Thesis (MScVoedselwet)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Milk has been identified as having the potential of being a carrier of human
pathogens, and it is thus essential to eliminate or reduce the likelihood of milk borne
contamination. This problem of milk contamination is generally solved by the process
of pasteurisation which is achieved by heating the "raw" material for a sufficient
period of time to destroy any pathogenic and spoilage bacteria which may be present
at a temperature of below 100°C. Presently, there are two basic methods of
pasteurisation in use in the dairy industry, the LTLT and the HTST methods, where
the applied heat treatment is considered sufficient to ensure public safety and
adequate keeping quality. In addition to these, there is another method, the "pot"
pasteurisation, to be found in Southern Africa that was designed to eliminate
potential pathogenic and spoilage bacteria present in raw milk. As far as it is known
no thermal studies have been done on the "pot" pasteurisation method. The
objectives of this study were to determine the impact of different milk pasteurisation
temperature and time combinations on the survival of selected microbes. The
accuracy of the "pot" pasteurisation method and how it differs from the other
pasteurisation methods was also determined using the same selected microbes.
The six selected microbes were thermally inactivated by using the LTLT,
HTST and the "pot" pasteurisation methods at low and high inoculum levels of 104
and 106 cfu.ml-1. The thermal death curves were constructed for each selected
species. The selected microbes included the strains Bacillus cereus (S4),
Chryseobacterium meningosepticum (S5), Pseudomonas putida (S6), Acinetobacter
baumannii (C3), Escherichia coli (58) and Candida lipolytica (G1). Survivors were
enumerated after heating for 0, 5, 10, 15, 20, 25, 30, 35 and 40 min for both the
LTLT and HTST pasteurisation methods and after heating for 0, 10, 20 and 30 min
for the "pot" pasteurisation method.
The results from this study showed that with the exception of the B. cereus
strain, the other selected microbes at both high and low concentration levels did not
survive the LTLT or the HTST pasteurisation methods. It was found that for all the
organisms used in this study, there was a rapid initial death rate just before the
required pasteurisation temperatures of 63°, 72° and 90°C were reached, during the
"come-up" period. In contrast, the results from the "pot" pasteuriser showed that theB. cereus (S4), Chr. meningosepticum (S5), P. putida (S6), A. baumannii (C3) and
E. coli (58) strains survived the pasteurisation conditions applied.
From these results it was thus concluded that the "pot" pasteuriser under the
conditions evaluated in this study, did not pasteurise effectively. Therefore, it is
recommended that the manufacturer improves the heating quality of the "pot"
pasteuriser. As it was found that only the B. cereus (S4) strain survived all the
different pasteurisation methods, future research needs to be done to determine at
which temperature this heat resistant bacterial strain will be destroyed. This is very
important because there is a need to destroy all the spoilage microorganisms that
can lead to the deterioration of food products. / AFRIKAANSE OPSOMMING: Melk is 'n potensiële draer van mikrobes wat patogenies is vir die mens. Dit is dus
essensiëel om die besmetting van melk te verlaag of te elimineer. Die probleem van
melkbesmetting word opgelos deur die proses van pasteurisasie. Die proses word
toegepas deur verhitting van die rou material vir 'n voldoende periode om
patogeniese en bederf organismes te vernietig. Temperature onder 100°C word
gebruik. In die suiwelbedryf word twee basiese metodes gebruik: die LTLT (lae
temperatuur, lang tyd) metode en die HTKT (hoë temperatuur, kort tyd) metode.
Albei hittebehandelings is voldoende om publieke veiligheid en 'n genoegsame
rakleeftyd te verseker. 'n Derde metode, "pot" pasteurisasie, word in Suidelike Afrika
gebruik. Die metode is ontwikkel om potensiële patogene en bederf organismes in
rou melk te elimineer. Die probleem is dat daar geen navorsing op die temperatuur
eienskappe van die “pot" metode gedoen is nie. Die doelwitte van hierdie navorsing
was om die effek van verskillende temperatuur:tyd kombinasies op die oorlewing van
sekere mikrobes te bepaal. Die akkuraatheid van die "pot" metode en die manier hoe
dit van ander metodes verskil, is ook in ag geneem. Die navorsing is ten alle tye
gebaseer op die geselekteerde mikroorganismes.
Die ses geselekteerde spesies van mikrobes is vernietig deur middel van die
LTLT, HTKT en "pot" pasteurisasie metodes. Die mikrobes is geïnaktiveer teen lae
en hoë inokulums van 104 en 106 kve.ml-1. Terminale dodings kurwes is opgestel vir
elke geselekteerde spesie. Die mikrobes van belang is Bacillus cereus (S4),
Chryseobacterium meningosepticum (S5), Pseudomonas putida (S6), Acinetobacter
baumannii (C3), Escherichia coli (58) en Candida lipolytica (G1). Die oorlewende
mikroorganismes is na hitte behandelings van 0, 5, 10, 15, 20, 25, 30, 35 en 40
minute vir beide die LTLT en die HTKT pasteurisasie metodes en na hitte
behandelings van 0, 10, 20, en 30 minute vir die "pot" pasteurisasie metode getel.
Die resultate van die navorsing dui aan dat, behalwe vir B. cereus, die
geselekteerde mikrobes teen beide lae en hoë konsentrasies nie die LTLT en die
HTKT metodes oorleef het nie. Daar is gevind dat, vir al die organismes, vinnige
aanvanklike dodingstempos teenwoordig was net voor die noodsaaklike
pasteurisasie temperatuur van 63°, 72° en 90°C bereik is, gedurende die "come-up"
periode. Inteenstelling hiermee het die resultate van die "pot" metode bewys dat B.cereus (S4), Chr. meningosepticum (S5), P. putida (S6), A. baumannii (C3) en E. coli
(58) stamme die pasteurisasie toestande oorleef het.
Uit die resultate is ’n gevolgtrekking gemaak dat die "pot" pasteurisasie
metode nie effektief was nie. Daar word dus aanbeveel dat die vervaardiger die
verhittings-kwaliteit van die "pot" pasteurisasie apparaat verbeter. Aangesien net die
B. cereus (S4) stam al drie pasteurisasie metodes oorleef het, moet toekomstige
navorsing gedoen word om die vernietigings temperatuur van dié hittebestande stam
te bepaal. Die navorsing is van belang weens die behoeftes om alle bederf
mikroorganismes wat tot die agteruitgang van voedsel produkte kan lei, te vernietig.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16316 |
| Date | 12 1900 |
| Creators | Dumalisile, Pholisa |
| Contributors | Britz, T.J., Witthuhn, R.C., University of Stellenbosch. Faculty of Agrisciences. Dept. of Food Science. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | ix, 84 leaves : ill. |
| Rights | University of Stellenbosch |
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