# New Insight on the Formation of 2-Aminoacetophenone in White Wines
## 4 Discussion  
Since the first empirical evidence of the development of ATA in white wines in the late 1980s, most of the published studies investigating the formation of 2-AAP in wine were carried out on Riesling [2]. This anecdotal observation suggests that the Riesling variety has been known for a long time to be sensitive to the formation of 2-AAP. On the other hand, very few studies have investigated a potential varietal effect on 2-AAP concentration in wine. [PERSON] and [PERSON] [15] analyzed 21 Slovenian wines, not including Riesling, and more recently, [PERSON] et al. [16] measured 2-AAP in 20 Croatian white wines from different varieties, including Riesling. While the latter study found that the highest concentrations of 2-AAP were measured in Riesling wines, it is difficult to highlight a consistent trend with such a low number of samples. With two distinctive surveys representing a total of 139 wines analyzed, the present study highlighted that Riesling wines significantly showed a higher concentration of 2-AAP in comparison to Chardonnay and some other local varieties from Central Europe such as Gruner Veltliner, Welschriesling and Zelen. The average 2-AAP concentration in Riesling wines was between 2 and 4 ug/L. This is above the perception threshold reported for white wines (0.5-1.5 ug/L) [2]. However, the variety that displayed the highest average concentration of 2-AAP was Muscat blanc, and that observation was somewhat unexpected since ATA has been rarely reported in Muscat wines. This is probably due to the presence of a high concentration of monoterpencols imparting an intense floral aroma, which strongly mitigates the impact of 2-AAP on Muscat wine aroma [12]. The wider distribution of 2-AAP concentrations after ageing for most of the varieties indicated an important matrix effect in the formation of this compound in white wines. In order to clarify the matrix effect and varietal differences on 2-AAP formation, the second survey, performed on Slovenian and Croatian wines, targeted free tryptophan metabolites known as potential precursors of 2-AAP. No relationship between the level of 2-AAP and its precursors could be observed in the wines analyzed in this survey, including the main known precursor 3-indoleacetic acid (3-IAA). The lack of correlation between free 3-IAA  
Figure 5: Levels of 2-AAP measured in wine before heat treatment and with application of different combination of metal ions (T0—control wine not exposed to heat treatment; C—wine exposed to heat treatment; MIX—mixture of Fe, Cu and Mn). Metal ions were added to reach 1 mg/L, 5 mg/L and 4 mg/L of Cu, Fe and Mn, respectively. Different letters above bars indicate significance at \(p\leq 0.05\) (Fischer’s LSD). All quoted uncertainty is the standard deviation of three replicates per treatment. and 2-AAP in wines has already been reported by several authors [8; 9; 17]. Levels of 2-AAP potential precursors were in accordance with previously published concentrations [18]. The most abundant tryptophan derivate was not 3-IAA but indoleactic acid (ILA). Interestingly, Riesling wines showed the highest ILA concentrations in comparison to other varieties. However, when ILA was added to a white blend, the concentration of 2-AAP after artificial ageing was similar to the same wine without ILA addition. Only the wine with an addition of 3-IAA showed a significantly higher level of 2-AAP (Figure 2). Therefore, the varietal differences observed in 2-AAP concentration in white wines were not directly linked to the levels of its precursors in wine. Further investigation on varietal factors that could be directly or indirectly involved in 2-AAP formation are needed. Moreover, [PERSON] et al. [19] suggested that glutathione and other yeast biomass derivates could limit 2-AAP formation, but this observation was not consistent with some other studies [20; 21]. In the present work, phenolic compounds such as gallic acid and commercial tannins were more efficient at limiting the formation of 2-AAP than GSH and IYDs.