Occurrence of methylguanidine and agmatine in foods

Methylguanidine (MG), a precursor of carcinogenic methylnitrosocyanamide and methylnitrosourea, has long been considered to occur widely in fresh beef and various fish muscles in fairly high concentrations. Agmatine (AG) has been reported to be easily nitrosated to give a potent mutagen under acidic conditions. A survey has been conducted on the MG and AG contents of various fresh and processed foods. The present study reveals that no appreciable amount, or only trace amounts, of MG could be detected in fresh beef, pork, chicken and various fish and shellfish. In addition, almost the same low levels of MG were detected in various processed foods, except in the case of smoked-dried fish products, where the MG values ranged from 18 to 178 mg/kg. Relatively high concentrations of AG, ranging from 40 to 200 mg/kg, could be detected in fresh abalone and top-shell muscles, while fairly high concentrations of AG could be detected in some processed foods. A dried squid product, in particular, was found to contain as high as 650 mg/kg of AG.