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

[摘要] ENGLISH ABSTRACT:Aspalafhus linearis is an indigenous fynbos plant cultivated in the Clanwilliam areaof the Western Cape, South Africa. The rooibos tea that is prepared from thisplant, has become popular worldwide mainly due to the alleged health properties.Studies on the anti-microbial properties of green, black and oolong teas haveshown that these teas have strong anti-microbial activity against a wide range ofmicrobes. No studies have been done on the anti-microbial activity of rooibos teaand the aim of this study was to determine what impact rooibos tea extracts wouldhave on the growth of different food spoilage and potential pathogenic microbes.Water and ethyl acetate extracts of fermented and unfermented rooibos teawere used to determine the inhibitory effect on the growth of an Escherichia colistrain. The E. coli culture was grown in tea-MRS with either added fermented orunfermented rooibos tea extracts. Both the water and ethyl acetate extractsshowed a strong inhibitory effect against the E. coli strain in that there was adecrease in the final bacterial cell density (Nmax)(from 0.59 00 to 0.25 00) andthe maximum specific growth rate (~max)(from 1.12 h-1 to 0.20 h-1) and an increasein the doubling time (~) (from 0.59 h to 1.80 h) and lag time (tlag)(from 4.81 h to6.60 h) as the concentration of the soluble solids of the tea extracts was increasedfrom 0.5 to 5.0 g.r1. Furthermore, it was found that the fermented rooibos tea hada much stronger inhibitory effect (69% decrease in growth at 5.0 g.r1 solublesolids) compared to the unfermented rooibos tea extracts (35.1% decrease ingrowth at 5.0 g.r1 soluble solids). The resulting data indicated that rooibos tea hada very strong inhibitory effect on the growth of the E. coli strain. It was also foundthat the water extracts of rooibos tea showed a stronger inhibitory effect on thegrowth of the E. coli than the ethyl acetate extracts, indicating that the antimicrobialactivity of rooibos tea is not exclusively due to the polyphenolic content -individual compounds. It was also determined that the rooibos tea water extractsshowed a bacteriostatic action against the E. coli strain in that as soon as the teais no longer part of the growth medium, the E. coli resumed a normal growthpattern. The data obtained showed that the inhibitory effect of rooibos tea waterextracts (69% decrease in growth) against the growth of E. coli was morepronounced than that found when black tea water extracts (25.7% decrease ingrowth) at the same concentrations were used.Rooibos tea water extracts (0.5 - 5.0 g.r1) of fermented and unfermentedtea were also used to determine the inhibitory effect on other food spoilagemicrobes and potential pathogens. Strains of Staphylococcus aureus, Bacilluscereus, Listeria monocytogenes, Streptococcus mutans, Saccharomycescerevisiae and Zygosaccharomyces rouxii were grown in the presence offermented and unfermented rooibos tea water extracts. The effect that fermentedrooibos 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% decreasein 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 thegrowth of all the microbes, with the exception of the Z. rouxii strain where thepresence of the tea water extracts was found to enhance the growth.The inhibitory effect of rooibos tea on the growth of these microbes wasshown by changes in the growth parameters with Nmax and IJmaxshowingdecreases, while the ld and tlagincreased as the concentration of the tea solublesolids was increased. As with E. coli, the fermented rooibos tea water extractsshowed the stronger inhibitory effect on the growth of the various microbes.The data obtained in this study suggests that rooibos tea is not effective asan anti-microbial agent against all yeast species, but will strongly retard the growthof specific Gram-positive and Gram-negative bacteria. As long as rooibos tea ispresent, strong anti-microbial activity will be observed at a cup of tea concentrationof 2.5 g.r1 soluble solids. These results may be of value to support the healthclaims associated with rooibos tea and may in the future lead to the use of rooibostea as a natural food preservative.

[发布机构] Stellenbosch University