Research On The Impact Of Cryoprotectant On Frozen Tilapia

The cryoprotective effect on frozen tilapia quality improvement was studied. Themethods of the study were as follows: the freezing point of tilapia decided the kinds ofcryoprotectants was measured by Electrical resistance and thermometry method.Developing the single factor experiments used the selected cryoprotectants. The indexeswith the solubility of salt extractable protein, Ca2+-ATPase activity, texture property andhistologic section were tested to make sure the range of four cryoprotectants. Responsesurface methodologies were done with the indicators of weighted average of the solubilityof salt extractable protein,Ca2+-ATPase activity and texture property of tilapia added withdifferent cryoprotectants (sucrose, sorbitol, trehalose and sodium lactate)during frozenstorage for1,2,4months, respectively. Compared with the Tg’ of fresh tilapia and frozentilapia with addition of cryoprotectants or not, we could draw the conclusion that the Tg’ offrozen tilapia was higher with addition of cryoprotectants.Experimental results summary as follows:1The freezing point of fresh tilapia was-4℃by means of Electric resistance andthermometry method. All present cryoprotectants (sucrose, sorbitol, trehalose and sodiumlactate) could lower the freezing point of tilapia fillet, and4%additive amount ofcryoprotectants was the best. Sucrose, sorbitol, trehalose and sodium lactate were chosenin view of their solubility and cryoprotective effects.2The result of the single factor experiments with the indexes of the solubility of saltextractable protein,Ca2+-ATPase activity and texture property has showed that4%and8%additive quantity of cryoprotectants were prior to others in retarding the protein changes.The organization structure of tilapia fillets was better with the increase of additive amountof cryoprotectants. Adding cryoprotectants to frozen tilapia could delay the proteindenaturation, maintain the integrality of organization structure and improve the quality offrozen tilapia fillets.3The response surface analysis experiment was designed according to four factorsand three levels of Box-Behnken. The optimal composition of cryoprotectants wasobtained according to the Synthetical value (10*protein content+10*Ca2+-ATPaseactivity+10*texture property) of tilapia fillets added with several cryoprotectants duringfrozen storage for1,2,4months, respectively. The content of salt extractable protein andCa2+-ATPase activity declined with the extended storage time. The texture properties (consistency and elasticity) decreased in the first two months, but increased after fourmonths’ freezing. Because ice sublimate in the frozen tilapia, hardness and elasticity oftilapia fillets increased greatly, resulting to the synthetical value of tilapia fillets went downduring frozen storage. Considering of different properties of cryoprotectant applied intofrozen tilapia fillets, the constitution of cryoprotectants was confirmed as4%sodiumlactate,3.8%trehalose，3.2%sorbitol,2.6%sucrose.4The Tg’ of fresh was-68.9℃by use of DSC, and the Tg’ of frozen tilapia addedwith cryoprotectants or not after2months storage was-56.8℃and-66.2℃.Adding1%,4%,8%sodium lactate, sucrose, sorbitol and trehalose into tilapia fillets, two monthslater, the Tg’ of frozen tilapia respectively were-57.8℃,-53.6℃,-53.1℃;-59.8℃,-56.9℃,-52.3℃;-59.8℃,-54.8℃,-47.4℃;-57.2℃,-54.4℃,-49.4℃. Generally, the Tg’ of frozentilapia added with cryoprotectants was18.8℃. It was higher than tilapia withoutcryoprotectants. So the cryoprotectants could greatly improve the quality of frozen tlapia.