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Master's Dissertation
DOI
https://doi.org/10.11606/D.11.1982.tde-20220208-022044
Document
Author
Full name
Neliane Ferraz de Arruda
Institute/School/College
Knowledge Area
Date of Defense
Published
Piracicaba, 1982
Supervisor
Title in Portuguese
Efeito do tratamento térmico na duração da lag-fase de Escherichia coli IZ-923 e Staphylococcus aureus IZ-1974
Keywords in Portuguese
BACTÉRIAS PATOGÊNICAS
MICROBIOLOGIA DE ALIMENTOS
TRATAMENTO TÉRMICO
Abstract in Portuguese
No presente trabalho foi feito um estudo da duração da lag-fase de Escherichia coli IZ-923 e Staphylococcus aureus IZ-1974 apõs serem submetidos aos tratamentos térmicos de 50, 55 e 60°C em leite bovino e em extrato de soja por 20 minutos. Apôs o aquecimento, a taxa de crescimento, o número de gerações e o tempo de geração foram determinados pelo cultivo deE. coli e S. aureus a 32°C no mesmo meio de aquecimento e semeados em nutriente agar com extrato de levedura. As unidades formadoras de colônia após incubação a 32°C por 48 horas foram utilizadas para calcular o tempo de geração, número de gerações e taxa de crescimento em ambos os substratos. Considerando que durante o período de lag-fase os parâmetros acima mencionados permanecem praticamente constantes, os resultados deste estudo mostram que, para a E. coli IZ-923 a extensão da lag-fase em leite bovino esteve entre l 1/2 a 2 horas e entre 3 a 4 horas após o aquecimento de 50°C/20 minutos e 55 a 60°C/20 minutos respectivamente. No extrato de soja, a duração da lag-fase esteve entre 2 a 3 horas para os tratamentos térmicos. Para o S. aureus IZ-1974, não foi evidenciado o período de "lag-fase" após o aquecimento a 50°C/20 minutos em ambos os substratos, demonstrando que esse tratamento térmico não foi suficiente para danificar células vegetativas dessa bactéria. Porem uma "lag-fase" entre 1 1/2 e 2 horas para os tratamentos térmicos de 55 e 60°C/20 minutos, em ambos os substratos foi observada.
Title in English
not available
Abstract in English
Heat-treatment effect on the extent of lag-phase of Escherichia coli IZ-923 and Staphylococcus aureus IZ-1974 The present work was undertaken to study the extent of the lag-phase of Escherichia coli IZ-923 and Staphylococcus aureus IZ-1974 after being heated at 50, 55 and 60°C in bovine milk and soybean extract for 20 minutes. After heating, the growth rates, number of gene- rations and generati'on time were determina-ted by culturing E. coli and S. aureus at 32 C in the sarne media of heating and plating on nutrient agar fortified with yeast extract. The colony forming unit after incubation at 32 C were used to calculate the generation time, number of generations and growth rates in both substrate. Considering that during the "lag-phase" period the parameters above mentioned remaing praticaly constant, the results of the study show that for E. coli IZ-923 the lag-phase extent in bovine milk were between 1 and 1 1/2 hour, and 2 and 3 hours after heating at 50 C for 20 minutes, and 55 and 60 C for 20 minutes respectivily. In soybean extract, the lag-phase duration was between 2 and 3 hours for all heating treatments. For S. aureus IZ-1974 no lag-phase period was evident after heating at 50 C for 20 minutes in both substracts showing that this heat treatments was not sufficient to injury S. aureus the vegetative cells. But a lag-phase between 1 and 1 1/2 hours for the heating treatments at 55 and 60 C for 20 minutes in both media was observed.
 
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Publishing Date
2022-02-08
 
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