Food Lipids: Chemistry, Nutrition, and Biotechnology

Figure 4 Examples of vitamin D 3 analogs.
228 nm, and a molar extinction coefficient of 18,200. Since they possess intense
ultraviolet absorption, they are labile to light-induced isomerization. In addition, the
triene system is easily protonated, resulting in isomerization that produces isotachysterol,
which is essentially devoid of biological activity. The lability of the triene
structure has markedly limited the chemical approaches to modification of this molecule.
There is a great deal of chemistry relating to the chemical properties and
syntheses of vitamin D compounds. The detailed chemistry and chemical synthesis
of the D vitamins are beyond the scope of this chapter, and interested readers are
referred to reviews in this important area [52,53].
F. Analysis of Sterols
1. Extraction of Sterols
To analyze the sterols in specific biological tissues, sterols are first extracted from
these tissues with organic solvents. The choice of an extraction technique is often
determined by the nature of the source and the amount of information the investigator
chooses to obtain concerning the forms of sterols present as free, glycosylated, and/
or esterified through the 3-hydroxy group. Different extraction procedures may vary
dramatically depending on the extraction efficiency required for different classes of
sterols [54,55]. Irrespective of the nature of the source, one of four methods of
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