Cholesterol oxidation derivatives display a wide range of undesirable biological properties, and their presence in foodstuffs has raised much concern and attention. We have developed a method allowing quick, simple, and reliable quantification of cholesterol oxidative degradation in food. After lipid extraction and mild saponification, the unsaponifiable fractions from food samples are deposited on thin-layer chromatography plates and developed in hexane-ether (70:30); cholesterol oxides, migrating in a single band, are resolved from cholesterol, and both areas are scraped and analyzed as trimethylsilyl derivatives by capillary gas chromatography. 19-Hydroxycholesterol and cholestanol are used as internal standards for the quantification of cholesterol oxides and of cholesterol, respectively. We have shown that moderate heating of butter leads to the formation of cholesterol oxides, in amounts increasing with temperature, length of heating, and storage times. Cholesterol oxides are also present in commercial egg powder, egg mixes, and butter cookies or cakes. This method is a useful tool in assessing the quantitative importance of cholesterol oxides in the human diet and their formation during food processing or storing.Cholesterol can easily undergo oxidation in air, and the many substances derived from this oxidation, the so-called cholesterol oxides or oxysterols, have recently received much attention in view of their biological activities (Smith, 1981). Some cholesterol oxides display angiotoxic properties both in vivo and in vitro (Imai et al., 1976;Jacobson et al., 1985;Matthias et al., 1987) or act as mutagenic or carcinogenic compounds (Sevanian and Peterson, 1986;Raaphorst et al., 1987). Their presence in processed food has attracted much concern since cholesterol oxides have been detected in several food ingredients such as egg powder, milk powder, or heated tallow (Nourooz-Zadeh and Appelqvist, 1988; Park and Addis, 1986), and they are readily absorbed and incorporated into circulating lipoproteins (Peng et al., 1987). Thus, it is important to assess the daily ingestion of oxysterols from the diet. However, progress in this field has been hampered by difficulties associated with the isolation and analysis of these compounds. Gas-liquid chromatography (GLC) has been used in several studies (Park and Addis, 1985; Nourooz-Zadeh and Appelqvist, 1987; de Bovenkamp et al., 1988), but complete resolution of major cholesterol oxides is not always achieved; highperformance liquid chromatography methods have been developed (Csiky, 1982;Kou and Holmes, 1985;Sugino et al., 1986), but oxysterols are poorly detected by UV spectrometry. Moreover, because of their low concentrations in lipid extracts from food samples rich in cholesterol, it is necessary to separate the oxysterols from cholesterol to facilitate proper quantification: the isolation and concentration steps are long and tedious procedures that generally include several steps of liquid chromatography (Csiky, 1982; Higley et al, 1986; van de Bovenkamp et a...

The effect of cooking time and method and freezer storage on the oxidation of cholesterol in muscle food such as beef, veal, and pork was studied by capillary gas chromatography. Cholesterol was oxidized in meat samples during household cooking, and the rate of oxidation differed according to the cooking time and cooking temperature. The range of total amount of oxysterols produced varied from 0.3 to 0.8 % cholesterol. There was a greater increase in primary oxysterols (oxidized on carbon 7 or side chain) than in secondary derivatives (cholesterol epoxides and cholestanetriol) during cooking of fresh meat. All oxidized derivatives increased progressively in meat samples stored for 3 months at -20 °C in both raw and cooked meat. The sum of oxysterols doubled in the commercially available precooked frozen meals after 3 months at -20 °C with the secondary oxysterols showing the highest increase. We may assume from our observations that the daily dietary intake of oxysterols derived from meat source must probably include between 0.5 and 1% total cholesterol.

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