## 4 Conclusions  
Through systematic experimental design and data analysis, this study conducted an in-depth exploration of the preparation, purification, structural characterization, antioxidant activity, and stability of collagen peptides derived from grass carp swim bladders (GCPs). Then, ultrafiltration and chromatography were performed on the preliminarily prepared GCPs, and the samples obtained by chromatography were named GCP-I, GCP-II, and GCP-III, respectively. After an analysis of the results of previous antioxidant experiments, GCP-II was selected as the main sample for the synthetic peptide experiments. The sequence of GCP-II was analyzed, from which seven bioactive fragments with high antioxidant potential were selected and synthesized. Their sequences were EKAPDPFRHE, GLITLKYPI, GERGPGPPM, ILTERGYSFVT, QGPGPGPS, VLSLYASGRTT, and DGSYNIGQR and were named as peptide 1, peptide 2, peptide 3, peptide 4, peptide 5, peptide 6, and peptide 7, respectively. Among them, the two sequences with the highest comprehensive antioxidant activity were peptide 3 and peptide 6, and these two peptides showed synergistic effects in many antioxidant experiments. The research results indicated that GCPs, as a polypeptide with considerable antioxidant activity, maintains high antioxidant activity under the influence of different environments and concentrations of food ingredients, thus demonstrating good overall stability.  
The findings demonstrate that grass carp swim bladder-derived peptides (GCP-II) and their synthetic counterparts exhibit robust antioxidant properties with significant practical potential. The thermal stability of GCP-II (>90% retention at 100 \({}^{\circ}\)C) and its resistance to NaCl/citric acid position it as a viable natural preservative for thermally processed foods (e.g., baked goods) and acidic beverages, addressing clean-label demands in the food industry. Additionally, the synergistic effects of peptides 3 and 6 highlight their promise in nutraceuticalts targeting oxidative stress-related pathologies. These results advocate for the sustainable valorization of underutilized fish processing by-products in functional ingredient development.  
However, there were still some limitations in this study. For instance, although peptide segments with high antioxidant activity have been screened out, further in-depth research is needed to investigate their specific antioxidant mechanisms. Additionally, the safety and effectiveness of GCPs in practical applications need to be verified through more animal experiments and clinical trials.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/foods14071216/sl](https://www.mdpi.com/article/10.3390/foods14071216/sl)]([https://www.mdpi.com/article/10.3390/foods14071216/sl](https://www.mdpi.com/article/10.3390/foods14071216/sl)).  
Conceptualization, S.L. and J.G.; data curation, S.L., W.Q., and W.S.; formal analysis, S.L., J.G., and Y.L.; funding acquisition, W.S.; investigation, S.L. and Y.L.; methodology, S.L., J.G., and Y.L.; project administration, S.L.; resources, W.Q. and W.S.; software, S.L.; supervision, W.Q. and W.S.; validation, S.L. and J.G.; visualization, S.L. and J.G.; writing--original draft, S.L. and W.S.; writing--review and editing, S.L. All authors have read and agreed to the published version of the manuscript.  
This study was supported by the National Key Research and Development Program of China (grant number 2019 YED0902003) and SciTech Funding by CSPFTZ Lingang Special Area Marine Biomedical Innovation Platform.  
The animal study protocol was approved by the Ethics Committee of Shanghai Ocean University (protocol code SHOU-DW-2023-088, approved on 1 June 2023).  
Not applicable.  
The original contributions presented in the study are included in the article; further inquiries can be directed to the corresponding authors.  
The authors declare no conflicts of interest.