Study On Optimization Of Thawing Methods For Tuna Chunk

Tuna is kind of migratory species fish which lives in middle or surface water area, the scope of its activity is the high seas which is high salty, so the meat quality of tuna is in low pollution. Meanwhile, tuna has to keep high speed moving to maintain its vigour, so the meat quality of tuna is tasty. More than that, tuna contains high protein and low fat, as well as mineral and vitamin. As a kind of red meat fish, the muscle of tuna contains more lipid than other fish, and the majority of its fatty acid is unsaturated fatty acid, especially the EPA and DHA , which is honored as a nutritional food for us.For tuna, the time from ocean to table needs 1.5² years, in order to keep the its high quality, the storage temperature needs -55℃or lower. This asks for the suitable thawing methods before processing in order to keep the high quality of tuna.There has a lot of factors effects the tuna quality and the thawing methods do has a direct and important relation. This article used bigeye tuna dorsal flesh, comparing the four traditional thawing methods for tuna including air thawing, cold storage thawing, salt-water thawing and static water thawing, come to the conclusion that salt-water thawing is the best way to thawing tuna chunk. Then we optimized the thawing process by the means of L₉ (3⁴ ) orthogonal test. After that combined the optimized process to microwave thawing in order to shorten the thawing time. At last using these methods to thawing yellowfin tuna chunk. We can find that these optimized thawing methods can do a great effect to thawing tuna chunk. Meanwhile, this article summarize the research of tuna thawing home and abroad. The judgement index of tuna quality mentioned in this article provided a credible theory gist for the tuna-study of our country, it also can be an assistance to establish concerned criterion and standard. The main conclusions are as follows:1) In order to ensure the quality of bigeye tuna chunk after thawing, thawing time and the color, shear stress, pH value, total viable count and sensory evaluation in 72h after thawing were assessed to investigate the relationship between thawing methods and tuna quality, Normal temperature air thawing, cold-storage thawing, salt water combined thawing and the static water thawing are the common thawing methods of tuna. Compared the result of five indexes in different thawing methods, it concluded that salt water combined thawing was the best method. The a* value of tuna chunk after thawing was 12.30, the shearing force is 342.48g and the sensory score is 12.80, The total viable colony (TVC) was within the occupation standard in 48h. Meanwhile, the changes of color and shear stress described a better capability to characterize the quality change of tuna. Hoping it can be an assistance to establish concerned criterion for shelf life of tuna.2) In order to ensure the quality of bigeye tuna chunk after thawing, salt-water thawing and refrigerated thawing methods were combined to defrost the bigeye tuna chunk from deep freezing. Physicochemical sensory and E-nose analysis were used to evaluate the thawing technology, and get the optimal thawing process. Texture and color were assessed to investigate the major factor which effect the tuna quality, including the salt content, salt-water temperature and immersion time. The thawing process was optimized by the means of L₉ (3⁴) orthogonal test . The optimized result was 40℃salt-water temperature, 3% salt content and 90s immersion time. Under the optimization condition, the equal temperature time is 12 h, and the tuna chunk had 26.27 a* value, 570.05 chewiness and 7.20 sensory scores, with the microbial index is under the industry standard. E-nose analysis shows the salt content has a significant effect on the odor of tuna chunk.3) In order to ensure the quality of bigeye tuna chunk after thawing and shorten the thawing time, microwave thawing and normal temperature air thawing methods were combined to defrost the bigeye tuna chunk from deep freezing. Physicochemical sensory and sensory analysis were used to evaluate the thawing technology and get the optimal thawing process. Comparing the texture, color and sensory indexes after thawing, confirmed the optimized process condition was 220W microwave power, 3% salt content, and 6min microwave time. Under this optimization condition, the equal temperature time is 45 min, and the tuna chunk had 25.06 a* value, 402.84 chewiness and 6.80 sensory scores, with the microbial index is under the industry standard. Microwave time and quality comparison also draw the conclusion that the microwave power suit for the tuna thawing is under 300W.4) In order to verify the application of these optimized thawing methods, using the methods to thawing yellowfin dorsal flesh and abdominal flesh chunk, get the conclusion that combined salt-water methods is the most suitable thawing process for yellowfin tuna chunk, 220W is the most suitable power for microwave thawing. For the abdominal flesh contains more fat and protein than dorsal flesh, the sashimi for the former is more red and the mouthfeel is more soft, but come to the sensory evaluation, the both has no significant difference.