**3.2. Procedure**

Chemical component groups of essential oils are readily converted by oxidation, isomerization, cyclization, or dehydrogenation, which are reactions that can be enzymatically or chemically triggered, and these processes are usually associated with a loss of quality. For example, terpenoids tend to be volatile and thermolabile and can be readily oxidized or hydrolyzed, depending on their structure. Further, the maintenance of essential oil composition depends strongly on the conditions under which it is processed and how it is handled and stored upon production. Certain factors are crucial for maintaining the stability of essential oils, such as temperature, light, and oxygen availability. Therefore, these factors need to be carefully con-

In this way, it is possible to infer that the conditions in which these essential oils are kept are fundamental to their characteristics. Rowshan et al. [50] studied the thermal stability of the *Thymus daenensis* essential oil by storing it at room temperature, under refrigeration (4°C) and frozen (−20°C). The authors verified that the oil composition was a function of temperature and that when frozen, the oil composition underwent only minor changes, and the primary quality was maintained, demonstrating the oil degradation effect under high temperature. The ambient temperature crucially influences the essential oil stability in several respects, and as a rule, chemical reactions are accelerated with increasing temperature because the reaction

Turek and Stintzing [51] evaluated the impact of different storage conditions on four essential oils (lavender, pine, rosemary, and thyme) to verify the influence of light and temperature on their composition. The authors obtained interesting results, stating that parameters such as pH, conductivity, and the chemical profile of the essential oils are severely altered when exposed to light and temperature, which modifies their quality. Their work also reinforced

One option for minimizing the exposure problems of essential oils is to make use of these compounds in encapsulated form, by means of a protective shell, to limit the degradation/ loss of biological activity during processing and storage and to control compound release at

Microencapsulation presents a great potential for improvement and development of structures for the conservation of natural products. In the last decade, there has been great progress in the development of microencapsulated compounds in the food and pharmaceutical industries, as they offer greater degradation resistance and compound stability [53, 55–59].

Encapsulation is the process of constructing a functional barrier between the core and the coating material to avoid chemical and physical reactions and to maintain the biological, functional, and physico-chemical properties of the core materials. The proper choice of encapsulation technique and the coating material depends on the end use of the product and the

that each essential oil responds differently to these external parameters.

sidered [49].

174 Cyclodextrin - A Versatile Ingredient

rates are increased by heat [49].

the time and site desired [52–54].

**3. Encapsulation**

**3.1. Approaches**

The encapsulation technique can be used for solid, liquid, or gaseous material packaging using fine polymer coatings to form macrocapsules (>5000 μm), microcapsules (0.2–5000 μm), or nanocapsules (<0.2 μm) [63, 64]. Nanoencapsulation is the coating of one or more substances within another material at the nanoscale. Microencapsulation is similar to nanoencapsulation, but it involves larger particles and is an already consolidated technique, with a longer study time compared to the nanoencapsulation process. On the other hand, macroencapsulation involves a larger scale than microencapsulation [65].

In general, the compound to be encapsulated is suspended in a solution containing the encapsulating agent, and then, this agent is dissolved and precipitated by coating the suspended material, or the compound to be encapsulated and the encapsulating agent are dissolved in a single solvent and simultaneously precipitated (coprecipitation). In this situation, various particles of the compound are within the layer of the encapsulating agent, with the capsule formation, which may be microcapsules and/or microspheres, for example [66]. The encapsulating agent protects the core by isolating it and allows release through a specific stimulus at the time and place desired [64]. **Figure 1** shows a schematic picture of microcapsules and microspheres.

Microcapsules are particles consisting of a substantial central inner core containing the active substance covered by a layer of the encapsulating agent, constituting the capsule membrane, while microspheres are matrix systems in which the nucleus is uniformly dispersed and/or dissolved in a polymer network. The microspheres may be homogeneous or heterogeneous

**Figure 1.** Types of microparticles: (a) microcapsules and (b) microspheres. Source: Adapted [67].

depending on whether the core is in the molecular state (dissolved) or in particle form (suspended), respectively [64, 68].

air temperature, atomizing air flow, liquid flow rate, vacuum aspirator velocity, and solid concentration, among others [73]. The success in obtaining particles using the spray drying method depends on factors such as the choice of polymer and the size distribution of the oil

β-Cyclodextrins as Encapsulating Agents of Essential Oils http://dx.doi.org/10.5772/intechopen.73568 177

The main advantages of the spray drying technique are the combination of particle formation and drying in a single step, the possibility of using a wide variety of encapsulating agents, potentially large-scale production, simple equipment, low operating costs, high quality capsules with good yield, quick solubility of the capsules, small size, high capsule stability, and continuous operation [61, 64, 73, 76, 77]. The disadvantages are variations in the particle size and shape distribution, high temperatures, and rapid drying rates that normally do not allow

Gallo et al. [76] studied the influence of the operation conditions of the spray drying method on the physical properties of *Rhamnus purshiana* extract powder. Roccia et al. [73] evaluated the influence of spray-drying operation conditions on the qualities of powdered sunflower oil. Fernandes et al. [78], Goñi et al. [79], and Oliveira et al. [80] microencapsulated essential oil of rosemary, eugenol, and passion fruit seed oil, respectively, using the dying spray technique. Gallardo et al. [81] microencapsulated linseed oil by spray-drying for application in

Coacervation is one of the oldest and most widely used encapsulation techniques, and it involves electrostatic attraction between two oppositely charged polymers and the formation of coacervates over a narrow pH range. This technique involves the addition of a coacervating agent to a homogeneous polymer solution. The coacervation agent desolvates the polymer solution in a coacervate (polymer rich phase) and coacervation medium (poor polymer phase). During the encapsulation process, the bioactive compound is encapsulated within the

The coacervation technique may be simple or complex. What differentiates them is the method of phase separation. In simple coacervation, the polymer is salted by the action of electrolytes, such as sodium sulfate, or desolvated by the addition of a water-miscible nonsolvent, such as ethanol, or by increasing/decreasing the temperature. These conditions promote macromolecule-macromolecule interactions, allowing the production of microcapsules containing hydrophobic substances, such as essential oils. Simple coacervation offers important advantages over complex coacervation in terms of cost savings and flexible operations. To induce phase separation, simple coacervation uses cheap inorganic salts, while complex coacervation is more sensitive even at small pH changes. In addition, complex coacervation uses expensive

On the other hand, complex coacervation involves complexation between two oppositely charged polymers (commonly a polysaccharide and a protein). Complex coacervation involves three basic steps. The first step consists of the formation of an oil/water (o/w) emulsion, and the second step consists of separation of the liquid phase rich in the insoluble polymer; this phase

droplets in the emulsion [74, 75].

functional foods.

*3.3.2. Coacervation*

polymer rich phase [7, 8].

hydrocolloids [8, 82].

encapsulation of thermosensitive compounds [61, 64, 73, 77].

The encapsulating agent should not react with the core, and it should have the ability to seal and hold the core within the capsule, protecting it from adverse conditions. Interactions between the wall material and the core can affect the release rate as well as the core volatility and particle size [63, 69].

The mechanisms involved in the core release are diffusion, where the active compound is released slowly by permeating the wall of the coating without compromising its physical integrity, or through a release trigger, which involves a change in pH, mechanical stress, temperature, enzymatic activity, time, or osmotic force, among other triggers, that promotes capsule breakdown and instantly releases the active compound [70].
