Ocorrencia, multiplicação e produção de toxina diarreica por cepas mesofilas e psicotroficas de Bacillus cereus, em leite pasteurizado

AUTOR(ES)
DATA DE PUBLICAÇÃO

2000

RESUMO

The incidence of Bacillus cereus, its spoilage potential in relation to the incubation temperature and the capacity of diarrheic enteroxin prodution were evaluated in commercial pasteurized milk samples. A total of 240 samples of pasteurized milk types A, B and C were analysed for the incidence and counts of mesophilic and psycrotrophic B. cereus. The results showed the occurrence of B. cereus in the 116 (48.3%) of the examined samples with higher incidence in type C when compared to the types B and A (67,5, 50.0 and 27,5% of positive samples for types C, B and respectively). In most ofthe samples prevaled counts around 10 POT.2 CFU/mL,with higher values in type C milk when compared to types B and A. No sychrotrophic strains were isolated in the examined samples. In the experiments envolving inoculation of B. Bereus in mi1k samples followed by incubation at different temperatures it was noticed that B.cereus was not able to grow at refrigeration temperatures (5° and 10°C) but with fast growth and spoilage activity at higher temperatures (15°, 20° e 30°). The main evidences of spoilage were characterized by coagulation and clear separation of phases but without remarkable changes in pH and total acidity values. In an other experiment it was shown the possibility of gradual selection of psycrotrophic B. cereus strains originating from originally mesophilic cultures. However this selection was gradual and only afier an incubation period of 21 days the selected strains showed multiplication with a minimum "G" value of 2.17 days. Most of the tested strains originaly isolated from commercial milk samples showed capacity of diarrheic enterotoxin production both in culture media and milk samples. However in the inoculated milk samples the enterotoxin prodution was observed only in incubation temperatures above 15°C, without production at 7°C and 5°C even after 12 days of incubation

ASSUNTO(S)

refrigeração leite - pasteurização enterotoxinas

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