Changes in yolk states of duck egg during long-term brining.

To elucidate the relationship between shyandan yolk formation and NaCl penetration degree, fresh duck eggs were brined in 26% NaCl and a prolonged brining test was conducted for up to 24 weeks. Shyandan yolk was obtained from brine-cured duck shell eggs in 26% NaCl for 4-6 weeks and subsequently heated at 85 degrees C for 90 min. Though NaCl contents for albumen and yolk increased to 14.8 and 8.9%, respectively, during the prolonged test for up to 24 weeks, the R values (NaCl/water x 100) were similar (increased from 0.6 to 21) throughout the brining process. The oil-off ratio of the yolk increased rapidly from 14 to 50% (0-6 weeks) and gradually decreased during the extended brining. Granulation and gelation of yolk appeared in the different stages of the brining process. This study demonstrates that the formation of shyandan yolk was determined by the degree of NaCl penetration.