Is the oxygen radical absorbance capacity (ORAC) method a peroxyl-radical scavenging assayΔ

Yoshimi Sueishi, Daisuke Yoshioka, Shigeru Oowada, Nobuyuki Endoh, Shunji Kohri, Hirotada Fujii, Masashi Shimmei, Yashige Kotake

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Abstract

The oxygen radical absorbance capacity (ORAC) method employs a water soluble azo-radical initiator, AAPH (2,2'-azobis(2-amidinopropane) dihydrochloride) as a free radical generator, by which the fluorescent probe fluorescein is damaged to result in the loss of fluorescence. Antioxidants can protect the probe from the damage and the degree of protection is quantified. Because AAPH has been used as a lipid-peroxidation reagent, "oxygen radical" in ORAC is generally accepted as peroxyl radicals; however, in the present spin trapping experiments using a newly developed spin trap, CYPMPO, there was no indication of peroxyl-radical formation in AAPH decomposition in aqueous media. These spin trapping studies demonstrated that alkoxyl (RȮ) radical adduct was the sole product of AAPH decomposition. In contrast, alkylperoxyl (ROȮ) radical was spin-trapped during the decomposition of a lipid soluble azo-radical initiator AIBN (azobis(isobutyronitrile)) in non-aqueous media. We speculate that alkyl-peroxyl radicals are short-lived in water, rapidly converted into alkoxyl radicals. Although the possibility that ORAC method monitors peroxyl-radical scavenging activity cannot be completely eliminated, spin trapping evidence strongly indicates that ORAC method is a scavenging capacity assay for alkoxyl radicals.

Original languageEnglish
Pages (from-to)921-928
Number of pages8
JournalZeitschrift fur Physikalische Chemie
Volume224
Issue number6
DOIs
Publication statusPublished - Jul 1 2010

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ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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