Determination of free and conjugated indole-3-acetic acid, tryptophan, andtryptophan metabolites in grape must and wine

Tryptophan (Trp) and its metabolites, especially indole-3-acetic acid (IAA) , are considered to be potential precursors of 2-aminoacetophenone (AAP), a n aroma compound that causes an "untypical aging off-flavor" (UTA) in Vitis vinifera wines. In this study, RP-HPLC with fluorescence detection was use d for the qualitative and quantitative analysis of Trp and Trp metabolites in grape musts and wines to which different viticultural measures had been applied (time of harvest, soil treatment, leaf plucking, vine prune). An al kaline hydrolysis was developed to release bound IAA and Trp. A sensitive a nd selective determination of different Trp metabolites was achieved after solid phase extraction using a strong anion exchange material. In the exami ned grape musts, more than 95% of the total IAA was bound either as ester c onjugate or as amide conjugate. Free IAA and other Trp metabolites were bel ow the detection limit (<3 mug/L) or could be determined only in traces. Th eir amounts increased significantly during fermentation, whereas the amount of Trp decreased. It could be shown that the different viticultural measur es applied (except the vine prune) as well as the climatic conditions of th e vintage exhibited significant influences on the amounts of Trp and Trp me tabolites in grape musts or wines.