Effects of Salting Conditions on the Morphology and Composition of Cooked Salted Duck Eggs Yolk

In order to explore the effects of salting conditions on the morphology and composition of cooked salted duck egg yolk (SDEY), and reduce the content of hard core in the cooked SDEY, the physicochemical properties of different parts of salted egg yolk and the microstructure of raw and cooked salted egg yolk were analyzed through weighing, atomic flame absorption spectrometry, Kjeldahl method, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). The results revealed an appearance of the hard core of SDEY in the second week of the pickling process, which gradually increased with time. Specifically, the yolk hard core of the well-pickled salted duck egg accounted for 33.64%~44.80% of the total mass of the yolk and 21.47%~23.49% of the moisture content. The Na⁺ content of the hard core was 10.66~11.47 mg/g. Notably, the hard core of SDEY had lower free fat content, which was about 17.71%~27.90% compared with 34.79%~36.34% of the outer layer, while the free fat content of the hard core was positively correlated with the salt concentration of the pickling liquid. In addition, the protein content of the hard core of egg yolk increased to more than 30% after salted, which was higher than the outside. Moreover, it was found that the particle size of the yolk particles in the hard core was smaller after heating, which presented a continuous structure with smaller gaps. Thus, from the results, the order of salt penetration led to the differences in the structure and composition of different parts of salted egg yolk, which led to the differences in the hard core and the outside of the yolk after heating. Higher pickling time and salt concentration significantly aggravated the formation of the hard core. Therefore, using a concentration of 15% and pickling time for 4 week could make less hard core and better food quality. Hence, this study provides a guide to improving the quality of SDEY.