Food-grade Microemulsions As Nano-scale Controlled Delivery Vehicles - Food and Industrial Bioproducts and Bioprocessing - page 141

5 Food-grade Microemulsions
As Nano-scale Controlled
Delivery Vehicles
Natasha Berry, Rickey Yada and Dérick Rousseau
5.1 INTRODUCTION
Microemulsions were first recognized in the 1940s with the pioneering work of Hoar and
Schulman (Hoar and Schulman, 1943; Friberg and Venable, 1983; Karamustafa and Celebi,
2008) who referred to them as oleopathic hydro-micelles. In 1959, the term microemulsion
was coined by Schulman et al . (Schulman et al ., 1959 ; Friberg and Venable, 1983 ).
Microemulsions are now recognized as self-assembled nano-scale entities (Ruckenstein and
Chi, 1975 ; Friberg and Venable, 1983 ; Moulik and Paul, 1998 ; Flanagan and Singh, 2006 ;
Polizelli et al ., 2006; Karamustafa and Celebi, 2008). On the basis of size alone, however,
the term microemulsion is a misnomer, and has led to confusion. Vis-à-vis standard emulsions,
which normally consist of dispersed droplet sizes in the low micron range (1-20 μm),
microemulsion dispersed domains are normally well below 100 nanometres (nm) in
diameter. More recently, nano-emulsions have gained attention as vehicles for controlled
release and delivery. Despite the fact that these also consist of nano-scale droplets (typically
50-200 nm), they- lack the thermodynamic stability of microemulsions, which suggests the
need for kinetic stability (though practice often dictates otherwise).
Given their inherent stability and nano-sized domains, microemulsions have a number of
advantages for use in food, pharmaceuticals and other applications (e.g., cosmetics and
petrochemicals), including ease of preparation, a clear appearance promoting consumer
acceptance and patient compliance, the improved bioavailability of incorporated compounds
and a possible shelf life of many years (Oberdorster et al ., 2005 ; Chau et al ., 2007 ). As a
result, microemulsions have been investigated as delivery systems for pharmaceuticals,
nutraceuticals and ingredients, as they can improve the solubility of poorly-soluble compounds
(e.g., sterols) (Garti et al ., 2004), increase bioavailability (e.g., of oil-soluble vitamins) (Rozner
et al ., 2010) and protect labile compounds against light and/or enzyme-induced breakdown
(e.g., oxidation of omega-3 fatty acids) (Swenson and Curatolo, 1992; Flanagan and Singh,
2006; Sanguansri and Augustin, 2006). Given their high surface-to-volume ratio (Gaonkar
and Bagwe, 2002), microemulsions have also been used as nano-scale “bioreactors” for the
efficient synthesis of numerous compounds, including lysophospholipids, free fatty acids
(Morgado et al ., 1996) and 2-furfurylthiol, a key product associated with Maillard browning
(Vauthey et al ., 2000 ).