Research On Water Dynamics Of Instant Sea Cucumber In Multiple Freeze-thaw Processes

The instant sea cucumber is a most closed production to the fresh on the morphology and nutrition,which need to be stored and transported in the cold temperature.As present shortages of cold chain system,freeze-thaw cycles of instant sea cucumber could not be avoided.Instant sea cucumber was chosen as the research object in this article.Water dynamics of freezing-thawing process and multiple freeze-thaw cycle were studied.Besides,effects of multiple freeze-thaw cycles on physicochemical properties of instant sea cucumbers were studied.Water dynamics of freezing process and thawing process were studied by the low field nuclear magnetic resonance(LF-NMR).Several results were gotten like these.During water in instant sea cucumber were transited between solid state and liquid state in our studies,four water populations were observed.According to the length of transversal relaxation times,the fractions were defined as T2b,T21,T22 and T23,which was assigned as strongly bond water,weakly bond water,immobile water and free water.Among these,immobile water and free water were the two main populations.In the thawing process,populations of water increased gradually with the extension of thawing time.Transition occurred between immobile water and free water.The fluidity change of H protons of the instant sea cucumber was observed by NMR parameters,which indicated a strong correlation with core temperature of sample as the temperature rising to 0 ?.However,the freezing process showed an opposite change to the thawing process as populations of water increased gradually with the extension of freezing time.Data of signal intensity,obtained from instant sea cucumbers,detected by magnetic resonance imaging(MRI)were closely related to activities of H protons.Thus,the internal structure of instant sea cucumbers could be visualized presented by method of MRI in both freezing process and thawing process.Analyzing NMR data with principal components analysis(PCA),instant sea cucumber in different freezing and thawing time could be classified into different groups.Quality analysis of instant sea cucumber with multiple freeze-thawing cycles revealed that the thawing loss,expressible moisture,color stability(lightness was changed from 25.7 to 0.61),texture(hardness was changed from 4732.09g to 1790.60g)and collagen content of instant sea cucumber failed gradually.LF-NMR results showed that contents of immobile water and free water of instant sea cucumbers decreased as the increase of freeze-thaw cycles.MRI indicated a decline tendency of water signals,which certified an obvious loss of sample in multiple freeze-thaw cycles.Microstructure observation verified that instant sea cucumbers' structure was damaged more and more seriously as freeze-thaw cycles increased.Cavities,formed in tissue collagen fibers during different freeze-thaw cycles,have weakened tissue's ability of bonding water.The loss of free water population was particularly serious in multiple freeze-thaw cycles.Research results of this article provides changes of moisture state and water distribution of instant sea cucumber in the process of freezing and thawing.Information of sea cucumbers'quality changes in multiple freeze-thaw cycles was also provided.References were provided when nondestructive online monitoring method was needed to monitor of samples' freezing and thawing process in situ,or nondestructive testing method would be used to recognize effects of multiple freeze-thaw cycles on instant sea cucumber samples.