Isolation and Identification of Ellagitannins from White Oak Wood and an Estimation of Their Roles in Wine

Abstract

Aqueous ethanolic extracts of three sources of oak wood, a commercial American oak meal preparation, American white oak tank wood, and a French Limousin barrel sample, were examined using column chromatography and two-dimensional paper chromatography. Phenol content of the extract of commercial oak meal was almost 10% gallic acid, which is a hydrolytic product of some wood tannins. Ellagitannins were identified in all oak wood extracts through paper chromatographic Rf values and the use of chromogenic spray reagents specific for ellagitannins. Three distinct ellagitannins, visualized on paper chromatograms, were separated by Sephadex LH-20 chromatography. Hydrolysis of an isolated individual ellagitannin yielded ellagic acid, which confirmed its identification as an ellagitannin. Similar column fractionation of a commercial Chardonnay wine fermented and aged in oak produced a complex chromatogram in which ellagitannins were identified in two fractions. This shows that ellagitannins are extracted into wine through barrel aging and survive in wine for at least several years.