Study On The Antifreeze Mechanism And Effect On Quality Characteristics Of Red Sea Bream(Pagrosomus Major) By Herring Antifreeze Protein

Antifreeze proteins?AFPs?are a family of proteins for improving antifreeze ability of organism,which can reduce freezing point,modify ice crystal morphology,inhibit recrystallization.Their unique properties make it a promising application in the field of frozen food additives.In this paper,herring antifreeze protein?hAFP?was isolated and purified from herring,its interaction with ice crystals was studied by molecular simulation and its antifreeze mechanism was analyzed.Then the red sea bream was taken as research object,the effects of hAFP plus chitosan magnetic?CS@Fe₃O₄?nanoparticles on quality attributes in red sea bream were studied,and the effects of vacuum impregnation of red sea bream with hAFP combined with CS@Fe₃O₄ nanoparticles during freeze-thaw cycles were expounded.In order to provide theoretical basis and technical support for hAFP as food additive to improve the quality of aquatic products after thaw and freeze-thaw cycles.In this study,the antifreeze protein was extracted from herring,which thermal hysteresis activity of 0.84°C.The results of molecular dynamics simulation showed that hAFP could be stable in the ice-water mixed system,and bound to the ice crystal surface closely.If ice crystals continue to grow,will cause the increase of surface area,which requires energy from the outside,leading to a decrease in entropy and temperature of the system.Therefore,ice crystals need a lower temperature to grow,that is,the freezing point of the system decreases,resulting in thermal hysteresis.The effects on the quality of frozen red sea bream which were pretreated by soaking in solutions containing trehalose,CS@Fe₃O₄ nanoparticles and glycerin or hAFP were investigated in this study.The color,texture and shear force were used to analyze the physical changes of fish.DSC,dynamic rheology,Raman,intrinsic fluorescence and second derivative UV spectrometry were used to explore the structural changes of myofibrillar proteins.Surface hydrophobicity,particle size and zeta-potential were used to analyze protein aggregation.Solubility,protein total sulfhydryl/disulfide bond/carbonyl/dityrosine content,Ca²⁺-ATPase activity.SDS-PAGE were carried out to explore the degree of protein oxidation.LF-NMR was used to test water migration and distribution.SEM were performed to observe the changes in the microstructure of muscle fibers.Results indicated that hAFP plus CS@Fe₃O₄ nanoparticles treatment could minimize drip loss,preserve the meat tenderness and texture,improve the fish fillets thermal stability and stable protein conformation,decrease the degree of protein oxidation,degeneration and aggregation,reduce the damage of ice crystal to longitudinal and transverse fibers structure,and improve the water holding capacity of thawed samples.Furthermore,compared with traditional cryoprotectant?glycerol?,hAFP can better preserve the above characteristics of frozen food.Thus,the application potential of hAFP in frozen seafood was proved.The effects of vacuum impregnation of hAFP combined with CS@Fe₃O₄nanoparticles on protein conformation,oxidation,aggregation,moisture state and fiber microstructure of red sea bream were studied.Results showed that with the increase of freeze-thaw cycle,the thermal stability of fish protein was decreased,and the degree of protein oxidation and aggregation was increased.The muscle fiber tissue was broken seriously and the water holding capacity was decreased.However,due to the AFPs have the characteristics of preventing ice crystal growth,modifing ice crystal morphology and inhibiting recrystallization,the thermal stability of protein was improved.On the other hand,this treatment can stabilize the spatial conformation of protein,reduce the oxidation of protein,inhibit the protein aggregation,improve the stability of the solution,inhibit the degree of protein degradation,and the sample under this treatment had a high content of immobilized water.SEM indicated that the treatment could reduce the damage of ice crystals on muscle fibers,make the fiber surface smooth and dense,leading to a better water holding capacity of sample.