## 3 Results and Discussion
Nonetheless, independently of the processes explaining the presence of lag times in the kinetics, their lengths indicate different stoichiometry in the processes, reflecting the complexity of the reactions involved. Since a high concentration of peptides (1 mM) was necessary to protect PYR at the micromolar order (5 mM), the lengths of the lag times would suggest a very low yield of PYR repair by peptides (or reactions with ROO\({}^{\bullet}\)), explaining the low AC determined for the peptides investigated. Therefore, despite the complexity of the mechanisms, it is evident that the AC of Trp residues is considerably lower than that of classical antioxidants, such as a wide variety of phenols which have shown significant protection of PYR on a micromolar level [14]. Aiming to explore if the kinetics of PYR protection afforded by free Trp and the studied peptides depend on the PYR concentration, we developed experiments employing 1 mM PYR. If repairing PYR is the main process of the protective effect, the kinetics should be independent of the initial concentration of PYR, giving similar lag times or R\({}_{0}\) values. In contrast to the latter, if competition by ROO\({}^{\bullet}\) is the main reaction pathway, the pattern of kinetics should be affected by changes in the PYR concentration. In the absence of additives, the consumption of 1 mM PYR showed a similar R\({}_{0}\) to 5 mM PYR (-0.2-0.3 mM/min). As presented in Figure 3, Panel A, the protection of 1 mM PYR elicited by free Trp, Gly-Trp-Gly, and Asn-Trp-Asp-Asp-Met was not affected by the change in PYR concentration, i.e., similar R\({}_{0}\) values were determined at 1 and 5 mM PYR. This result would indicate that even in the absence of lag times, the reparation of PYR could be involved in the protection given by free Trp, Gly-Trp-Gly, and Asn-Trp-Asp-Asp-Met. By contrast, as presented in Figure 3, Panel A, the lag times generated by Glu-Val-Trp-Lys-Ser-Ala-Glu and Ser-Val-Trp-Ile-Gly-Gly-Ser-Ile were strongly affected by the change of PYR concentration. As presented in Figure 3, Panel B, 1 mM Ser-Val-Trp-Ile-Gly-Gly-Ser-Ile generated a 3-times shorter lag time at 1 mM PYR than those registered at 5 mM PYR. This behavior would imply a complex mechanism where the presence of lag times in the kinetics would not be exclusively associated with Reaction (8); however, the lower protection observed at 1 mMPYR is not easily explained by simple competitive reactions between PYR and the peptide for ROO\({}^{\bullet}\). As mentioned above, the pattern of the kinetics would represent a complex set of reactions with the participation of intermediates (particularly radicals) or oxidation products of Trp. In this context, it should be considered that the chemistry of Trp oxidation involves the formation of tryptophan radicals (Trp\({}^{\bullet}\)), which can react with O\({}_{2}\), (to form oxygenated products such as alcohols and hydroperoxides), dismutase, or generate Trp dimers by radical-radical reactions [25; 26]. Therefore, our results suggest that the presence of lag times only in the kinetics of the PYR protection elicited by Trp containing peptides does not necessarily imply PYR repair as unique mechanism. By contrast, the absence of lag times in the kinetics does not necessarily involve competitive reactions towards ROO\({}^{\bullet}\) as exclusive processes. Aiming to corroborate whether the obtained results agree with the PYR repair demonstrated in the presence of phenolic derivatives, we carried out experiments employing Trolox as an additive. In line with previous reports [13; 14], clear induction times were generated by the protection given by Trolox for PYR consumption (Figure 4, Panel A). The values of the lag times showed a linear dependence, with the initial concentration of Trolox indicating that \(\sim\)3.0 moles of ROO\({}^{\bullet}\) were trapped per each mole of Trolox. These lag times were not affected by changes in the PYR concentrations, evidencing that repairing PYR is the main reaction in the presence of this additive.