Quality Changes And Rapid Evaluation Of Raw Tuna Fillets

Tuna contain abundant nutritional composition, and rich in protein, fat, vitaminsA, D, minerals, DHA, the EPA, taurine and various trace elements. The structure ofnutritional composition has the characteristics of low-fat, low-energy and high-protein.Eating tuna regularly can contribute to the body’s nutritional balance. So tuna is oneof the best foods for urban people. The production of sashimi in China has a latebeginning, but it has developed rapidly, and the tuna sashimi gradually by more andmore domestic consumers. The study on tuna trading, resources, logistics, processing,sales and consumers has important theoretical and realistic significance. Nowadays,the industry ready-to-eat raw tuna standard has been set up, but the quality ofready-to-eat raw tuna and the rapid; effective; non-destructive evaluation for customhave not been developed.We have studied quality changes of raw tuna fillet at0、4、8、-18℃temperaturefirst. The raw-eaten endpoint of every cooling storage temperature was taken as20%(K value). In the process of cooling storage, the K value, pH value, the relativecontent of metMb, color difference and texture were tested to evaluate the quality toachieve the law of quality change and the prediction of the remaining shelf life ofraw-eaten tuna based on the quality.The result showed that the cooling storage temperature at0℃about68hours, atabout32hours at4℃, about20hours at8℃,about150days at-18℃. During thestorage, pH value of raw tuna fillet have no significant difference. For the fleshest rawtuna fillet, pH value can not evaluate the small differences of the degree of thefreshness. By analyzing the changes of metMb content, we have the storage time tokeep the better color of raw tuna fillet. The storage time should not more than24hours at4℃,18hours at8℃,40hours at0℃. The chewiness and springiness of rawtuna fillet declined slightly at0℃during the storage time, and declined obviously at4℃、8℃。And then based on the changes of K value of raw tuna fillet during the storage,we have found the result that it has a strong correlation between changes of K value and absorbance from the reaction of MTT、Hx、XOD. Then we have designed theresponse surface, and optimized the content of various components of the sensor. Wegot the response surface regression model at every storage temperature, which had ahigh degree of fit, and the experimental error was small. We also found it hadinteraction between Hx content and XOD additive amount. Therefore, the sensorcould be applied to rapid evaluation of the freshness of the tuna at0、4、8、-18℃storage temperature. The MTT sensor system buffer is:90%-1mol/L-ethanol-Tris-HCl,pH value8.2at0、4、8storage temperature, and7.8at-18storage temperature. By thespectral scanning, MTT and FMZ solution, the maximum absorption wavelength of565nm. The fit of response surface of sensor is R20℃=0.9514；R24℃=0.9287；R28℃=0.8980；R2-18℃=0.9726. The optimal condition of the sensor was that XOD contentwas0.5、0.5、0.4、0.48U，Hx content was2.2、2.4、2.4、1.5mg，MTT content was2.72、2.4、2.4、1.5mg respectively at0、4、8、-18℃.We have studied changes of organoleptic parameters of raw tuna fillet at0、4、8storage temperature during the different time, and organleptic parameters containcolor, odor, taste, exterior, texture and other sensory characteristics. We have gottenthe result.In terms of color characteristics, the highest evaluation of the color sensory is thetuna fillet which storaged during24-36h at different temperature. In terms of odor,after60h, did not exhibit adverse sour and fishy taste, the organoleptic evaluationscore did not change significantly during the storage time at different temperature. Interms of taste characteristics; the evaluation of tuna storaged at0℃and4℃.Thefreshness of raw tuna fillet declined, and had bad taste. In terms of exterior, theevaluation of exterior was poor relatively at0℃. Late in storage, which generatedshrinkage phenomenon, and organoleptic score reduced. In terms of texturecharacteristics, the better quality of raw tuna fillet on storage tine is36h at0℃;24h at4℃;12h at8℃. After PCA analysis, the affect of the organoleptic properties forsensory evaluation from strong to weak is color; taste; odor; exterior; texture. Thedifference of exterior; texture; odor were not significant, and it was quite different ofthe tuna fillet during different storage time and temperature in terms of color and taste.It can be seen that color plays an important role for sensory evaluation.The result showed that the downward trend of a*value was similar at0、4℃, anddecreased rapidly at8℃℃, becoming stable, changesobviously at0℃than4、8℃. The higher the storage temperature, the greater the of raw tuna fillet at0℃, and conductive storage at4℃. The result had a highcorrelation between image analysis and color meter to determinate the color of rawTherefore, we could use this method to establish the color card to evaluation thequality of raw tuna fillet. Lab parameters by computer analysis was43*63*56sensory bright red, best quality and freshness;58*47*42sensory red, good qualityfreshness;53*31*33senses dark red, raw-eaten endpoint.30*26*28for the sensesbrown red,.point for quality corruption. After selecting a reference color, weestablished the quality color card for tuna quality evaluation.