# Advances in the Application of Microcapsules as Carriers of Functional Compounds for Food Products
## 7 Release of Encapsulated Bioactives from Microcapsules  
One of the major challenges for the food industry is the development of effective systems for the controlled release of encapsulated bioactive compounds, which is dependent on the wall and core material types, microencapsulation method, particle morphology and size, and release conditions (e.g., solvent, pH, temperature) [23]. The phenolic compounds from grape marc extract were microencapsulated by spray-drying technology using maltodextrin, whey protein isolate, and pea protein isolate as wall materials [41]. The influence of the type of wall material on the release of total phenolic compounds and anthocyanins from the microparticles was evaluated under simulated gastrointestinal conditions over a period of 3 h. The release profile was similar for both simulated digestive fluids (gastric and intestinal). Protein-containing particles, especially with whey protein isolate, showed a slower release rate than other studied wall materials (maltodextrin and pea protein isolate). The authors report that the slower release of the phenolic compounds may be due to the smoother surface of the microparticles imparting a smaller contact area with the medium. [PERSON] et al. [37] evaluated the release of bioactive compounds from microcapsules of maltodextrin loaded with laurel infusions produced by spray-drying. Three different drying inlet temperatures (140, 160, and 180 \({}^{\circ}\)C) and two feed rates to the dryer (8 and 10 mL\(\cdot\)min\({}^{-1}\)) were used to produce the microcapsules. Both the feed rate and the drying temperature influenced the release of the core material in water (T = 37 \({}^{\circ}\)C, pH around 6). Microcapsules dried at 160 \({}^{\circ}\)C with a feed rate of 8 mL\(\cdot\)min\({}^{-1}\) had greater and more prolonged release of the core material. Approximately 70% of the bioactive compounds were released within 48 hours, which according to the authors suggests a good absorption of the polyphenols in the small intestine. The release rate of microencapsulated lime essential oil by spray-drying using mixtures of whey protein concentrate with different maltodextrin equivalent dextrose (5, 10, and 20 DE) was evaluated by [PERSON] et al. [22]. The release of the essential oil was studied in mineral oil at 25 and 45 \({}^{\circ}\)C. The percentage of the encapsulated core material that was released was less than 75% in both conditions. However, a greater essential oil release was observed with the increase of the degree of dextrose equivalent  
[PERSON] et al. [23] studied the release mechanism of microencapsulated coriander essential oil by spray-drying. Alginate, chitosan, chitosan/alginate, and chitosan/insulin were used as wall materials. In this study, in vitro release of essential-oil-loaded microparticles simulating pH and temperature (37 \({}^{\circ}\)C) conditions of the gastrointestinal tract and food product processing (65 \({}^{\circ}\)C) was evaluated. The results showed that the release of the essential oil from the particles was influenced by pH and temperature. For example, in an acidic fluid (pH 2.5) at 37 \({}^{\circ}\)C, there was a higher release rate from the chitosan particles. They showed a rapid release rate in the first 60 min, releasing almost 60% of the essential oil that was encapsulated. Thereafter, the release slowed to a peak of 74.5% after 120 min. In contrast, the alginate particles presented a lower release under the same conditions, almost 29% after 120 min. This difference in the release of the essential oil from the microparticles was justified by the low degree of swelling of the alginate microparticles and their rigid polymeric chains, which hindered the release by diffusion. In terms of temperature, as the temperature increased to 65 \({}^{\circ}\)C, the rate of release of the essential oil also increased for both pH values. The release profile of microparticles loaded with carotenoid-rich palm oil incorporated into food matrices was evaluated by [PERSON] et al. [53].