Effects of Different Thawing Methods on the Quality of Sashimi

Frozen rainbow trout (Oncorhynchus mykiss) fillets were thawed by four different thawing methods including refrigerator thawing, water bath thawing, microwave thawing, and room temperature air thawing to investigate the effects of thawing methods on the quality of sashimi. The sensory quality, thawing rate, thawing loss percentage, color, total viable count (TVC), total volatile basic nitrogen (TVB-N) content, microstructure, textural characteristics, water migration, and volatile odor characteristics of fillets were determined. The results showed that the sensory score of fillets subjected to refrigerator thawing was significantly higher, while the thawing rate was significantly lower compared with those thawed by the other three thawing methods (P < 0.05). The thawing loss percentage of fillets subjected to water bath thawing was significantly lower than that of those thawed by the other three thawing methods (P < 0.05), which was beneficial to the moisture retention of fillets, and the TVB-N content and TVC were only 1.02 mg/100 g and 0.46 (lg(CFU/g)) higher than those of microwave thawed fillets, respectively; the sensory score was only 3.19 points lower than that of refrigerator thawed fillets. Microwave thawing was superior to the other thawing method in terms of whiteness, TVC, and TVB-N content, and effectively inhibited the color change and microbial growth and alleviated the production of alkaline nitrogenous substances such as ammonia and amines in fillets during thawing. However, microwave thawing caused uneven heating of fillets, which resulted in partial cooking and poor sensory and textural properties. Therefore, it was not suitable for thawing fillets.Compared with the other three thawing methods, room temperature air thawing was inferior with respect to all quality parameters tested. In summary, water bath thawing can avoid undesirable changes to the greatest extent while maintaining the quality of raw fish fillets.