Monomeric and dimeric phenolic acids released from cell walls of grasses by sequential treatment with sodium hydroxide

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Abstract
Cell walls of tall fescue Festuca arundinacea Schreb and coastal bermudagrass Cynodon dactylon L Pers were treated sequentially with increasing concentrations of sodium hydroxide (0·1 M to 10 M) to release monomeric and dimeric phenolic acids. (E)‐p‐Coumaric and (E)‐ferulic acids were the major monomers released. Most of the saponifiable feruloyl groups (97% for tall fescue, 89% for coastal bermudagrass) were released with 0·1 M sodium hydroxide. Much lower proportions of saponifiable p‐coumaroyl groups (67% for tall fescue, 46% for coastal bermudagrass) were released with this treatment. The major dimers from both grasses were 4,4′‐dihydroxy‐α‐truxillic, 4,4′‐dihydroxy‐3‐methoxy‐α‐truxillic, and 4,4′‐dihydroxy‐3,3′‐dimethoxy‐α‐truxillic acids, and were mainly released with 0·1 M sodium hydroxide. Similar proportions of the monomers and dimers were released from the cell walls of each grass with the 0·1 M and 1 M sodium hydroxide sequential treatments. It is probable that most if not all of the monomers and dimers released by the sequential alkali treatments were originally ester linked to the cell walls. If it is assumed that the cell wall bound dimers are formed photochemically from p‐coumaroyl and feruloyl groups during plant growth, it is calculated that, for the two grasses, between 12 and 17% of the monomer units were converted to dimers.