## 3 Results and Discussion
#### 3.2.5 Total Free Sulfhydryls  
At 18 or 45 \({}^{\circ}\)C, the control wine samples exhibited a decrease in the content of total free sulfhydryls with respect to storage time (Figure 4a,b; Table S8). A linear correlation was found between wine samples undergoing oxidation at 18 \({}^{\circ}\)C and at 45 \({}^{\circ}\)C, pointing out that the differences in the content of total sulfhydryls are owed to the time demanded for each oxidation. There was a statistically significant positive correlation between the content of total sulfhydryls at 45 \({}^{\circ}\)C and the content of total sulfhydryls at 18 \({}^{\circ}\)C in the control samples of the Roditis-Malagouzia wine (\(r=0.992\), \(p=0.008\)). These results indicate that total free sulfhydryls may be a suitable index of white wine oxidation at both room and higher temperatures. Glutathione comprises the main thiol of wines, while the glutathione equivalent capacity has been proposed as a new quantitative criterion for white wine characterization [40,41]. In addition, [PERSON] et al. [42] reported a decrease in glutathione content of Sauvignon blanc wine during storage.  
Moreover, a significant decrease of glutathione in white wines during an accelerated test at 55 \({}^{\circ}\)C has also been reported by others [23]. It should be noted that wines contain significant levels of total free sulfhydryls [31].  
At 18 \({}^{\circ}\)C, the addition of Fe (II) + H\({}_{2}\)O\({}_{2}\) mixture increased the reduction of total sulfhydryls with respect to the storage time of the studied wine sample. The higher the concentration of Fe (II) + H\({}_{2}\)O\({}_{2}\) mixture added, the greater the decrease in the content of total sulfhydryls (Figure 4a; Table S8). There was a statistically significant positive correlation between the content of total sulfhydryls in the control wine samples and with those to which the low concentration of Fe (II) + H\({}_{2}\)O\({}_{2}\) mixture was added (\(r\) = 0.954, \(p\) = 0.046).  
On the other hand, there was no statistically significant correlation between the content of total sulfhydryls in the control wine samples and with those to which the high concentration FeCl\({}_{2}\)\(\times\) 4H\({}_{2}\)O and H\({}_{2}\)O\({}_{2}\) was added (\(r\) = 0.938, \(p\) = 0.062). At 45 \({}^{\circ}\)C, the addition of Fe (II) + H\({}_{2}\)O\({}_{2}\) mixture accelerated the decrease of total sulfhydryls in wine with respect to storage time. The higher the concentration of Fe (II) + H\({}_{2}\)O\({}_{2}\) mixture added, the greater the reduction of total sulfhydryls (Figure 4b; Table S8). There was a statistically significant positive correlation between the content of total sulfhydryls in the control samples and those to which the low and high concentration of Fe (II) + H\({}_{2}\)O\({}_{2}\) were added. The correlation coefficient in the first case was \(r\) = 0.996 (\(p\) = 0.004) and in the second, \(r\) = 0.996 (\(p\) = 0.004).  
Figure 4: (**a**). Effect of Fe (II) + H\({}_{2}\)O\({}_{2}\) on the levels of total free sulfhydryls of Roditis–Malagouzia wine during storage at 18 \({}^{\circ}\)C. C1: low concentration: FeCl\({}_{2}\)\(\times\) 4H\({}_{2}\)O = 0.10 mM/H\({}_{2}\)O\({}_{2}\) = 0.63 mM. C2 high concentration: FeCl\({}_{2}\)\(\times\) 4H\({}_{2}\)O = 0.25 Mm/H\({}_{2}\)O\({}_{2}\) = 1.575 mM. (**b**). Effect of Fe (II) + H\({}_{2}\)O\({}_{2}\) on the levels of total free sulphhydryls of Roditis–Malagouzia wine during storage at 45\({}^{\circ}\)C. C1: low concentration: FeCl\({}_{2}\)\(\times\) 4H\({}_{2}\)O = 0.10 mM/H\({}_{2}\)O\({}_{2}\) = 0.63 mM. C2 high concentration: FeCl\({}_{2}\)\(\times\) 4H\({}_{2}\)O = 0.25 Mm/H\({}_{2}\)O\({}_{2}\) = 1.575 mM.  
Present results indicate that total free sulfhydryls may be considered as a suitable index to follow the forced oxidative browning of white wine by adding Fe II + H\({}_{2}\)O\({}_{2}\) at 45 \({}^{\circ}\)C.