Thesis (MSc Food Sc)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT:Aspalafhus linearis is an indigenous fynbos plant cultivated in the Clanwilliam area
of the Western Cape, South Africa. The rooibos tea that is prepared from this
plant, has become popular worldwide mainly due to the alleged health properties.
Studies on the anti-microbial properties of green, black and oolong teas have
shown that these teas have strong anti-microbial activity against a wide range of
microbes. No studies have been done on the anti-microbial activity of rooibos tea
and the aim of this study was to determine what impact rooibos tea extracts would
have on the growth of different food spoilage and potential pathogenic microbes.
Water and ethyl acetate extracts of fermented and unfermented rooibos tea
were used to determine the inhibitory effect on the growth of an Escherichia coli
strain. The E. coli culture was grown in tea-MRS with either added fermented or
unfermented rooibos tea extracts. Both the water and ethyl acetate extracts
showed a strong inhibitory effect against the E. coli strain in that there was a
decrease in the final bacterial cell density (Nmax)(from 0.59 00 to 0.25 00) and
the maximum specific growth rate (~max)(from 1.12 h-1 to 0.20 h-1) and an increase
in the doubling time (~) (from 0.59 h to 1.80 h) and lag time (tlag)(from 4.81 h to
6.60 h) as the concentration of the soluble solids of the tea extracts was increased
from 0.5 to 5.0 g.r1
. Furthermore, it was found that the fermented rooibos tea had
a much stronger inhibitory effect (69% decrease in growth at 5.0 g.r1 soluble
solids) compared to the unfermented rooibos tea extracts (35.1% decrease in
growth at 5.0 g.r1 soluble solids). The resulting data indicated that rooibos tea had
a very strong inhibitory effect on the growth of the E. coli strain. It was also found
that the water extracts of rooibos tea showed a stronger inhibitory effect on the
growth of the E. coli than the ethyl acetate extracts, indicating that the antimicrobial
activity of rooibos tea is not exclusively due to the polyphenolic content -
individual compounds. It was also determined that the rooibos tea water extracts
showed a bacteriostatic action against the E. coli strain in that as soon as the tea
is no longer part of the growth medium, the E. coli resumed a normal growth
pattern. The data obtained showed that the inhibitory effect of rooibos tea water
extracts (69% decrease in growth) against the growth of E. coli was more
pronounced than that found when black tea water extracts (25.7% decrease in
growth) at the same concentrations were used.Rooibos tea water extracts (0.5 - 5.0 g.r1) of fermented and unfermented
tea were also used to determine the inhibitory effect on other food spoilage
microbes and potential pathogens. Strains of Staphylococcus aureus, Bacillus
cereus, Listeria monocytogenes, Streptococcus mutans, Saccharomyces
cerevisiae and Zygosaccharomyces rouxii were grown in the presence of
fermented and unfermented rooibos tea water extracts. The effect that fermented
rooibos tea had on the growth of all the microbes tested was in the following order:
Staph. aureus (90.8% decrease in growth) > L. monocytogenes (89.2% decrease
in growth) > Strep. mutans (84.1% decrease in growth) > B. cereus (80.3%
decrease in growth) > Sacch. cerevisiae (77.7% decrease in growth) > E. coli
(69.0% decrease in growth). The rooibos tea clearly had an inhibitory effect on the
growth of all the microbes, with the exception of the Z. rouxii strain where the
presence of the tea water extracts was found to enhance the growth.
The inhibitory effect of rooibos tea on the growth of these microbes was
shown by changes in the growth parameters with Nmax and IJmaxshowing
decreases, while the ld and tlagincreased as the concentration of the tea soluble
solids was increased. As with E. coli, the fermented rooibos tea water extracts
showed the stronger inhibitory effect on the growth of the various microbes.
The data obtained in this study suggests that rooibos tea is not effective as
an anti-microbial agent against all yeast species, but will strongly retard the growth
of specific Gram-positive and Gram-negative bacteria. As long as rooibos tea is
present, strong anti-microbial activity will be observed at a cup of tea concentration
of 2.5 g.r1 soluble solids. These results may be of value to support the health
claims associated with rooibos tea and may in the future lead to the use of rooibos
tea as a "natural" food preservative. / AFRIKAANSE OPSOMMING:Aspalathus linearis is 'n inheemse fynbosplant wat gekultiveer word in die
Clanwilliam area van die Wes Kaap, Suid-Afrika. Rooibostee, wat gemaak word
van hierdie plante, het baie gewild geword wereldwyd a.g.v. die
gesondheidsaspekte van hierdie tee. Studies toon dat groen, swart en oolong tee
sterk anti-mikrobiese aktiwiteit het teen 'n wye reeks mikrobes. Aangesien daar
voorheen geen studies gedoen is op die anti-mikrobiese aktiwiteit van rooibostee
nie, was die doel van hierdie studie om die effek van rooibostee te bepaal op die
groei van verskillende voedselbederwers en potensiele patogeniese mikrobes.
Water- en etielasetaat-ekstrakte van gefermenteerde en ongefermenteerde
rooibos tee is gebruik om die inhiberende effek op die groei van Escherichia coli te
bepaal. Escherichia coli is gegroei in tee-MRS met bygevoegde gefermenteerde
of ongefermenteerde rooibostee-ekstrakte. Seide die water- en etielasetaatekstrakte
van rooibostee het 'n sterk inhiberende effek gewys teen E. coli en dit
word gestaaf deur 'n afname in die finale bakteriese seldigtheid (Nmax)(vanaf 0.59
00 tot 0.25 00) en die maksimum spesifieke groeitempo (lJmax) (vanaf 1.12 h-1 tot
0.20 h-1) en 'n toename in die verdubbelingstyd (~) (vanaf 0.59 h tot 1.80 h) en die
sloerfase (tlag)(vanaf 4.81 h tot 6.60 h) 5005 wat die konsentrasie van oplosbare
vastestowwe van die tee toeneem van 0.5 tot 5.0 g.r1
. Verder is daar gevind dat
die gefermenteerde rooibostee 'n baie sterker inhiberende effek het (69% afname
in groei by 5.0 g.r1 oplosbare vastestowwe) in vergelyking met die
ongefermenteerde rooibostee-ekstrakte (35.1% afname in groei by 5.0 g.r1
oplosbare vastestowwe). Die resultate van die data dui aan dat rooibos tee 'n
baie sterk inhiberende effek het op die groei van die E. coli spesie. Die waterekstrakte
van rooibostee het 'n sterker inhibisie getoon teen die groei van E. coli
as die etielasetaat-ekstrakte, wat aandui dat die anti-mikrobiese aktiwiteit van
rooibostee nie eksklusief toegeskryf kan word aan die polifenoliese samestelling
nie. Daar is ook gevind dat rooibostee water-ekstrakte 'n bakteriostatiese effek
het teen E. coli, want sodra die tee ekstrakte nie meer teenwoordig is in die
groeimedium nie, hervat E. coli normale groei. Die data wys ook dat die
inhiberende effek van rooibostee water-ekstrakte (69.0% afname in goei) teen E.
coli baie sterker is as die van swart tee water-ekstrakte (25.7% afname in groei) by
dieselfde konsentrasies.Rooibostee water-ekstrakte (0.5 - 5.0 g.r1) van gefermenteerde en
ongefermenteerde rooibostee is ook gebruik om die inhiberende effek te bepaal
teen ander voedselbederwers en potensiele patogene. Spesies van
Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes, Streptococcus
mutans, Saccharomyces cerevisiae en Zygosaccharomyces rouxii is gegroei in die
teenwoordigheid van gefermenteerde en ongefermenteerde rooibostee waterekstrakte.
Die effek wat gefermenteerde rooibostee het op die groei van die
getoetste mikrobes is 5005 volg: Staph. aureus (90.8% afname in groei) > L.
monocytogenes (89.2% afname in groei) > Strep. mutans (84.1% afname in groei)
> B. cereus (80.3% afname in groei) > Sacch. cerevisiae (77.7% afname in groei)
> E. coli (69.0% afname in groei). Rooibostee het 'n duidelike inhiberende effek
gehad teen al die organismes, behalwe teen Z. rouxii spes ie, waar die
teenwoordigheid van rooibostee die groei van die organisme bevorder het.
Die inhiberende effek van rooibostee teen die groei van hierdie mikrobes
word ondersteun deur die groei parameters waar die Nmaxen IJmaxafgeneem het
terwyl die ~ en tlagtoegeneem het 5005 wat die konsentrasie van die oplosbare
vastestowwe toeneem. Die gefermenteerde rooibostee water-ekstrakte het ook 'n
sterker inhiberende effek op die groei van die verskillende mikrobes net 5005 met
E. coli.
Die data wat verkry is van hierdie studie dui aan dat rooibostee nie effektief
sal wees as 'n anti-mikrobiese middel teen aile gis spesies nie, maar dit sal die
groei van spesifieke Gram-positiewe en Gram-negatiewe bakterie sterk vertraag.
So lank as wat rooibostee teenwoordig is, sal sterk anti-mikrobiese aktiwiteit
waargeneem word by 'n koppie-tee konsentrasie van 2.5 g.r1 oplosbare
vastestowwe. Hierdie resultate kan help om die gesondheidseienskappe
geassosieer met rooibostee te ondersteun en help om die gebruik van rooibostee
as 'n "natuurlike" preserveermiddel te bevorder.
dedicated to my parents
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/18345 |
| Date | 12 1900 |
| Creators | Schepers, Sonette |
| Contributors | Britz, T. J., Witthuhn, R. C., Joubert, E., Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 112 p. : ill. |
| Rights | Stellenbosch University |
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