The history and the background of dairy products, specifically fermented milk
products and foodborne diseases were reviewed. The constructed literature
review also gave details of the microbial and nutritional compostion of fermented
milks and examples of African traditional fermented milks. Health benefits of
these dairy products were also included. Furthermore, the most common
foodborne pathogens and their survival in dairy products were discussed.
The survival of Escherichia coli O157:H7, non pathogenic Escherichia coli,
Listeria monocytogenes, Staphylococcus aureus, Salmonella spp. and Shigella
spp in plain and fruit yoghurt during cold storage at 4 °C was investigated. The
survival of these microbial pathogens ranged between 1-14 days in both types of
yoghurt, with Staphylococcus aures being the most sensitive pathogen to the
yoghurt enviroment. Lactic acid bacteria and yeasts counts remained fairly stable
at an average of 8 log cfuml-1 and below 10cfuml-1 respectively. A reduction in pH
was noticed during yoghurt storage. The high numbers of LAB and low pH played
a major role in the inhibition of the food borne pathogens over time in both plain
and fruit yoghurt.
The survival of the same microbial pathogens in fruit yoghurt during temperature
abuse at 25°C was investigated. There was a rapid die-off of the food borne
pathogens at this temperature. Their survival in the yoghurt ranged between 1-3
days. There was a rapid decrease in pH and an increase in the LAB and these
together with the high temperature played a major role in the higher death rate of
the foodborne pathogens in the fruit yoghurt. Yeasts grew to high levels that
caused the yoghurt to spoil.
When comparing yoghurt stored at 4 °C and 25°C a conclusion was made:
yoghurt stored at 4 °C will be of good quality but will not be regarded as safe as
pathogens survival for a long period, and yoghurt stored at 25°C will be regarded
as safe but will not be of good quality as high yeasts counts will result in spoilage. The microbial pathogens were also inoculated into yoghurt and their survival at 4
°C after temperature abuse at 12 °C and 37 °C for 4-6 hours was studied. The
pathogenic microorganisms died-off at a higher death rate during temperature
abuse at high temperatures than at a low temperature at 4 °C. At 4 °C the death
rate decreased and the survival in yoghurt ranged between 1-11 days. A rapid
decrease in pH and a slight increase in LAB were observed during and after
temperature abuse. The yeast increased during the storage of yoghurt. This
study showed that inhibition of foodborne pathogens is high at higher
temperatures.
The survival of the microbial pathogens in milk during the production of Sethemi
at 25 °C and 37 °C was studied. The pathogens increased, growing to high
counts during the first 24hrs of fermentation. After 24hrs growth of some
pathogens was inhibited, however, all the pathogens could still be detected even
at the end of fermentation at both temperatures. Yeasts grew to some extend and
the lactic acid bacteria grew to high levels during the fermentation of milk at both
temperatures. The lactose produced by LAB decreased with time and there was
a slight increase in galactose. A rapid increase in lactic acid was noted after a
few hours of fermentation, this caused a decline in pH which resulted in the
inhibition of pathogens. The inhibition was most effective at 37 °C.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-02032010-090307 |
| Date | 03 February 2010 |
| Creators | Lefoka, Mamajoro |
| Contributors | Prof BC Viljoen |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-02032010-090307/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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