Ferulic acid dehydrodimers from wheat bran: Isolation, purification and antioxidant properties of 8-O-4-diferulic acid

M. T. Garcia-Conesa, G. W. Plumb, K. W. Waldron, J. Ralph, G. Williamson

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Abstract

Wheat bran contains several ester-linked dehydrodimers of ferulic acid, which were detected and quantified after sequential alkaline hydrolysis. The major dimers released were: trans-5-[(E)-2-carboxyvinyl]-2-(4-hydroxy-3-methoxyphenyl)-7-methoxy-2,3 -dihydrobenzofuran-3-carboxylic acid (5-8-BendiFA), (Z)-β-{4-[(E)-2-carboxyvinyl]-2-methoxyphenoxy}-4-hydroxy-3-methoxycinnamic acid (8-O-4-diFA) and (E,E)-4,4'-dihydroxy-5,5'-dimethoxy-3,3'-bicinnamic acid (5-5-diFA). trans-7-hydroxy-1-(4-hydroxy-3methoxyphenyl)-6-methoxy-1,2-dihydro-naphthalene -2,3-dicarboxylic acid (8-8-diFA cyclic form) and 4,4'-dihydroxy-3,3'-dimethoxy-β,β'-bicinnamic acid (8-8-diFA non cyclic form) were not detected. One of the most abundant dimers, 8-O-4-diFA, was purified from de-starched wheat bran after alkaline hydrolysis and preparative HPLC. The resultant product was identical to the chemically synthesised 8-O-4-dimer by TLC and HPLC as confirmed by 1H-NMR and mass spectrometry. The absorption maxima and absorption coefficients for the synthetic compound in ethanol were: λ(max): 323 nm, λ(min): 258 nm, ε(λmax) (M-1cm-1): 24800 ± 2100 and ε280 (M-1cm-1): 19700 ± 1100. The antioxidant properties of 8-O-4-diFA were assessed using: (a) inhibition of ascorbate/iron-induced peroxidation of phosphatidylcholine liposomes and; (b) scavenging of the radical cation of 2,2'-azinobis (3-ethyl-benzothiazoline-6-sulphonate) (ABTS) relative to the water-soluble vitamin E analogue, Trolox C. The 8-O-4-diFA was a better antioxidant than ferulic acid in both lipid and aqueous phases. This is the first report of the antioxidant activity of a natural diferulate obtained from a plant.

Original languageEnglish
Pages (from-to)319-323
Number of pages5
JournalRedox Report
Volume3
Issue number5-6
DOIs
Publication statusPublished - 1 Jan 1997
Externally publishedYes

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