## 3 Results and Discussion
### Verification of Physicochemical Properties of Synthesized Peptides
#### 3.9.3 Verification of Antioxidant Activity of Synthetic Peptides  
Determination of ABTS Radical Scavenging Activity  
As shown in Figure 11, the overall ABTS radical scavenging activity of the seven synthetic peptide segments is relatively good. Among them, peptide 6 exhibits the highest activity, with a scavenging rate of 63.31% at a concentration of 1 mg/mL. In addition to peptide 6, peptides 1, 4, and 7 also demonstrate considerable ABTS radical scavenging abilities, all exceeding 40%. Notably, these three peptides contain the aromatic amino acid Y (Tyr). Studies have indicated that all phenolic hydroxyl groups on tyrosine significantly impact the antioxidant activity of active substances [36]. These hydroxyl groups can act as hydrogen donors to capture radicals, and the phenoxy radicals released after a series of reactions exhibit strong stability, thereby enhancing the ABTS radical scavenging capacity of these active substances [37]. Furthermore, research has found that H (His) also exerts a certain influence on the antioxidant activity of active fragments [38; 39]. However, in comparison, the antioxidant activity of the peptide GQCHV was substantially improved. For the peptide GQCH, both activities were substantially enhanced. When C was replaced with A, both activities were significantly reduced, and the removal of H resulted in the loss of antioxidant activity [40]. This indicates that the aromatic amino  
Figure 11: ABTS\({}^{+}\): scavenging activity at various concentrations for each synthetic peptide. acids Tyr (Y) and His (H) have a beneficial effect on the ABTS radical scavenging activity of substances [41]. Determination of DPPH Radical Scavenging Activity  
The DPPH radical scavenging activity of each active fragment increased steadily with increasing concentration, but the overall scavenging activity was lower than that observed for ABTS radicals, which was similar to the trend observed for GCPs. As shown in Figure 12, peptide 5 exhibited the relatively strongest DPPH radical scavenging activity, reaching 49.98%, followed by peptides 1 and 3 with 37.73% and 35.41%, respectively. The higher scavenging activity of peptide 5 may be attributed to the significant impact of proline at the third position from its N-terminus on its antioxidant properties, which was similar to the results obtained by [PERSON], [PERSON] [42] for the DPPH radical scavenging activity of short peptides synthesized from oligopeptide sequences derived from the enzymatic hydrolysis products of grass carp fish meat. Furthermore, researchers studied and analyzed the DPPH radical scavenging activity of GL-9 and found that it exhibited high scavenging activity with a trend similar to that of glutathione [43]. Another study indicated that the sequence obtained from the digestive hydrolyses of halfbeak anchovy possesses relatively high DPPH radical scavenging ability [44]. Researchers extracted a peptide with a sequence from cheddar cheese, which  
Figure 12: DPPH- scavenging activity at various concentrations for each synthetic peptide. exhibited DPPH radical scavenging activity comparable to that of commercial antioxidants such as BHA, t-BHQ, and ferulic acid [45]. Taken together, the content of proline, histidine, glycine, and tryptophan has a significant impact on the DPPH radical scavenging capacity of active fragments. Determination of Hydroxyl Radical Scavenging Activity  
As shown in Figure 13, in the experiment assessing hydroxyl radical scavenging activity, peptides 3 and 6 demonstrated strong scavenging capabilities, with scavenging rates of 55.98% and 55.42%, respectively, at a concentration of 1 mg/mL. Overall, the hydroxyl radical scavenging activity of all synthetic peptides was considerable, with scavenging rates almost exceeding 30% at the highest concentration and maintaining above 10% even at the lowest concentration of 0.1 mg/mL.