## 4 Recent Progress in Microencapsulation Techniques for Natural Bioactive Compounds
### Spray-Based Techniques
It was used for the microencapsulation of rosemary essential oil [28] with powder recovery, surface oil, oil retention, and hygroscopicity varying from 17.25-33.96%, 0.03-0.15%, 7.15-47.57%, and 15.87-18.90%, respectively. Vitamin E and provitamin A were extracted from red pepper byproducts using the supercritical fluid extraction technique, and the extracts were microencapsulated by spray drying with gum arabic as a wall material to prevent their degradation during the subsequent storage [111]. [PERSON] et al. [112] used cellulose as the wall material for encapsulation of _Bidenspilosa_leaf extract at 13.37% concentration. The powder had a favorable particle size, residual moisture content, solubility, flow properties, and drying efficiency. Since no single compound can provide all the essential characteristics to the microcapsules with desired quality attributes, a combination of different compounds as the wall material is also a better option to improve the encapsulation efficiency and stability of microcapsules. A combination of gum arabic and maltodextrin as the wall material has been studied [29] for the microencapsulation of essential oil from the fruits of _Pterodone-marginatus_ using the spray drying technique. These authors noticed that a ratio of 1:3:3.6 of essential oil: gum arabic: maltodextrin had shown around 98.63% encapsulation and entrapment efficiency, with the best protection of \(\beta\)-caryophyllene, which is the major component of these essential oils. [PERSON] et al. [30] studied the effects of spray drying temperatures and wall materials (konjac glucomannan and gum arabic) on the functional properties of kaffir lime oil microcapsules. The combination of konjac glucomannan and gum arabic enhanced the yield and retention of total oil in the microcapsules more than any of the wall materials used alone. Spray chilling or spray congealing is a low-cost convenient microencapsulation technique that is also an easy process to scale up. It does not require organic solvents or the application of high temperature; hence, it is suitable for thermo-sensitive bioactive compounds such as enzymes, vitamins, and probiotics. In the spray coagulation technique, alginate is frequently used as a thickening and stabilizing agent, and its coagulation is facilitated by external gelation using calcium chloride or internal gelation using calcium carbonate as a calcium source. [PERSON] et al. [113] carried out the microencapsulation of phenolic extracts from _Rubusulimifolia_ flower buds in an alginate-based matrix. The yogurt containing the microcapsules of _Rubusulimifolia_ flower buds extract showed a slightly higher antioxidant activity than other samples. The matrix structure and presence of core droplets on the surface of encapsulates during spray-drying, leads to the rapid release of core materials [114]. Furthermore, this release becomes more rapid (which may not be desired in some cases) in water and in digestive enzymes by using water-soluble encapsulants such as modified starch, protein, maltodextrin, whey protein [103]. [PERSON] et al. [101] encapsulated natural antimicrobial agents, e.g., eugenol by spray drying process by using whey protein isolates or lecithin in maltodextrin. The core active ingredient released rapidly and significantly inhibited _Escherichia coli_ and _Listeria innocua_ within 30 min. Alternatively, a controlled faster release at the beginning followed by a slower release at the later phase of active core ingredients from encapsulates formed by the spray drying process could be achieved by utilizing low-solubility encapsulants [101, 115] ethyl cellulose and copolymer Eudragit RS 100 [116] cross-linked casein [117]. This targeted and controlled release could be due to the release of core droplets present at encapsulates at the beginning, followed by a slower release later due to the protection of the wall/shell. [PERSON] et al.