Studies On The Effects Of Ultrasound-assisted Thawing On Qualities Of Chinese Shrimp

With the development of cold chain industry,the proportion of frozen materials in the secondary operation of aquatic products becomes higher and higher.Thawing treatment is a required step before the secondary operation of aquatic products and has an important impact on the qualities of them.Ultrasound technologies are widely applied in food industry,mainly focused on extraction,sterilization and so on,while ultrasound-assisted thawing as a new type of thawing technology has gradually aroused people’s attention.Chinese shrimp is delicious and rich in nutrients,always in the form of being frozen for circulation and sales and storage.Many research findings have mainly been focused on physicochemical properties of Chinese shrimp during storage,but not much information has been reported about the changes of muscle quality of Chinese shrimp by some noval thawing methods.Therefore,this paper took Chinese shrimp as the research object and compared four thawing methods,to explore the effects of ultrasound-assisted thawing on qualities of Chinese shrimp and select an appropriate way.The main research contents and conclusions are as follows:(1)The effects of different thawing methods on physicochemical properties and sensory properties and thawing rate of Chinese shrimp were compared.After ultrasound-assisted thawing,a*and b*value of samples did not significantly differ from the fresh control(p>0.05),the TBARS value and pH value of muscle was lower compared with samples thawed by other three methods.Air thawing significantly increased(p<0.05)the TBARS value of samples,and resulted in the deterioration of color.Low-temperature thawing contributed to the least thawing loss and cooking loss and maintained the color of muscle well.SEM results showed that ultrasound-assisted thawing process induced little gap between muscle fibers,which had little negative effect on the microstructure of muscle.Water immersion thawed samples also showed some gaps between muscle fibers by SEM images.The microstructure of low-temperature thawed samples was more similar with fresh control samples.There were no significant differences in texture characteristics between four thawing methods,but hardness and elasticity and resilience declined compared with fresh control.The sensory evaluation of ultrasound-assisted thawed samples was significantly better than samples thawed by the other three methods,and could be maintained well after 24 h of cold storage.Comparing the thawing rete of four thawing methods,ultrasound-assisted thawing took 4.3 minutes for completion of thawing process,which had the fastest thawing rate among all the four thawing processes and could pass through the zone of maximum ice crystal formation quickly.Water immersion thawing and air thawing took about 8.5 and 60.6 minutes,respectively,while low-temperature thawing had the slowest thawing rate which took 154.7 minutes.Based on above mentioned,ultrasound-assited thawing was a better thawing way.(2)Changes in protein structure and functional characteristics of Chinese shrimp treated by different thawing methods were studied,based on the degradation of muscle protein.Air thawing process increased protein carbonyl content which was the highest compared with the other three methods and reached at 2.70 nmol/mg(p<0.05),decreased total sulfhydryl content and protein solubility,resulting in the protein oxidation of Chinese shrimp.Total sulfhydryl content of ultrasound-assisted thawed samples was higher than the other three methods(p<0.05),and surface hydrophobicity of low-temperature thawed samples was lower(p<0.05).Therefore,these two methods effectively control the degree of protein denaturation.The thermal stability of muscle thawed by ultrasound decreased slightly,but the enthalpy of denaturation of actin thawed by water-immersed decreased by about 40%.The maximum absorption wavelength of fluorescence showed no significant change,while fluorescence intensity was remarkably enhanced thawed by four methods,which meant that thawing treatment had an impact on the tertiary structure of protein.There was no difference in myosin heavy chain and actin by the SDS-PAGE pattern.But the density of 70-100 kDa protein band of ultrasound and low-temperature thawed samples slightly turned lighter or harder compared with fresh samples,showing that protein degraded and cross-linked to a certain degree.Consequently,ultrasound-assisted thawing could reduce the deterioration of functional properties of protein,but it had an unnoticeable effect on the structure of protein.(3)A mathematical model coupled heat transfer with pressure acoustics was established,using finite element method to simulate the process of ultrasound-assisted thawing.The results showed that the RMSE was 0.9433 of ultrasound-assisted thawing and the maximum temperature deviation between the predicted value and the experimental value was 1.6℃;the RMSE of control(water thawing)was 0.9077 and the maximum temperature deviation was 1.3 ℃.The small difference between the simulated value and the experimental value was noticed,so this model fit the ultrasound-assisted thawing process experiment very well.Furthermore,ultrasound-assisted thawing could reduce thawing time by 35.9%,significantly improved the thawing rate compared with water thawing.From the temperature pattern,temperature of each point in the cross section of the muscle thawed by ultrasound was higher than that of control because of heat absorption of external and internal tissue.It is further proved that ultrasound-assisted thawing is a fast and efficient way.