# D-Limonene: Promising and Sustainable Natural Bioactive Compound
## 7 Application: Nanotechnology and D-Limonene
### Nanotechnology: Improving Properties and Enhancing Biodiversity  
Different encapsulation techniques, such as spray drying, thin-layer drying, freeze-drying, emulsification, coalescence, and ionic polymerization, have been used to improve the physicochemical properties and bioactivity of D-limonene to form polymeric materials, such as nanoemulsions, nanoparticles, nanogels, and microcapsules, whereas gum arabic, chitosan, alginate, and maltodext are common loading materials [186; 193; 25; 194; 195; 196; 197; 198].  
[PERSON] et al. [186] used brea gum as an encapsulating wall material to produce D-limonene microcapsules and they found that brea gum allowed good encapsulation and  
Figure 4: The application of D-limonene: (**a**) D-limonene using a novel organogel-based nanoemulsion (Reprinted from [PERSON] et al. [187]). (**b**) D-limonene-loaded nanoemulsions (Reprinted from [PERSON] et al. [188]). (**c**) D-limonene-loaded edible film (Reprinted from [PERSON] et al. [189]). (**d**) D-limonene-thioctic acid-ionic liquid polymer (Reprinted from [PERSON] et al. [190]). (**e**) Electrosppin polyvinyl alcohol/D-limonene fibers (Reprinted from [PERSON] et al. [191]). (**f**) Microcapsules loaded with D-limonene (Reprinted from [PERSON] et al. [192]).  
protection of D-limonene. Microcapsules made from 20% \(w/w\) brea gum solution had the best stability and there was no significant difference in the average particle size after 7 days of storage at room temperature. In addition, using high-viscosity sodium alginate and gelatin (type A) as wall materials and fabricated composite coalescent microcapsules, we encapsulated D-limonene by a spray drying and in situ composite coalescence method, which had 75% \(\pm\) 6% of the degree of reconsolidation and retained up to 82.7% of the D-limonene during drying and 80% of the D-limonene when stored at room temperature for more than 72 days [194]. In a study, D-limonene, lipoic acid, and 1-ethyl-3-methylimidazole sulfate were used to prepare a D-limonene-lipoic acid-ionic liquid polymer that exhibited long-term stability and moderate strain, high bond strength to various substrates, good self-healing ability due to the presence of disulfide and hydrogen bonds, and excellent antibacterial ability [190] and the electrostatic spinning technology can be used to prepare a new antibacterial active packaging fiber of polyvinyl alcohol/D-limonene with excellent tensile strength and elongation at break, which exhibited optimal degradability, antibacterial properties, and the lowest oxygen permeability at a polyvinyl alcohol:D-limonene ratio of 7:3 [191]. In another study, zein-based microcapsules loaded with D-limonene were prepared using an antisolvent method, which resulted in good stability and lower initial release compared to whey protein isolate (WPI)-stabilized emulsions, and it exhibited better retention as the duration phase tended to be progressive [192].  
This shows that nanotechnology can not only improve the physicochemical properties of D-limonene and make it applicable to more fields but can also enhance its biological activity, which is valuable for in-depth research.