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

Abstract

Kuokuang Road, Taichung, Taiwan, ROC Duck eggs treated with 1.0 N HCI up to 120 min to adjust the permeability of the shell were immersed in 269~;o 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 HCI 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 HCI 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 I N HCI 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 HCI 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.Keywords: duck egg, brlning, yolk, NaCl penetration, gelation, granulation Salted duck egg, shyandan, is a traditional and popular egg product in Taiwan. It is made by brining the egg in saturated saline or by coating with red soil paste mixed with salt for 20-30 days and subsequently heating the egg (Peh et al, 1982;Lln et al, 1984;Chang & Lin, 1986). In addition to supplying for regular diet as a whole-egg type, the yolks are also utilized as stuffing material in some Chinese foods such as moon cake and glutinous rice dumpling (Chiang & Chung, 1986).Hard-cooked eggs are also used to produce salted or pickled eggs in the Occident (Angalet et al, 1976; Fischer et al, 1985). Hard-cooked egg yolk has a crumbly and mealy texture. Chicken eggs held in brines for up to 4 weeks are altered in appearance, and the yolk index of raw yolks changes only slightly in texture profile relative to that of cooked yolks (Woodward, 1988). The phenomena are qulte different from those of shyandan which are generally considered to have excellent properties with granular texture and oil-off after cooking (Peh et al, 1982;Chiang & Chung, 1986;Wang, 1992). From the standpoint ofcustomers, the granular texture should resemble that of bean filling, and the oil-off phenomenon should resemble that of caviar. However, no scientifically defined criteria are suitable to describe the quality of shyandan. In order to maintain the albumen functionalities, several research groups (Chiang & Chung, 1986;Chen et al, 1991; Wang, 1991Wang, , 1992 have tried to manufacture the salted yolks separated from eggs. Most of these salted processes were unsuccessful in obtaining shyandan yolks. Wang (1991) indicated that the formation of shyandan yolk is probably related to the diffusion speed and final concentration of NaCl.With heat (Wo...

Changes in lipid properties of duck egg yolks under extreme processing conditions

“…Thus, the increase of salt content in egg yolks gradually increased the amount of oil exudation of egg yolks with the increase of pickling time ( Lai et al, 2010 ). The reason why the CSEY had a higher oil exudation than RSEY after it was pickled for 21 to 35 days could lie in that some lipids in CSEY became free after being heated ( Lai et al, 1997 ). Because heating treatment might destroy more LDL and denature other proteins that stabilized the lipid in egg yolks ( Kaewmanee et al, 2011 ).…”

Effects of Green Tea and Chinese Tea on the Composition and Physical Properties of Pidan White

“…2004). Shell thickness of less than 0.2 mm was observed when soaking the egg in 0.1 N HCl for 30 min (Lai et al . 1997).…”

“…This reaction causes the decrease in shell thickness (Nys et al2004). Shell thickness of less than 0.2 mm was observed when soaking the egg in 0.1 N HCl for 30 min (Lai et al 1997). The pore sizes of eggshell became larger after pretreatment with acetic acid when examined under SEM (data not shown).…”

“…Acid pretreatment has been used to shorten the salting time of duck egg. The salt penetration into egg was enhanced 2–10‐fold when duck eggs were treated with 0.1 N HCl (Lai et al . 1997).…”

“…Acid pretreatment has been used to shorten the salting time of duck egg. The salt penetration into egg was enhanced 2-10-fold when duck eggs were treated with 0.1 N HCl (Lai et al 1997). However, pretreatment of egg using inorganic acid might not be acceptable for consumers, and organic acids may be a promising alternative with the safety concern.…”