Page 81 - Natural Antioxidants, Applications in Foods of Animal Origin

60 Natural Antioxidants: Applications in Foods of Animal Origin
VetBooks.ir 2.10 PHYTOSTEROLS

PS are steroid alcohols and resemble cholesterol in structure, the predomi-
nant sterol found in animals both in their biological function and chemical
structure. PS are fat-soluble nutrients and are biosynthetically derived from
squalene and belong to the group of triterpenes. They are made of tetracy-
clic cyclopentaphenanthrene ring and long flexible side chain at the C-17
carbon atom (Clifton, 2002; Moreau et al., 2002). The 3-hydroxyl group of
free sterols may be esterified by a fatty acid or a phenolic acid or β-linked
to a carbohydrate. Plant sterols are primarily present in plasma membrane,
the mitochondria, and endoplasmic reticulum, and to a large extent deter-
mine the properties of the membranes (Jonker et al., 1985). Plant sterols are
white powder and solid at room temperature and the melting point of sitos-
terol, campesterol, and stigmasterol are 140 °C, 157–158 °C, and 170 °C
(Nes, 1987). Plant sterols are divided into three different kinds based on
structures namely, 4-desmethyl sterols, 4-methyl sterols, and 4,4-dimethyl
sterols. The 4-desmethyl sterols family includes three different kinds of PS
which accounts for most of the total PS mass. They are β-sitosterol (include
an extra methyl group at C-24 position), campesterol (includes an additional
ethyl group at C-24 poisition), and stigmasterol (includes an additional
ethyl group at C-24 position and a double bond at C-22 position). All these
PS account for about 65, 30, and 3% of the total dietary PS intake (Weihr-
auch & Gardner, 1978; Moreau et al., 2002; Ostlund, 2002). The chemical
difference among 4-desmethyl sterols resides in number of carbon atoms in
carbon-17 branch chain and in presence or absence of a double bond at posi-
tion 22. The 4-methyl sterols and 4,4-dimethyl sterols are minor components
in plant sources. PS are structurally similar to cholesterol (steroid nucleus
and a hydroxyl group at C-3 position) and are differentiated by their degree
of saturation and side chain configuration at C-24 position (Clifton, 2002;
Moreau et al., 2002). Analysis of sterols provides a powerful tool for quality
control of vegetable oils, and for the detection of oil as well as blends not
recognized by the fatty acids’ profile (Ramadan, 2012). Structures of some
4-desmethylsterols of vegetable oils are provided in Figure 2.5. The PS
levels and composition of some vegetable oils are provided in Table 2.6.

2.10.1 FOOD APPLICATIONS OF PHYTOSTEROLS

A dark chocolate containing PS esters was developed to reduce cholesterol
in individuals. However, oxidative instability during chocolate processing