| Tuna is an important fish species due to their high economic value and high polyunsaturated fatty acids,which account for a large proportion of the fishery economy.Frozen storage is one of the most importent and effective way for long-term storage of tuna,which can furthest guarantee the nutrition of aquatic products.Frozen foods need to be thawed before they are consumed,while certain changes in the quality of the meat will occur in the freezing and thawing process.Based on the ultrasonic technology and its unique cavitation in frozen,sterilization,assistant extraction,and inspection of food,this thesis mainly focus on the ultrasonic thawing characteristic of tuna quality,physico-chemical properties,gel properties and structure of myofibrillar proteins under ultrasound to expand the relevant research.It provides a basis for the application of ultrasonic technology in freezing frozen proteins products.The results are as follows:1.Ultrasounic thawing can shorten the thawing time,improve the thawing rate and maintain the high water holding capacity of the frozen tuna which were thawed by ultrasonic thawing?0 W,160 W,280 W,400W?and water thawing.The thawing loss of fillet was significantly increased?p<0.05?by the use of ultrasound at 160 W<P<400 W,hovever,there was no significant difference?p>0.05?in the thawing loss and reactive sulfhydryl content compare to the control.The S0-ANS decreased significantly and then increased significantly with increasing ultrasonic power.Hovever,there was no significant difference in the S0-ANS compare to the control as the applied power was further increased?to 400 W?.The Raman spectra of tuna showed that the?-helices had a tendency to transform into?-turns and random coils as power increased compared to water thawing.Microstructure of the tuna indicated that the muscle fibres were separated and destroyed after thawed by ultrasounic thawing and water thawing,and the tuna fish thawed at 280 W suffered fewer negative effects on its microstructure.2.The effects of ultrasonic time?0 min,6 min,12 min,18 min and24 min?at 280 W and ultrasonic power?0 W,160 W,280 W and 400 W?for 12 min on physico-chemical properties and structure of tuna myofibrillar proteins were evaluated.The results showed that the reactive sulfhydryl content of tuna myofibrillar proteins decreased,while the S0-ANS is increased with increasing ultrasonic time.There was no significant difference?p>0.05?in reactive sulfhydryl content with increasing ultrasonic power.The particle size and and protein solubility tuna myofibrillar proteins are decreased after the ultrasonic treatment,and the intrinsic fluorescence of tuna myofibrillar proteins intensity decreased and then increased with increasing ultrasonic power and time.In addition,the r value of second-derivative UV spectra decreased and then increased with increasing ultrasonic power compared to the control?280 W,0 min?,while decreased with increasing ultrasonic time.The Dynamic rheology results indicated that the storage modulus G'and the loss modulus G''are increased,this results indicating the viscoelasticity of the myofibrillar proteins were increased significantly during gel formation?p<0.05?.3.The effects of ultrasonic time?0 min,6 min,12 min,18 min and24 min?at 280 W and ultrasonic power?0 W,160 W,280 W and 400 W?for 12 min on physico-chemical properties and structure of tuna myofibrillar proteins gels were evaluated.The results showed that there were no significant difference?p>0.05?in the color and the reactive sulfhydryl content of tuna myofibrillar proteins,while the S0-ANS were increased compared to the control.The water holding capacity of the gel were increased after long-time ultrasonic treatment??18 min?.Gel texture results indicated that the springiness of gel was increased with increasing ultrasonic time,while the hardness,cohesiveness,gumminess,and chewiness were decreased at high time ultrasonic treatment.The r value of second-derivative UV spectra decreased and then increased with increasing ultrasonic power,while it decreased with the increase of ultrasonic time.Intrinsic fluorescence spectra showed that the fluorescence intensity after ultrasonic treatment was higher than the control,indicating that the the microenvironment of tryptophan and tyrosine was changed by ultrasonic.In addition,the particle size of the gel of myofibrillar proteins was decreased at ultrasonic treatment.The results of SDS-PAGE showed that the myosin heavy chain and actin bands became lighter and then slightly deepened with increasing ultrasonic time,indicating that a part of proteins was degraded at the ultrasonic treatment. |
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