Effects of radiofrequency-assisted freezing on microstructure and quality of rainbow trout ( Oncorhynchus mykiss ) fillet

In this research, freezing was combined with radiofrequency waves (RF) as a novel method and its application was investigated on rainbow trout fish. The main purpose of this study was determination of the effect of RF waves on freezing process and quality characteristics of fish after thawing as compared to the conventional air blast freezing method. The effects of three radiofrequency pulse patterns and three electrode gaps (2, 3 and 4 cm) on the quality of frozen fish such as drip loss, colour, texture and microstructure were investigated. As compared to the control sample, RF-assisted freezing reduced drip loss, however no significant difference was observed in weight loss on freezing. Textural analysis showed that hardness, gumminess and chewiness of RF treatments were similar to the fresh sample (unfrozen) and no significant difference was found between them. The colour of frozen fillets was not significantly influenced by RF application. Histology tests conducted to investigate the microstructure of frozen fish indicated that the size of the formed ice crystals was significantly reduced under RF-assisted freezing and at the minimum electrode gap it was about 75% of the size of the ice crystals of the control sample frozen without RF.