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Master's Dissertation
DOI
https://doi.org/10.11606/D.11.1985.tde-20210918-201106
Document
Author
Full name
Silvia Helena Olitta Morato do Amaral
Institute/School/College
Knowledge Area
Date of Defense
Published
Piracicaba, 1985
Supervisor
Title in Portuguese
Influência da espécie bacteriana e da temperatura da amostra no teste de redutase para leite com azul de metileno e rezasurina
Keywords in Portuguese
AZUL DE METILENO
BACTÉRIAS LÁTICAS
LEITE
RESAZURINA
TEMPERATURA
TESTE DE REDUTASE
Abstract in Portuguese
A influência da espécie bacteriana e da temperatura da amostra na descoloração dos corantes azul de metileno e rezasurina normalmente empregados no teste de redutase para se avaliar a população bacteriana do leite, ao chegar à plataforma da indústria, foi estudada. Para tal foram elegidas seis culturas de microrganismos que normalmente estão presentes em leite cru, como descritos por vários autores FOSTER et alii (1957), DONNELLY (1968), BABEL (1953), MARTH & FRAZIER (1957), Essas culturas são: Escerichia coli, Staphylococcus aureus, Streptococcus algalactiae, Streptococcus faecalis, Streptococcus lactis, Pseudomonas fluorescens. As temperaturas iniciais das amostras, foram escolhidas baseando-se no uso ou não de resfriamento na propriedade e no tempo decorrido entre ordenha e recebimento do leite na plataforma. Desta forma trabalhou-se com 5°, 10°, 15°, 20°, 25°, 30° e 35°C, como temperaturas iniciais das amostras. O inóculo foi preparado de culturas puras de cada espécie de microrganismos, baseando-se na escala de McFarland, pela leitura espectrofotométrica a 420nm, comparada com o tubo nº 4 da referida escala e que corresponde a uma população de 4,5 x 108 bactérias/ml. Após acertada a população bacteriana inicial, 1 ml das suspensões era inoculado em 8,0 ml de leite esterilizado já ajustado à temperatura desejada em tubos de cultura com tampa de rosca. Nestes eram adicionados 1,0 ml da solução do corante e imediatamente levados à incubação em banho maria a 37° ± 0,2°C. O tempo de redução do corante pelos microrganismos foi avaliado pela diferença do tempo de entrada da amostra no banho-maria, até a descoloração total (forma leuco), para ambos os corantes. A análise estatística dos resultados mostrou que os microrganismos se comportaram diferentemente em relação à temperatura inicial da amostra e ao tempo de descoloração dos corantes, com variações que não permitem apontar o corante mais adequado para o teste de redutase em relação à temperatura da amostra.
Title in English
Bacterial specie and sample temperature influence on the reductase test for milk with methylene blue and rezasurine
Abstract in English
This work was undertaken to study the influence of bacterial species and the sample temperature on the reduction of methylene blue and rezasurine dyes usually used for the reductase test, to check the milk bacterial population at its arriving at the dairy plant. Six microrganisms species reported by many authors FOSTER et alii (1957), DONNELLY (1968), BABEL (1953), MARTH & FRAZIER (1957) as usually found in raw milk were selected. These cultures were: Escerichia coli, Staphylococcus aureus, Streptococcus algalactiae, Streptococcus faecalis, Streptococcus lactis, Pseudomonas fluorescens. The temperatures of the samples were chose based on the use or not of refrigeration of the milk at the dairy farm and on the time elapsed from milking until the arrive of the milk at the plant. Though, the temperature of the samples were adjusted to 5°, 10°, 15°, 20°, 25°, 30° and 35°C, before, testing. The inoculum was prepared from pure cultures of each specie of microorganism, based on the Mc Farland?s scale, by the spectrofotometric reading of a suspension of microorganisms, at 420 nm, compared to the nº 4 tube of this scale, which represents a population of 4.5 x 108 bacteria /ml. The reductase test was perforrned by inoculating 1.0 ml of the microbial suspension prepared as previously in 8.0 ml of steril milk adjusted to the desired temperature, in screw capped tubes and addiction of 1.0 ml of the dye tested. Then the tubes were immediately put into the water-bath 37° ± 0,2°C. The reduction time was taken as the difference between the time of mixting the dye with the sample and the complete reduction of the dye. The statistical analyses of the results show a different behavior among the microorganism tested, as related to the initial temperature of the sample and the reduction time of the dye, the variations were such, that make it difficult to point out which dye was more adequate for the reductase test in relation to the initial temperature of the sample.
 
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Publishing Date
2021-09-18
 
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