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Vekst av patogene mikroorganismer ved ulike temperaturer

Røine, Marianne
Master thesis
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Masteroppgave Marianne Røine, IKBM 2010 .pdf (3.686Mb)
URI
http://hdl.handle.net/11250/186303
Date
2010-10-22
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  • Master's theses (KBM) [742]
Abstract
Oppgaven er en del av forskningsprosjektet ”Bedre mattrygghet i hjemmet gjennom risikoanalyse av forbrukerhåndtering av mat og evaluering av risikoreduserende tiltak”, et

samarbeid mellom Nofima Mat og SIFO (statens institutt for forbruksforskning). En

casestudie utført ved Nofima Mat, hvor 45 frivillige forbrukere ble tildelt temperaturlogger viste at gjennomsnittlig temperatur for kjøttpålegg var 6,2 °C, og at pålegget daglig ble utsatt for temperaturer over 20 °C i gjennomsnittlig 47 minutter (Røssvoll 2010). Hensikten med masteroppgaven var å se på bakterievekst og toksindannelse ved gjentatte korte opphold ved romtemperatur, og ved lagring ved ulike temperaturer. De patogene mikroorganismene Bacillus cereus, Bacillus weihenstephanensis, Listeria

monocytogenes, Staphylococcus aureus og Yersinia enterocolitica ble valgt fordi de har evnen til å vokse ved kjøleskapstemperaturer. Bakteriene ble lagret ved 4 og 8 °C i ti dager (S.

aureus ble lagret ved 8 og 12 °C). Skålene ble inkubert ved 25 °C daglig i henholdsvis 30 minutter, en time og to timer. Bakterievekst og toksindannelse ble sammenliknet med skåler inkubert ved 4 og 8 °C gjennom hele forsøksperioden. Forsøkene viste at daglige uttak ved

25 °C øker mikrobiell vekst i produktet, og forringer holdbarheten til matvarene betraktelig. B. cereus, B. weihenstephanensis og S. aureus ble undersøkt for toksindannelse ved de samme

betingelsene som for bakterievekst. Forsøkene viste relativt liten toksinproduksjon, både for

B. weihenstephanensis og S. aureus, selv om antall bakterier var tilstrekkelig for

toksinproduksjon. This study is a part of a larger research project between Nofima Mat and The National Institute for Consumer Research. The focus of the project is to achieve better food safety in the domestic environment, by risk analysis of consumer food handling and evaluation of riskreducing measures. A case study was performed at Nofima Mat with 45 volunteers, where they received a temperature logger to bring with them in the Easter and Christmas holiday of

2009 and 2010. The temperature loggers were to be treated as cold cuts of boiled ham during the vacation. Average temperature in which the cold cuts were stored varied greatly from 2,

9ºC to 12, 0 ºC with a total sample mean of 6, 2 ºC. The cold cuts were exposed to room

temperature every day for up to 113 minutes, with the total sample mean being 47 minutes (Røssvoll 2010). The aim of this study was to evaluate bacterial growth and production of toxins, for elected

pathogenic bacteria, at different periods of incubation at room temperature (25 °C). Bacterial growth with incubation at 25 °C was compared to bacterial growth at continuous storage at refrigerator temperatures (4 and 8 °C). The pathogenic bacteria Bacillus cereus, Bacillus weihenstephanensis, Listeria

monocytogenes, Staphylococcus aureus and Yersinia enterocolitica were chosen because of their ability to grow at refrigerator temperatures. The bacteria were incubated on agar plates at 4 and 8 °C for 10 days. S. aureus was stored at 8 and 12 °C. The plates were exposed to room

temperature (25 °C) every day for 30 minutes, 1 hour and 2 hours, respectively, and compared to the plates incubated at constant temperature of 4 and 8 °C throughout the study. The results indicated that short term storage at room temperature increase the microbial

growth in cold cuts, and reduce the shelf-life of the products. B. cereus, B. weihenstephanensis and S. aureus were analyzed for production of toxins at the

same conditions as the agar plates for growth investigation. The study showed very little production of toxins.

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