Evaluation of Vacuum Microwave Thawing on Quality and Flavor Profiles of North Pacific Krill (Euphausia pacifica) for Potential Human Consumption

Ultra-fresh quality frozen North Pacific krill (Euphausia pacifica) were thawed using vacuum microwave thawing (VM) and compared with traditional thawing methods of running water (RW) thawing and ice water (IW) thawing. Samples were stored from 0 to 21 h post-thawing. The metabolic, structural and sensory evaluation changes including pH, ATP-related compounds, free amino acids, color, microstructure, and sensory properties were analyzed. The results indicated that VM thawing effectively maintained pH, with a value of 7.95 at 0 h post-thawing, close to the value of the fresh sample. ATP degradation primarily followed the ATP → ADP → AMP → IMP → HxR → Hx pathway, with VM thawing showing the most pronounced delay in ATP breakdown and the relatively highest accumulation of IMP compared to RW and IW thawing. VM-thawed samples retained higher levels of free amino acids, particularly those contributing to sweetness and umami, enhancing overall flavor complexity. However, bitterness also increased with extended thawing time and was the highest one among the thawing methods. Scanning electron microscopy (SEM) revealed that VM thawing better preserved the structural integrity of myofibrillar proteins, with a clear Z-line visible. VM thawing also minimized color changes, as shown by a smaller decrease in L* and better retention of a*, and achieved higher sensory evaluation scores. Although VM thawing did not inhibit endogenous enzymatic activity responsible for blackening, it significantly shortened the thawing time by 62.48 min compared to IW thawing and improved the overall post-thawing quality of North Pacific krill in the initial thawing period, supporting its potential for human consumption.