Food-grade Microemulsions As Nano-scale Controlled Delivery Vehicles - Food and Industrial Bioproducts and Bioprocessing - page 156

(1) the possibility of tailored absorption (rate and predictability) and enhanced bioavailability
of poorly-soluble bioactive compounds;
(2) higher solubilization capacity and/or entrapment rate of lipophilic bioactives;
(3) aqueous dosage form for hydrophobic compounds, given the much smaller domain size;
(4) better protection of labile compounds (e.g., against oxidation) and flavors/aromas;
(5) improved transdermal penetration compared to other matrices, given the much smaller
domain size;
(6) straightforward preparation and scaling up for industrial production, though this also
applies to emulsions.
Generally, the poor aqueous solubility of most drugs and nutraceuticals can result in
low absorption after in vivo administration, thus limiting biological efficacy. Enhancement
in biological efficacy and lowering of toxicity may be achieved through judicious encapsu-
lation and delivery of the bioactive compound in aqueous- or oil-based microemulsion
delivery systems (Garti and Aserin, 1996).
5.11.5 Microemulsions as nano-reactors
Properties such as large interfacial area and an ability to solubilize both oil-soluble and water-
soluble reactants in a single phase system makes microemulsions ideal as reaction media
(Flanagan and Singh, 2006; Gaonkar and Bagwe, 2002). For example, Morgado and co-workers
(1996) used a continuous reversed micellar system to synthesize lysophospholipids and
free fatty acids from lecithin hydrolysis, with applications to the food, pharmaceutical and
chemical industries. Hydrolysis was catalyzed by porcine pancreatic phospholipase A 2 .
Carvalho and Cabral (2000) reviewed the use of reversed micellar systems as reactors to carry
out lipase-catalyzed esterification, biocatalysis, transesterification, and hydrolysis reactions.
The Maillard reaction is a reaction between a reducing sugar and an amino acid at high
temperatures which is responsible for many color and flavor compounds in foods. Microemulsions
have served as nano-reactors for such reactions given their ability to enhance reaction yield and/
or pathway (Leser et al ., 2006). Vauthey and co-workers (2000) studied the Maillard reaction
between furfural and L-cysteine at 100 °C in microemulsions and cubic phases. The systems
comprised monoglycerides and water where the production of 2-furfurylthiol, a compound with
distinct sensory properties, was monitored. The authors reported a significant increase in the
reaction yield of this compound compared to the reaction in the phosphate buffer at pH 5 with
the use of microemulsions. Garti and co-workers (Garti et al ., 2000b ; Fanun et al ., 2001a ) studied
the same reaction and found similar results, that is, enhanced formation of 2-furfurylthiol
in sucrose stearate-dodecane-butanol w/o microemulsions at 60 °C. They noted that the
partitioning of the co-surfactant butanol between the water phase, the water/oil interface and
the oil phase significantly altered the overall reaction rate.
5.12 CONCLUSIONS
There has recently been tremendous progress made in the development of microemulsion
formulations for food use. However, there remains a limited understanding of how these
systems interact within the body and if they are toxic, given currently insufficient safety
testing and assessment in food environments. With the ever increasing development of nano-