Fish and other marine products are transported in refrigerated or frozen temperature zones until they reach the consumer. Still, at the time of consumption, the fish meat must be thawed, and the increase in temperature of the fish meat may cause a significant loss of freshness due to the coarsening of ice crystals and enzymatic reactions. When assuming general household consumption, microwave, room temperature thawing, refrigerated thawing, submerged thawing, or running water thawing are candidates for standard thawing methods in the home. Since direct and indirect energy inputs that affect environmental impact are used during thawing, the environmental impact differs depending on the thawing process, and it is assumed that there is an interrelationship between quality and environmental impact. Therefore, in this paper, a combined evaluation of five thawing methods for frozen mackerel was conducted, combining the freshness of fish meat by the electrical impedance measurement and environmental impact based on LCA. Because the dripping water from the mackerel, depending on ambient temperature and residual time, flows out. In the environmental impact assessment, GWP (GHG emissions) was used as the evaluation index, and the functional unit(FU) was assessed as 60 g of edible portion of approximately one mackerel fillet until it was thawed.
Consequently, the impedance is affected. From the viewpoint of freshness, it was suggested that quality was maintained by thawing the fish over a more extended period while keeping the temperature low. This is because lower temperatures slow down the breakdown of cells during thawing and slow down the deterioration of meat quality. Impedance measurements were made at a voltage of 50 mV and a frequency range of 100 kHz to 10 Hz. 100 Hz results showed that the smallest impedance was 40.8 Ω during flow-thawing.
In contrast, the thawing method with the highest impedance was refrigerated thawing at 69.0 Ω. In addition, the environmental impact (GHG emissions) considering thawing time and direct and joint energy input was the highest for running water thawing at 14.2 g-CO2 eq./FU. This is due to the high indirect energy consumption from water consumption. The other thawing methods were 0.124 g-CO2 eq./FU for refrigerated thawing, 0.196 g-CO2 eq./FU for submerged thawing, and 0.005 g-CO2 eq./FU for microwave thawing.
Finally, a combined evaluation of the environmental impact and freshness of mackerel using microwave thawing as the base case suggested that refrigerated thawing was preferable to room temperature thawing in terms of maintaining freshness.
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