Physical properties and microstructure of pidan yolk as affected by different divalent and monovalent cations

Changes in physical property and microstructure of pidan yolk were monitored during pickling in the presence of different divalent (CaCl2, MgCl2) and monovalent (KCl) cations at different levels (2 and 5 g kg−1) up to 3 weeks, followed by ageing for another 3 weeks. Pidan prepared following the commercial process, in which PbO2 or ZnCl2 at a level of 2 g kg−1 was incorporated, was also tested. Hardness, hardening ratio, NaCl content and pH of yolk gradually increased, whereas moisture content, cohesiveness and adhesiveness decreased as the pickling/ageing time increased up to 6 weeks, regardless of cations used. During pickling/ageing, L* and b* values of interior yolk and a* of exterior yolk decreased, while L* and b* values of exterior yolk and a* value of interior yolk increased (P < 0.05). Yolk of pidan treated with PbO2 at a level of 2 g kg−1 was semisolid with lower hardening ratio, hardness, cohesiveness and adhesiveness, compared with those from other treatments. Those treated with ZnCl2 or CaCl2 at a level of 2 g kg−1 yielded higher hardening ratio, hardness and cohesiveness but lower adhesiveness than others. Confocal laser scanning microscope indicated that the greater dehydration and release of lipids took place in pidan yolk during pickling/ageing of 6 weeks.