Food Lipids: Chemistry, Nutrition, and Biotechnology

Table 1 Macromolecular Mesophases
Adopted by Phospholipids
Phase Phase structure
Liquid Fluid lamellar
Hexagonal
Complex hexagonal
Rectangular
Oblique
Cubic
Tetragonal
Rhombohedral
Solid Three-dimensional crystal
Two-dimensional crystal
Rippled gel
Ordered ribbon phase
Untilted gel
Tilted gel
Interdigitated gel
Partial gel
membrane. Permeability coefficients of liquid crystalline lipid bilayers for water are
in the range of 10 �2 –10 �4 cm/s, indicating a high permeability [3]. The relative
permeability of different membrane systems to water can be monitored by means of
light scattering techniques that measure swelling rates when osmotic gradients are
applied [4]. Results obtained from such studies indicate that increased unsaturation
of the fatty acids of the membrane causes increases in water permeability. Since
cholesterol reduces water permeability, the general conclusion has been made that
factors contributing to increased order in the hydrocarbon region reduce water
permeability.
The diffusion properties of nonelectrolytes (uncharged polar solutes) also appears
to depend on the properties of the lipid matrix in much the same manner as
does the diffusion of water. That is, decreased unsaturation of phospholipids or increased
cholesterol content results in lower permeability coefficients. In the case of
Table 2 Phase Preference of Membrane Phospholipids
Bilayer Hexagonal H II
Phosphatidylcholine
Sphingomyelin
Phosphatidylethanolamine
Phosphatidylserine Phosphatidylserine (pH < 3)
Phosphatidylglycerol
Phosphatidylinositol
Phosphatidic acid Phosphatidic acid (� Ca 2� )
Phosphatidic acid pH < 3)
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