Chemistry Reference
In-Depth Information
monooleate (GMO) + ethanol + water, which was designated as a Q
L
phase.
We describe this type of system as 'modified' because, unlike previously
reported cubic structures that are semi-solid or gel-like, our mesophase is
characterized by its low viscosity (
40 Pa s), high fluidity and transparency.
This micellar cubic phase has a body-centred cubic (bcc) symmetry and it seems
to belong to P4
2
32 (Q
208
) space group. The P4
2
32 space group belongs to
incommensurate crystals, i.e., crystals consisting of a basic ordered structure
that is perturbed periodically and 'modulated' by a sub-system.
17,18
The struc-
ture with the P4
2
32 symmetry is characterized by at least four periodicities,
three of which represent known cubic symmetries of crystalline structures.
In water, the monoglyceride GMO is ordered in various liquid crystalline
phases depending on the water content, temperature and other physical con-
ditions.
19,20
We are concentrating our efforts in revealing the possible types of
self-assembly. We have found that, once a controlled quantity of a 'lamellar
structure-breaker' (such as short-chain alcohol) is carefully added to the binary
mixture, some unique discontinuous structures are formed. We recently
described and partially characterized one such mesophase denoted as the Q
L
phase.
15,16
GMO is widely used as a food emulsifier,
21
and its liquid crystalline
phases have the potential of serving as sustained release carriers of nutraceuticals,
aromas and drugs.
19-23
In this work we report on the solubilization patterns of
two of these nutraceuticals (lycopene and phytosterols), which are practically
insoluble in water but which have been solubilized in the Q
L
mesophases.
Phytosterols (plant sterols) belong to the tri-terpene family of natural prod-
ucts which includes over 200 different sterols.
24-26
Phytosterols are a mixture of
sterols that are structurally similar to cholesterol, but with the inclusion of an
extra hydrophobic carbon chain at the C-24 position (each phytosterol has an
additional side chain) [Figure 1(a)]. Phytosterols in their alcoholic-'free' form
are non-esterified sterols. Sterols can be esterified to form the corresponding
fatty acid esters (phytosterol esters). Sterols and sterol esters are recognized as
cholesterol reducing agents. Phytosterols act in the digestive track and are not
transported to the blood stream, and therefore they exhibit virtually no side
effects and no mutagenic activity or sub-chronic toxicity in animals. Phyto-
sterols and phytosterol esters are hydrophobic structures poorly soluble in
food-grade oils and in water, which limits their application in water-based
applications such as clear beverages.
Lycopene is a unique carotenoid known to contribute to a lower risk factor
for coronary heart disease and some types of cancer.
27
Lycopene is a straight
chain hydrocarbon,
28
highly unsaturated, consisting of all-trans conjugated
double-bonds
28-31
[Figure 1(b)]. Lycopene is an extremely insoluble compound;
its solubility in both water and food-grade solvents is extremely low (several
hundred parts per million). Lycopene exists in tomatoes in its crystalline form
and as such it has very low bioavailability. For nutraceutical applications, raw
powdered tomatoes or lycopene powdered matter containing large crystals
cannot be used because the bioavailability is so very low. It has therefore been
recognized by formulators and manufacturers that, for improved bioavailabil-
ity, the crystalline lycopene must be 'micronized' or reduced to nanometre-sized
B
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