Peroxidase-dependent cross-linking reactions ofp-hydroxycinnamates in plant cell walls

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Peroxidases are heavily implicated in plant cell wall cross-linking reactions, altering the properties of the wall and impacting its utilization. Polysaccharide-polysaccharide cross-linking in grasses is achieved by dehydrodimerization of hydroxycinnamate-polysaccharide esters; a complex array of hydroxycinnamic acid dehydrodimers are released by saponification. Ferulates are the major cross-linking agents, but sinapate-ferulate cross-products have been discovered implicating sinapates in a similar role. New dehydrodimers have been authenticated, expanding our knowledge of the chemistry, role, and extent of cross-linking reactions. Ferulate dehydrotrimers have been discovered; whether these trimers truly cross-link three independent polysaccharide chains or only two remains to be determined. Hydroxycinnamates and their dehydrodimers also undergo radical coupling reactions with lignin monomers and possibly oligomers, resulting in lignin-polysaccharide cross-linking in the wall. Both polysaccharide-polysaccharide and lignin-polysaccharide cross-links inhibit the enzymatic hydrolysis of cell walls. The cross-linking process has particular relevance to plant physiology, human and animal nutrition and health, and food technology.Abbreviations: CW - cell wall; DFA - dehydrodiferulic acid (or dehydrodiferulate in context); DSA - dehydrodisinapic acid; TFA - dehydrotriferulic acid; SA - sinapic acid (1S); TA - thomasidioic acid (5C3SS); IDF - insoluble dietary fiber; SDF - soluble dietary fiber; GC-MS - gas chromatography-mass spectrometry; NMR - nuclear magnetic resonance (spectroscopy).

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