Myofibrillar protein (MP) aggregation in solutions with NaCl concentrations below 0.3 M results in poor solubility. Ultrasound-assisted glutaminase treatment (UGT) was applied to improve MP solubility in a low-salt solution (containing 0.1 M NaCl). The solubility increased with ultrasonic power and time, peaking at 44.34% (480 W, 15 min) and reaching 61% after UGT. Subsequently, the effect of post-sonication heat treatment (60 °C, 30 min) on the physicochemical and structural characteristics of ultrasound-enzyme treated MP (UEMP), prepared under specific ultrasonic conditions (480 W, 20 min), was systematically investigated. The findings revealed that UEMP exhibited higher hydrophobicity, sulfhydryl content, and turbidity, but reduced particle size, ζ-potential, and fluorescence, suggesting disulfide disruption and exposure of hydrophobic residues. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed weakened high-molecular weight bands and intensified low-molecular weight bands. Fourier-transform infrared spectroscopy confirmed these structural rearrangements, with a blue-shifted amide A band and decreased amide I intensity. Heating further increased the hydrophobicity and fluorescence without altering the size, ζ-potential, or molecular weight. The red shift in the amide A band suggests reinforced local ordering. Rheology analysis showed non-Newtonian shear-thinning behavior, which was unchanged by UGT or heating. Collectively, UGT with moderate heating enhances MP solubility and thermal stability by disrupting stabilizing bonds and modulating the structure.

Sodium hypochlorite solution has a good bacterial reduction effect. Thus, in order to understand the effect of sodium hypochlorite on tilapia storage, in this study, tilapia fillets were treated with sodium hypochlorite and Proclin 300 rinsing, the activity of histatinase protease was measured, and the muscle quality was assessed by the texture, colour, pH, myofibrillar fibril fragmentation index (MFI) and its structural changes. The results showed that sodium hypochlorite rinsing could significantly reduce the activities of histatinase enzymes B, L and D. Meanwhile, the sodium hypochlorite-treated group showed less degradation of myosin heavy chain, pro-myosin and myosin light chain, less degradation of texture and colour, better integrity in the fish myocytes, and a lower myofibrillar fragmentation index (MFI). In conclusion, sodium hypochlorite improved the storage quality of tilapia in several ways. Firstly, it inhibited protease activity, thereby maintaining the structural integrity of fish muscle fibres. Secondly, it reduced the rate of deterioration during storage.

The objective of this study is to identify the antioxidant peptides from shrimp by-products and clarify the underlying protective mechanism involved in HepG2 cells with oxidative stress induced by H₂O₂. Protein from shrimp by-products was hydrolyzed by three enzymes (neutral protase, alcalase, and Protamex) and the hydrolysates were separated by using Sephadex G-15 gel filtration, among which the A3 (fraction of alcalase-hydrolysate) displayed a significant 1,1-diphenyl-2-picrylhydrazyl radical and 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) cation radical scavenging ability. A total of 3 480 peptides were identified through nano-high performance liquid chromatography-tandem mass spectrometry, with the prediction of five discovered antioxidant peptides (DYPLVPPYF, HFVPVYEGF, GFPPFTGGPFR, EGYPFNPLL, and RVSDGPWLGR). Notably, HFVPVYEGF and EGYPFNPLL emerged as the potent antioxidant peptide, displaying lower half maximal inhibitory concentration. Furthermore, HFVPVYEGF and EGYPFNPLL obviously relieved oxidative stress in HepG2 cells, which strengthened the activity of total-antioxidant capocity, catalase, glutathione peroxidase, and superoxide dismutase, with diminishing the intensity of malondialdehyde and intracellular reactive oxygen species. Molecular docking results revel that HFVPVYEGF and EGYPFNPLL can bind to Kelch-like ECH-associated protein 1 with hydrophobic interactions. The results provided theoretical basis for the production and application of the by-product of shrimp. And a further study should be carried out to examine the bioavailability and in vivo activity of HFVPVYEGF and EGYPFNPLL which identified from shrimp by-products.

Thermal processing plays a crucial role in tilapia consumption. To investigate the effects of heat treatment on tilapia protein quality and biological activity, this study employed three methods—steaming, microwaving, and baking to process tilapia protein, followed by static INFOGEST In Vitro digestion. Protein quality assessment indicators included degree of hydrolysis, molecular weight distribution, amino acid composition, and scoring. Bioactivity was verified through In Vitro experiments and computer simulations. Results indicate that thermal processing significantly enhances protein digestibility and amino acid availability by moderately altering protein structure and exposing enzymatic cleavage sites. Among the treatments, baked achieved the highest degree of hydrolysis, essential amino acid index, and biological value; while steaming exhibited the highest amino acid release rate and essential amino acid score. Concurrently, thermal processing significantly enhanced tilapia protein bioactivity: Baked markedly increased hypoglycemic activity, with the α-amylase and α-glucosidase inhibitory activities after gastrointestinal enzyme hydrolysis in the baked group reaching 51.48% and 51.74%, respectively, significantly higher than the 42.72% and 41.17% in the fresh group. Steaming substantially elevated antioxidant activity, with ABTS radical scavenging activity reaching 69.00% compared to 57.96% in the fresh group.