# Advances in the Application of Microcapsules as Carriers of Functional Compounds for Food Products
## 2 Methods for the Production of Microcapsules Loaded with Bioactive Compounds
The temperature inside the microparticles, where the core material is present, is normally below 80 \({}^{\circ}\)C, which helps to minimize the thermal degradation of the material [1; 2; 62]. The properties of the resulting powder are influenced by the type of atomizer, feed physicochemical properties, drying air inlet and outlet temperatures, as well as the type and concentration of wall and core materials. When microcapsules are produced with hydrophobic active ingredients dispersed in feed emulsions, the microencapsulated bioactives are normally distributed within the thin wall and/or in the inner space. However, microencapsulated bioactives are more likely to be distributed within the thin wall if they are completely soluble in the feed solution along with the wall materials. Microcapsules usually show a spherical shape, with a low average particle size ranging from 5 to 50 \(\upmu\)m, and have a smooth outer surface or exhibit the formation of teeth or concavities with an irregular shape [1; 63; 64]. Microencapsulation by freeze-drying is a process in which the feed containing the wall and core materials is frozen at temperatures below \(-40\)\({}^{\circ}\)C and dried by sublimation under low pressure. The freeze-drying technique is simple and suitable for the microencapsulation of biological materials sensitive to heat and oxygen due to the application of low temperatures and removal of oxygen during the drying process. Different active ingredients such as phenolic compounds, carotenoids, and probiotic bacteria have been stabilized by the freeze-drying method [64; 65]. However, this technique has some constraints, such as high energy consumption and operational cost due to the long processing time (above 20 h). In comparison to spray drying, the freeze-drying method can be up to 50 times more expensive. Furthermore, the dried material has a porous structure which exposes the active ingredient encapsulated to the atmosphere, thus offering low protection for a prolonged shelf life of that compound [20; 61; 66]. Coacervation is a process in which the separation of two liquid phases in an aqueous colloidal solution occurs. One phase is rich in colloid/polymer (coacervate) and the other phase, called the \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Wall Material** & **Core Material** & \begin{tabular}{c} **Core Material** \\ **Source** \\ \end{tabular} & \begin{tabular}{c} **Main Properties/Applications** \\ **Studied** \\ \end{tabular} & **Refs.** \\ \hline Arabic gum & \begin{tabular}{c} \\ \end{tabular} & \
\begin{tabular}{c} _Lactobacillus_ \\ _paracasei_ \\ _Lactobacillus_ \\ _paramplantarum_ \\ \end{tabular} &
\begin{tabular}{c} Stabilization of active ingredient \\ _In vitro_ simulated \\ gastrointestinal digestion release \\ of probiotics from microcapsules \\ Stabilization of active ingredient \\ Controlled release of bioactives \\ from microcapsules \\ \end{tabular} & [28] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Cont. equilibrium solution, is poor in polymer. This phase separation may be induced by changing the ionic strength, temperature, pH, or solubility of the dissolving medium [20; 62]. The process of coacervation in aqueous phase is classified as simple coacervation when it is induced in a system where the wall material is a single polymer, or complex coacervation that is characterized by the interaction between oppositely charged wall materials, usually a protein and a polysaccharide, leading to a phase separation due to the electrostatic attraction between macromolecules. Several polymers have been used to produce complex coacervates, such as gelatin, arabic gum, whey protein isolate, chitosan, pectin, pea protein, and alginate, among others (Table 1) [20; 62; 67]. Complex coacervation has been used for the microencapsulation of different unstable active ingredients such as carotenoids [21; 52; 54], oils [53; 55], phenolic compounds [50; 51; 56], and probiotic bacteria [28; 57] (Table 1).