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dc.contributor.authorOgwaro, B.A.
dc.contributor.authorGibson, Hazel
dc.contributor.authorWhitehead, Michael P.
dc.contributor.authorHill, David J.
dc.date.accessioned2008-06-04T09:45:46Z
dc.date.available2008-06-04T09:45:46Z
dc.date.issued2002
dc.identifier.citationInternational Journal of Food Microbiology, 79(1-2): 105-112
dc.identifier.issn0168-1605
dc.identifier.pmid12382690
dc.identifier.doi10.1016/S0168-1605(02)00184-8
dc.identifier.urihttp://hdl.handle.net/2436/29458
dc.description.abstractGrowth and survival of a nontoxigenic strain of Escherichia coli O157:H7 (ATCC 43888) was determined in traditionally fermented pasteurized milk. Preheated milk was inoculated with 1% (v/v) of a mixed culture of Lactobacillus delbrueckii ssp. bulgaricus (NCIMB 11778) and Streptococcus salivarius ssp. thermophilus (NCIMB 110368) and incubated at 25, 30, 37 or 43 degrees C for 24 h. E. coli O157:H7 (10(5) CFU/ml) were introduced into the milk pre- and post-fermentation. Fermented milk samples were subsequently stored at either 4 degrees C (refrigerator temperature) or 25 degrees C (to mimic African ambient temperature) for 5 days. After 24 h of fermentation, the pH of the samples fermented at the higher temperatures of 37-43 degrees C decreased from 6.8 to 4.4-4.0 ( +/- 0.2) whereas at the lower temperature of 25 degrees C, the pH decreased to pH 5.0 +/- 0.1. During this period, viable counts for E. coli O157:H7 increased from 10(5) to 10(8) - 10(9) CFU/ml except in milk fermented at 43 degrees C wherein viability declined to 10(4) CFU/ml. In fermented (25-30 degrees C) milk stored at 4 degrees C for 5 days, E. coli O157:H7 viability decreased from 10(8-9) to 10(6-7) CFU/ml whereas milk fermented at 43 degrees C resulted in loss of detectable cells. In contrast, storage of fermented milk samples at 25 degrees C for 5 days eventually resulted in complete loss of viability irrespective of fermentation temperature. Stationary phase E. coli O157:H7 inoculated post-fermentation (25 and 43 degrees C) survived during 4 degrees C storage, but not 25 degrees C storage. Fermentation temperature and subsequent storage temperature are critical to the growth and survival of E. coli O157:H7 in traditional fermented products involving yoghurt starter cultures.
dc.language.isoen
dc.publisherElsevier Science Direct
dc.relation.urlhttps://www.sciencedirect.com/science/article/pii/S0168160502001848?via%3Dihub
dc.subjectEscherichia coli O157:H7
dc.subjectLactobacillus delbrueckii ssp. bulgaricus
dc.subjectStreptococcus salivarius ssp. thermophilus
dc.subjectpH
dc.subjectTemperature
dc.subjectFermentation
dc.subjectAcid
dc.subject.meshColony Count, Microbial
dc.subject.meshEscherichia coli O157
dc.subject.meshFermentation
dc.subject.meshFood Contamination
dc.subject.meshFood Handling
dc.subject.meshFood Microbiology
dc.subject.meshHydrogen-Ion Concentration
dc.subject.meshLactobacillus
dc.subject.meshStreptococcus
dc.subject.meshTemperature
dc.subject.meshYogurt
dc.titleSurvival of Escherichia coli O157:H7 in traditional African yoghurt fermentation.
dc.typeJournal article
dc.identifier.journalInternational Journal of Food Microbiology
html.description.abstractGrowth and survival of a nontoxigenic strain of Escherichia coli O157:H7 (ATCC 43888) was determined in traditionally fermented pasteurized milk. Preheated milk was inoculated with 1% (v/v) of a mixed culture of Lactobacillus delbrueckii ssp. bulgaricus (NCIMB 11778) and Streptococcus salivarius ssp. thermophilus (NCIMB 110368) and incubated at 25, 30, 37 or 43 degrees C for 24 h. E. coli O157:H7 (10(5) CFU/ml) were introduced into the milk pre- and post-fermentation. Fermented milk samples were subsequently stored at either 4 degrees C (refrigerator temperature) or 25 degrees C (to mimic African ambient temperature) for 5 days. After 24 h of fermentation, the pH of the samples fermented at the higher temperatures of 37-43 degrees C decreased from 6.8 to 4.4-4.0 ( +/- 0.2) whereas at the lower temperature of 25 degrees C, the pH decreased to pH 5.0 +/- 0.1. During this period, viable counts for E. coli O157:H7 increased from 10(5) to 10(8) - 10(9) CFU/ml except in milk fermented at 43 degrees C wherein viability declined to 10(4) CFU/ml. In fermented (25-30 degrees C) milk stored at 4 degrees C for 5 days, E. coli O157:H7 viability decreased from 10(8-9) to 10(6-7) CFU/ml whereas milk fermented at 43 degrees C resulted in loss of detectable cells. In contrast, storage of fermented milk samples at 25 degrees C for 5 days eventually resulted in complete loss of viability irrespective of fermentation temperature. Stationary phase E. coli O157:H7 inoculated post-fermentation (25 and 43 degrees C) survived during 4 degrees C storage, but not 25 degrees C storage. Fermentation temperature and subsequent storage temperature are critical to the growth and survival of E. coli O157:H7 in traditional fermented products involving yoghurt starter cultures.


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