A study of the proline isomerisation in typical Italian wines

In this paper the presence of the D isomer of proline in wine was investiga ted. The analyses were carried out on samples of two different types of Ita lian red wines, 'Merlot' and 'Cabernet', at different stages of aging durin g the period 1987-1996. The quantitative determination was performed using an RP-HPLC apparatus equipped with a diode array detector. Marfey's reagent , (1-fluoro-2,4-dinitrophenyl)-5-L-alanine amide (FDAA), was used for the d erivatisation, and the obtained diastereomers were separated on a Supelcosi l LC-18 analytical column (25 cm x 0.4cm id), adopting a gradient procedure and making use of water/acetonitrile buffer as the mobile phase. L-Norluec ine was used as the internal standard for quantitative determination, and t he detection of the derivatised components was made at a fixed wavelength o f 340nm. The data obtained show an interesting correlation between the age of the sample and the presence of the D-proline isomer, due to a racemisati on process that can be described as a first-order kinetic reaction. The val ues of the kinetic constants obtained for the two wines are very similar bu t differ significantly from those observed for wines aged for more than 10 years. This is probably due to enzymatic degradation processes, which can o ccur in wine after longer periods of time. (C) 1999 Society of Chemical Ind ustry.