The effects of low‐molecular‐weight fucoidan on the quality of frozen <scp> <i>Litopenaeus vannamei</i> </scp>

Abstract BACKGROUND Aquatic products are highly valued for their rich nutrient content and unique flavors. However, they are particularly vulnerable to microbial contamination during transportation and storage, which can lead to spoilage. Fucoidan exhibited a broad spectrum of biological activities. Nevertheless, research on its application as an antifreeze agent remains limited. The practical application of high‐molecular‐weight fucoidan is constrained to some extent by its high viscosity and poor solubility. Conversely, low‐molecular‐weight fucoidan (WIF) prepared via physical, chemical, or enzymatic degradation methods may offer superior permeability and biological activities, making it a promising, novel, and highly efficient cryoprotectant. RESULTS In this study, WIF was prepared through irradiation degradation using fucoidan as the material. The relative molecular weights of WIF obtained via 50 kGy γ‐ray irradiation ranged from 4.97 × 10 3 to 3.25 × 10 4 Da. It was found that the irradiation degradation method reduced the molecular weight and altered the original chemical composition. Following irradiation, the protein content decreased from 0.94% ± 0.02% to 0.24% ± 0.04%, whereas the reducing sugar content increased from 0.69% ± 0.01% to 6.25% ± 0.36%. Results indicated that soaking treatments with various concentrations of WIF solution exhibited excellent cryoprotective properties and water holding capacity in frozen Litopenaeus vannamei . Notably, after 180 days of frozen storage, the group treated with 15 g L −1 WIF maintained a myofibrillar protein Ca 2+ ‐ATPase activity of 0.0338 U mg −1 prot and a total sulfhydryl content of 30.06 μmol g −1 prot, both of which were significantly higher than those of the other groups ( P &lt; 0.05). Furthermore, at day 180, the surface hydrophobicity of the 15 g L −1 WIF group was 61.35 μg mg −1 prot, significantly lower than that of the control groups ( P &lt; 0.05). CONCLUSION These findings demonstrate that WIF effectively inhibits the decline of Ca 2+ ‐ATPase activity, the oxidation of sulfhydryl groups, protein carbonylation, the exposure of hydrophobic residues, and the accumulation of malondialdehyde. In conclusion, WIF with lower molecular weight shows superior antifreeze and water retention abilities compared to high‐molecular‐weight fucoidan. © 2026 Society of Chemical Industry.