Abstract
The purpose of this study was to investigate the effects of temperature, oxidation time, presence of water, pH, type of buffer and form of substrate used on cholesterol oxidation. Microcrystalline cholesterol films, both solid and melted, and aqueous suspensions of film fragments were used as substrates. Use of dispersing agents was avoided. Quantitative analysis of the unaltered substrate and the products of its autoxidation was carried out by gas chromatography over the course of oxidation. Solid cholesterol films were found to be resistant to autoxidation in the dry state. However, when heated at 125°C, a sudden increase in oxidation rate occurred at a point coinciding with the visible melting followed by a plateau of the oxidation rate. All of the autoxidation products formed underwent further decomposition. Film fragments of cholesterol oxidized at a faster rate in aqueous suspensions than when oxidized in the dry state. In aqueous suspensions, the differences in the resistance of cholesterol to oxidation were not significant within the pH range 6.0–7.4, except for the early stages of oxidation. The 7-ketocholesterol/7-hydroxycholesterol ratio dropped significantly with increasing pH. However, at all pH levels tested, this ratio remained relatively constant during the 6 h of heating. While the 7β-hydroxycholesterol/7α-hydroxycholesterol ratio was not affected by pH in the range of 6.0–7.4, at pH 7.4 a high preference was observed for the cholesterol β-epoxide over its α-isomer. The β/α-epoxide ratio decreased with time of heating and with decreasing pH. The data show that the physical state of the substrate exerts a major influence on the oxidative behavior of cholesterol.
Similar content being viewed by others
Abbreviations
- BSTFA:
-
N,O-bis(trimethylsilyl)trifluoracetamide
- GC:
-
gas chromatography
- HPLC:
-
high-performance liquid chromatography
- TEA:
-
triethanolamine
- TMCS:
-
trimethylchlorosilane
- Tris:
-
tris(hydroxymethyl)aminoethane
References
Smith, L. (1981)Cholesterol Autoxidation, pp. 125–458, Plenum Press, New York.
Smith, L.L. (1987)Chem. Phys. Lipids 44, 87–125.
Maerker, G. (1987)J. Am. Oil Chem. Soc. 64, 388–392.
Maerker, G., and Bunick, F.J. (1986)J. Am. Oil Chem. Soc. 63, 771–776.
Kimura, M., **, Y., and Sawaya, T. (1979)Chem. Pharm. Bull. 27, 710–714.
Teng, J.I., Kulig, M.J., Smith, L.L., Kan, G., and van Lier, J.E. (1973)J. Org. Chem. 38, 119–123.
Smith, L.L., Matthews, W.S., Price, J.C., Bachmann, R.C., and Reynolds, B. (1967)J. Chromatog. 27, 187–205.
Kimura, M., Kawata, M., and Sawaya, T. (1976)Chem. Pharm. Bull. 24, 258–2261.
Zulak, I.M., and Maerker, G. (1989)J. Am. Oil Chem. Soc. 66, 1499–1503.
Nawar, W.W., Kim, S.K., and Vajdi, M. (1991)J. Am. Oil Chem. Soc. 68, 496–498.
Mosbach, E.J., Nierenberg, M., and Kendall, F.E. (1953)J. Am. Chem. Soc. 75, 2358–2360.
Sevanian, A., and McLeod, L.L. (1987)Lipids 22, 627–636.
Gumulka, J., St. Pyrek, J., and Smith, L.L. (1982)Lipids 17, 197–203.
Smith, L.L., Kulig, M.J., Miller, D., and Ansari, G.A.S. (1978)J. Am. Chem. Soc. 100, 6206–6210.
Weiner, N.D., Noomnont, P., and Felmeister, A. (1972)J. Lipid Res. 13, 253–255.
Maerker, G., and Unruh, Jr., J. (1986)J. Am. Oil Chem. Soc. 63, 767–771.
Chicoye, E., Powrie, W.D., and Fennema, O. (1968)J. Food Sci. 33, 581–587.
Park, S.W., and Addis, P.B. (1985)J. Food Sci. 50, 1437–1441, 1444.
Tsai, L.S., and Smith, L.L. (1971)Lipids 6, 196–202.
Author information
Authors and Affiliations
About this article
Cite this article
Kim, S.K., Nawar, W.W. Parameters influencing cholesterol oxidation. Lipids 28, 917–922 (1993). https://doi.org/10.1007/BF02537501
Received:
Revised:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF02537501