**2. Conclusions**

*Nanoemulsions - Properties, Fabrications and Applications*

produces nanoparticles or microparticles without any trace of solvent, thus high purity. CO2 is a cheaper fluid, nontoxic, and non-flammable. Its low critical temperature of 31.1°C makes it an ideal fluid for sensitive or thermally labile materials. An active ingredient is regarded to be in a supercritical state if its temperature and pressure are above its critical values. Based on the solubility of active ingredient in CO2 (or any inert gas) fluid, particles can be formed by using two approaches as depicted in **Figure 5**: (a) rapid expansion of supercritical solution (RESS) and (b) rapid expansion of supercritical solution into a liquid solvent (RESOLV) [45]. In order to perform RESS, high solubility in the supercritical fluid is required. However, some of the active nutraceutical ingredients are organic polar compounds. CO2, due to its low polarity, is not a proper fluid for these materials. The nutraceutical ingredients are ideal for RESOLV. In RESOLV, an organic solvent is required to dissolve the vitamins expanding in the SCF. As discussed in Section 2.3, solid lipid nanoparticles are spherical nanoparticles produced from solid fat. Instead of melting the lipids in an appropriate organic solvent, vitamin B2 was encapsulated in SNL using SCF [46]. The lipids are saturated with CO2 in order to decrease the melting point. However, Couto and colleagues modified the SCF, in which the lipid, bioactive, and surfactant mix expanded with CO2 was decompressed into a water stream containing a stabilizer. Vitamin B2, the hydrophilic bioactive, was encapsulated in fully hydrogenated canola oil (the solid lipid), using sodium lauryl sulfate as surfactant and polyethylene glycol as stabilizer. Vitamin B2 participates in a range of redox reactions central to human metabolism, and its deficiency has been linked to fetal developmental abnormalities and deficiencies in the production of red blood cells. Due to its hydrophilic nature, it is easily absorbed, but it is not stored in the body, leading to the need for

*A Schematic representation of particle formation by rapid expansion of supercritical solution. In conventional RESS, blank particles are formed dissolving the solute, that is, polymer in a supercritical fluid to form a solution. This is followed by the rapid expansion of the solution across an orifice or a capillary nozzle into ambient air. The high degree of supersaturation, accompanied by the rapid pressure reduction in the expansion unit, ideally results in homogenous growth of particles and, thereby, the formation of well-dispersed particles. However, results obtained from mechanistic studies of different model solutes for the RESS process indicate that* 

*both nanometer- and micrometer-sized particles are usually present in the expansion unit [46].*

**38**

**Figure 5.**

Numerous delivery systems such as nanoemulsions, microemulsions, liposomes, lipid nanoparticles, polymeric micelles, and nanoparticles have been reported extensively for encapsulating nutraceuticals especially liposoluble vitamins. The lipid-based nanoformulations were highly recommended by various studies as compared to others due to their better absorption when ingested, improved stability, and low degradation in the gastrointestinal tract. However, more efforts need to be focused on their toxicity and regulatory issues for the faster development of industrially processed nanoformulated nutraceuticals from the lab-scale research discoveries. It is widely anticipated that over the next couple of years, nanoformulated delivery systems of essential nutraceuticals will continue to evolve and many novel food products are expected to be used with an enormous positive impact on addressing malnutrition challenges in children.
