Study On Quality Changes Of Pseudosciaena Crocea Subject To Different Freezing Methods

The quality changes of Pseudosciaena crocea frozen by different methods (Slow freezing,abbreviated as SF; Quick freezing by immersing in ultra-low temperature ethanol, abbreviated asQF-UTE; Quick freezing by immersing in liquid nitrogen, abbreviated as QF-LN) or storage atdifferent temperatures (-20℃,-40℃,-80℃) were studied in this paper. Physical and chemicalindex (pH, drip loss, TVBN, extraction yield of salt soluble protein), texture profile, microstructurecharacteristics, water mobility and second structure of fish protein were analyzed periodically toinvestigate the effects of freezing methods or storage temperatures on quality changes ofPseudosciaena crocea. The result turned out that:1.Based on the freezing curves of Pseudosciaena crocea frozen by different methods, theQF-LN samples had the shortest times to pass the zone of most crystallization and reached-40℃among the three freezing methods.2.The quick frozen samples revealed a relatively lower freezing loss and thawing loss,otherwise a relative higher juice loss and cooking loss, compared to the SF treated samples. Quickfrozen samples showed a higher texture property in hardness, adhesiveness, chewiness andresilience, while the adhesiveness, springiness and cohesiveness of SF samples were relativelycloser to those of unfrozen fish. The transverse relaxation time of Low-field1H NMR indicatedthat the mobility of bound water, extra-cellular water and free water in Pseudosciaena croceaincreased after frozen by three methods, and the mobility increased in order of unfrozen sample,SF, QF-UTE and QF-LN. The content of bound water and extra-cellular water of the quick frozensamples were higher than that of SF treated samples, while free water content was lower than SF.Significant correlations were found between the NMR parameters and water holding capacityindices. The Raman spectra showed that the α-helix turned into β-sheet after freezing.3.The quality of Pseudosciaena crocea frozen by different methods decreased with theextension of frozen time. Samples frozen by LN and storage ate different temperatures revealed thathe lower the frozen storage temperature, the better quality and longer shelf life the samples wouldget.