2009_Book_FoodChemistry

232 3 Lipids
Gas chromatographic-mass spectrometric
studies have also revealed the presence of 4,4-
dimethylsterols in the steroid fraction of many
plant oils:
α-Amyrine
(3.113a)
β-Amyrine
(3.113b)
Cycloartenol (3.114)
Fig. 3.43. Sterol detection according to Lieberman–
Burchard. Reactions involved in color development
Oleanolic acid has long been known as a constituent
of olive oil. Methyl- and dimethylsterols
are important in identifying fats and oils
(cf. Fig. 3.44).
3.8.2.4 Analysis
Oleanolic acid (3.115)
Lup-20(29)-en-3β-ol (Lupeol) (3.116)
Qualitative determination of sterols is conducted
using the Liebermann–Burchard reaction, in
which a mixture of glacial acetic and concentrated
sulfuric acids reacts directly with the fat
or oil or the unsaponifiable fraction. Several
modifications of this basic assay have been
developed which, depending on the steroid
and the oxidizing agent used, result in the
production of a green or red color. The reaction
is more sensitive when the SO 3 oxidizing agent
is replaced by the Fe 3+ ion. The conversion
of sterols into a chromophore is based on the