## 4 Recent Progress in Microencapsulation Techniques for Natural Bioactive Compounds
### Coacervation Technique  
Coacervation refers to the production of complexes between oppositely charged biopolymers upon mixing core materials with charged biopolymer solutions. In this, an oppositely charged biopolymer is added, which forms a complex entrapping the core material and precipitates. These are collected and dried under suitable conditions, and complexes with a sphere or irregular shapes are obtained [119]. Coacervation is the process of separation of colloidal solutions into two phases, viz., a colloid-rich and colloid-poor phase. Under this process, the precipitation of wall materials is performed around the active core by altering pH or temperature or the addition of electrolyte or non-solvent compounds [25]. Depending upon the phase separation methodology, the aqueous coacervation can be classified into either simple or complex. Under simple coacervation, the phase separation is facilitated by promoting interaction between macromolecules at the cost of macromolecule-solvent interactions with the help of electrolytes such as sodium sulfate or desolvate and by the addition of solvents such as ethanol or manipulating temperature [120]. The complex coacervation is facilitated by attraction forces of oppositely charged hydrocolloids such as pea proteins, gelatin, alginates, gum Arabic, pectins, etc., and forming a matrix wall around the active ingredient previously suspended or emulsified in the wall materials. This is mostly applied for encapsulating antimicrobial compounds [121]. [PERSON] et al. [120] noted the very high cost, complex process, and use of glutaraldehyde as a cross-linking material as the main challenges during the commercialization of coacervation technology in the industry. In contrast, this technology has the advantage of being a simple process, having high loading capacity, no need for sophisticated equipment, low stirring needed, working at low temperature leading to very less evaporative losses and thermal degradation, as well as an adaptability to a range of raw materials, etc. [96]. Coacervation is a phase separation encapsulation process that is most commonly used after spray drying [122]. This is the first reported process for the industrial production of microcapsules. The coacervation technique is widely employed for the production of gelatin and gelatin-acacia microcapsules. It provides high encapsulation efficiency with a triggered controlled release, which broadens its application in the food systems. In the simple coacervation technique, a single polymer is used; while in complex coacervation, two oppositely charged polymeric materials such as acacia and gelatin are used. Pectin, alginate, and milk proteins are commonly used wall materials for simple coacervation. The three basic steps for complex coacervation involve the formation of three immiscible phases, deposition, and rigidization of the coatings. [PERSON] et al. [123] developed complex coacervates of gelatin and sodium hexametaphosphate to microencapsulate tuna oil fortified with vitamin A, D\({}_{3}\), E, K\({}_{2}\), curcumin, and coenzymes Q\({}_{10}\). They reported this process as an effective method for the encapsulation of lipid-soluble bioactive compounds. [PERSON] et al. [124] microencapsulated \(\alpha\)-linolenic-acid-rich oil from _Lepidium sativum_ seed using the coacervation technique. Gum ghatti, gum arabic, and soy protein isolate were used to prepare an oil-in-water emulsion, and the coacervates were then lyophilized to produce the microcapsules. The authors suggested that optimized \(\alpha\)-linolenic-acid-rich oil capsules can be used for the development of novel food products. [PERSON] et al. [125] used the emulsion phase inversion technique for encapsulation of orange and limonene flavor oils using low-energy nanoemulsions. This type of emulsion has the potential for the delivery of lipophilic bioactive compounds as nutraceutical agents. An oily dispersion of lycopene was encapsulated by a complex coacervation technique using gelatin and pectin [126].