ANTI-NUTRITIONAL CONSTITUENT OF COLOCASIA ESCULENTA ...

C.1.2.2
and fungal cells contain one major sterol: cholesterol and ergosterol, respectively. More
than 100 different types of phytosterols (plant sterols) have been identified (Morean et
al., 2002). Seeds, nuts, fruits and vegetable oils are some ofthe different parts of a plant
that contain significant amounts ofplant sterols (Weihrauch and Gardner, 1978; Moreau
et al., 2001). The phytosterol content ofthese vegetables and fruits is not influenced by
intense processes such as boiling, bleaching and deodorizing since phytosterols are very
stable compounds (Normen et aI., 1999; Bortolomeazzi, 2000). The human body is
unable to produce plant sterols: thus, all plant sterols are regulated by dietary intake. Beta
-sitosterol, stigmasterol and campesterol are the most abundant in plants (Rosenblum et
al., 1993; Law 2000; Hicks and Moreau, 2001).
Pbarmacochemistry and pharmacokinetics
Researchers have been fascinated by the concept of a protein-mediated transport system
responsible for intestinal uptake of cholesterol for more than a decade (Thwnhofer and
Hauser, 1990). Identification of the molecular defects responsible for phytosterolemia
(Berge et al., 2000; Lee et al., 200 I) and possible confirmation of the existence of a
specific transport protein located in the brush border membrane mediating intestinal
sterol absorption (Detmers et al., 2000; Hemandez et aI., 2000; Kramer et al., 2000) has
shed new light on the cellular transport of cholesterol and plant sterols. Plasma
phytosterol levels are generally very Iow compared to cholesterol levels in mammalian
tissues. This is due primarily to poor absorption from the intestine and faster excretion
from the liver (Ling and lones, 1995). Absorption of beta-sitosterol is also made difficult
during its passage through the gut because these phytosterols are bound to the fibers of
the plant (Bouic, 1998).
The plant sterol mixture has very Iow solubility (Moghadasian, 2000): it is not soluble in
either water or oil (Kim et aI., 2002). About five per cent of an ingested dose of
supplemental beta-sitosterol is absorbed from the gastrointestinal tract and is transported
via the portal circulation to the liver (Salen et al., 1970). Systemic circulation is
183