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

Incidence and characterisation of Bacillus sporothermodurans isolated from UHT milk

Tabit, Frederick Tawi 16 June 2011 (has links)
Bacillus sporothermodurans, which was first detected in UHT milk in Germany in 1990, can affect the stability and shelf life of contaminated commercial UHT milk and cause economic losses. Due to the unusual thermal resistance of B. sporothermodurans spores, B. sporothermodurans can survive UHT treatment and proceed to grow in stored products causing instability because of their proteolytic activity (Huemer et al., 1998). This study was conducted to determine the level of B. sporothermodurans contamination in South African dairies and to understand the mechanism of B. sporothermodurans spore destruction in order to investigate ways of inactivating these spores without severe heating. The objectives were to determine the presence of Bacillus sporothermodurans in retail UHT milk along with milk from different points of a processing line and isolates from UHT milk in South Africa, UP20A and a reference strain of B. sporothermodurans, DSM 10599 from Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH (DSMZ) in Germany were characterised using PCR. The effect of chilling, pre-heating, UHT, reprocessing and H2O2, individually and in combination, on the survival of B. sporothermodurans was also investigated in broth. Spores were heated at 130 °C for 4, 8 and 12 min in order to investigate the mechanism of structural damage and survival. The adopted real time (RT) PCR with SYBR Green method was effective for the confirmation of B. Sporothermodurans. The structural damage on heated spores was determined using the Transmission Electron Microscopy (TEM), while High Performance Liquid Chromatography (HPLC) and spectrophotometry were used to quantify Dipicolinic acid (DPA) and soluble proteins released from the filtrate of heated spore suspensions. All statistical analyses were done using STATISTICA. B. sporothermodurans was detected in retail UHT milk packs from only one processor. The combination of chilling and UHT was more effective in eliminating B. sporothermodurans spores to a non detectable level than UHT treatment alone. H2O2 was also effective in eliminating B. sporothermodurans spores, from 6.31 to 1.64 log cfu/ml after 15 min of exposure and. The release of DPA during wet heat treatment coincides with visible signs of structural damage and significant inactivation of spores. Visible signs of spore structural damage emanate at different rates. The amount of protein release seems to be strain specific. This research is the first to detect the presence of B. sporothermodurans in UHT milk in South Africa and to determine the effect of UHT processing stresses on its survival. These results can be used to design processing parameters so as to effectively eliminate B. sporothermodurans spores during UHT processing. Similarly, this research is the first in which RT PCR with SYBR Green has been used to characterise B. sporothermodurans as well as to determine the effect of wet heat treatment on the structure of B. sporothermodurans spores. This research aims to contribute to the insight regarding the mechanisms of destruction of B. sporothermodurans spores by wet heat. / Thesis (PhD)--University of Pretoria, 2010. / Food Science / unrestricted
2

Isolamento e caracterização de microrganismos em leite cru refrigerado e leite UHT no estado de Goiás e desenvolvimento de filme ativo antimicrobiano para inibição de Bacillus sporothermodurans / Isolation and characterization of microorganisms in refrigerated raw milk and UHT milk in the state of Goias and development of antimicrobial active film for inhibition of Bacillus sporothermodurans

PEREIRA, Flavio Evans Vilela 26 February 2010 (has links)
Made available in DSpace on 2014-07-29T15:22:58Z (GMT). No. of bitstreams: 1 dissertacao flavio pereira.pdf: 1203680 bytes, checksum: bcaf62e9eb5545119172fb4728bdaaee (MD5) Previous issue date: 2010-02-26 / Raw milk is a natural culture medium for the microbial growth and easy deterioration, because of that, thermal processing is needed as soon as possible. A new technology has been used to improve the food quality, active packaging, such as antimicrobial films, wich the intention to control the microbial growth in the products. The aim of this study was to evaluate the UHT milk quality produced in Goiás State, isolation and identification of Bacillus sporothermodurans, beside create a antimicrobial film for inhibition of this microrganism high heat resistance spore former. The isolation of psychrotrophic in raw milk was used PCA with incubation at 21 °C for 72h. To evaluate the UHT milk has been doing research on aerobic mesophilic in PCA with incubation at 30 °C for 72h and to thermoresistents microrganisms was in ABHI with incubation at 35 °C for 48h. The identification of isolates was performed according to convetional methods of biochemistry identification. From raw milk, the psychrotrophic microrganisms most isolates were Staphylococcus sp. and Corynebacterium sp., both with 21,5% from 70 isolates, verifying a higher contauge of Gram-positive microrganisms (82,85%). Considering the 157 UHT isolates, just 31 were identified as Gram-positive microrganisms through biochemical tests, only 2 correponded to B. sporothermodurans, although there are differences from the tests and their results between various authors, requiring more accurate identification using molecular biology. The antimicrobial film maded of cellulose acetate with addition of nisin to inhibit the development of B. sporothermodurans, the results indicated action of nisin in inhibition this microrganism, however, when incorporated into the film, did not show the expected results in both tests, solid and liquid medium, although the specific rate (μ) growth of the microrganism was changing iin the lowest concentration tested. There is a need to conduct testing in foods, mainly in dairy products which have been reported contamination by B. sporothermodurans. / O leite por ser um alimento rico, constituí-se em um meio natural para o desenvolvimento de vários microrganismos, principalmente bactérias; desta forma, muito perecível. É necessário tratamento térmico o mais rápido possível, a fim de manter a qualidade. Uma nova tecnologia vem sendo utilizada na melhoria dos alimentos, denominada de embalagem ativa, como os filmes antimicrobianos, na intenção de controlar o desenvolvimento microbiano no produto. O objetivo deste trabalho foi de avaliar a qualidade de leite UAT produzido no Estado de Goiás, assim como isolar e identificar microrganismos psicrotróficos de leite cru e microrganismos de leite UAT, sendo que para este direcionado para identificação de Bacillus sporothermodurans, bem como criação de filme antimicrobiano para inibição deste microrganismo produtor de esporos altamente resistentes. Para o isolamento de psicrotróficos em leite cru, foi utilizado PCA e incubação à 21°C por 72h. Para avaliação de qualidade do leite UAT, foi feito a pesquisa de aeróbios mesófilos em PCA com incubação à 30°C por 72h e o isolamento de microrganismos termorresistentes foi realizado em ABHI com incubação a 35°C por 48h. A identificação dos isolados foi realizada conforme metodologias clássicas de identificação bioquímica. Segundo esta identificação, os microrganismos psicrotróficos mais isolado foram Staphylococcus sp. e Corynebacterium sp. com 21,5% cada, dos 70 isolados, verificando uma percentagem maior de microrganismos Gram-positivos (82,85%). Considerando os isolados de leite UHT, dos 157, apenas 31 foram identificados como sendo bastonetes Gram-positivos que submetidos a testes bioquímicos, apenas 2 corresponderam ao B. sporothermodurans seguindo-se os resultados conforme registrado, apesar de haver divergências quanto a alguns testes e seus resultados, necessitando de identificação mais apurada utilizando-se de biologia molecular. Quanto ao filme antimicrobiano a base polimérica utilizada foi o acetato de celulose com incorporação de nisina, a fim de inibir o desenvolvimento do B. sporothermodurans com o intuito de verificar a ação deste peptídeo antimicrobiano frente a este microrganismo. Os resultados obtidos indicaram ação da nisina na inibição do microrganismo estudado, no entanto, quando incorporado ao filme, não apresentou o resultado esperado, tanto em testes em meio sólido como em meio líquido, apesar de ter alterando a velocidade específica (μ) de crescimento do microrganismo na concentração mais baixa testada. Há a necessidade de realização de teste em alimentos, especialmente em leite e derivados em que foram relatados a contaminação pelo B. sporothermodurans
3

Adesão de esporos de Bacillus sporothermodurans ao aço inoxidável e sua resistência a sanificantes químicos em condições de uso simulado / Adherence of Bacillus sporothermodurans on stainless steel and their resistance to chemical sanitizers in simulated use conditions

Akutsu, Cleusa Kiyomi 21 May 2001 (has links)
Submitted by Nathália Faria da Silva (nathaliafsilva.ufv@gmail.com) on 2017-07-12T12:26:28Z No. of bitstreams: 1 texto completo.pdf: 451562 bytes, checksum: 6f7e57c6a3ba3860fe5ea9a087da2f4a (MD5) / Made available in DSpace on 2017-07-12T12:26:28Z (GMT). No. of bitstreams: 1 texto completo.pdf: 451562 bytes, checksum: 6f7e57c6a3ba3860fe5ea9a087da2f4a (MD5) Previous issue date: 2001-05-21 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Esporos de Bacillus sporothermodurans CCT6247 foram avaliados quanto à adesão em cupons de aço inoxidável e resistência a sanificantes químicos, em condições de uso simulado, utilizando um modelo de linha de circulação de leite, em aço inoxidável AISI 304. Seis cupons de prova, sendo dois em formato de cotovelo 90º, dois cilíndricos e dois em T, foram inoculados com uma suspensão, em tampão fosfato, de 0,31 M em pH 7,0±0,1, contendo cerca de 10^5 esporos/mL por 12 horas a 30°C. A quantificação dos esporos foi feita em três dos seis cupons após rinsagem com tampão fosfato, durante 15 minutos, plaqueando diluições adequadas por espalhamento superficial em ágar BHI e incubação a 37°C/24h. Depois, os seis cupons foram conectados, em pontos específicos, no modelo utilizado. Simulou-se um processo de sanificação, circulando-se 15 L dos sanificantes por 15 minutos a uma velocidade de 1,5 m/s, à temperatura ambiente (20-25°C), pelas tubulações. Verificou-se que não houve diferença (P ≥0,05) na adesão entre os cupons cotovelo 90º, cilíndrico e T. O log10 do número de esporos aderidos por cm² nesses cupons foi, respectivamente, de 4,01, 3,88 e 4,03, correspondentes a 3,93, 2,55 e 4,46% de adesão. Nenhum dos sanificantes obteve três reduções decimais (RD) na população de esporos, valor sugerido na aprovação de sanificantes, atuando sobre microrganismos aderidos. Não houve diferença (P≥0,05) entre os sanificantes, com exceção do hipoclorito de sódio a 100 mg/L de CRT, em pH 9,45, que apresentou a menor eficiência (1,57 RD), e também não se observou influência do tipo de cupom na ação dos sanificantes. Os números de reduções decimais obtidos, em ordem descrescente, foram 2,84; 2,77; 2,67; 2,47; 2,43; e 2,26 RD para as soluções de hipoclorito contendo 100 mg/L em pH 7,0; de cloramina orgânica contendo 100 mg/L em pH 7,18; de hipoclorito contendo 100 mg/L em pH 8,0; de cloramina orgânica contendo 60 mg/L, em pH 7,18; de ácido peracético a 60 mg/L em pH 3,4; e de ácido peracético a 30 mg/L em pH 3,7, respectivamente. Portanto, os resultados sugerem que o uso de hipoclorito corrigido para pH 8,0 ou 7,0 pode ser escolhido sem prejuízo da eficiência do processo de higienização, além de apresentar menor custo. Avaliando a higienização dos cupons pela técnica de ATP bioluminescência, verificou-se inconsistência entre os resultados desta técnica e do método tradicional de contagem em placa na detecção de esporos aderidos ao aço inoxidável, em razão, provavelmente, do baixo nível de ATP detectável desses esporos. / Bacillus sporothermodurans CCT 6247 spores were evaluated for attachment on stainless steel coupons and resistance to chemical sanitizing agents, under simulated conditions, using a milk circulation AISI 304 stainless steel pipe system. Six coupon tests (two 90° elbow, two cylindrical and two T- piece) were inoculated in a phosphate buffer, 0.31M, pH 7.0 ± 0.1 suspension, containing around 10^5 spores/ mL during 12 h at 30°C. Spore quantification was performed in 3 of 6 coupons following phosphate buffer rinsing for 15 min., plating adequate dilutions on BHI agar plate and incubation at 37°C/24h. The six coupons were then connected at specific points in the model. A sanitizing process was simulated by circulating 15 L of the sanitizing agents for 15 min. at a speed of 1.5 m/s at room temperature (20-25°C) through the tubes. No difference (P≥0.05) was verified in the attachment among the 90º elbow, the cylindrical and the T-piece coupons. The spore number log10 attached per cm² on these coupons were, respectively, 4.01, 3.88 and 4.03, which correspond to 3.93, 2.55 and 4.46%. None of the sanitizing agents obtained 3 decimal reductions (DR) within the spore population, a value suggested for the sanitizing agents approval, when acting on the attached microorganisms. No difference was found (P≥0.05) among the sanitizing agents, except for sodium hypochlorite at 100 mg/L of CRT, pH 9.45, which showed the least efficiency (1.57 DR) nor any influence of the type of coupon was observed on the sanitizing agents’ action. The decimal reductions number reached, in decreasing order, 2.84, 2.77, 2.67, 2.47, 2.43 and 2.26 DR for the hypochlorite solution containing 100 mg/L, pH 7.0; the organic chloramine solutions containing 100 mg/L, pH 7.18; hypochlorite containing 100 mg/L, pH 8.0; organic chloramine containing 60 mg/L, pH 7.18; peracetic acid at 60 mg/L in pH 3.4; and of peracetic acid at 30 mg/L in pH3.7, respectively. Thus, the results suggest that the use of hypochlorite corrected for 8.0 or 7.0 can be chosen without compromising the process of hygienization, besides presenting lower cost. When evaluating the coupons higienization by bioluminescence ATP technique, inconsistency between the results of this technique and those of the traditional method of plate counting was observed in detecting spores attached to the stainless steel, this being probably due to these spores low detectable ATP levels.

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