Chemistry Reference
In-Depth Information
negatively curved phases. Mezzenga et al.
78
showed that the presence of mon-
osaccharides, oligosaccharides or polysaccharides in the bicontinuous cubic
mesophase results in a lowering of the cubic-to-hexagonal transition tempera-
ture. The authors state
78
that, in the presence of hydrophilic compounds with a
strong hydrogen bond acceptor, the number of water molecules hydrating the
monoglyceride polar head is reduced. Thus, provided that the polysaccharide is
small enough to fit within the water channels of the cubic phase, the change in the
critical packing parameter is proportional to the number of hydrophilic groups
(i.e., the carbohydrate concentration) dissolved in the aqueous phase.
2.8 Phytosterol Solubilization into Mesophases
Phytosterols reduce the absorption of cholesterol and lower the serum concen-
trations of cholesterol and low-density lipoproteins (LDL). Their effectiveness
is highly dependent on the molecular structure and their physical state.
Enrichment of foods with natural, non-esterified (free) phytosterols is dicult,
since plant sterols are insoluble in water and are also poorly soluble in oils.
Lipid solubility can be enhanced by esterification of phytosterols with fatty
acids. The incorporation of plant stanol esters into margarine is one of the first
examples of a functional food with proven cholesterol-lowering effective-
ness.
79,80
One mechanism suggested for the cholesterol-lowering effect of plant
stanols/sterols is a reduction in intestinal cholesterol absorption, a process in
which changes in micellar composition are thought to play a major role.
Another mechanism is the process in which plant stanols/sterols actively
influence cellular cholesterol metabolism within intestinal enterocytes.
81,82
The food matrix has a strong influence on lowering the LDL cholesterol level
via plant sterols, with milk and yoghurt being more effective than bread and
cereals.
83
Microcrystalline-free plant sterols have been shown
84
to be effective
for both serum and LDL cholesterol lowering. In the non-esterified form, the
presence of lecithin- or monoglyceride-solubilized stanols incorporated in O/W
emulsions massively reduces cholesterol absorption.
4,5
The amphiphilic char-
acter of non-esterified phytosterols facilitates their solubilization into meso-
phases (Figure 4), thereby considerably increasing the absorption capacity in
the digestive tract.
5
2.9 Colloid Science and Nutrition
We have reviewed some of the self-assembly processes of polar lipids involved
in the digestion processes of dietary lipids, as well as the multitude of self-
assembled structures that can be engineered into colloidal particles. Similar
self-assembled colloidal structures that occur during digestion are currently
being exploited to increase bioavailability of poorly water- and oil-soluble
bioactives such as non-esterified plant esters. However, the development of self-
assembly delivery systems is still mostly being done independently of the
transformation processes occurring during digestion. Emerging colloidal
Search WWH ::
Custom Search