Gyrometrin is the formyl-methylhydrazone of acetaldehyde (Figure 3.3a), a volatile and unstable compound. By hydrolysis, which occurs in the cooking process as well as in the GI tract, gyrometrin is cleaved into formyl-methylhydrazine (Figure 3.3b), and further into monomethylhydrazine, MMH (Figure 3.3c), representing the real poison. Both reaction products are volatile, therefore intoxications may also occur by inhalation of the fumes emitted during cooking. However, insufficient cooking, or cooking in a covered pot, may increase toxicity by leaving too much of the toxin in the meal. Fresh mushrooms contain 0 to 1.5 mg/g of the poison. The estimated lethal dose for humans has been estimated as 20 to 50 mg/kg body weight, less for children, i.e., 10 to 30 mg/kg body weight. Formyl-methylhydrazine and methylhydra-zine are reported to be cancerogenic, possibly by methylating guanine moieties in DNA (Bergman and Hellenas, 1992).
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