Calcium chloride-mediated regulation of shell-surface transport behavior, alkali diffusion, and gel stability in duck eggs during alkaline pickling.

Preserved eggs are produced by alkaline pickling, during which uncontrolled hydroxide diffusion can cause excessive egg-white liquefaction. Calcium chloride was evaluated as a modulator of alkali diffusion and gel stability during pickling. Eggs were pickled in 4% NaOH containing 0-0.8% CaCl2 or 0.2% CuSO4 for six weeks at 25 °C. Eggshell surface morphology, internal alkalinity, moisture redistribution, protein cross-linking, and gel structure were examined. At the 0.2% CaCl2 treatment, regulated hydroxide diffusion promoted controlled protein unfolding, more balanced thiol-disulfide transition, and cohesive egg-white gel formation, producing mechanical properties comparable to those obtained using CuSO4. In contrast, higher CaCl2 levels (≥0.6%) reduced effective alkalinity, delayed protein transformation, and produced weak, heterogeneous gels. Overall, divalent cation concentration was associated with coordinated diffusion-related and structural changes during alkaline pickling, and the 0.2% CaCl2 treatment provided a food-grade strategy for stabilizing egg-white gel structure while reducing reliance on heavy-metal salts.