Evaluation of Feruloylated and p-Coumaroylated Arabinosyl Units in Grass Arabinoxylans by Acidolysis in Dioxane/Methanol

The arabinosyl side chains of grass arabinoxylans are partially acylated by p-coumarate (pCA) and ferulate (FA). These aromatic side chains can cross-couple wall polymers resulting in modulation of cell wall physical properties. The determination of p-coumaroylated and feruloylated arabinose units has been the target of analytical efforts with trifluoroacetic acid hydrolysis the standard method to release feruloylated and p-coumaroylated arabinose units from arabinoxylans. Herein, we report on a more robust method to measure these acylated units. Acidolysis of extractive-free grass samples in a dioxane/methanol/aqueous 2 M HCl mixture provided the methyl S-O-p-coumaroyl- and S-O-feruloyl-L-arabinofuranoside anomers (pCA-MeAra and FA-McAra). These conjugates were readily analyzed by liquid chromatography combined with both UV and MS detection. The method revealed the variability of the relative acylation of arabinose units by pCA or FA in grass cell walls. This methodology will permit delineation of hydroxycinnamate acylation patterns in arabinoxylans.