Genotoxicity of cocoa examined by microbial and mammalian systems.

Unroasted or roasted cocoa powder dispersed in water and applied to Chinese hamsters by stomach tube caused elevated numbers of SCEs in the sister-chromatid exchange test (bone-marrow cells). Roasted cocoa freed from fat produced distinctly higher SCE values with a linear dose-response relationship, whereas cocoa butter had no influence on SCE levels. Positive results in the SCE test (1.5-fold values of the controls) were obtained after application of about 5 g cocoa/kg b.w. Presumably, because of the smaller quantities that could be administered in this way, positive test results were not found when cocoa was given in the diet instead of being administered by stomach tube. Cocoa from which theobromine was extracted by chloroform did not affect SCE levels. Pure theobromine increased SCE levels in a dose-dependent way. Theobromine was also positive in the micronucleus test at 2 X 40 mg/animal and negative in the chromosome aberration test at 1 X 40 mg/animal. Cocoa and the theobromine were negative in the Salmonella/mammalian microsome mutagenicity test both with and without metabolic activation.