Lipid Profile and Oxidative Stability of Commercial Egg Products
LI-YUN LIU1, MING-HUA YANG2, JEN-HORNG LIN1 AND MIN-HSIUNG LEE3*
1.Graduate Institute of Food and Nutrition, Shih-Chien University, 70 Ta-Chih St., Taipei City 104, Taiwan, R.O.C.
2. Department of Food and Nutrition, Hung-Kuang University, 34 Chung-Chi Rd., Shalu Township, Taichung County 433, Taiwan, R.O.C.
3. Graduate Institute of Agricultural Chemistry, National Taiwan University, 1, Sec. 4, Roosevelt Rd., Taipei City 106, Taiwan, R.O.C.
(Received: May 6, 2004; Accepted: December 15, 2004)
ABSTRACT
This work was conducted to investigate the quality of lipids in various commercial egg products. Lipids of egg yolk were extracted from fresh egg, Pidan (preserved egg), tea egg, simmered egg, iron egg (deeply simmered and dried egg) and salted egg by Folch reagent, a mixture of chloroform and methanol at 2:1 volume ratio. The extracts and commercial yolk oil were analyzed to determine lipid profile, fatty acid composition, thiobarbituric acid value (TBA value), acid value and peroxide value. Results showed that the quality of yolk lipids was quite different. The lipid content ranged from 27% for Pidan to 46% for iron egg. Phospholipid content was highest in fresh egg (about 351 mg/g oil), while lowest in Pidan (about 175 mg/g oil). Cholesterol content of fresh egg yolk oil was the highest, about 38 mg/g oil, while the Pidan yolk oil contained the least cholesterol (28.51 mg/g oil). On the other hand, fatty acid compositions of all yolk lipids were consistent. Oleic, palmitic and linoleic acids were the three most abundant fatty acids. Acid and TBA values of lipids in processed eggs were generally higher than those in fresh eggs. Commercial yolk oil products also showed significant differences in lipid profile and fatty acid composition. The ranges of triglyceride, cholesterol and phospholipid contents were 59-95%, 0.9-18% and 1.8-33%, respectively. The yolk oils with higher liquid characteristic showed lower content of phospholipid and higher triglyceride content. Meanwhile, the yolk oil products with higher phospholipid content contained more 18:0, 20:4 and 22:6 fatty acids and less 16:1 and 18:1 fatty acids. Peroxide value was not detectable in all egg yolk extracts and yolk oils.
Key words: yolk oils, phospholipids, cholesterol, fatty acid composition, acid value, TBA value