Quantification of oxysterols in Dutch foods: egg products and mixed diets.

A sensitive and specific method is described for quantifying various cholesterol oxidation products in foodstuffs, including 7 beta-hydroxycholesterol, cholesterol-alpha-epoxide, cholestane-triol, 7-ketocholesterol and 25-hydroxycholesterol. A chloroform-methanol extract of the food was fractionated over two successive silica columns. Two fractions containing different classes of oxysterols were then analyzed as trimethylsilyl derivatives by capillary gas liquid chromatography, using on-column injection and a temperature gradient from 70 to 200 degrees C. The detection limit was about 0.5 microgram/g dry weight for egg yolk powder. Fresh egg yolk contained only 1.2 micrograms/g of total oxides per g dry weight, showing that artifactual oxidation during the procedure was minimal. Recovery of 5 pure oxysterols added to egg yolk at levels of 6.5 and 10 micrograms/g was between 93 and 102%. In commercial egg yolk and whole egg powder stored for one year, total amounts of oxysterols ranging from 21 to 137 micrograms/g dry weight were found. In duplicates of mixed Dutch diets, total amounts ranged from 3.6 to 6.2 micrograms/g dry weight. Duplicates containing mostly fried and baked foods did not have higher levels than duplicates in which foods had been prepared by boiling or left raw. We conclude that a normal mixed diet provides only minor amounts of cholesterol oxidation products.