Indole-3-acetic acid and tryptophan in Istrian Malvasia grapes and wine

The phenomenon of "untypical aging off-flavor" (UTA) is associated with higher concentrations of 2-aminoacetophenone (2-AAP) in Vitis vinifera white wines. It can stem from some technological treatments applied in grape and wine production. In order to find out if a wine is liable to "untypical aging off-flavor", it is necessary to determine the concentrations of indole-3-acetic acid (IAA) and L-tryptophan, the main precursors of 2-aminoacetophenone. The formation of 2-AAP is caused by an oxidative degradation of the phytohormone indole-3-acetic acid, triggered by sulfuration after fermentation. Metabolism of tryptophan and indole-3-acetic acid formation during vinification is correlated with yeast strain. 2-AAP formation considered to be greater in wines from grapes which where grown under stress conditions like insufficient water or nitrogen supply in soil. The purpose of this investigation was to determine the influence of soil type and different yeast strains on the levels of L-tryptophan and indole-3-acetic acid in the Malvasia wine from Istria. Grapes were harvested from two different soil type locations in Istria (terra rossa and terra bianca) wine growing region and separately undergo alcoholic fermentation, spontaneous fermentation and by use of 4 commercial yeast strains (Fermol Cryoarome, Fermol Assosiee, Uvaferm CS2, Anchor VIN 13). Young wine samples were taken for analysis immediately alter completed alcoholic fermentation. Chemical analyses of compared musts and wines showed differences in L-tryptophan and indole-3-acetic acid concentrations that depend more upon the soil type than yeast strain used in this investigation. More intense use of tryptophan was noticed during fermentation of must from terra bianca soil. Significantly higher concentrations of indole-3-acetic acid were noticed in wines produced by indigenous yeasts.