Study On Hydration Characteristics Of Meat Batters During Heat-induced Processing

The 1H distribution and migration in meat batters during heat-induced processing was investigated.Transition temperatures were determined by the trend in variation of G?.Then the effect of chemical interactions and protein conformation changes of meat batters on water distribution and mobility at various phase transition temperatures were investigated by LF-NMR T2 relaxation,FT-IR spectroscopy and Raman spectroscopy.Furthermore,the relationship was analyzed combining the indicators colour,textural properties and water retention capabilities of emulsified meat,aiming to establish correlation of protein hydration characteristics,conformational change associated with the quality of emulsified meat,to provide some theoretical bases for the practical production.The main research conclusions were as follow:1.Moisture content was gradually decreased and the centrifugal loss was gradually increased with rising temperature.Simultaneously,the T22 relaxation time and its peak area fraction,which attribute to immobilised water decreased with increasing temperature,but the T23 water fraction which attribute to the amount of free water gradually increased.The result of correlation analysis indicated that there was a very positive significant(P < 0.01)correlation between the moisture content(r = 0.755)and the peak area fraction of T22,and a very negative significant(P < 0.01)correlation was found between the peak area fraction of T23(r =-0.990),the centrifugal loss(r =-0.798),the L* value(r =-0.597),pH(r =-0.573)and the peak area fraction of T22 respectively.With the formation of heat-induced emulsion gel,the water molecules combined with protein more tightly and parts of immobilized water turn into free water.Simultaneously,the water holding capacity of meat batters was decreased and the L* value and pH was increased.2.The T22 relaxation time and its peak area ratio of immobilised water decreased consistently as the final temperature increased from 39 to 74 ?,and a new relaxation time T23 corresponding to the free water appeared at 50 ?,which indicated that protein denaturation by heating could constrain the migration of protons and the WHC of meatbatters decreased.While partial transformation of the ?-helix into ?-sheets were observed,accompanied by the increasing surface hydrophobicity and the formation of disulphide bonds during heat-induced processing.These changes in protein structure and water distribution of meat batter would induced the decrease in moisture content,a* and b* and lead to the increased water loss,L* and pH.The G? gradient increased as the temperature increased from 55 to 66 ?,indicating the formation of an elastic gel network,which leads to a very significant(P < 0.05)decrease in water holding capacity.Therefore,the phase transition temperature can provide critical information about the water migration,its distribution,and the progress of protein structural change during heat-induced processing.3.The heat-induced processing of meat batters occurs mainly in two steps measured by the variation of G? and WHC.55 ? and 66 ? were critical phase transition temperatures.There was no significant changes in cooking loss before 55 ?,and significant(P < 0.05)increases from 55 ? to 66 ?.A new relaxation time T23 corresponding to the free water appeared at 55 ? and The G? gradient increased as the temperature increased from 55 to66 ?.During heat-induced processing,ionic bonds and hydrogen bonds decreased significantly(P < 0.05),while hydrophobic interactions,disulfide bonds,and non-disulfide covalent bonds increased significantly(P < 0.05).Raman spectral analysis revealed that,partial transformation of the ?-helix into ?-sheets,?-turns and random coil were observed.Moreover,intermolecular bonds,protein conformations changes and WHC showed a significant correlation.Therefore,the formation of meat batters gel and the changes in water distribution during heating would be correlated with conformational changes of proteins and intermolecular bonds.4.Effect of heating methods on physicochemical properties and in vitro digestibility of meat batters were investigated.The center temperature at 75 ? sample(group 1)was the optimal heating method in this work,which had the lowest cooking loss.While the peak area proportion of T22(P22)and the in vitro digestibility of meat proteins by trypsin were highest.Compared group 2(30 min at 75 ?)with group 3(60 min at 75 ?),increasing heating times from 30 to 60 min decreased ?-helical contents,but increased?-sheet,?-turns and random coil structures,which resulted the slight increase of cooking loss and hardness.In addition,in term of protein digestibility,there was no significant changes(P > 0.05)among common heated groups(group 1,2,and 3).However,an important decrease of the pepsin and trypsin + ?-chymotrypsin activity on proteins was observed after secondary heated treatment(30 min at 100 ?).While the cooking loss andhardness was significantly(P < 0.05)increased,along with partial transformation of the?-helix into ?-sheets,?-turns,random coil structures and a significant(P < 0.05)decrease of relaxation time T22 and its peak area P22.Moreover,protein conformations changes,water characteristics,textural properties and in vitro digestibility of meat proteins showed a significant correlation.Therefore,the different heating methods could affect the physicochemical properties and in vitro digestibility of meat batters by changing water-protein interactions(water characteristics)and protein-protein interactions(protein conformations changes).