Effect of Ultrasound-Assisted Thawing on the Quality of Euphausia superba and Its Changes during Cold Storage

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.