Study On The Quality Changing And Water Migration Mechanism Of Beef In Sub-Freezing Preservation

In this paper,the mechanism of sub-freezing storage on beef quality and water migration was investigated,to provided the theoretical basis for the storage and transportation of fresh beef.Firstly,the quick-freezing experiments were performed at-80?and the temperature zone of sub-freezing was determined by low-field nuclear magnetic resonance?LF-NMR?and H proton imaging?MRI?.Then compared 3 meat preservation method?4?,ice-temperature and-18??with sub-freezing storage to determine the storage period of beef in sub-freezing storage mode and the quality change of meat quality during storage.Finally,according the characteristics of protein hydration during the storage process and the change of the microstructure of beef to describe the mechanism of water migration during the storage of beef was discussed.The specific results are as follows:Sub-freezing storage?-6?,-9?,-12??has much longer storage time than 4?and ice-temperature.The storage time of each preservation method is 84 d?-6??,126 d?-9??,168 d?-12??,10 d?4??and 24 d?ice-temperature?.At meantime,the meat quality of sub-freezing?-6?,-9?,-12??was significantly better than 4?and superchiling.While had no significant difference with the quality of stored meat samples at-18?.This result showed that the sub-freezing temperature zone storage beef has a significant effect on prolonging the storage period of fresh beef and is also beneficial to keep the meat quality in the storage period.It is also beneficial to maintain the consumption and commercial value of beef.With the storage time prolonged,the protein quality of beef was deteriorating in different degree of storage.The solubility of protein in frozen storage decreased by 25.61%?4??,22.62%?ice-temperature?,19.10%?-6??,18.68%?-9??,17.99%?-12??,17.12%?-18??.Sub-freezing storage and-18?frozenpreserved beef protein solubility is better.When at the end of each storage,the carbonyl content of the sub-freezing meat sample?-6?,84 d?was 19.39 nmol/mg protein which was0.31 nmol/mg and 0.43 nmol/mg lower than 4??14 d?and ice-temperature?28 d?respectively.The content of Sulfhydryl was 75.82 nmol/mg protein in sub-freezing beef?-6?,84 d?which is higher than4??53.70 nmol/mg?and ice-temperature?60.82 nmol/mg?significantly.Beef preserved in 4?had the fastest hydrogen bond content decreasing speed,the content of hydrogen bonds in protein samples was 0.61 mmol/mg at the 14th day.Which was significantly lower than that of-6?sub-freezing preserved beef?0.97 mmol/mg?and-18?frozen beef samples?1.09mmol/mg??p<0.05?.The results of Ca²⁺-ATPase activity showed that sub-freezing storing could slow down the speed of Ca²⁺-ATPase activity deterioration.The results of SDS-PAGE showed that the protein was cross-linked,degraded and denatured during storage,but the protein denaturation at 4?and ice-temperature was significantly higher than that in sub-freezing storage group and-18?storage group.So that sub-freezing storing can delay protein denaturation to maintain beef quality.The thermal stability of beef stored at sub-freezing and-18?was significantly higher than that beef stored at 4?and ice-temperature.At the same time,the hydrophobicity of the protein in sub-freezing and-18?storing was significantly lower?p<0.05?.The secondary structure of the protein also showed that the secondary structure of the sub-freezing storage protein was more complete and the degree of denaturation was lower.The microstructure and ultrastructure of beef samples were determined,the result showed that sub-freezing storing could maintain the integrity of myofibrils in beef.According to the LF-NMR detection result,sub-freezing storage and-18?had less free water in beef than in 4?and ice-temperature,which means less immobile water transferred into free water,beef had better water holding capability.The above results show that sub-freezing storage can reduce the denaturation and deterioration of meat protein effectively and improve the water retention ability of muscle protein also the integrity of muscle fiber bundle structure.What'more,slowed down the degree of muscle contraction and water"state transferring"trend.Therefore,sub-freezing storage can reduce protein degradation during storage,improve the quality of stored beef and achieve long-term storage.