## 3 Results and Discussion
### Browning Rates
However, they measured the browning index and not the rate of browning development in their study. As it is shown in Table 2, the obtained values were strongly dependent on both the temperature and the presence of Fe\({}^{2+}\) and H\({}_{2}\)O\({}_{2}\). The higher the temperature and the Fe\({}^{2+}\) and H\({}_{2}\)O\({}_{2}\) content, the higher the k value. As expected, the higher temperature (50 \({}^{\circ}\)C) resulted in higher browning rates in agreement with other published data [26; 37]. It has been shown that parameters such as light and temperature could have a strong influence on wine color through hydrolysis, oxidation, and condensation reactions [38]. The higher temperature employed (50 \({}^{\circ}\)C) for the browning test increased the rate of the reactions \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample Code** & **k (day\({}^{-1}\)) \(\times\) 10\({}^{-3}\)** & **k (day\({}^{-1}\)) \(\times\) 10\({}^{-3}\)** & **\%AA\({}_{420}\)** & **\%AA\({}_{420}\)** \\
35 \({}^{\circ}\)C & **50 \({}^{\circ}\)C** & **35 \({}^{\circ}\)C** & **50 \({}^{\circ}\)C** \\ \hline M & 1.0 \({}^{\text{a}}\) & 7.5 \({}^{\text{a}}\) & 10.37 \({}^{\text{a}}\) & 97.70 \({}^{\text{a}}\) \\ Fe min & 1.4 \({}^{\text{b}}\) & 15.8 \({}^{\text{b}}\) & 27.76 \({}^{\text{b}}\) & 205.15 \({}^{\text{b}}\) \\ Fe max & 4.7 \({}^{\text{c}}\) & 43.8 \({}^{\text{c}}\) & 162.21 \({}^{\text{d}}\) & 312.04 \({}^{\text{c}}\) \\ Se min & – & 8.8 \({}^{\text{a}}\) & – & 107.73 \({}^{\text{a}}\) \\ Se max & – & 7.7 \({}^{\text{a}}\) & – & 101.17 \({}^{\text{a}}\) \\ All min & 1.6 \({}^{\text{b}}\) & 16.6 \({}^{\text{b}}\) & 25.10 \({}^{\text{b}}\) & 220.20 \({}^{\text{b}}\) \\ All max & 5.1 \({}^{\text{c}}\) & 45.5 \({}^{\text{c}}\) & 136.8 \({}^{\text{c}}\) & 338.74 \({}^{\text{c}}\) \\ \hline \hline \end{tabular}  
\({}^{\text{a}}\) = Different letters at each column indicate statistically significant differences (\(p<0.05\)).  
\end{table} 
Table 2: Browning rate constants (k) and percentage changes in absorbance at 420 nm (A\({}_{420}\)). involved, thus reducing the time needed for color change. The browning rate of the control wine was increased 7.5 times along with the temperature increase from 35 to 50 \({}^{\circ}\)C, while that of the samples containing the high and low concentrations of Fe\({}^{2+}\) and H\({}_{2}\)O\({}_{2}\) showed an increase of about 10- and 11-fold respectively. Similar results were observed by [PERSON] et al. [1] during their study which involved six Italian wines. During accelerated ageing at higher temperatures, the browning rate showed an Arrhenius-type dependence from temperature allowing to estimate the activation energies of the reaction. There are only a few publications regarding the effect of temperature on browning rate of wine, although the practical importance is very high. [PERSON] [39] provided data showing that the browning rate of a white wine increased 2.9 times along with a temperature increase from 10 to 20 \({}^{\circ}\)C. When temperature reached 40 \({}^{\circ}\)C, the rate of browning development occurred 20.7 times faster. These values were calculated using the Arrhenius equation assuming pseudo-first-order kinetics with respect to the depletion of dissolved oxygen. The addition of Fe\({}^{2+}\) and H\({}_{2}\)O\({}_{2}\) resulted in reaching higher A\({}_{420}\) values in a shorter time. Regarding \(\Delta\)A\({}_{420}\) of control wine stored at 35 \({}^{\circ}\)C, the % change (Table 2) was increased almost 1.7- and 16-fold after the addition of the low and high concentration of Fe\({}^{2+}\) and H\({}_{2}\)O\({}_{2}\), respectively. At 50 \({}^{\circ}\)C, the increase in A\({}_{420}\) was more profound for all samples studied, including the control. However, the addition of Fe\({}^{2+}\) and H\({}_{2}\)O\({}_{2}\) resulted in two- and three-fold percentage increases in the absorbance at 420 nm. Oxidation in wine is a complex reaction with numerous steps, and browning development is determined by the rate-limiting step.