## 7 Encapsulation of Terpene Derivatives to Improve Their Stability and Antimicrobial Activity  
Encapsulation of terpene derivatives is a promising approach to overcome the aforementioned challenges by protecting them from heat, light, and oxygen. It promotes their solubility and stability, increases bioavailability, masks flavors, and reduces contamination risk [254]. Microencapsulation is a technique whereby liquid droplets, solid particles, or gas compounds are entrapped into thin films of food-grade encapsulating agents called wall material. The retention of the encapsulated compounds depends on their chemical structure, solubility, polarity, and volatility. Most microcapsules are small particles with diameters between a few micrometers and a few millimeters. The size and shape of the microcapsules depend on the materials and processes used to prepare them. Different types of capsules can be produced from a wide range of wall materials (polysaccharides, proteins, monomers, etc.) and by a large number of different processes, such as spray drying (Figure 6), freeze drying, extrusion, coacervation, liposome entrapment, and interfacial polymerization. Among these techniques, spray drying is the most common technology used in the food industry due to the low cost and availability of equipment. Depending on the core material and the characteristics desired in the final product, wall materials can be selected from a wide variety of natural and synthetic polymers or monomers. This process can produce powdered microcapsules from a liquid in a single simple and scalable operation [255]. It is possible to prepare mixtures of natural antimicrobials and biopolymers. The wet suspensions/emulsions are then be converted to powders by evaporating the majority of the water using an appropriate dehydration method. The resulting powder is evaluated for activity, density, flow, size, stability, and redispersion. Spray drying is the most common method of encapsulating bioactive ingredients. It can produce powdered microcapsules from a liquid in a single simple and scalable operation [256]. As represented in Figure 6, spray drying of hydrophobic compounds comprises four steps: (1) emulsion preparation by high-pressure homogenization, (2) wall material addition, (3) dispersion in small droplets by atomization, and (4) dehydration of the atomized particles. This method entails creating an emulsion containing the wall material and the core, then spraying it into a drying chamber with circulating hot air; when  
Figure 6: Schematic representation of the spray-drying microencapsulation process. the water comes into contact with the hot air, it evaporates immediately, and the core is entrapped into the wall material matrix [257; 258; 259]. Since almost all spray-drying processes in the food industry are carried out with an aqueous feed formulation, the wall material must be soluble in water and should possess good emulsification, film-forming, and drying properties, and the concentrated wall solutions should have low viscosity. Many available wall materials possess these properties, but the number of materials approved for food uses is limited. Despite the beneficial effects of terpen and their derivatives (antimicrobial, antifungal, anticarcinogenic, and pharmacological properties), they are subject to a number of drawbacks, such as their low miscibility in water (which lowers their bioavailability) and their degradation by light and temperature, as they are sensitive to environmental conditions and undergo volatilization. To overcome the chemical instability of certain terpen, encapsulation of these compounds has been used to address this issue [233; 260]. Antimicrobial activity is typically unaffected by covering the \"active\" ingredient (which may include volatile substances) in a protective matrix. The used polymers are basically inert to the encapsulated material and can offer excellent protection against degradation or evaporation.