# Microencapsulation of Natural Food Antimicrobials: Methods and Applications
## 2 Encapsulation Methods
### Spray Drying  
Spray drying is the most popular and simple encapsulation technology applied in the food industry because of its low cost and readily available equipment [39] (Figure 2). Encapsulation of active compounds by spray drying for eliminating undesirable properties such as strong and unpleasant taste and odor and preserving them from deterioration by oxygen, light and interactions with other substances as well as transforming liquids to powders has been reported since the late 1950s [38]. Spray drying has been used to improve delivery systems of food active agents such as antimicrobials, antioxidants and EOs [16; 17; 18; 40]. Spray drying positively charged antimicrobial agents such as nisin and lysozyme-negatively charged polysaccharides complexes can lead to the encapsulation of the active agents within various polysaccharide networks. Lysozyme (0.714 g/L concentration) has been encapsulated by spray drying it on lysozyme-low methoxyl pectin (LMP) complexes with different polysaccharide concentrations (0-4 g/L). The antimicrobial activity and the molecular structure of lysozyme were protected during spray-drying when lysozyme was complexed by intermediate LMP concentrations [16].  
The selection of an appropriate wall material for the spray-drying microencapsulation process depends upon the end use of the product and has an essential effect on achieving high EE and physicochemical properties and stable microencapsulated powders [42]. Selected wall materials must be highly soluble in water as nearly all spray-drying processes in the food industry are carried out with aqueous feed formulations. Additionally, the wall materials should have acceptable emulsifying, film-forming and drying properties with low viscosity in a wall-concentrated solution [43]. Common shell materials are gum acacia, maltodext with different dextrose equivalents (DE), hydrophobically modified starch and their mixtures. Despite having good solubility, bland flavor, low cost and low viscosity at high solid content, the main disadvantage of carbohydrates such as maltodext and starch as encapsulant agents is their low emulsifying capacity, as they should be mixed with other materials such as proteins (whey protein, soy protein... ) and gums [44]. Inulin can be used as a new material in the production of spray-dried microcapsules containing active substances because of its ability to decrease moisture content and hygroscopicity of complexes under high relative humidity as well as its ability to preserve the glassy state of gum arabic and starch powders [17]. The effect of different wall materials, such as inulin, gum arabic, starch and maltodext, has been studied during the microencapsulation of rosemary EO by spray drying. High oil retention was obtained for microcapsules of modified starch and maltodext mixtures, which can be considered as alternatives for the encapsulation of rosemary EO due to their low cost compared to gum arabic [17].  
High oil retention in microcapsules produced by spray drying can be achieved by applying a high inlet temperature, leading to the rapid formation of a semi-permeable membrane at the surface of particles in a short time. High feed rates can also cause high oil retention in microcapsules due to the increased solid contents in the drying chamber, resulting in the fast formation of semi-permeable membranes on microparticle surfaces [45]. High oregano (_Origanum vulgare_) EO retention in spray-dried microcapsules of modified starch-gum arabic-maltodextrins emulsion was obtained at high inlet temperatures/low feed rates and low inlet temperatures/high feed rates [18].  
Figure 2: Microencapsulation process via spray drying (adapted from [PERSON] et al., 2016 [41]).