## 3 Results and Discussion
### Oxidation Shelf-Life Study of Beef Burgers
& *** & ** & *** & * & \\ \hline \multirow{4}{*}{d-Limonene} & 0 & nd \({}^{\text{b}}\) & nd \({}^{\text{b}}\) & 3.74 \({}^{\text{a}}\) & 3.27 \({}^{\text{a}}\) & 0.67 & *** \\  & 3 & nd \({}^{\text{b}}\) & nd \({}^{\text{b}}\) & 3.68 \({}^{\text{a}}\) & nd \({}^{\text{b}}\) & 0.60 & ** \\  & Sig. & ns & ns & ** & & \\ \hline \multirow{4}{*}{(E)-2-Heptenal} & 0 & nd \({}^{\text{b}}\) & nd \({}^{\text{b}}\) & nd \({}^{\text{b}}\) & 2.88 \({}^{\text{a}}\) & 0.48 & *** \\  & 3 & nd \({}^{\text{b}}\) & nd \({}^{\text{b}}\) & 5.72 \({}^{\text{a}}\) & 2.38 \({}^{\text{a}}\) & 0.89 & *** \\ \cline{1-1}  &However, the addition of artichoke improved the results obtained in the fat-replaced burgers, resulting in a significant decrease at day 0 of 37.4-41.5% with respect to FRB and 46.0-49.6% regarding CB. The lowest values of thiol groups at the end of storage were obtained for the FRB-AE sample. The main reaction products of protein oxidation are disulfide bridge formations, which have been shown to have a strong impact on meat quality, increasing its toughness and decreasing its tenderness. Furthermore, it has been shown that artichoke by-products have a high antioxidant power due to polyphenols (Table 3). These bioactive compounds could prevent the oxidation of myofibrillar proteins by hydroxyl radicals (OH\({}^{-}\)), avoiding the formation of cross-links and the consequent formation of disulfides, which is related to the increase of the myosin heavy chain (MHC) [42; 71] and the fragmentation, aggregation, and polymerization of proteins. Other natural ingredients with high antioxidant capacity, such as green tea [72], pomegranate [73], or rosmary [74], have also demonstrated a protective action against the oxidation of amino acids, providing valuable alternatives in the preservation of meat products. Additionally, the volatile compounds produced at the beginning and at the end of storage at 4 \({}^{\circ}\)C were measured. The presence of compounds related to lipid autoxidation (pentanal and 2,4-decadienal) was only detected in the control formulation, whereas the production of these compounds was not detected in the formulations with fat substitution and added artichoke. The reformulation with artichoke also influenced the presence of other aldehydes such as benzaldehyde, 2,3-Octanedione, and hexanal, where reformulations with artichoke resulted in significant differences over the control formulation. Some of these aldehydes provoke unpleasant odors in meat products even at very low concentrations, as they are the result of the oxidation of phospholipids and PUFAs. For instance, pentanal correlates negatively with taste quality and may indicate taste impairment [75], while 2,3-octanedione and 2,4-decadienal originate from the oxidation of linoleic acid [76]. The formation of these compounds presented a clear significant relationship (\(p<0.05\)) with the lipid and protein oxidation results obtained in this study (Table 7), highlighting the formation of hexanal (R = 0.939; \(p<0.001\)), associated with the apparition of rancid flavors, as well as painty and waxy descriptors [77]. Hexanal formation was reduced by 71.6-84.2% at day 0 and by 86.0-87.3% at the end of storage after the addition of AE and TAE, indicating a strong protective effect against oxidation. The presence of artichoke extracts also delayed the presence of certain alcohols, which was not observed at the beginning of the shelf-life study. Both 1-pentanol (R = 0.895; \(p<0.01\)) and 1-hexanol (R = 0.933; \(p<0.001\)) correlated with the TBARS assay results. 1-Octen-3-ol was also affected at both the beginning and end of storage after fat reformulation and artichoke addition. These compounds are generated by the degradation of oleic acid and are the most frequently reported volatile compounds in the literature, considered key indicators of lipid oxidation in meat [78]. Other researchers have found the positive effects of different natural ingredients in the reduction of volatile compounds related to meat oxidation, such as pitanga, guarana [60], or rosmary [79].