Analysis of the Causes of the "Black Circles" in the Vacuum Cooked Salted Duck Eggs
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Abstract:
In order to determine the cause of the “black circle” phenomenon in the yolk of vacuum cooked salted duck eggs, the physico-chemical analyses were carried out on the black circle parts of the eggs with black circles and the corresponding parts of the non-black circle in the yolk of vacuum-cooked salted duck eggs in. The changes in the substances related to the formation of black circle were further studied after a preliminary determination. The results showed that the protein content of the black circle in the eggs with black circles decreased, the protein electrophoresis band at the molecular mass of 36 kDa became lighter, the microstructure of the egg yolk particles was in a mess, and the change of protein altered the pH value of the black circle region from 6.20 to 7.90, causing the change of the pigment color from yellow to yellow-green; The sulfur content is evenly distributed in the yolk of the non-black circled egg, while the sulfur content of the black circle part in the black circled egg was 5.17 mg/100 g, which is higher than that of the non-colored part (2.31 mg/100 g); The color reaction of S2- with egg yolk components indicated that it only led to a color reaction with metal ion-containing phosvitin, which can make the color of normal egg yolk turn black, darkening the egg yolk color, and promoting the formation of dark circles; The contents of Fe, Zn, and Cu in the black circled egg all increased to a certain extent, and all exhibited a color reaction with S2-, although only the color resulting from the reaction between Fe and S2- was in accordance with the characteristic color of the black circle. Further studies revealed the positive correlation between the Fe content and the degree of yolk black circle. In summary, the formation of black circle was caused by the combined action of protein, Fe, S2- and pigment.
