Study On Characteristic Of Ternary Refrigerants And Immersion Freezing Of Grass Carp (Ctenopharyngodon Idellus)

The thermal physical properties （ex. freezing point and so on） of refrigerant was studiedbecause of the defects of the refrigerant and the penetration of Solute. A new refrigerantcomposed of ethanol, propylene glycol and water was put forwarded. The penetration ofSolute of the grass carp in different freezing conditions was studied, too. Finally the changesof the physical characteristic and the microstructure of the fish frozen under different freezingtemperatures were determined. Detailed results are as follows:（1）The freezing point, density, water holding capacity and thermal properties of thedifferent component refrigerant under temperature were determined. The result showed that,when the mass fraction of alcohol are respectively fixed, freezing point almost linearlydecreased with propylene glycol concentration increasing. Reduction rates of freezing point ofpropylene glycol decreased, along with the increasing concentration of ethanol. Withpropylene glycol concentration increasing, Reduction rates of freezing point of ethanol variedsmoothly. The same concentration of the solution with the concentration increasing, firstly,freezing point decreased gradually with the concentration of ethanol increasing, but then asthe concentration increased, the freezing point of changed slowly.Six total mass concentration of53%refrigerant A, B, C, D, E and F （alcohol content asfollows:10%,15%,20%,25%,30%,35%） were selected by freezing point. heat capacityraised with the concentration of ethanol increasing. Density of the six refrigerants decreased.when the temperature was fixed, the density decreased with the concentration of ethanolincreasing. Viscosity gradually increased with temperature decreasing and increasing rateincreased gradually. Kinematic viscosity of the refrigerants decreased with the concentrationof ethanol increasing. Kinematic viscosity reduces quickly from A to D, but not obvious fromD to F.The D refrigerant （25%ethanol,28%propylene glycol,47%water） whose Kinematicviscosity is low, moderate alcohol content, specific heat capacity value is moderate, is betterthan others can be used to freeze food under-30℃.（2）The grass carp was frozen at different temperatures and penetration of solute wasdetermined. The results showed that solute penetration decreased with the freezingtemperature decreasing. Reduction rate of Solute penetration while the freezing temperaturechanged from-15℃to-25℃lower than from-25℃to-35℃.Three pieces of fish blocks was respectively frozen under-15℃,-35℃,-35℃transfer to -15℃to study the effect on solute penetration of different structure of ice crystal. The resultshowed that, solute penetration of fish frozen under-35℃was the lowest, then was from-35℃to-15℃, solute penetration of-15℃was the highest. The result of-35℃to-15℃close to-35℃. The solute penetration of second process of from-35℃to-15℃is lowerthan-15℃（p<0.05）. The result illustrated the different crystal structures can influencedsolute penetration. The ice crystal structure of the fish was compared. between fish frozenunder-15℃and from-35℃to-15℃. The result showed that uniform distribution of icecrystal structure can play a better role to prevent mass transfer.（3）The fish was frozen under different temperatures in the selected refrigerant. The physicalproperties and microstructure of the fish were determined. The result was showed that thetexture was better and water holding capacity increased with the freezing rate increasing（P<0.01）. The activity of Ca²⁺-ATPase increased with the freezing rate increasing（p<0.05）.The photos show that the muscle fibers of frozen fish showed a certain degree ofdeformation, shrinkage and the phenomenon of uneven. With the freezing rate decrease, holesbetween muscle fiber increases gradually.