| This paper aims at studying the related basic issues about alkali induced egg white gelatinization, emphases on the change of the gel and protein structure during the formation of the gel, and provides a theoretical foundation and experimental basis for preserved egg production and development. Main research results are as follows:The preserved egg was cured in NaOH solutions of different concentrations under constant temperature of22±2℃. Sample tests were held at regular intervals to test the concentration of the feed liquid NaOH, the free alkalinity, the moisture content and texture properties of the egg white and other index. By the regression equation between the alkalinity of the egg white of the preserved egg and the number of curing days and the concentration, the free alkalinity of the contents of the preserved egg can be predicted based on the known curing concentration and number of curing days.We have studied the change rule of the rheological property of a preserved egg when processing it. During the process, the egg white of the preserved egg remained to be pseudo plastic fluid before the solidification; during the whole process, the storage modulus (G’) and the loss modulus (G") firstly decreased, then increased and then decreased, while its phase angle first increased then decreased, verifying that during the process of the formation of the preserved egg, the egg white changed through three stages: Firstly changed from sol to solution (clearing), then from solution to gel (solidification) and finally degraded from gel to solution (thinning).We also have studied the mechanism of alkali induced egg white gelatinization. During the process of curing, the water content of the egg white decreased, the alkali content increased, the alkalinity of the feed liquid decreased, the mucoprotein, conglycinin and ovotransferrin completely degraded, part of the ovomucoid and ovalbumin degraded, the free amino acid increased by5times more than that of fresh egg white, and each group of egg white contains18kinds of amino acid, including8essential amino acid. In the egg white cured in different alkali liquor, the content of the essential amino acid valine, isoleucine, leucine, phenylalanine, lysine and the arginine of the semi-essential amino acid increased greatly, while the y-aminobutyric acid, ornithine and tryptophan in the egg white and other free amino acid degraded. During the process of curing, the intensity of the hydrophobic interaction increased as the alkali concentration and curing time increased, and the bimolecular structure changed significantly, where before the gel formed, the percentage of the a-helix decreased, and the percentage of the β-pleated sheet increased, illustrating that the α-helix changed into β-pleated sheet, the proportion of the P-pleated sheet increased and the ordering of the molecular geometry of the protein decreased, and after the gel formed, the content of the disulfide bond increased, the content of the a-helix and β-pleated sheet increased, the random coil structure disappeared and the ordering of the molecular geometry of the protein increased. During the process of the formation of the alkali induced egg white gel, the ionic bond and hydrogen bond decreased significantly and the hydrophobic interaction increased significantly.We explored the state of aggregation of the egg white under different pH, the influence of the egg white protein pH on the egg white protein denaturation aggregation, and the formation mechanism of different egg white gels in terms of the property of denaturation and aggregation and others. We found that when the pH was9-12, the solubility of the egg white protein soared rapidly, and the absorbance increased when it was320nm, showing that with the influence of the alkali, the egg white protein expanded to have higher solubility and exposed part of the hydrophobic group, as a result, the absorbance increased, becoming solution. When the pH was12.5, the viscoelasticy was relatively strong, the egg white quickly changed into gel, and thus the solubility decreased to the utmost. When the pH was13, with the strong alkali influence, the network structure of the egg white gel was destructed, as a result, the gel turned into solution, showing good solubility.We have discussed the influence of different concentration of curing alkali liquor on the quality of duck egg shell. Through electron microscopy observation, we found that there was no air hole on the surface of the shell of fresh duck eggs. However, the compact layer on the surface of the shell of cured duck egg gradually disappeared and air holes with a diameter of10μm～40μm occurred. The egg shell holes of duck egg cured in alkali liquor of different concentrations could be seen after10d. From the egg shell holes on the surface of the egg, the deposit sediment was observed gradually blocking the holes. Compared with fresh egg, the number of air holes on the shell of the eggs cured in alkali liquor of different concentrations significantly increased (P<0.05), and compared with the eggs having been cured for10～15d, the number of air holes on the shell of the eggs having been cured in alkali liquor of different concentrations for20～30decreased significantly. During the curing, the alkali acted on the surface of the egg shell, destructing the outer membrane of the protein on the egg shell, as a result, the intensity of the egg shell decreased. In the early stage of curing, the alkali destructed the surface of the egg shell and exposed the air holes, therefore, the number of the detected air holes increased. In later stage, as the metal salt ion formed into various precipitate which deposited in and blocked the air holes, therefore, the number of detected air holes decreased. |
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