Study On The Thawing Effect Of High Voltage Electrostatic Field On The Quality Of Tilapia And Its Mechanism

This paper researched on the High Voltage Electrostatic Field(HVEF)thawing technology of tilapia fillet.In order to screen the optimal freezing and thawing conditions,we detected many indicators,such as HVEF freezing rate,thawing rate and quality indicators.The effect of HVEF thawing on the quality of tilapia fillets was conducted by investigating the quality indicators of tilapia fillets in the HVEF.We explored the mechanism of thawing on tilapia fillets of HVEF by investigating the change rule of the biochemical characteristics on fish actin,protein denaturation and microstructure during storage.The paper provides a basic theoretical for the application to thawing of food in HVEF,also,which promotes the development of tilapia fillet thawing technology,thus improves the competitiveness of preservation technology on tilapia fillet.The main contents and conclusions are as follows:1.Screening of freezing and thawing conditions for HVEF.The optimum freezing conditions are screening by freezing temperature curve and quality indicators during freezing in different HVEF(0,1.8 and 3.8 kV).The results show that HVEF can make thawing fillets pass through the freezing point more quickly,thus accelerate the freezing of tilapia fillets..Both the fastest freezing speed and the lowest TVB-N value happened in 3.8kV HVEF.Therefore,3.8kV is the optimal HVEF in freezing condition.The optimum thawing conditions are screening by thawing curve,thawing time,thawing rate and quality changes of freezing tilapia fillets during thawing in different HVEF(0,1.8 and 3.8 kV)and different thawing temperatures(25 ?,15 ? and 5 ?).The results show that the fastest thawing rate and the shortest thawing time are observed at 3.8 kV HVEF for each thawing temperature group.At 5 ?,the thawing rate of 3.8 kV HVEF was 1.59 times than that in the control group.TVB-N values and TVC in HVEF groups were significantly lower than those in the control group.Overall,thawing in HVEF can not only accelerate the thawing of freezing tilapia fillets,but also maintain a better quality of fish.Therefore,15 ? and 3.8 kV HVEF is considered the optimal thawing conditions in this study.2.The effect of HVEF thawing on the quality changes of freezing tilapia fillets The freezing tilapia fillets are thawed in different HVEF(0,1.8 and 3.8 kV),and then storage at 4? in the ordinary refrigerator.In order to explore the effect of HVEF thawing on the fillet quality and its mechanism,we investigated the changes of fillet quality at 0,1,3,5 and 7 days after thawing at HVEF.The results show that,HVEF can effectively inhibit the growth of TVB-N value and TVC.The TVB-N value and TVC during the storage after the 3.8 kV HVEF thawing was lower than those in1.8 kV group and the control group.The TBA value increased with the increasing storage time,and the pH value decreased first and then increased with the increasing storage time.However,the effect of HVEF thawing on them was not significant(p > 0.05).The texture parameters,such as hardness elasticity and chewiness decreased with increasing storage time,while the cohesion changed no significantly(p > 0.05).The fillet was thawing uniformly by HVEF,the hardness and chewiness thawing in HVEF groups were better than that in the control group.Overall,HVEF thawing may maintain a better quality of freezing tilapia fillets.3.The effect of HVEF thawing on the biochemical characteristics of protein during the storage of frozen tilapia filletsThe freezing tilapia fillets are thawed in different HVEF(0,1.8 and 3.8 kV),and then storage at 4? in the ordinary refrigerator.In order to explore the mechanism of HVEF thawing,we investigated the changes of protein biochemical properties at 0,1,3,5 and 7 days after thawing at HVEF.The results show that the HVEF has some inhibitory effect on the denaturation and degradation of the protein,the salt soluble of myofibrillar protein,the mercapto content of actomyosin and the activity of Ca2 +-ATPase in HVEF groups were significantly higher than those in control group,and the surface hydrophobicity was lower than that in control group.However,the salt soluble of myofibrillar protein,the mercapto content of actomyosin and the activity of Ca2 +-ATPase are not significant different among the three groups after 7 days storage(P> 0.05).,and the SDS-PAGE results show that the actin was degraded significantly,and the myosin was observed to a certain degree of degradation with the increasing storage time,while the Myosin heavy chain(MHC)showed no significant degradation(P> 0.05).Overall,HVEF can effectively slow down the denaturation of protein.4.The effect of HVEF thawing on water retention and microstructure of tilapia filletsThe freezing tilapia fillets are thawed in different HVEF(0,1.8 and 3.8 kV),and then storage at 4? in the ordinary refrigerator.In order to explore the mechanism of HVEF thawing,we investigated the water retention and microstructure at 0,1,3,5 and 7 days after thawing at HVEF.The results show that,HVEF thawing may effectively reduce the juice losses;the pressure loss rate and the cooking loss rate in HVEF groups were significantly lower than those in control group(p< 0.05),while the water holding capacity was no significant difference among the HVEF groups and the control group(p>0.05).Therefore,we believe that the water retention in HVEF groups was better than that in control group.Compared to the control group,we found that the sarcomere of tilapia muscle was longer in HVEF groups,and,were no lesion and no gap between the cells when observed by the optical microscopy.The array of muscle bundle in HVEF groups was more neatly than that in control group,and the muscle fibers without bending in HVEF groups,while muscle fibers bending deformation,muscle bundle loose were observed in control group by scanning electron microscopy.These results were similar to the previous water retention results.