Semi-preparative isolation and physico-chemical characterization of 4-coumaroylquinic acid and phloretin-2′-xylogluco side from laccase-oxidized apple juice

Two not commercially available apple polyphenols, 4-coumaroylquinic acid and phloretin-2 '-xyloglucoside, were isolated from an apple juice previously oxidized with a laccase (polyphenol oxidase, EC 1.10.3.2). Juice oxidation in combination with ultrafiltration removed polyphenols with ortho-dihydroxyphenol structures, e.g. caffeic acid, flavanols and flavonols, which led to a reduced number of peaks in the chromatogram. Subsequently, a polyphenol extract from this juice was manufactured using an adsorber resin technique. The extract served as a basis for the proper isolation of the target substances by means of semi-preparative RP-HPLC. The structures of 4-coumaroylquinic acid and phloretin-2 '-xyloglucoside were confirmed with LCMS- and NMR-data, respectively. The use of the isolated target substances as quantification references improved the quantitative HPLC of apple juices distinctly. Besides the reference compounds could be used for testing their biological activity. (C) 2006 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved.