Absence of Mutagenicity, Genotoxicity, and Subchronic Oral Toxicity of Touchi Extract

Touchi, a traditional Chinese food used mainly for seasoning is obtained by first steaming soybeans followed by fermentation with Aspergillus oryzae (koji). A series of toxicological studies was conducted to evaluate the mutagenic and genotoxic potential and subchronic toxicity of a water extract of Touchi, a known inhibitor of α-glucosidase activity. Touchi extract (TE) did not induce reverse mutations in Salmonella typhimurium strains TA98, TA1537, TA100, TA1535, and Escherichia coli WP2uvrA at concentrations up to 5000 μg/plate, in either the absence or presence of exogenous metabolic activation. No deaths occurred and no abnormal clinical signs were observed in any animal in any group in an in vivo micronucleus test, and TE was devoid of clastogenic activity when administered orally to mice at doses up to 2000 mg/kg/day. Thus, TE was evaluated as negative in the bacterial reverse mutation and mouse bone marrow micronucleus tests under the conditions of these assays. To evaluate its subchronic toxicity, SPF rats were administered TE at doses of 0,250,1000, and 2500 mg/kg/day via oral gastric intubation. No treatment-related toxic changes were seen in clinical signs, body weight, food consumption, urinalysis, hematology, blood chemistry, necropsy, organ weight, or histopathology. The no observed adverse effect level for TE was thus considered to be more than 2500 mg/kg/day in both males and females. These results are consistent with Touchi’s status as a traditional Chinese food derived from fermented soybeans and its purported long history of use. Specifically, these data are consistent with the expected safety of human consumption of TE up to at least 5 g/day.