Identification and quantification of cholesterol oxides in grated cheese and bleached butteroil

Butteroil samples bleached with benzoyl peroxide (BP) and 17 commercial cheeses were screened for oxidized sterols by thin layer chromatography (TLC). Ungrated cheeses made from bleached milk and freshly bleached butteroil contained no detectable oxidized sterols. Oxidized sterols were detected in stored, bleached butteroils and in grated cheeses. Four major oxidation products were the isomeric 5,6-epoxycholesterols and the epimeric 7-hydroxycholesterols identified by TLC, high performance liquid chromatography (HPLC) and mass spectrometry (MS). Additional sterol oxides (tentatively identified and not quantified) present in these samples included low levels of 7-ketocholesterol and cholesta-3,5-dien-7-one. The epimeric 7-hydroxycholesterols were detected in bleached butteroils stored in air (BP-A) and nitrogen (BP-N) for 22 days at 15 C. Butteroil, after 90 days of storage at 15 C, had 30 (BP-N) and 60 (BP-A) µg total oxides/g of bleached oil and, after 1-year at ?20 C, had 70 (BP-N) and 180 (BP-A) µg/g butteroil. A grated, unbleached cheese packaged in clear glass contained the most oxidized sterols (44 µg/g). Sterol oxides were not detected in bleached cream using a simulated industrial process.