Oxidative cross-linking of corn bran hemicellulose: Formation of ferulic acid dehydrodimers

The aim of this study was to investigate the nature and extent of ferulate dehydrodimer cross-links formed during peroxide and peroxidase-catalysed gelation of an arabinoxylan ferulate polysaccharide from American Corn Bran (Zea mays L.). Alkali-soluble phenolics from the arabinoxylan (AXF) and its gel (AXFG), were identified and quantified by HPLC. AXF was rich in trans-ferulic acid and contained small quantities of 8-0-4'-diferulic acid ((Z)-beta-(4-((E)-2-carboxyvinyl)-2-methoxyphenoxy)-4-hydroxy-3-methoxycinnamic acid; 8-0-4'-DiFA); 8,5'-diferulic acid benzofuran form (trans-5-((E)-2-carboxyvinyl)-2-(4-hydroxy-3-methoxyphenyl)-7-methoxy-2,3-dihydrobenzofuran-3-carboxylic acid; 8,5'-FiFA benzofuran form); and 5,5'-diferulic acid ((E,E)-4,4'-dihydroxy-5,5'dimethoxy-3'-bicinnamic acid; 5,5'-DiFA) in addition to vanillin and trans-coumaric acid. Gel formation resulted in a considerable increase in the levels of 8-0-4'-DiFA, 8,5'-DiFA benzofuran form and the appearance of significant quantities of 8,8'-diferulic acid open form (4,4'-dihydroxy-3,3'-dimethoxy-beta,beta'-bicinnamic acid; 8,8'-DiFA); 8,5'-diferulic acid open form ((E,E)-4,4'dihydroxy-3,5'-dimethoxy-beta,3'-bicinnamic acid; 8,5'-DiFA) and 8,8'-diferulic acid aryltetralin form (trans-7-hydroxy-1-(4-hydroxy-3-methoxy-phenyl)-6-methoxy-1,2-dihydronaphthalene-2,3-dicarboxylic acid; 8,8'-DiFA aryl form). The results confirm that peroxidase/peroxide-induced gelation results from oxidative cross-linking of ferulic acid moieties. (C) 1997 Elsevier Science Ltd.