Nanotechnology for Foods: Delivery Systems
421
dissolved in chloroform and dried by a stream of nitrogen followed by overnight drying under vacuum. The dried lipid combinations were then rehydrated and ultrasonicated to initiate encapsulation and liposome formation. Vesicles collected by centrifugation were then separated from unencapsulated antimicrobials using size exclusion chromatography. The authors produced liposomes from different formulations and showed that indeed, for each antimicrobial peptide, there is an optimal composition based on compatibility of the lipid and the antimicrobial. As for nanoparticles, the number of methods that could be utilized for their formation is as high as the various formulations proposed. In one case, phase separation was used by Parris et al. (2005) to form zein nanoparticles. The authors used the method to form nanospheres to carry essential oils of oregano, thyme, and cassia. Here, the particles were formed by dissolving the oil and the coating/matrix material in 85% ethanol. Particles were formed by rapid dispersion of the solution during high-speed mixing into water. The dry form of the particles was obtained by freeze-drying the opaque solution. The authors reported a yield of 65–75%. In principle, this approach can be used to form starch-inclusion nanocomplexes (Lalush et al., 2005; Shimoni et al., 2006, U.S. patent). Starch and ligand could be codissolved in DMSO or alkali solution, and then either diluted in water or acidified, respectively. The result in both cases is the formation of conditions that promote the sedimentation (e.g. phase separation) of the starch while forming inclusion complexes. The continuous dual feed jet homogenization developed for the process provides sub-micron size particles. A similar approach was used by Chen and Wagner (2004) to form vitamin E nanoparticles. They used a microfluidics homogenizer to form the nanoparticles, which were further dried with a spray dryer. Fibers are also potent tools for protection, delivery, and controlled release systems. Electrospinning was demonstrated by Jiang et al. (2006) in the formation of biodegradable core-shell fibers. By applying high voltage to a spinneret, an electric jet of viscous polymer solution can be formed. By stretching the jet prior to its reaching the target, it is possible to evaporate the solvent quickly. The resulting fibers have a tremendously high surface of porosive matrix. Spinnerets, composed of two coaxial capillaries, can simultaneously electrospin two different solutions to form core and shell nanofibers. Jiang et al. (2006) demonstrated the use of the technique to incorporate and control the release of proteins from a biodegradable nanofiber. An interesting point is their use of polyethylene glycol (PEG) as the shell, and of dextran as a core polymer. These two are compatible with food systems, and thus one can clearly see the potential of the method for future food applications.