Emulsions, Nanoemulsions and Solid Lipid Nanoparticles as Delivery Systems in Foods - Food and Industrial Bioproducts and Bioprocessing - page 168

(1) Separation and direct analysis in one of the phases. If the aqueous phase can be separated
and analyzed it is possible to measure the proportion of BLI associated with the droplets
(surface and core) by difference. Unfortunately, fine particles are hard to filter or
separate by sedimentation. More aggressive separation procedures (e.g., solvent
extraction) often destroy the equilibrium under investigation (especially surface and
Laplace pressure effects). Alternatively, a volatile BLI can be determined in the
headspace allowing its activity coefficient in the emulsion to be determined non-
destructively (Ghosh et al ., 2006 ).
(2) Chemical degradation kinetics. An indirect method to determine the distribution of BLI
is to measure their chemical degradation kinetics in response to an aqueous oxidizing
agent, radical source, or acid. The assumption in these studies is usually that BLI at the
interface will degrade faster than those in bulk. Studies of BLI stability are obviously
valuable in their own right. However, care must be taken in inferring distribution between
microenvironments, as the assumption that molecules at the surface are most vulnerable
to degradation is rarely confirmed by other methods. For example, Boon and co-workers
(2008) compared lycopene oxidation kinetics in lipid nanoemulsions of different lipid
and surfactant types. They showed that the oxidative stability was affected by surface
properties, and higher in emulsions stabilized with cationic and non-ionic surfactants
than in emulsions stabilized with anionic surfactants. In another study, Jenning and
Gohla (2001) compared the chemical stability of selected drug ingredients (i.e., retinoids)
with different hydrophobicity in SLN and lipid nanoemulsions and argued that
crystallization of the lipid droplets resulted in concentration of drug molecules on the
droplet surface while encapsulation efficiency was improved by increased lattice defects.
In contrast, Helgason and co-workers (2009) used this approach to argue that high
melting lecithin prevented the accumulation of

-carotene at the surface of a SLN.
(3) Spectroscopic methods. The spectroscopic signal of many molecules is sensitive to their
immediate chemical environment. If the spectroscopic method is capable of analyzing
the BLI (or more likely a labeled analog) in situ in the emulsion then there will be
distinguishable signals for the proportion in each microenvironment. For example,
Arboleya and co-workers (2005) prepared a palm oil-in-water emulsion containing a
stable free radical spin probe in the lipid phase. The probes were monitored using
electron paramagnetic resonance (EPR) spectroscopy and the investigators were able to
deconvolute the spectra and determine the proportion in the lipid and aqueous phases.
The molecular mobility of the probe as a function of lipid crystallization was also
determined. Nuclear magnetic resonance (NMR) spectroscopy is a similar technique to
EPR, and can similarly be used to probe the properties of different compartments. For
example, proton NMR (H 1 -NMR) was used to investigate the mobility and distribution
of a liquid lipid (medium chain TAG) loaded into solid lipid droplets (long chain TAG)
(Jenning et al ., 2000 a, 2000 b).

β

6.4 EMULSIONS AS DELIVERY SYSTEMS

Emulsion-based delivery systems (EBDS) has been introduced as successful carrier systems
for BLI. For example, -3 fatty acid-rich TAGs were incorporated as emulsions into

different food products, such as milk, yogurts, ice cream, and meat patties (Chee et al .,
2005 , 2007 ; Lee et al ., 2005 , 2006a , 2006b ; McClements and Decker, 2000 ; Sharma, 2005 ).

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