Determination of oak lactones in barrel-aged wines and in oak extracts by stable isotope dilution analysis

Abstract

The cis- and trans-isomers of 5-butyl-4-methyl-4,5-dihydro-2(3H)-furanone, the so-called oak lactones, are derived from oakwood, and the cis-isomer is an important contributor to wine flavour. Their deuterium-labelled forms, [ 2H 4] cis-oak lactone and [ 2H 4] trans-oak lactone, were synthesised from the unlabelled analogues, and were utilised in a new method employing gas chromatography–mass spectrometry to determine the concentration of these compounds in wine or extracts of oak shavings in a single analysis. The method can employ either liquid–liquid extraction or solid-phase microextraction, and is both rapid and accurate. There was some artefactual generation of cis-oak lactone during the analysis of model wine extracts of unheated oak shavings when diethyl ether extraction and injector block temperatures at or above 225°C were employed.