An evaluation of instant and regular coffee in the Ames mutagenicity test.

High concentrations of "home brew" and instant coffe induced revertants 2--3-fold the spontaneous level with the Ames Salmonella tester strain TA 100 but not with the strains TA 98, TA 1535, TA 1537 and TA 1538. This borderline effect, which may also have been due to non-mutagenic interactions (false positives) occurred only at bacterial levels of coffees and was completely abolished in the presence of the microsomal "metabolic activation system". Negative results were obtained in host-mediated assays when mice received up to 6 g instant coffee/kg body weight. An extrapolation in respect of possible carcinogenic risks is dubious.