Two properties of soybean isoflavones were examined in in vitro systems: (1) their antioxidative potency by measuring the extent of inhibition of lipoxygenase action and (2) their antihemolytic activity by measuring their ability to prevent peroxidative hemolysis of erythrocytes. The extent of the antioxidative capacity of isoflavones is positively correlated to the number of hydroxyl groups in the isoflavone nucleus. Glycosidation of isoflavones depressed their antioxidative activity considerably. A different susceptibility of erythrocytes of sheep, rats, and rabbits to the antihemolytic activity of isoflavones was found. Very high antihemolytic activity of some isoflavones such as daidzein was exerted toward sheep erythrocytes, very little and only by genistein was exerted toward rat erythrocytes, and no antihemolytic effect was noted at all on rabbit erythrocytes. A hemolysis enhancing activity of small amounts of isoflavones on rabbit erythrocytes, but not on those of sheep and rats, has been observed. The antioxidative and antihemolytic activities of isoflavones toward sheep erythrocytes were differently affected by structural differences of isoflavones.

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