Study On The Relationship Of The Structure And Heat-Induced Gelation Of Pork Myofibrillar Proteins Based On Different PH

Myofibrillar proteins are a group of meat proteins mainly including myosin, actomyosin which have the capacity of gelation. The heat-induced gelation is very important to the texture, water holding capacity(WHC) and other characters of meat products. At present, there are already many studies on the gelation, while not so many on the structure and the relationship between the structure and the gelation characters. THis study took the pork as material, exacted the myofibrillar proteins, and took the pH as the factor,studied the changing of the secondary structure during the heating,tested the denaturing temperature, rheological character and turbidity and so on, meanwhile, also tested the functional characters of the heat-induced gel like the gel strength,WHC and so on to provide thero for better meat products. The results of the study on the relationship between the structure and gelation stated as follows:1The effect of heating and pH on the structure of pork myofibrillar proteinsThe structure of pork myofibrillar proteins at different pH(5.0,5.5,6.0,6.5,7.0)during heating and after heating were tested by circular dichrosim spectra(CD) and raman spectra, the result showed that during the heating,the secondary structure of the proteins at different pH changed as the α-helix turn into reduced and the β-sheet increased, which means that heating made the α-helix turn into the β-sheet structures; from the test of the tertiary structure of proteins,it can be found that during the heating,the hydrophobic environment of the tryptophan residues at pH5.0changed first increase then decrease,the hydrophobic environment of the tyrosine residues changed first decrease then increase, while the hydrophobic environment of the tryptophan and tyrosine residues at other pH changed first increase then decrease then incraese. Comparing the effect of pH on the proteins’ secondary structure at the state of solution and gel after heating,it can be found that the α-helix was less and β-sheet structures more when the proteins were near the PI(about5.0to5.2) which means the acid can cause the α-helix turen into β-sheet structures;at te gel state,the effect of pH on the hydrophobic environment showed that from the pH5.0to7.0, the hydrophobicity of the aromatic acids low at the ph neat PI. 2The relationship of the DSC,rheology and some physiochemical characters of pork myofibrillar proteins and their structures at different pHThe heat stability,rheological character and some physiochemical characters of the myofibrillar proteins at different pH(5.0,5.5,6.0,6.5,7.0)were tested by differential scanning calorimetric(DSC),rheological machine and colorimetry,the result showed that when the pH went away from the PI(about5.0to5.2),the first denaturing temperature of the most useful component for the gelation myosin became high,which means the heat stability became high. During the heating,the solubility of proteins reduced and the turbidity increased. As the pH stayed away from the PI,the solubility increased and the turbidity reduced. As been heated,the decrease of the solubility and increase of the turbidity went with the changing of the α-helix to β-sheet,lower pH decreased the stability of the α-helix structure of the proteins,made them aggregated earlier,lowered the solubility and increased the turbidity.3The relationship of the structure of myofibrillar proteins and the functionalities of their heat-induced gelation at differen pHThe gel strength, water holding capacity (WHC),microstructure and the state of water (T2relaxation) of myofibrillar proteins at different pH(5.0,5.5,6.0,6.5,7.0)were tested by Texture analysis, scanning electron microscope (SEM), centrifugation and nuclear magnetic resonance (NMR),the results showed when the pH increased,the WHC of the heat-induced gel increased,while the gel strength and the hardness increased and decreased, reaching the highest at pH6.0. The result of NMR showed,the T21and T22increased as the pH became high, means the mobility of the water between the gel’s struncture increased,T22represented the most useful water for the WHC, the decrease of this part means the increase of the dissociation water. The result of SEM showed that the gel had polymer when neat PI, and the structure was unordered, coarse, while ordered, even when the proteins were away from the PI.The α-helix structure had positive correlation of the WHC,while no evident correlation with the gel strength which had evident positive correlation with the hydrophobic environment of the aromatic acids.As stated before,heating caused the α-helix of myofibrillar proteins turn into β-sheet, and made the solubility decreased and the turbidity increased; lower the pH to the PI,the stability of the structure of the proteins decreased,moer α-helix turned into β-sheet,the solubility and WHC decreased and turbidity increased; the gel strength had notable positive relationship between the hydrophabicity of the aromatic acids. So there is tightly relationship between the secondary and tertiary structure of the myofibrillar and its heat-induced gelaion.