The Mechanism Of Thawing Drip "Reabsorption" Mediated By Muscle Protein Freezing Denaturation

In the present paper,the mechanism of thawing drip“reabsorption”mediated by muscle protein freezing denaturation were investigated,in order to provide the basis for the control of thawing loss.Firstly,the effect of frozen temperature on myofibrillar protein denaturatio n and WHC?water holding capacity?were studied and the connection between myofibri llar protein denaturation and WHC of thawed beef was discussed.Secondly,the effect of the interaction between protein and ice crystal on potential“reservoir”and“channel”of free water was explored.At last,the quality of thawed beef treated with low voltage electrostatic field thawing?LVEFT?were compared with refrigerator thawing?RT,4°C?,and the effects of LVEFT on the changes in physiochemical properties of myofibrillar protein during thawing process were investigated.The results were listed as below:1.The changes of myofibrillar protein denaturation and muscle WHC were observed at freezing temperatures?-9,-18,-23 and-38°C?.The results show that the beef got the lower the denaturation degree of myofibrillar protein and the higher WHC under lower freezing temperature.The results of correlation analysis shows that the physical and chemica l properties of myofibrillar protein(protein solubility,Ca²⁺-ATPase activity,sulfhydr yl content,total denaturation enthalpy)after freezing were significantly correlated?P<0.01?with the WHC indexes?thawing loss and press loss?.In addition,after thawing,L*value,b*value and shear force of beef were also significantly correlated?P<0.01?with WHC The results show that there was a causal relationship between the denaturation of myofibri llar protein caused by freezing and the decrease of WHC after thawing,which would lead to color deterioration,tenderness decrease and thawing loss after thawing.2.The shape of ice crystals frozen in muscle fibefs at lower temperature samples were smal er and denser.The equivalent diameter of ice crystals samples frozen at-23 and-38?were 11.82 um and 6.06 um,significantly less than 33.9 um and 15.78 um of-9 and-18??P<0.05?.SDS-PAGE results show that the structure of myofibrillar protein was damaged under-9 and-18?freezing.The equivalent diameters of ice crystals were significa nt l y correlated with the proportion of?-helix and?-sheet of myofibrillar protein and the content of dityrosine?P<0.05?,which verified the the damaging effects of ice crystals growing on protein structure.The beef samples frozen at lower temperatures had lower water mobilit y with higher immobile water and lower free water,which explained the results of WHC.During freezing process,the ice crystals formed a“reservoir”of free water,and the gap between muscle fibers formed a“chanel”.Due to the protein denaturation and the decreasing of hydration ability caused by freezing,free water migrated along the water“chanel”and forming the thawing loss.3.Fourier transform infrared?FTIR?results suggested that the denaturated myofibri llar protein?caused by freezing?would renaturate with thawing time,and the results of surface hydrophobicity and protein solubility were corresponded with it.The bonding capacity between protein and water?ionic bonds and hydrogen bonds?also increased with thawing time.The renaturation of protein during thawing process explain the mechanism of thawing drip“reabsorption”.In addition,it is demonstrated that LVEFT can effectively reduce quality loss of beef and accelerate the renaturation of protein during thawing process while significantly shortening thawing time?P<0.05?.The bonding capacity between protein and water?ionic bonds and hydrogen bonds?also increased with thawing time.Through the whole thawing process,LVEFT samples had higher protein solubility,surface hydrophobicity,ionic bonds and hydrogen bonds than that of RT,which explain the higher WHC of LVEFT beef.