Quantitative determination of free and hydrolytically liberated beta-damascenone in red grapes and wines using a stable isotope dilution assay

Quantitative analysis of free and hydrolytically liberated beta-damascenone in grapes and wines was developed, using a stable isotope dilution assay. Free beta-damascenone was isolated from grapes and wines by diethyl ether-h exane (1:1, v/v) extraction and the precursor(s) (glycosidic, polyols) of b eta-damascenone using Sep-Pak Plus C-18 RP cartridges. Hydrolytically liber ated beta-damascenone was generated by acid hydrolysis from the precursor(s ) extract. Red wines from Bordeaux (Merlot, Cabernet Sauvignon and Cabernet Franc, 1995 and 1996 vintage), Burgundy (Pinot Noir, 1995 and 1996 vintage ) regions and Grenache wines from Chateauneuf du Pape and Cotes du Rhone (1 995 vintage) were analysed to quantify free beta-damascenone. The wines mad e from Grenache and Cabernet Sauvignon (1996 vintage) grapes presented the highest mean amounts of free beta-damascenone, 5.4 and 5.5 mu g l(-1), resp ectively. Merlot, Cabernet Sauvignon and Cabernet Franc grapes of Bordeaux (1996 vintage) and their corresponding wines were analysed for quantificati on of free and hydrolytically liberated beta-damascenone. The levels of hyd rolytically liberated beta-damascenone in grapes could predict closely the levels of free beta-damascenone in the corresponding wines after one year o f ageing, i.e., almost half the levels found for the grape samples. The inf luence of enzyme and heat treatment of Merlot wine samples on their beta-da mascenone levels was studied. Heat treatment doubled the levels of this com pound, but enzyme treatment generated, in the corresponding wines, half the levels of beta-damascenone found in the non-enzyme treated wines. (C) 1999 Elsevier Science B.V. All rights reserved.