substrate hydrolysis, compared with the other materials, with enzymatic activity of 0.895 U/ml. The ideal pH to conduct the enzymatic hydrolysis was 4.8 at 50°C for 50 minutes. The mass fraction of the substrate and enzyme concentration affects the enzymatic activity by a linear dependence. The pretreated materials provided higher enzymatic activity results than the untreated materials. The highest activity enzymatic results were obtained with H2O2 treated substrates, with enzymatic activity of 0.655 U/ml for the sugarcane bagasse, 0.892 U/ml for the corn straw and 0.801 U/ml for the wheat straw. Also, the results show that the H2O2 pretreated materials can be submitted up to, at least, four successive hydrolysis with the second one yielding the highest enzymatic activity for all pretreated residues. / Os resíduos lignocelulósicos são os mais abundantes no mundo e atualmente há uma preocupação mundial em aproveitá-los como matéria-prima na produção de bioetanol. Isto é possível visto que tais resíduos são ricos em celulose. A celulose é um biopolímero composto por moléculas de glicose unidas por ligações glicosídicas ß-1-4. A glicose pode ser transformada em etanol por via fermentativa e pode ser obtida da celulose via hidrólise enzimática utilizando as enzimas celulases. As celulases podem ser produzidas por diversos micro-organismos sob condições adequadas. Dentre esses micro-organismos, destaca-se o fungo Aspergillus niger. Neste trabalho, celulases foram obtidas cultivando-se A. niger em meio de cultura com os resíduos lignocelulósicos bagaço de cana-de-açúcar, palha de milho e palha de trigo pré-tratados com NaOH 4% como única fonte de carbono. Observou-se a cinética da fermentação com bagaço de cana-de-açúcar pré-tratado com NaOH 4% como fonte de carbono. Foram analisadas diversas variáveis que afetam a hidrólise enzimática utilizando os três resíduos lignocelulósicos pré-tratados com NaOH 4% como substrato. As variáveis analisadas foram: pH, temperatura, tempo de hidrólise enzimática, fração mássica de substrato e diluição do caldo enzimático. Avaliou-se a eficiência dos pré-tratamentos dos resíduos com NaOH 4% e com H2O2 1%. Avaliou-se o comportamento da atividade enzimática submetendo os resíduos lignocelulósicos a hidrólises enzimáticas sucessivas. A desativação enzimática foi avaliada nas condições de resfriamento e congelamento do caldo enzimático. Nas condições estudadas, foi concluído que o Aspergillus niger produz celulases quando cultivado em meio com resíduos lignocelulósicos pré-tratados como fonte de carbono. O tempo ideal para coleta do caldo enzimático, com produtividade máxima, foi de aproximadamente 7 dias. O complexo celulásico não sofre desativação se armazenado a temperatura de -18°C (freezer) por 43 dias, mas perde sua atividade em 43% após 48 h se armazenado a 4°C (geladeira). A palha de milho apresentou melhores resultados como fonte de carbono na fermentação e como substrato na hidrólise, comparada com os outros resíduos, com atividade enzimática de 0,895 U/mL. O pH ideal para se conduzir a hidrólise foi 4,8 na temperatura de 50ºC por 50 minutos. A fração de substrato e a concentração das enzimas afetam linearmente a atividade enzimática. Os resíduos pré-tratados proporcionaram melhores resultados de atividade enzimática do que os resíduos não tratados. Os melhores resultados de atividade foram obtidos com os resíduos tratados com solução de H2O2 1%, com atividade de 0,655 U/mL para o bagaço de cana, 0,892 U/mL para a palha de milho e 0,801 U/mL para a palha de trigo. Além disso, os resíduos tratados com H2O2 podem sofrer quatro processos de hidrólise sucessivos, com o segundo processo rendendo a maior atividade enzimática para todos os resíduos pré-tratados.