Determination of etherified hydroxycinnamic acids in cell walls of grasses

Abstract

A comparison is made between acid and alkaline treatments for the measurement of total amounts of ether- plus ester-linked hydroxycinnamic acids associated with extract-free wheat internodes. Although acid hydrolysis in a mixture of dioxane-2M HCI (9:1 by volume) under reflux for 2 hr releases most of the esterified ferulic acid (FA), considerable amounts of both esterified and etherified p-coumaric acids (PCA) and etherified FA remain. In addition, under these conditions, there are substantial losses of released PCA and FA (82 and 92%, respectively), and probably also of acids bound to wall polymers. These factors make the acid digestion procedure unsuitable for quantitative analyses. Alkaline hydrolysis at 170° with 4 M NAOH in stainless steel reaction vessels, although also leading to significant losses of released hydroxycinnamic acids, is the preferred method for measuring etherified hydroxycinnamic acids.