Effect of NaCl Penetration Rate on the Granulation and Oil-Off of the Yolk of Salted Duck Egg

Duck eggs treated with 1.0 N HCl up to 120 min to adjust the permeability of the shell were immersed in 26% NaCl (0-40 days) and subsequently heated at 85°C for 90 min to obtain the salted eggs in order to investigate the effect of NaCl on the granulation and oil-off of the yolk formed. During brining, the NaCl contents of the yolk and albumen were increased 2-10 fold due to HCl treatment of the shell. The oil-off ratio, defined as the ratio of the free lipid to the lipid content of the yolk, was also affected by the penetration rate and brining time. Eggs treated with 1.0 N HCl for 120 min showed reduced time required to achieve the maximum lipid content and oil-off ratio and had a lower maximum value of oil-off ratio than eggs treated with 1 N HCl for 0-80 min. The yolk of HCl-treated (1.0 N, 80 min) egg changed in appearance mealy form to be granulous at 5-10 days and to a soft gel at 15-20 days after brining. In comparison, the eggs without HCl treatment respectively required 20-25 and 40 days for these changes. This study suggests that sustained brining may result in the formation of a gel-state yolk, and the NaCl penetration rate affects only the time for the change in forms.