Distribution of free and combined phenolic acids in wheat internodes

Abstract Finely ground residues of mature and maturing wheat internodes after extraction with 80% ethanol were successively extracted with 96% dioxane to give milled lignin (ML 1 ) and water soluble (MC 1 ) fractions. The residue was treated with a polysaccharide hydrolase mixture to give a residue (ER 1 ). Quantitative analyses of phenolic acids were made on each of these fractions. Alkaline nitrobenzene oxidation and alkaline hydrolysis were used to determine the chemical state of the phenolic acids in the fractions. Very low quantities of free phenolic acids were found in the 80% ethanol extracts but significant amounts of esterified and etherified phenolic acids were present. The amounts of phenolic acids in the extract-free residue after alkaline nitrobenzene oxidation at 170° were always higher than those liberated by alkaline hydrolysis at room temperature. In mature internodes, 24% of the total p -coumaric acid (PCA) plus ferulic acid (FA) remained after mild alkaline hydrolysis. PCA is the major ester linked phenolic acid in ML 1 , whereas FA is the major ester linked phenolic acid in MC 1 . In ER 1 the predominant esterified phenolic acid is PCA, but FA is found both in ester and ether linked forms. The major changes in the ratio of esterified PCA/FA and the increases in etherified FA during maturity coincide with decreases in the digestibility of wheat internodes.

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