Peroxidase-dependent cross-linking reactions of p-hydroxycinnamates in plant cell walls

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 (1 S); TA – thomasidioic acid (5C3 SS); IDF – insoluble dietary fiber; SDF – soluble dietary fiber; GC-MS – gas chromatography-mass spectrometry; NMR – nuclear magnetic resonance (spectroscopy).