The mutagenic potency of onion juice vs. its contents of quercetin and rutin.

In spite of its considerable value as a predictor of in vivo genotoxicity and even for carcinogenicity, false positive cases were reported for the Ames test, e.g., with a number of natural food constituents. Here we analyzed the effects of juice of Allium cepa, the common onion, a staple food and traditional remedy used in many civilizations, in the Ames fluctuation assay. We could find mild mutagenicity with an onion juice extract in Salmonella typhimurium strains TA98 and TA100, the latter being less sensitive towards the extract. Mutagenicity was not influenced markedly by the presence of rat liver S9 mix. Onion juice also exerted some toxicity to the bacteria in the same concentration range. Comparative studies with quercetin and rutin, major flavonoid glycosides in onions, revealed a mutagenic potency of quercetin with an EC-value of 4 μM in TA98. The contents of quercetin and rutin in onion juice were determined as 0.71 ± 0.20, and 0.71 ± 0.21 mg/kg. Calculations of quercetin and rutin concentrations in mutagenic dilutions revealed that both compounds are highly unlikely to cause the mutagenic effects of onion juice and that other yet undefined constituents must be responsible for these effects.