Self-Assembly in Food – A New Way to Make Nutritious Products - Food Colloids: Self-Assembly and Material Science - page 25

drug lipophilicity. Kossena et al. 57 suggested that, in their in vitro model test,
the action of SEIF might result in the formation of a lamellar droplet surface
with C 8 and C 12 lipids, whereas with C 18 lipids an additional cubic phase layer
might form, the obtained phase/solubility trends indicating that poorly water-
soluble drugs are transported across the intestinal colloidal species that form
during the digestion of lipid-based drug delivery systems. These observations
are of importance for food, as the different mesophases formed could have an
influence on the bioavailability of oil-soluble and amphiphilic bioactives
present in chyme.
A comparison of in vitro equilibrium structures 28 with structures obtained
from aspirated duodenal contents 29 shows that the sizes of the micelles are
comparable, whereas the unilamellar vesicles in vivo are substantially smaller.
Borne´ et al. 58-61 studied the effect of lipase on different liquid crystalline phases
in water, such as lamellar (monoolein + sodium oleate), reversed bicontinuous
cubic (monoolein + oleic acid) and reversed hexagonal (monoolein + diolein).
Under their experimental conditions they could not detect any difference
in enzyme activity when comparing cubic to hexagonal phases. They do
not exclude the possibility, however, that other experimental conditions
(different mesophases or sample compositions) could result in different enzyme
activities.
2.5 Oil Droplet Digestion
The digestion and lipid absorption from emulsions with different droplet sizes
has been investigated in humans by Armand and co-workers. 35,36 Healthy
subjects received intragastrically in random order a coarse lipid emulsion
(10 mm diameter) and a fine lipid emulsion (0.7 mm diameter); the emulsions
were of identical composition. Gastric and duodenal aspirates were collected
throughout digestion in order to measure changes in fat droplet size, gastric and
pancreatic lipase activities and fat digestion. Despite an increase in droplet size
in the stomach (2.75-6.20 mm), the fine emulsion retained droplets of smaller size
and its degree of lipolysis was greater than that of the coarse emulsion (37%
compared with 16%; P o 0.05). In the duodenum, the extent of lipolysis of the
fine emulsion was on the whole higher (73% compared with 46%). The overall
0-7-h plasma and chylomicron responses given by the areas under the curve
were not significantly different between the emulsions, but the triacylglycerol
peak was delayed with the fine emulsion (4 h compared with o 3 h),
as previously shown in rat experiments. 37 These data suggest that emulsions
with different particle sizes lead to different time courses of plasma lipids
postprandially. Although lipid digestion was faster for the finer emulsions -
as is to be expected, owing to the larger interface area - the appearance of
triacylglycerol in the blood was found to be slower. The authors mention as
possible causes for the latter a difference in the rate of gastric emptying, the
formation of intermediate phases such as mixed micelles, and vesicles, and a
difference in the diffusion of lipids through the unstirred water layer. It might