Acid and heat stability of the anticoagulative activity of an onion extract.

An onion extract possessed anticoagulative activity apparently by inhibiting thrombin, and it was dependent upon the concentration of onion extract added. Boiling the onion extract at 100 degrees C for 30 min made no difference to its anticoagulative activity compared to that of fresh onion. The anticoagulative activity of the onion extract was also retained after an acid treatment by incubating at pH 2.0 for 4 hrs. However, dialyis of the extract substantially eliminated the anticoagulative activity. Therefore, the anticoagulant in the onion extract seems to have been a heat- and acid-stable substance of low molecular weight.