Natural bio-antimutagenic activity of rooibos tea (Aspalathus linearis) as expressed by the Ames, Toxi-Chromo and SOS-Chromo tests

[摘要] ENGLISH SUMMARY: Rooibos tea (Aspalathus linear is), an indigenous fynbos plant, is cultivated in theClanwilliam area of the Western Cape and has become increasingly popular dueto its alleged health properties. The confirmation of antimutagenic potential inRooibos tea is important and research on its chemo-preventive properties wouldsubstantiate it as a health promoting agent. The antimutagenic properties offermented and unfermented Rooibos were determined and compared to that ofgreen and black teas (Camellia sinensis).The Ames test, using Salmonella typhimurium TA 98 and the mutagen 2-acetylaminofluorene (2-AAF), was performed on the ethyl acetate and water-solublefractions of the four tea extracts. The green tea had the strongestantimutagenic potential (67.6% inhibition), followed by the unfermented Rooibostea (59.1 % inhibition). The fermented Rooibos (47.3% inhibition) and black(46.5% inhibition) teas showed the lowest antimutagenic potential. The ethylacetate extracts had the stronger antimutagenic potential, indicating that mostcompounds responsible for the teas antimutagenic potential are probably found inthis extract.At a standardised total polyphenol content the green (75.5% inhibition) andunfermented Rooibos (75.1 % inhibition) teas had very similar antimutagenicpotentials. The fermented Rooibos (73.0% inhibition) had a higher antimutagenicpotential than the black tea (70.5% inhibition).Ames tests done on samples from the five processing stages in themanufacture of Rooibos tea revealed that processing does cause a reduction inthe antimutagenic potential of the tea. The major decrease in antimutagenicpotential occurred after the fermentation stage (P<0.05).Since, aspalathin is one of the major polyphenols found in Rooibos tea, theAmes test was performed using a crude aspalathin fraction to determine ifpolyphenols or more specifically aspalathin, are responsible for the antimutagenicproperties in Rooibos tea. The Ames test revealed that the aspalathin fraction hadantimutagenic potential that, on average, was 5 - 15% lower when compared tothe antimutagenic potential in Rooibos tea water-soluble extracts. The results of the Ames tests performed, using S. typhimurium T A 98, onrandom Rooibos tea samples from five commercial retailers revealed that theprocessing of Rooibos tea produces tea with fairly uniform antimutagenic potential.The SOS-Chromotest, to test for genotoxicity and the Toxi-Chromotest, totest for toxicity of the four tea extracts (fermented Rooibos, unfermented Rooibos,green and black tea), were also performed. These tests are based on mutantstrains of Escherichia coli and depend on a colour reaction to determine results ofthe tests. Colour profiles from the SOS-Chromotest were too faint to determineresults from, whereas the Toxi-Chromotest colour profiles indicated that the fourtea extracts probably had a toxic effect on the mutant bacteria. Furtherinvestigations were conducted to try and explain these inconclusive results andgrowth studies to determine if the tea was having an-inhibitory effect on the growthof the bacteria were performed on the bacterial tester strains and a standard E.coli culture (ATCC 58). The resulting data indicated that fermented andunfermented Rooibos had a very strong inhibitory effect on the growth of thebacteria while the green and black teas had lower inhibitory effects on the growthof the bacteria.

[发布机构] Stellenbosch University