# New Insight on the Formation of 2-Aminoacetophenone in White Wines
## 4 Discussion
While commercial tannins reduced the concentration of 2-AAP in both trials, GSH and IYDs had an impact only on one wine. [PERSON] et al. [3] recently published similar results using GSH, ellagic tannins, galla and grape tannins. They found that galla and grape tannins were the most efficient at limiting the 2-AAP concentration in the wine and that ellagic tannins had a stronger impact than GSH. In the present study, the mixture of grape and ellagic tannins (TA2) was also slightly more efficient than pure ellagic tannins (TA1). However, [PERSON] et al. [3] added antioxidants in must at higher levels in comparison to the present study, where the doses reflect additions suggested by manufacturers to be used in white wine. The addition of tannins in white wine at the upper limit of the recommended range often strongly impacts wine sensory profile. For that reason, our second trial targeted two levels of tannins addition corresponding to 10 g/hL (100 mg/L) and 1 g/hL (10 mg/L), respectively. The higher dosage was the most efficient to reduce 2-AAP concentration. All these results suggest that when wines are aged in a barrel on gross lees, the tannins extracted from wood might be more efficient to limit the formation of 2-AAP than the antioxidant activity from the lees. Some synergistic effect between both classes of antioxidants cannot be excluded in some wines, as observed during the first trial where the addition of IYD with TA1 was slightly more efficient at reducing 2-AAP than TA1 alone (Figure 3). However, such an effect was not observed in the second wine, irrespective of tannin dosage (Figure 4). Transition metal ions are known to catalyze many chemical reactions, but in a winelike medium, mainly Fe, Cu and, to a lesser extent, Mn have been studied for their role in wine oxidation and reduction [12; 22]. [PERSON] et al. [5] speculated that transition metals could potentially influence the formation of 2-AAP in wine without studying this hypothesis. [PERSON] et al. [13] reported higher ATA perception in Riesling wines due to the presence of Fe and Cu but 2-AAP was not quantified. The present study is therefore the first to our knowledge to explore the impact of metal ions on 2-AAP production in wine. In the same preliminary study as mentioned earlier, a 2-fold increase in 2-AAP concentration (0.22 to 0.45 ug/L) was observed in the Chardonnay wine aged in an inox tank after the addition of a mixture of Fe, Cu and Mn in order to reach a final concentration at 5, 1 and 4 mg/L, respectively. In contrast, the 2-AAP level did not change when the same addition was made in the wine aged on gross lees in a new oak barrel. This observation suggests that antioxidants from oak or lees could also limit the influence of metal ions in the formation of 2-AAP. When Fe, Cu and Mn were added together at the same level in two white blends, 2-AAP concentration after artificial ageing was not affected in the first wine (Figure 4) and was decreased in the second wine (Figure 5). Interestingly, the presence of higher concentrations of Fe, Cu and Mn in a mixture significantly improved the efficiency of antioxidants to reduce the 2-AAP concentration, while no metal ion effect was observed in the wines without antioxidant addition. Commercial tannins remained the most efficient antioxidant to limit 2-AAP concentration in the presence of metal ions. These results highlight some complex interaction between metal ions and wine matrix involved in the formation of 2-AAP. Metal ions' reactivity is closely dependent on their redox potential, which is significantly influenced by the presence of ligands such as tartaric acid, malic acid, polyphenols or other antioxidants [23]. Fe(III/II) redox potential is also influenced by the presence of Cu and Mn [22; 24]. Copper accelerates Fe(II) oxidation, and that in turn can promote sulfite oxidation [23; 25], which is suspected to form the superoxide radical responsible for 2-AAP formation in white wines [5]. In contrast, in our experiment, the addition of Cu(II) tended to decrease the 2-AAP concentration.