A radical scavenger in accordance with the present invention comprises, as an effective ingredient, a phenylenediamine derivative or a pharmacologically acceptable salt thereof expressed by the following formula 1: ##STR1## wherein R.sub.1 represents a lower alkyl group; and each of R.sub.2 and R.sub.3 represents a hydrogen atom, an alkyl group having 1-10 carbon atoms, an alkenyl group having 1-10 carbon atoms, or benzyl group. The phenylenediamine derivative above mentioned, as a radical scavenger, has a lipid peroxidation inhibitory activity so as to be available for inhibiting brain infarction or brain edema.
An object of the present invention is to provide a platelet aggregation inhibitor without side effects and a supplement food effective for inhibiting platelet aggregation. The platelet aggregation inhibitor has nattokinase as an active ingredient and has Bacillus natto culture extract, containing a high proportion of nattokinase containing 1 .mu.g/g or less of vitamin K.sub.2 on a dry weight basis, as an active ingredient. The supplement food effective for inhibiting platelet aggregation has nattokinase as an active ingredient and has Bacillus natto culture extract, containing a high proportion of nattokinase containing 1 .mu.g/g or less of vitamin K.sub.2 on a dry weight basis, as an active ingredient.
