The oxidation of cholesterol in the yolk of selective traditional Chinese egg products.

The yolks of traditional chicken egg products (Tiedan, Ludan, and Chayedan) and duck egg products (raw and cooked Xiandan, immersed and coated Pidan) were subjected to moisture, lipid, and thiobarbituric acid (TBA) determinations as well as cholesterol and cholesterol oxidation products (COP) analysis. The main COP detected for these egg products included 20-hydroxycholesterol and 7beta-hydroxycholesterol, other types of COP were not detected. The contents of COP formed in traditional egg products varied, depending upon the types of egg products. The cholesterol oxidation ratio for traditional Chinese chicken egg products ranged from 1.14 to 1.75%, whereas that for traditional Chinese duck egg products ranged from 1.18 to 1.90%. Those traditional egg products that required pickling in salt or alkaline, cooking, hot air drying, and exposure to oxygen and heat all produced COP.