Metabolic fates in humans of linamarin in cassava flour ingested as stiff porridge

Insufficiently processed products from cassava roots may contain residual amounts of cyanogenic glucosides, mainly linamarin. The fate of orally ingested linamarin was studied following a meal of cassava porridge prepared from cassava flour from southern Tanzania with 82 mg cyanide equivalents (3035 μmol) of linamarin per kg dry weight. Following ingestion of amounts of porridge containing 243–571 μmol linamarin by 15 healthy adults a mean (range) of 21% (1–47%) of the linamarin ingested was excreted in the urine within 24 hours and a mean of 1% in the next 24 hours. Serum thiocyanate, the main cyanide metabolite, increased in all subjects from a mean (± SD) of 34±26 to 78±28 μmol/litre (P<0.001). In a second group of seven subjects we found that the ingestion of porridge with a mean (range) of 431 μmol (203–669%) of linamarin resulted in a mean linamarin excretion of 127 μmol/litre and an excess thiocyanate excretion of 118 μmol/litre and that 216 μmol was unaccounted for. We conclude that less than one-half of orally ingested linamarin is converted to cyanide and hence thiocyanate, about one-quarter is excreted unchanged and another quarter is metabolized into an as yet unknown compound.