Formation mechanism and inhibition of black spots on eggshell membranes during high-temperature pickling of duck eggs

This research provides a comprehensive analysis of black spot formation on eggshell membranes (ESM) during high-temperature pickling of duck eggs, focusing on chemical composition, formation mechanisms, and preventive strategies. Metal sulfides are identified as the primary component of black spots through Propidium iodide (PI), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Inductively coupled plasma mass spectrometry (ICP-MS) analysis reveales that during pickling, metal ions migrate from the yolk to the ESM, where they are intercepted by its dense microstructure. Treatment with 0.1 % Ethylenediaminetetraacetic acid disodium (EDTA-2Na) achieves a black spot inhibition rate exceeding 95 %, increases the whiteness value of the egg white by 7.82 %, while maintains the mechanical strength and thickness of the eggshell. These findings offer molecular-level insights into the formation mechanism of black spots and provide practical solutions for optimizing the high-temperature pickling process, thereby improving the quality of salted duck eggs.