FERULIC ACID DEHYDRODIMERS FROM WHEAT BRAN - ISOLATION, PURIFICATION AND ANTIOXIDANT PROPERTIES OF 8-O-4-DIFERULIC ACID

Wheat bran contains several ester-linked dehydrodimers of ferulic acid , which were detected and quantified after sequential alkaline hydroly sis. The major dime rs released were: enyl)-7-methoxy-2,3-dihydrobenzo furan-3-carboxylic acid (5-8-BendiFA), yl]-2-methoxy-phenoxy}-4-hydrox y-3-methoxycinnamic acid (8-O-4-diFA) and E,E)-4,4'-dihydroxy-5,5'-dim ethoxy-3,3'-bicinnamic acid (5-5-diFA). 6-melhoxy-1,2-dihydro-naphthal ene-2,3-dicarboxylic acid (8-8-diFA cyclic form) and ,4'-dihydroxy-3,3 '-dimethoxy-beta,beta'-bicinnamic acid (8-8-diFA non cyclic form) were not detected. One of the most abundant dimers, 8-O-4-diFA, was purifi ed from de-starched wheat bran after alkaline hydrolysis and preparati ve HPLC. The resultant product was identical to the chemically synthes ised 8-O-4-dimer by TLC and HPLC as confirmed by H-1-NMR and mass spec trometry. The absorption maxima and absorption coefficients for the sy nthetic compound in ethanol were: lambda(max): 323 nm, lambda(min): 25 8 nm, epsilon(lambda min) (M(-1)cm(-1)): 24800 +/- 2100 and epsilon(28 0) (M(-1)cm(-1)): 19700 +/- 1100. The antioxidant properties of 8-O-4- diFA were assessed using: (a) inhibition of ascorbate/iron-induced per oxidation 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. Th e 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 activi ty of a natural diferulate obtained from a plant.