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Master's Dissertation
DOI
https://doi.org/10.11606/D.11.1997.tde-20220207-175925
Document
Author
Full name
Daniel Mário TapiaTapia
Institute/School/College
Knowledge Area
Date of Defense
Published
Piracicaba, 1997
Supervisor
Title in Portuguese
Resistência térmica de esporos de Bacillus cereus IAL 2599 frente a vapor superaquecido com atividade de água menor que 1,0
Keywords in Portuguese
BACTÉRIAS
MICROBIOLOGIA DE ALIMENTOS
RESISTÊNCIA TÉRMICA
Abstract in Portuguese
No presente trabalho foi estudada a resistência térmica de esporos de Bacillus cereus IAL 2599 frente a vapor superaquecido a 100°C; 110°C; 120°C; 130°C; 140°C; 150°C e 160°C que nas condições de pressão atmosférica média de 715 mm Hg corresponde às atividade de água (Aa) de 0.951; 0,672; 0,482; 0,355; 0,264; 0,20 e 0,153 respectivamente. Nas temperaturas experimentadas foram observados fenômenos de ativação e inativação simultâneos ou sequenciais, com exceção de 140°C e Aa = 0,264. As frações mais resistentes da população tratada não são quantitativamente iguais nas temperaturas estudadas. A aplicação da fórmula de Stumbo (1973), para o cálculo de um valor D que representa toda a população tratada não se mostrou conveniente para o presente estudo. A determinação de um valor D por meio de uma equação de regressão calculada com pontos escolhidos da fração da mais resistente da população, introduz um fator subjetivo que pode levar a superestimação da resistência real. No caso de uso de portadores de Bacillus cereus IAL 2599 como bioindicador em processos por calor seco o número de esporos inoculados pode ser limitado a Nx10E+6 o que garante um fator de segurança satisfatório em processos térmicos de natureza semelhante ao estudado. Nas temperaturas estudadas, no caso de emprego de esporos de Bacillus cereus como bioindicadores de processos térmicos por calor seco, os tempos recomendados de tratamento de objetos infestados por populações naturais de esporos seriam, respectivamente, 10 min. a 100°C; 30 min a 110°C; 50 min. a 120°C; 20 min.130°C; 20 min a 140°C; 10 min. a 150°C e 5 min. a 160°C.
Title in English
Thermal resistance determination of Bacillus cereus IAL 2599 spores faced to superheated steam with water activity less than 1,0
Abstract in English
In the present paper was studied the thermal resistance of Bacillus cereus IAL 2599 spores faced to superheated steam at 100°C; 120°C; 130°C; 140°C; 150°C and 160°C, that in the average atmospheric conditions correspond to the following water activities (Aa) 0,951; 0,672; 0,482; 0,355; 0,264; 0,20 and 0,153 respectively. At the experimental temperatures, simultaneous or sequential activation and inactivation phenomena were observed except at 140°C and Aa = 0,264. The most resistant fraction of the treated population are not quantitatively the same at the studied temperatures. The utilization of the formula according to Stumbo 1973, to calculate the D value, which represents all the population did not show to be convinient in the present study. The determination of a D value through a regression equation calculated with the chosen points from the most resistant fraction of the population, put in evidence a subjective factor that can lead to a superstimation of the real resistance. In case of using carriers of Nacillus creeus IAL 2599 spores as bioindicators in thermal processes by dry heat the number of inoculated spores in the carrier, can be limited to N x10+6, which give a satisfactory factor of security in thermal processes with the same nature as the one studied here. At the studied temperatures, in case of using Bacillus cereus spores in thermal processes as bioindicator by dry heat, the recommended treatments of contamined objects by natural spores populations, would be: 10 min. at 100°C; 30 min. at 110°C; 50 min at 120°C; 20 min. at 130°C; 20 min. at 140°C; 10 min at 150°C and 5 min. at 160°C respectively.
 
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Publishing Date
2022-02-07
 
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