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-hexane (1:1, v/v) extraction and the precursor(s) (glycosidic, polyols) of beta-damascenone using Sep-Pak Plus C18 RP cartridges. Hydrolytically liberated 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 Côtes du Rhône (1995 vintage) were analysed to quantify free beta-damascenone. The wines made from Grenache and Cabernet Sauvignon (1996 vintage) grapes presented the highest mean amounts of free beta-damascenone, 5.4 and 5.5 micrograms l-1, respectively. Merlot, Cabernet Sauvignon and Cabernet Franc grapes of Bordeaux (1996 vintage) and their corresponding wines were analysed for quantification of free and hydrolytically liberated beta-damascenone. The levels of hydrolytically liberated beta-damascenone in grapes could predict closely the levels of free beta-damascenone in the corresponding wines after one year of ageing, i.e., almost half the levels found for the grape samples. The influence of enzyme and heat treatment of Merlot wine samples on their beta-damascenone levels was studied. Heat treatment doubled the levels of this compound, but enzyme treatment generated, in the corresponding wines, half the levels of beta-damascenone found in the non-enzyme treated wines.