Antioxidant Activity of Phytic Acid in Lipid Model System

Free radicals formed during thermal (60 degrees C, 24 h) and catalytic (Fe(2+) ions, room temperature (23 +/- 1) degrees C, 3 h) oxidative degradation of hydroperoxyde-enriched soybean oil (HESO) were stabilized in the presence of spin trap N-tert-butyl-alpha-phenylnitrone (PBN) and detected by electron spin resonance (ESR) spectrometry. In both thermal and catalytic oxidation of HESO, the same hyperfine coupling parameters (a(N)=14.75 G and a(H)(beta)=2.80 G) confirmed the generation of PBN-OOL/-OL spin adducts. The antiradical activity (AA) of phytic acid, in the 0.076-0.30 mM concentration range, was tested by measuring its ability to inhibit the generation of PBN-OOL/-OL spin adducts during thermal and catalytic oxidation of HESO. Phytic acid did not inhibit the thermal oxidation of HESO and showed no effect in the beta-carotene bleaching test (AOA). Contrary to this, phytic acid exhibited antioxidant effect on the catalytic oxidation of HESO by chelating Fe(2+) ions. The mechanism of antioxidant activity was confirmed by the results of chelating activity on Fe(2+) in Fe(2+)-ferrozine test where a dose-dependent chelating activity of phytic acid was obtained.