Chemical composition, physical properties and microstructure of pidan white as affected by different divalent and monovalent cations

Changes in chemical composition, physical property and microstructure of pidan white were monitored during pickling in the presence of different divalent (CaCl ₂, MgCl ₂) and monovalent (KCl) cations at different levels (0.2 and 0.5%) up to 3 weeks, followed by aging for another 3 weeks. Pidan prepared following the commercial process, in which 0.2% PbO ₂ or 0.2% ZnCl ₂ was incorporated, was also tested. Hardness, cohesiveness and adhesiveness of pidan white gradually increased during pickling, but these parameters decreased during aging time (P<0.05), regardless of cations used. Nevertheless, pidan white treated with 0.2% PbO ₂ retained hardness and cohesiveness but had a slight decrease in adhesiveness, when pickling/aging time increased up to week 6 (P<0.05). Transmission electron microscopic studies indicated that the aggregation of egg proteins took place in pidan white gels treated with 0.2% PbO ₂, 0.2% ZnCl ₂ or 0.2% CaCl ₂ during pickling. However, the degree of aggregation varied with cations used. PRACTICAL APPLICATIONS: Pidan has been of safety concern for the consumers due to the presence of lead, commonly used to stabilize egg white gel and render the dark brown color. The use of cations, especially divalent such as CaCl ₂ at an appropriate level, could be an alternative process to make the pidan without toxicity from heavy metal. Furthermore, it can serve as the additional source of calcium for pidan.