2009_Book_FoodChemistry

228 3 Lipids
Table 3.49. Cholesterol content of some food
Food Amount (mg/100 g)
Calf brain 2000
Egg yolk a 1010
Pork kidney 410
Pork liver 340
Butter 215–330
Pork meat, lean 70
Beef, lean 60
Fish (Halibut;
Hypoglossus vulgaris) 50
a Egg white is devoid of cholesterol.
peroxy radicals, proceeds through the intermediary
3β-hydroxycholest-5-en-7α- and 7βhydroperoxides,
of which the 7β-epimer is more
stable because of its quasi-equatorial conformation
and, hence, is formed predominantly. Unlike
autoxidation, the photosensitized oxidation (reaction
with a singlet oxygen) of cholesterol yields
3β-hydroxycholest-6-en-5α-hydroperoxide.
Among the many derivatives obtained by the
further degradation of the hydroperoxides,
cholest-5-en-3β,7α-diol, cholest-5en-3β,7β-diol,
3β-hydroxycholest-5-en-7-one, 5,6β-epoxy-5βcholestan-3β-ol
and 5α-cholestan-3β,5,6β-triol
have been identified as major products. These
so-called “oxycholesterols” have been detected
as side components in some food items (dried
egg yolk, whole milk powder, butter oil and
heated meat). It is difficult to quantify these
oxidation products because significant losses can
occur in the clean-up of the analyte, e. g., in the
case of polar cholestantriol. In addition, artifacts
are easily formed. For this reason, quantitative
values found in the literature are frequently only
approximations.
In the animal organism, cholesterol is the starting
point for the synthesis of other steroids,
such as sex hormones and bile acids. In fact,
GC-MS analyses and radio immunoassays show
that among the sex hormones, progesterone
(I in Formula 3.102) appears most often in
animal food. It is enriched in the fat phase,
leading to relatively high concentrations in butter
(Table 3.50). Traces of this steroid also occur in
plant foods. Testosterone (II in Formula 3.102),
3,17-estradiol (III) and 17-estrone (IV) are other
sex hormones which have been identified as
Table 3.50. Progesterone in foods
Food
Progesterone
(µg/kg)
Beef, male a 0.01–5
Beef, female a 0.5–40
Pork (muscle) 1.1–1.8
Chicken 0.24
Turkey 8.18
Chicken egg 12.5–43.6
Skim milk (0.1% fat) 1.3–4.6
Whole milk (3.5% fat) 9.5–12.5
Cream (32% fat) 42–73
Butter (82% fat) 133–300
Cheese (Gouda, 29% fat) 44
Potatoes 5.1
Wheat 0.6–2.9
Corn germ oil 0.3
Safflower oil 0.7
a edible parts.
natural trace components of meat, milk and their
products.
(3.102)
Products of cholesterol metabolism include
C 19 -sterols which produce the specific smell
of boar in boar meat. Five aroma components
(Table 3.51) were identified; 5α-androst-16-en-
3α-ol (Formula 3.103) has also been detected in
truffels (cf. 17.1.2.6.1).
(3.103)