Abstract: This study was conceived in order to clarify the effect of the freshness of raw eggs on the gel quality and the ultrastructure of eggshell membrane during the curing of preserved eggs. Duck eggs with different freshness were used to make preserved eggs in the same way. The ultrastructure of eggshell membrane was observed by scanning electron microscopy (SEM), and Image J software was used to process the image data to obtain eggshell membrane status. Besides, eggshell membrane porosity, and gel pH, water content, hardness and elasticity were measured and the correlation between them was analyzed. The results showed that during the curing process, the pH of preserved egg white decreased first, then slowly increased, and finally decreased sharply; the hardness and elasticity of preserved egg gels showed a fluctuating trend. The lower the freshness of raw eggs, the higher the porosity of eggshell membrane, and the shorter the curing cycle of preserved eggs. The porosity of eggshell membrane had a significantly negative correlation with the freshness of raw eggs (P < 0.01), and a significantly positive correlation with gel hardness (P < 0.01) and elasticity (P < 0.05). As a result, a decrease in the freshness of raw eggs could affect eggshell membrane as the permeation channel for the brine, which could in turn lead to variability in the quality of preserved eggs. Moreover, the yield of preserved eggs decreased with a decrease in the freshness of raw eggs. Therefore, the freshness of raw eggs is closely related to the quality of preserved eggs. This study provides a new idea for controlling the quality change of preserved eggs during the pickling process.

Key words: preserved eggs; gel quality; eggshell membrane; ultrastructure; freshness