## 4 Recent Progress in Microencapsulation Techniques for Natural Bioactive Compounds
### Micelle and Liposome Based Techniques  
Liposome refers to lipid-based small membrane vesicles formed by phospholipid hydration and is gaining popularity in the development of functional food, medical uses, nutraceuticals, and cosme for the delivery and sustainable release of bioactive compounds [143, 144, 145]. Phospholipids form a major part of liposomes, and the most commonly used phospholipids are natural, such as soy lecithin, egg lecithin, and marine lecithin, or semisynthetic or synthetic phospholipids such as DPPC (dipalmitoylphosphatidylcholine), etc., with cholesterol commonly added in the formulations for providing structural stability [146, 147]. During the preparation of liposomes, mechanical treatments such as heating and stirring facilitate phospholipid bilayers to encircle the aqueous medium-forming vesicle in which hydrophilic groups are arranged towards aqueous phase and hydrophobic ends are arranged toward the inner phospholipid bilayer, leading to the entrapping of both hydrophobic and hydrophilic substances [148, 149, 150]. Some authors [148, 151] noted the critical role of phase transition temperature (Tt) in the formation of liposomes as the temperature below Tt, and phospholipids present in gel state instead of crystalline phase, resulting in a problem in formation of liposomes due to very close arrangement of hydrophobic tails in such a state [145, 152]. Liposome varies in size (from 0.025 \(\upmu\)m to 5.0 \(\upmu\)m) and layers, viz., a single bilayer membrane (unilamellar vesicle; LUV) and more than one layer (multilamellar vesicle; MLU, diameter ranging from 200 nm to 10 \(\upmu\)m) [3]. LUVs are further categorized into two types based on diameter, viz., small LUVs with a diameter of \(<\)200 nm and large LUVs with a diameter \(>\)200 nm [153, 154]. [PERSON] et al. [145] describe four important stages during the preparation of liposomes, viz., lipid drying in a suitable organic solvent, adding the lipid to aqueous media, purification, and analysis. A liposome delivery system is adopted for encapsulating bioactive compounds that have poor water solubility and/or are chemically unstable. It provides higher encapsulation efficiency and bioavailability of active ingredients. This technology has limitations to scaling up due to the high cost involved, the poor chemical and physical attributes, the uneven particle size, being more prone to lipid oxidation, and the requirement of post-processing, etc. [96,154]. This technique has been used by many researchers to microencapsulate a variety of compounds without any deterioration in their bioactivity. [PERSON] et al. [155] reported an increase in the oxidative stability of microencapsulated polyunsaturated fatty acids in liposomes. [PERSON] et al. [144] incorporated microencapsulated nisin in liposomes system in dairy products and observed significant improvement in stability by preventing enzymatic degradation, targeted availability, and the release of nisin. [PERSON] et al. [147] encapsulated nisin in liposomes formed by using soy lecithin and observed equal concentrations of free and encapsulated nisin more effective in inhibiting the growth of _Listeria monocytogenes_ as compared to using only encapsulated nisin. [PERSON] et al. [156] used novel proliosomes to encapsulate curcumin for increasing its water solubility (80% curcumin even after 2 months storage) and chemical stability by utilizing a combination of phospholipids and micro-ionized sucrose. These have good potential to be used in the preparation of functional food products. These proliosomes were changed to liposomes by applying xanthum gum, guar gum, and hydration, and 72% curcumin was observed after 1 month of storage. The ethanolic coconut husk extract (ECHE) contains a large amount of several bioactive compounds, but the dark brown color limits their use. ECHE was encapsulated by using liposomes with soy phosphatidylcholine and cholesterol to improve the antimicrobial activity as well as minimize the adverse effects on product color [157].