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)-β-(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′-DiFA 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-β, β′-bicinnamic acid; 8,8′-DiFA); 8,5′-diferulic acid open form ((E, E)-4,4′ dihydroxy-3,5′-dimethoxy-β,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.