## 3 Results and Discussion
### Total Flavanol and Hydroxycinnamic Content  
Non-enzymatic oxidation of wine is favored by the oxidation of phenols containing a catechol (ortho-hydroxybenzene) or a galloyl (1,2,3-trihydroxybenzene) moiety in their molecules. Flavanols such as catechin and epicatechin, caffeic acid and its esters, and gallic acid are the most readily oxidized wine components. These compounds are oxidized to quinones which are unstable and may undergo further reaction, leading to the formation of brown products [5]. Given the importance of these groups of compounds in browning development, it was of interest to monitor their evolution during the accelerated test and to have a better understanding of their role in oxidation of white wines. Regarding total flavanol (TF) content, there was a decrease with time at both temperatures studied (Figure 4a,b). This is in agreement with other studies, where similar results were obtained [16; 38; 47]. Within the flavonoid class of white wines, flavanols are the most sensitive compounds to heat, and there is substantial evidence that they may have an active role in the development of brownish shades [14; 16]. Numerous studies have shown a positive correlation between flavanol content and browning degree of white wines, confirming their implication in the oxidation process [26; 27; 48]. After 12 days of heating, the highest statistically significant reduction in FC was observed in the samples which contained the highest concentration of Fe\({}^{2+}\) and H\({}_{2}\)O\({}_{2}\) (Figure 4a,b). This observation was irrespective of the temperature and the presence of Se. In addition, at 50 \({}^{\circ}\)C, the presence of the low contents of Fe\({}^{2+}\) and H\({}_{2}\)O\({}_{2}\) resulted in significantly lower TF contents than those in the control, however, still higher than that of the samples which contained high concentrations of the oxidants. It seems, therefore, that the crucial factor for browning development was the presence of iron and hydrogen peroxide, and the addition of antioxidants such as Se might not be able to inhibit the initiation of the oxidation process. Figure 4c,d shows the evolution of total hydroxycinnamic content (HC) during heating time. As it can be observed, there was no clear trend regarding concentration change. In samples with absence or low contents of Fe\({}^{2+}\) and H\({}_{2}\)O\({}_{2}\), an increase of HC after the heating period was noted at both temperatures. This might have been probably due to the acceleration of the hydrolyzation reactions which took place during heating. These results are in agreement with the findings of other studies where the concentrations of hydroxycinnamic acids increased significantly with time [26; 49]. However, in the case of the samples with high Fe\({}^{2+}\) and H\({}_{2}\)O\({}_{2}\) contents, HC content did not show a similar increase and was significantly lower than that of the rest of the samples. The abundance of the strong oxidants probably resulted in condensation reactions involving these compounds. In addition, it was interesting to note that in samples with high contents of oxidants, a sharp decrease of HC content was observed (at day 1 at 50 \({}^{\circ}\)C and at days 1 and 4 at 35 \({}^{\circ}\)C). This decrease might have been due to oxidation of these compounds, since together with flavanols they are considered the most susceptible to oxidation due to the catechol moiety in their structure [5]. However, afterwards, their content was increased gradually, probably due to the simultaneous presence of flavanols which are the primary oxidation substrates and probably more actively participated in the oxidation process, thus limiting oxidation of other compounds. The presence of Se at 35 \({}^{\circ}\)C seems to have retarded the initiation of this process, since the highest decrease in HC was observed after four days, while in the sample without Se addition, this occurred much faster (day 1).