Biomedical Engineering Reference
In-Depth Information
bioavailability of lycopene entrapped within whey proteins was similar to that provided by
tomato paste (Richelle et al ., 2002) and much greater than in unprocessed tomato. In another
work, casein micelles were introduced as a potentially useful delivery system for the lipid
soluble vitamin D2 (Semo et al ., 2007). Moreover, spray-dried starch-based delivery systems
were studied in order to encapsulate phytochemicals, such as carotenoids from carrots
(Wagner and Warthesen, 1995 ).
In the second group of delivery systems, the BLI is incorporated into a thermodynamically
stable surfactant self-association structure (e.g., a microemulsion). For example, Amar and
co-workers (2003) used microemulsions of different surfactant types to improve the
solubilization of lutein and lutein esters, which are otherwise insoluble in water and have
limited solubility in food-grade oils. In the final group of delivery systems, the BLI can be
dissolved in a lipid carrier and subsequently homogenized to form fine emulsion droplets.
This final group is known as emulsion-based delivery systems (EBDS) and is the focus of
this chapter.
Emulsions are attractive candidates for delivery systems, as they are already widespread
in foods and utilize commonly available ingredients and process technologies. There is a
parallel between the need to encapsulate BLI in foods with the need to incorporate poorly-
soluble drugs in a form that can be ingested, injected or applied topically. Indeed, in the
pharmaceutical industry lipophilic drugs are delivered parenterally as commercial EBDS
products (Mehnert and Mader, 2001; Muller et al ., 2000 ). The lipid phase provides a
reservoir for the BLI, which can then be uniformly dispersed in an aqueous food by
homogenization and stabilized with emulsifiers. It is possible to tune the performance of the
delivery system by altering the size or number of the lipid droplets, or by altering the
interfacial and/or lipid composition. Work in pharmaceutical EBDS has pioneered the use of
solid lipid nanoparticles (SLN) and nano-structured lipid carriers (NLC), fine crystalline
emulsion droplets, as delivery systems (Bonacucina et al ., 2009 ; Mehnert and Mader, 2001 ;
Muller et al ., 2000). Several workers have considered parallel applications in foods
(McClements et al ., 2007 , 2009 ; Velikov and Pelan, 2008 ; Weiss et al ., 2008 ). In this chapter,
the relationships between structure of emulsions and crystalline emulsions, both micro- and
nano-scale, and their functionality as delivery systems in foods are examined.
An emulsion is a mixture of two immiscible liquids, one of which is uniformly dispersed
within the other as small droplets (i.e., droplet diameter in the range 0.1-100
(McClements, 2005 ). In this chapter, the concern is exclusively with dispersions of oil in
water, that is, oil-in-water emulsions. Advances in homogenizer technology have allowed
the development of nanoemulsions with droplets far smaller and with more uniform size
distributions than commonly seen in manufactured foods (Weiss et al ., 2008 ). There is not
a commonly accepted size cut-off for nanoemulsions and different researchers have used
different definitions: below 1000 nm (Muller et al ., 2000 ), 500 nm (Anton et al ., 2008 ),
200 nm (Higami et al ., 2003 ; Solans et al ., 2005 ), and 100 nm (Luykx et al ., 2008 ).
Emulsions with nano-scale crystalline droplets are sometimes referred to as solid lipid
nanoparticles (SLN).
Emulsions are formed either by using mechanical energy to reduce the particle size of a
coarse mixture or, less frequently, by a controlled phase separation (e.g., on dilution of raki
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