Monomeric Ellagitannins in Oaks and Sweetgum

Ellagitannins are plant phenolics characterized by biaryl-coupled gallic acid moieties esterified to a D-glucose core. They are widely distributed through higher plants. In the case of oaks, ellagitannin concentrations in heartwood can reach up to 10 % (dry wt. basis). These secondary metabolites are not only important physiologically but also influence the economic value and quality of wood products that contain them. Efforts were made to develop and validate the methods used to quantify both soluble and insoluble ellagitannins. First, the efficiencies of the two commonly used extraction solvents, aqueous acetone and aqueous methanol were evaluated. The results showed that aqueous acetone is superior to aqueous methanol in obtaining higher vescalagin and castalagin yields. In a separate study, the method used for determining insoluble ellagitannins was found to under-estimate the contents of insoluble ellagitannins in wood products. Anhydrous methanolic HCl was found to be an excellent reagent for releasing insoluble ellagic acid and gallic acid (as methyl gallate) from biomass substrates. Optimization of both the reaction conditions and the gradient HPLC analysis has led to th