Self-Assembly in Food – A New Way to Make Nutritious Products - Food Colloids: Self-Assembly and Material Science - page 24

Figure 2 Oil droplets and vesicles identified during in vitro digestion of lipids. Fat
digestion (Pancreatin, Sigma) was simulated in an artificial bile at pH ¼
6.5, as described by Kossena et al., 51 incubating 4 mg of soybean oil emulsified
by 1% lecithin (fat/pancreatin ratio ¼ 6). After incubation for 1 h at 371C, 30
mL of digestion medium were collected and transferred into a 100- m m deep
chamber covered with a coverslide coated with a film of Nile Red (Sigma) to
stain lipids. Real-time imaging was achieved at room temperature using the
'time series' functions of the Zeiss LSM510 confocal microscope over periods of
4 min at B 0.8 s intervals
(Copyright Nestec Ltd (2006))
performed a systematic phase equilibrium investigation of model lipid systems
corresponding to lipid compositions typical of upper intestinal contents during
lipid digestion in adult humans; the systems contained bile salts, mixed intes-
tinal lipids, partially ionized fatty oleic acids, monooleylglycerol and choles-
terol at 371C, pH ¼ 6.5 and ionic strength ¼ 0.15M (Na 1 ). They identified a rich
phase behaviour, particularly the formation of metastable unilamellar vesicles
of variable sizes in coexistence with thermodynamically stable saturated mixed
micelles. So it is very likely, as also suggested by Hernell and Blackberg, 56 that
vesicles are directly involved in lipid absorption, since bile salt-deficient subjects
can take up 50-75% of dietary lipids.
Kossena and co-workers 57 established phase diagrams to determine the
behaviour of the digestion products of common formulation lipids (C8:0,
C12:0 and C18:1) under model physiological conditions. Pseudo-ternary phase
diagrams were constructed using varying proportions of simulated endogenous
intestinal fluid (SEIF), fatty acids and monoglycerides (as representative of
exogenous lipid digestion products). A change from liquid crystals to mixed
micelles and vesicles was observed with decreasing fatty acid/monoglyceride
concentrations. Large solubilization enhancement ratios for a series of poorly
water-soluble compounds such as hydrocortisone and its esters were measured
relative to the intrinsic solubility in buffer, resulting in an increased solubilizat-
ion capacity in lamellar liquid crystal phases (a factor of 10-2000) and cubic
liquid crystal phases (a factor of 10-30,000). Positive correlations were
observed between the solubilization benefit provided by each phase and the