## 3 Results and Discussion
### Oxidation Shelf-Life Study of Beef Burgers
An increase in L* and a decrease in a* in beef burgers is related to a higher oxidation of iron (II) in the heme group, causing a discoloration of the reddish color of the burgers [65]. The antioxidant effect of artichoke in reducing color loss during storage has been supported by other research, including Ergezer et al. [27], who found that the addition of artichoke prevents changes in L* and a* parameters during storage at 2 \({}^{\circ}\)C for 7 days under atmospheric conditions. Moreover, Table 6 presents the results for lipid and protein oxidation parameters, as well as the formation of volatile compounds in the burgers throughout the shelf-life study. Lipid oxidation is the main process responsible for the deterioration of the quality of meat and meat products, reducing their shelf life. Lipid oxidation occurs after a chain reaction of free fatty acids involving molecular oxygen, and three phases can be distinguished: initiation (formation of the lipid radical), propagation (formation of the peroxyl radical), and termination (creation of oxidation secondary products responsible for the alterations associated with rancidity) [69]. The TBARS assay can be used to determine the secondary products of lipid oxidation in meat products. Lipid oxidation increased in CB over the days of storage at 4 \({}^{\circ}\)C, with TBARS values doubling by the end of storage. Fat replacement exhibited a preventive effect on lipid oxidation in relation to the control burger, with a significant reduction (\(p<0.05\)) observed both at the beginning and at the end of the shelf-life study. Although MUFA and PUFA are more susceptible to oxidative degradation than SFA, several researchers stated that oleic acid (the main fatty acid in EVOO) is less susceptible to oxidative processes than PUFAs [8], which could explain the findings of this study. In addition, the jellifying agent used contains sodium ascorbate, an antioxidant compound that can exert a protective action in the emulsion. These beneficial effects against oxidation have also been reported by other authors in algae [70] and tiger nut [28] emulsions. Moreover, the incorporation of artichoke improved the results obtained with fat-replaced burgers, also resulting in a significant decrease at the beginning and end of storage compared to CB and FRB. For burgers with added artichoke, lipid oxidation was not significantly increased during the three days of storage, even showing a reduction for FRB-AE. This protective effect against lipid oxidation of artichoke has been verified by other researchers in raw beef patties, where a reduction in oxidation was found at 7 days of storage [27]. Phenolics present in artichoke may act against the agents responsible for this lipid oxidation, preventing the production of secondary products such as the reactive carbonyl species 4-hydroxynonenal (4-HNE) and MDA. The result of replacing animal fat with EVOO and incorporating artichoke resulted in very positive results in the lipid stability of the burgers. Unlike CB, the reformulated burgers at the end of storage did not exceed the TBARS values below the threshold limit that could be perceived by consumers (2 mg MDA/kg sample), which could be considered the maximum acceptable value [65]. Table 6 also illustrates the protein oxidation of beef burgers, which is directly related to the concentration of free thiol groups. No significant differences were found between days within the same treatment, indicating that storage time did not greatly affect the loss of protein thiol groups in the meat products, although a general downward trend was observed. However, similar to lipid oxidation results, a significant decrease in protein oxidation was observed in FRB in relation to CB at the beginning and end of storage at 4 \({}^{\circ}\)C. Nieto et al. [18] reported similar results in chicken sausages with EVOO-replaced fat, showing a decrease in protein oxidation after 21 days of storage.