3.8 Unsaponifiable Constituents 229Table 3.51.Odor-active C 19 -steroids
Compound Odor threshold
(mg/kg ; oil)
5 α-Androst-16-en-3-one 0. 6
5 α-Androst-16-en-3α-ol 0. 9
5 α-Androst-16-en-3β-ol 1. 2
4,16-Androstadien-3-one 7. 8
5,16-Androstadien-3β-ol 8. 9
3.8.2.2.2 VitaminD
Cholecalciferol (vitamin D 3 ) is formed by pho-
tolysis of 7-dehydrocholesterol, a precursor in
cholesterol biosynthesis. As shown in Fig. 3.42,
UV radiation opens the B-ring. The precalcif-
erol formed is then isomerized to vitamin D 3 by
a rearrangement of the double bond which is in-
fluenced by temperature. Side-products, such as
lumi- and tachisterol, have no vitamin D activ-
ity. Cholecalciferol is converted into the active
hormone, 1,25-dihydroxy-cholecalciferol, by hy-
droxylation reactions in liver and kidney.
7-Dehydrocholesterol, the largest part of which is
supplied by food intake and which accumulates
in human skin, is transformed by UV light into
vitamin D 3. The occurrence and the physiologi-
cal significance of the D vitamins are covered in
Sect. 6.2.2.
Ergosterol (ergosta-5,7,22-trien-3β-ol), which
occurs in yeast, moulds and algae, is provita-
min D 2. It can serve as an indicator for fungal
contamination. A tolerance limit of 15 mg/kg
solid has been proposed for tomato products.
Table 3.52.Average sterol composition of plant oilsa
Component Sun- Peanut Soya Cotton- Corn Olive Palm
flower seed
Cholesterol 0. 56. 20. 50. 50. 50. 50. 5
Brassicasterol 0. 50. 50. 50. 50. 50. 50. 5
Campesterol 242 278 563 276 2655 19 88
Stigmasterol 236 145 564 17 499 0. 542
β-Sitosterol 1961 1145 1317 3348 9187 732 252
5
-Avenasterol 163 253 46 85 682 78 0. 5
7
-Stigmasterol 298 0 .592 0.596 0. 551
7
-Avenasterol 99 34 63 18 102 30 0. 5
24-Methylene- 204 0 .553 0.5 425 580 0. 5
cycloartenol
aValues in mg/kg.
3.8.2.3 PlantSteroids(Phytosterols)
The sterols and stanols (hydrogenation products
of sterols) occurring in plants are known as phy-
tosterols. The best known representatives are the
desmethylsterols shown in 3.8.2.3.1.
The phytosterols are of interest from a nutritional
and physiological point of view because they
lower the concentration of cholesterol and LDL in
the blood plasma (cf. 3.5.1.2). The absorption of
cholesterol is inhibited, a significant effect being
reached with an intake of 1 g/day of phytosterol.
Since the normal dietary intake amounts to only
200–400 mg/day of phytosterol, margarines are
enriched with phytosterols. However, as the free
sterols are only poorly soluble in the fat phase,
sterol esters are used in the production of mar-
garine. Sterol esters are hydrolysed in the diges-
tive tract. The starting material for the extraction
of phytosterols is plant oils and tall oil (Swedish
“tall” = pine), which accumulates as a by-product
in the production of paper and pulp. Tall oil is
rich in phytostanols, mainlyβ-sitostanol.3.8.2.3.1 Desmethylsterols........................................
Cholesterol, long considered to be an indicator of
the presence of animal fat, also occurs in small
amounts in plants (Table 3.52). Campe-, stigma-
and sitosterol, which are predominant in the sterol
fraction of some plant oils, are structurally re-
lated to cholesterol; only the side chain on C-17 is
changed. The following structural segments (only