| Dynamic high-pressure processing is considered as one of the most potential and promising physical modification technologies in the latest food processing and preservation development. In the process of dynamic ultra-high pressure micro-fluidization, materials received strong shear, high-speed collision, intensive shake, the instant release of the pressure force and so on, which may lead to the changes in the structures of large molecules, especially in protein. In view of this fact that there are few researches on the application of ultra-high pressure micro-fluidization in the modification of protein, and that the in-depth studies on the functional property changes are still lacking both at home and abroad, this paper focuses on the changes in the functional properties of the soy protein isolate, peanut protein and egg white protein after ultra-high pressure micro-fluidization treatment, preliminary discussing the mechanism of the modification technology of the micro-fluidization in protein and the safety evaluation of the modified products. This paper offers a new approach to the protein modification as well as a new method on the application of dynamic ultra-high pressure micro-fluidization. The experimental results of this paper are summarized showed as follows:1. Mean particle size is greatly changed by dynamic ultra-high pressure micro-fluidization: the mean particle size of the soy protein isolate, peanut protein, and egg white protein significantly decreases after the dynamic ultra-high pressure micro-fluidization treatment. The mean particle size of the soy protein isolate reaches the minimum of 167.2nm at 140MPa; the peanut protein reaches the minimum of 281.8nm at 140MPa; while egg white protein reaches the minimum of 229.0nm at 160MPa.2. Functional groups are changed by dynamic ultra-high pressure micro-fluidization with the results showed as follows: the -SH content of soy protein isolate increases with the pressure, then decreases at 100MPa, and then rises continuously up to 160MPa; after treatment by dynamic ultra-high pressure micro-fluidization, the -SH content in peanut protein decreases with the pressure; while the -SH content in egg white protein decreases with the pressure at first, then increases at 120MPa and continuously rises up to 160Mpa. The content of surface hydrophobicity group of soy protein isolate and egg white protein reaches the maximum at 100MPa; for peanut protein it increases with the pressure; the UV absorbing intensity of soy protein isolate and egg white protein reach the maximum at 80Mpa, and their DSC's curve peak moves rightward.3. The following is the changes of functional properties of the protein in different concentration after dynamic ultra-high pressure micro-fluidization treatment: the changes of soy protein isolate and peanut protein are similar. The solubility of the lower concentration ones increase significantly, the emulsifying properties of the higher concentration (4%,6%,8%) proteins after micro-fluidization by dynamic ultra-high pressure decrease, the foaming capability of soy protein isolate with higher concentration is better than that with lower concentration and the viscosity of soy protein isolate increases with the concentration; the solubility of egg white protein increases with the concentration, the emulsifying properties of 2% and 4% egg white protein increase, while those of 6% and 8% egg white protein decrease, the foaming capability of 6% and 8% egg white protein are better than that of 4% and the flow pattern of different concentration egg white protein are different.4. The changes in the functional properties of the protein in different temperatures after treatment are listed as follows: lower temperature (20℃) is helpful to the improvement of the solubility of soy protein isolate, but temperature makes little impact on other functional properties; the temperature effect on peanut protein is small; temperature (20℃,30℃,40℃) causes the changes in the flow pattern of the egg white protein, but leaves little changes in other functional properties.5. The effect of pressure on the changes in the functional properties of the protein are indicated as follows: the solubility, foaming capability, gel property and rheological property of soy protein isolate and peanut protein have been improved; the solubility of egg white protein changes little with the pressure but the foaming capability, gel property, and rheological property have been improved.6. The changes in the functional properties of the protein after treatment by different micro-fluidization passes are showed as follows: the solubility, emulsifying property, and emulsifying stability of soy protein isolate decrease, while there is a little improvement in its foaming capability, but it gains a better foaming stability, as the number of pass increases. Meantime, it gains a better rheological property. There are little changes in the solubility, emulsifying property and emulsifying stability, foaming capability and foaming stability of the peanut protein, but it gains a better rheological property. As to egg white protein, the solubility increases, emulsifying property and emulsifying stability decreases, the foaming capability improves a little but its rheological property is changed and its flow pattern is also changed (how).7. The changes in the secondary structure of protein by micro-fluidization are shown as follows: The results of Circular Dichroism (CD) spectroscopy shows that dynamic ultra-high pressure micro-fluidization has a great influence on 7S globulin of soy protein isolate, theα-helix ratio of 7S globulin increases by normal homogenization, whileβ-sheet ratio decreases. There are no significant changes in the structure of 11S globulin. The results of infrared reflectance spectroscopy show that the peak of N-H stretching vibration moves to the low wave number, which confirms that dynamic ultra-high pressure micro-fluidization causes changes in the hydrogen bond of soy protein isolate; and the absorption peak of amide group shows thatβ-sheet decreases, indicating different micro-fluidization pressures make different impacts on the secondary structure of protein.8. The following summarizes the studies on the mechanism of the dynamic ultra-high pressure micro-fluidization treatment on the functional properties of soy protein isolate: the improvement of solubility is made possibly because the dynamic ultra-high pressure micro-fluidization makes globate soy protein isolate disaggregate and extend gradually, and makes the hydration of protein increase. The infuence on emulsifying property may be because homogenization destroys the hydrophobic interaction inside protein, producing and exposing more hydrophobic regions, increasing the contents of the super-hydrophobic characteristics. Thus the emulsifying property increases. However, when the pressure rises above 100MPa, protein molecular aggregates and hydrophobic characteristic decreases, which causes the decrease of emulsifying property. The improvement in foaming capability is partly because the solubility of soy protein isolate increases and discloses more hydrophobic region. The rheological property changes possibly because the weak binding bond is ruptured by dynamic ultra-high pressure micro-fluidization which aggregates originally, and because the protein aggregation is disassociated, friction resistance decreases, shear thinning phenomena appears and the fluid behaves closer to the Newtonian fluid. The improvement of gel property might result from the significant decrease of mean particle size of soy protein isolate, hydrophobic groups expose and protein conformation changes, which help to form the gel network. The improvement of filming ability is partly because homogenization makes more hydrophobic bond unfolded, the bonding sites of the protein molecular increases and interaction increases.9. The preliminary safety evaluation results of the proteins after homogenization by dynamic ultra-high pressure micro- fluidization are showed as follows: soy protein isolate, peanut protein, and egg white protein have little influence on the growth of mouse and no adverse effects were found.
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