In order to study the effect of ultrasound-assisted thawing on the quality of Antarctic krill (Euphausia superba) and its changes during cold storage, frozen Antarctic krill was placed into net bags or polyethylene (PE) bags and thawed by water immersion with or without ultrasound treatment. The quality changes of thawed samples during cold storage were evaluated in terms of sensory scores, microbial growth, hardness, total volatile basic nitrogen (TVB-N) content, polyphenol oxidase (PPO) activity and trypsin activity as well as the signal intensity of hydrogen protons in low field nuclear magnetic resonance. The thawing time was 105 and 145 min for net bag and plastic bag packaging combined with water immersion thawing, respectively, while it took only 65 and 75 min for net bag and plastic bag packaging combined with ultrasound-assisted immersion thawing. After thawing, the sensory score of Antarctic krill continued to decline during storage at 4 ℃ and reached an unacceptable level after 24 h of storage. However, the total viable count remained less than 2.5 (lg (CFU/g)) before and after thawing and during subsequent cold storage for 28 h, but the activity of PPO and trypsin increased firstly and decreased at the end of storage, while TVB-N content increased during storage. The quality of thawed Antarctic krill contained in net bags deteriorated more slowly than in plastic bags. Collectively, net bag packaging combined with ultrasound-assisted thawing can not only accelerate the thawing rate, but also improve the storability of Antarctic krill.

The preservation effect of modified atmosphere packaging (MAP) on seafood has been applied widely, but packaging with high concentrations of CO₂ will have adverse effects on seafood. This study aimed to elucidate the potential mechanism of the adverse effects caused by MAP with high CO₂ concentration at 4 °C. The changes in the quality of salmon fillets under high concentrations of CO₂ packaging were demonstrated in this article through indicators such as total volatile basic nitrogen content, microbial counts, thiobarbituric acid reactive substances (TBARS) value, and drip loss. The underlying mechanisms were further explained from the perspectives of protein degradation and endogenous enzymes. The study indicated that the microbial counts in the 90% CO₂/10% O₂ group were higher than both the 75% CO₂/10% O₂/15% N₂ and 60% CO₂/10% O₂/30% N₂ groups on the 12^th day, and there was also an increase in TBARS value and drip loss. On the 2^nd day, the caspase-3 relative activity in the 90% CO₂/10% O₂ group (119.96%) was found to be higher than the 75% CO₂/10% O₂/15% N₂ group (111.99%). On the 12^th day, the relative activities of caspase-3 in the 90% CO₂/10% O₂ group and the 75% CO₂/10% O₂/15% N₂ group were 34.13% and 25.77%, respectively, the latter exhibited the lowest cathepsin activity and the minimum myofibril fragmentation index. The results of free amino acids analysis indicated that the 90% CO₂/10% O₂ group was also accompanied by an accumulation of more bitter amino acids during storage. The MAP with 75% CO₂ had better effect on inhibiting caspases and cathepsins, which could be the main reason to a better muscle quality of salmon fillets at 4 °C.