Anti-microbial activity of rooibos tea (Aspalathus linearis) on food spoilage organisms and potenial pathogens

Schepers, Sonette (2001-12)

Thesis (MSc Food Sc)--University of Stellenbosch, 2001.

Thesis

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

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