# Advances in the Application of Microcapsules as Carriers of Functional Compounds for Food Products
## 3 Wall Materials  
Wall materials have different chemical structures and physicochemical properties that influence the efficiency of the microencapsulation process. As such, their correct selection is an important step due to their direct effect on the stability of the microcapsules, efficiency of core material retention, and shelf life [66; 69]. The wall material must have suitable rheological properties at high concentrations and the ability to emulsify the active material, stabilize the produced emulsions, and keep the core material within its structure during processing or storage [66; 70]. It is also quite important the purpose for which the microcapsules are produced, such as easier dosage and increased stability during storage, to mask undesirable taste of the core material, or the controlled release on a specific site in the human gastrointestinal tract [71]. Various types of wall materials have been used for the production of microcapsules, such as polysaccharides (e.g., starches, carrageenan, maltodext, and arabic gum), lipids (e.g., stearic acid, mono- and diglycerides), proteins (e.g., albumins, pea protein, gelatin, and casein), and their mixtures (Table 1). Of these, maltodextrin and arabic gum are two of the most commonly applied [31; 72; 73]. Arabic gum (_gun acacia_) is a complex exudate of acacia trees, of which there are many species distributed over tropical and subtropical regions. The most important growing areas for species that give the best gum are Sudan and Nigeria. Arabic gum is commonly used as a purified spray-dried powder [31; 74]. It is a highly branched edible biopolymer and is chemically described as a mixture composed of carbohydrates consisting of D-glucuron acid, L-Hammose, D-galactose, 4-O-methyl-D-glucuronic acid, and L-arabinose, including approximately 2% protein [47; 75]. Due to its highly ramified structure, it is easily dispersed when stirred in water in concentrations of up to 50%. This gum is used in the fabrication of microcapsules mainly due to its low viscosity at high concentrations, good emulsifying properties that are especially interesting to the microencapsulation of oils and flavors [31; 73], compatibility with high sugar concentrations, subtle taste, and high oxidative stability [73; 74]. Other applications of arabic gum in food are as a component of the glaze or coating of pan-coated candies in confections with high sugar and low water contents such as caramels, toffees, and juibes. In confections, it prevents sucrose crystallization and emulsifies and distributes fatty components [74]. Nonetheless, arabic gum has some disadvantages, such as high cost and limited supply, as it is only produced in regions that are subject to unpredictable climate variations [75; 76]. Maltodext are produced from starch hydrolysis with values of dextrose equivalent (DE) below 20. The degree of hydrolytic conversion of starch, expressed as DE value, is the criterion for the classification and characterization of hydrolysates. The higher the value of DE, the higher the degree of hydrolysis the product was subjected to. For DE values above 20, the hydrolysate is termed syrup solids or dextrin [77; 78]. Maltodextrin has been widely used in the microencapsulation of bioactive compounds due to its satisfactory performance, low relative cost, and neutral taste and aroma. It is characterized by high solubility in water, low viscosity at high concentrations, film forming capacity, and good protection against the oxidation of core materials. On the other hand, the main disadvantage of the use of maltodextrin in the microencapsulation process is the low emulsifying ability. Thus, to form stable emulsions, mixing with other wall materials such as arabic gum, modified starch, and proteins is encouraged [69; 73; 79]. [PERSON] et al. [31] evaluated the influence of maltodextrin alone and mixed with gelatin or arabic gum when used as wall material in the microencapsulation of natural anthocyanins by spray drying.