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Master's Dissertation
DOI
https://doi.org/10.11606/D.11.1991.tde-20210919-105728
Document
Author
Full name
Roseli do Carmo Freitas da Silva
Institute/School/College
Knowledge Area
Date of Defense
Published
Piracicaba, 1991
Supervisor
Title in Portuguese
Controle de qualidade de iogurte comercial e estudo do poder acidificante de suas culturas láticas
Keywords in Portuguese
ACIDIFICAÇÃO
CONTROLE DE QUALIDADE
CULTURAS LÁTICAS
FERMENTAÇÃO LÁTICA
IOGURTE
Abstract in Portuguese
Amostras de quatro marcas diferentes de iogurte disponíveis no comércio de Piracicaba, SP, foram coletadas durante cinco meses para análises de verificação do peso líquido, acidez titulável, pH, número de coliformes, fungos e leveduras, bem como, isolamento, purificação, identificação e estudo do poder acidificante das bactérias láticas presentes. Os resultados obtidos demonstraram variação no peso líquido dos iogurtes comerciais, com 75% das amostras abaixo do peso declarado na embalagem. Os valores de acidez titulável variaram entre 1,10 e 1,54% de ácido lático e o pH entre 3,87 e 4,42. As análises microbiológicas revelaram que, para uma das marcas, durante os três primeiros meses não foram detectadas bactérias láticas viáveis, enquanto todas as demais amostras apresentaram números desses microrganismos dentro dos limites relatados na literatura. As contagens de coliformes revelaram que 50% das amostras analisadas apresentaram valores acima de 10 u.f.c./ml do produto; para fungos e leveduras, 30% das amostras apresentaram mais que 10 u.f.c./ml do produto. As bactérias láticas de cada amostra foram isoladas, purificadas e identificadas, confirmando tratar-se de L. bulgaricus e S. thermophilus em todos os iogurtes amostrados. As culturas puras isoladas foram testadas quanto ao seu poder acidificante isoladamente e em culturas mistas resultantes dos pareamentos dos lactobacilos com os estreptococos. As três culturas mistas que apresentaram o melhor poder acidificante foram testadas quanto ao desenvolvimento da acidez durante um período de 4 horas de incubação a 42°C e, a seguir, durante um período de 31 dias de armazenamento a 7°C, utilizando-se leite desnatado, reconstituído com 12% SNG e esterilizado.
Title in English
Yoghurt quality control and study of the acidifying power of lactic cultures
Abstract in English
Samples of four different brands of commercial yoghurt available in Piracicaba, SP, were collected in five months for verification analysis of the net weight, titrable acidity, pH, coliform, mold and yeast numbers, and for isolation, purification, identification of the lactic bacteria presented as well. The results obtained showed a variation in the commercial yoghurt net weight, with 75% of the samples below the weight declared in the wrappings. The titrable acidity values varied between 1,10 and 1,54% of lactic acid and the pH between 3,87 and 4,42. The microbiological analysis revealed that, for one of the brands, during the first three months viable lactic bacteria were not detected, while the other samples showed these microorganism numbers within the limits related in the literature. The coliform enumeration revealed that 50% of the analysis samples, showed values over 10 cfc/ml of the product, as to molds and yeasts, 30% of the samples showed more than 10 cfc/ml of the product. The lactic bacteria of each sample were isolated, purified and identified, confirming to be L. bulgaricus and S. thermophilus in all the yoghurts examined. The isolated pure cultures were tested as to its acidifying power isolated and in mixed cultures resulting from the pairs of lactobacilli with streptococci. The three mixed cultures, which showed the best acidifying power, were tested as to the acidity development during a period of four hours of incubation at 42°C and then, during a period of 31 days of storage at 7°C using reconstituted with 12% SNG and sterilized skimmed milk.
 
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Publishing Date
2021-09-19
 
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