Nanoencapsulation of Phenolics and Antioxidants in Nanostructured Lipid Carriers
NLCs are the optimal form of SLNs. Indeed, the formulation and production of NLCs is similar to SLNs as explained in the previous section, with the exception that the lipid phase in NLCs contains liquid lipid (oil) mixed with solid lipid (Muller & Lucks, 1996; Muller et al., 2002). Applying liquid lipids in NLCs provides main advantages such as high encapsulation efficiency, better morphological characterization, minimized encapsulated ingredient expulsion during storage, and controlled bioactive release properties, with smaller particle sizes. Therefore, NLCs can provide an optimum nanoencapsulation system for phenolic compounds and antioxidants. For example, the ability of SLNs and NLCs has been evaluated for nanoencapsulation of RSV by Gokce et al. (2012). SLNs were prepared using glyceryl behenate followed by homogenization, and NLCs were also produced using the same method, by replacing 5%, 15%, 30%, and 45% of the solid lipid with liquid migliol oil. The mean particle diameter of resulting SLNs and NLCs were ~287 nm and 110 nm, respectively. Also, the encapsulation efficiency was 18% higher in NLC systems. As a result, RSV-loaded NLCs with smaller particle sizes and higher loading appeared to be superior to SLNs for dermal applications (Gokce et al., 2012).
Phenolics and antioxidants with regard to their nature, goal of encapsulation, formulation, and production method can be incorporated into NLCs in three forms including imperfect crystal, amorphous, and multiple types as shown in Fig. 2.2 (Muller et al., 2002; Souto et al., 2004). Many water- insoluble phenolics and antioxidants have been reported to be successfully loaded into NLCs resulting in higher bioavailability (Table 2.3). For instance, lutein as a potential natural antioxidant, was loaded into NLCs prepared by high-pressure homogenization (Mitri, Shegokar, Gohla, Anselmi, & Muller, 2011). The results showed that these nanocarriers can protect lutein from environmental stresses. (3-Carotene was also loaded into NLCs produced with Tween 20 and mixture of palmitic acid and corn oil by solvent diffusion method (Hejri, Khosravi, Gharanjig, & Hejazi, 2013). They found that the ultra-small NLCs with a high (3-carotene retention can increase the bioavailability of (3-carotene by its protection in lipid nanoparticles; therefore, NLCs could be an appropriate nanocarrier for (3-carotene in food formulations (Hejri et al., 2013). In another study, Teeranachaideekul, Souto, Junyaprasert, and Muller (2007) successfully loaded coenzyme Q10 in a nanoparticle of acetyl palmitate and caprylic/capric triacylglycerols by using high-pressure homogenization in an NLC system. The entrapment efficiency was 100%. They showed that varying the lipid and oil ratio had no effect on the particle size of NLCs. However, increasing the amounts of oil loading led to a less ordered structure within the particles (Teeranachaideekul et al., 2007).