Antioxidant properties of genistein and daidzein - Two potent soybean isoflavones

Abstract

Soybean and full-fat soybean products contain approximately 20% of oil and are susceptible to lipid peroxidation, particularly during the storage and distribution of raw material and thermal treatments used in full-fat soybean production. Antioxidant properties of soybean isoflavones (genistein and daidzein) have been investigated in soybean oil model systems by measuring the ability of genistein and daidzein to inhibit the formation of radicals which were stabilized in the presence of spin trap N-tert-butyl-a-phenylnitrone (PBN) and detected in by electron spin resonance (ESR) spectrometry. In both thermal and catalytic oxidation of soybean oil, the same hyperfine coupling parameters (aN=14.75 G and aHβ=2.80 G) confirmed the generation of PBN-OOL/-OL spin adducts (lipid oxyradicals). The antiradical activity of genistein and daidzein, in the 0.005-0.02% concentration range, was tested by measuring their ability to inhibit the formation of lipid oxyradicals during thermal and catalytic oxidation of soybean oil. The antioxidative nature of genistein and daidzein was also tested by using DPPH test and chelating activity on Fe2+ assay. It has been found that genistein inhibits the thermal oxidation of soybean oil by decreasing the concentration of lipid oxyradicals, while during the inhibition of catalytic oxidation of soybean oil it acts as a chain-breaking antioxidant and a metal chelator. Daidzein acts as a very weak chain-breaking antioxidant which does not demonstrate chelating activity on Fe2+ ions.