DETERMINATION OF ETHERIFIED HYDROXYCINNAMIC ACIDS IN CELL-WALLS OF GRASSES

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 HCl (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 degrees with 4M 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.