Effects Of PH And Temperature On Thermal Aggregation Behavior Of Myofibrillar Proteins From Mirror Carp

In this experiment,the myofibrillar protein of mirror carp was taken as the research object.Firstly,the effect of pH?4.5?8.0?on the thermal aggregation behavior of myofibrillar protein during heating was studied,and the optimum pH was screened.Then under these pH conditions,the effects of heat treatment conditions?heating temperature:30?90?;heating time:0?60 min?on the thermal aggregation behavior of myofibrillar protein were studied,and the heat treatment conditions were selected.Finally,the effect of the thermal aggregation behavior of myofibrillar protein caused by two-stage heating under the selected conditions on the gel properties of myofibrillar protein was analyzed.The main results are as follows:?1?Effect of pH on thermal aggregation behavior of myofibrillar proteins from mirror carp during heatingThe physical and chemical properties,thermal aggregation behavior and gel properties of myofibrillar protein under different pH conditions were analyzed.The results show that:30?and control group,there was no significant?P>0.05?difference in surface hydrophobicity between pH6.0 treated protein and pH 7.0 sample,the difference of?-helix structure was small,and the change of protein structure was small.With the increase of temperature?>40??,the solubility,total sulfhydryl content,maximum fluorescence intensity and?-helix structure of all samples decreased,while surface hydrophobicity and?-folding structure increased.Among them,the increase of surface hydrophobicity and the decrease of total sulfhydryl content of protein treated by pH 6.0 were higher than those of other samples.The acid-treated protein had higher turbidity,and when the temperature was higher than 50?,the turbidity of pH 6.0-treated protein was significantly higher?P<0.05?than that of other samples.The temperature at which the myosin heavy chain and actin band density of Sodium dodecyl sulfate-polyacrylamide gel electrophoresis?SDS-PAGE?bound to pH 6.0 without?-mercaptoethanol began to become shallow was lower than that of other pH samples.The values of D^[4,3],D^[3,2],D^[0.5]of pH 6.0 samples treated at 70?are the highest,which are 121?m,51.8?m and 104?m,respectively.Transmission electron microscopy?TEM?showed that the proteins treated by pH 6.0 formed reticular aggregates at 70?.It is known that myofibril proteins treated with pH 6.0 have good thermal aggregation behavior.Rheological analysis shows that acid treatment is beneficial to the formation of gel with good viscoelasticity.The rupture force of heat-induced gel formed by pH 6.0-treated protein at 70?90?was significantly higher?P<0.05?than that of other pH samples,which indicated that the myofibrillar protein treated by pH 6.0 had better gel properties.To sum up,the thermal aggregation behavior caused by the changes in the physical and chemical properties of pH6.0-treated proteins is conducive to the formation of gels with better gel properties.?2?Effects of heating temperature and time on thermal aggregation behavior of myofibrillar proteins from mirror carp.The physical and chemical properties,thermal aggregation behavior and gel properties of myofibrillar protein under heat treatment were analyzed.The results show that:When the heating time was constant,with the increase of heating temperature,the hydrophobicity and?-sheet structure of protein surface increased,while the solubility,sulfhydryl content and?-helix structure decreased.When the temperature was higher than 70?,the protein solubility,surface hydrophobicity and active sulfhydryl content remained stable.When the heating temperature was constant,the physical and chemical indexes of protein changed significantly?P<0.05?during0?15 min heat preservation treatment,and remained stable after 30 min.In addition,the protein turbidity increased significantly?P<0.05?with the increase of heating temperature?30?70??,and reached the maximum at 70?30 min.The rupture force of protein heat-induced gel increased significantly?P<0.05?with the increase of heating temperature?30?70??,and reached the maximum at 70?30 min?1.07 N?.In addition,the heat-induced gel rupture force of myofibrillar proteins from mirror carp treated at 80?and 90?decreased.The above results showed that the thermal aggregation behavior of myofibrillar proteins from mirror carp treated at 70?was beneficial to the formation of gel with better gel properties,and the heating time in 30 min basically satisfied the changes of protein indexes at different temperatures.?3?Effects of thermal aggregation behavior of myofibril proteins from mirror carp on its gel properties.Two-stage heating significantly improved the gel properties of myofibrillar proteins from mirror carp.Among them,the heat-induced gel was prepared by preheating at 40?15 min and then treated with 30 min at 70?.It had high rupture force?1.57 N?,water holding capacity?63.9%?,relative peak area of T₂₁?74.9%?and dense and smooth gel network structure.This showed that 40?15 min preheating had a positive effect on the formation of better network structure gel of myofibril proteins from mirror carp.The force analysis showed that hydrophobic interaction and disulfide bond were the main forces to maintain the gel structure,followed by ionic bond and hydrogen bond.To sum up,this study showed that the thermal aggregation behavior of myofibrillar proteins from mirror carp treated with pH 6.0 heated at 40?15min+70?30 min could form a better heat-induced gel.It provides theoretical guidance for the use of mirror carp in the processing of surimi products.