Self-Assembly in Food – A New Way to Make Nutritious Products - Food Colloids: Self-Assembly and Material Science - page 26

also be that the two emulsions studied had different interfacial composition, as
the total area was much higher in the fine emulsion.
All these results show that digestion is a complex biotransformation process
involving enzymes, amphiphilic substances and colloids. The mechanism of
final uptake of molecular species through the mucine-rich unstirred water layer
and the cell membranes into the enterocytes remains unresolved. Both passive
diffusion and carrier-mediated processes have been proposed. 62 For long-chain
fatty acids and cholesterol, the passage across the unstirred water layer is rate-
limiting, whereas the passage of short- and medium-chain fatty acids is limited
by the brush border membrane. The observation that polystyrene latex parti-
cles with sizes of 200 nm and 2 mm can be absorbed in the small intestine
indicates that absorption of colloidal particles even larger than micelles might
be possible, 63-65 although Rigler and co-workers 50 did not provide any evidence
for such a mechanism.
2.6 Emulsifier-Based Self-Assembly and Structuring of
Oil Droplets
The digestion of triacylglycerols or other lipids leads to the production of
numerous amphiphilic molecules such as emulsifiers, as discussed above. When
such surfactants are exposed to water, they exhibit a rich phase behaviour.
Especially of interest to us are self-assembled aggregates of mono- and diglyc-
erides because these emulsifiers are specified as GRAS (generally recognized as
safe), and so they can be used with confidence to study the phase behaviour in the
presence of oil and water, mimicking the phases that occur during digestion. The
glycerol fatty acid esters and their derivatives account for about 75% of the
world production of food polar lipids, and they are considered to be the most
important group of amphiphiles in food. 66 Their use dates back to the 1930s
when they were first used in margarine production. Their major applications
today are in bread, cakes, margarine, ice-cream and chewing gum. Bakery is by
far the biggest application, with approximately 60% of all monoglycerides being
used by this industry. 66 Luzzati 67 reported the first phase diagrams of mono-
glyceride+water systems. X-ray diffraction has allowed the unambiguous iden-
tification of the formation of the different mesophases. It was shown by Qui and
Caffrey, 68 for instance, that the monoolein+water system forms an inverted
bicontinuous cubic reversed hexagonal phase and W/O microemulsions.
Oil droplets in emulsions can be internally structured using self-assembly
principles by the addition of appropriate amphiphiles. 20 Such internally self-
assembled emulsion droplets are of interest in food technology as delivery
system for oil-soluble and amphiphilic bioactives. 69 In the context of the subject
of the present article, a deeper understanding of their phase behaviour in the
presence of water, oil and fatty acids is essential for further elucidating the
phase behaviour during lipid digestion. This knowledge will definitely be an
advantage for the development of lipid-based delivery colloids with specific
release functions for bioactives. The dispersion of reversed liquid crystalline