**3. CDs and essential oils**

The use of CDs for the essential oils encapsulation can protect the active compounds of essential oils from environmental conditions [13, 14] and improve the aqueous solubility of essential oils for increasing their capacity to functionalize the products in which it is used as additive [88]. As quote above, CDs are cyclic oligosaccharides consisting of glucopyranosyl units linked by α-(1,4) bonds [89]. The widely used natural CDs are α-, β- and γ-CD consisting of 6, 7 and 8 glucopyranose units, respectively [90, 91]. These molecules have a unique structure with a hydrophobic cavity and a hydrophilic surface, which can form inclusion complex with a wide variety of guests. They can be used to enhance the solubility of insoluble compounds, stabilize labile guests against oxidation, control volatility and sublimation, modify taste by masking off flavors, entrap odors and control the releasing of drugs and flavors [92]. Among those CDs, β-CD is the most widely applicable kind because of its suitable cavity size for common guests with molecular weights between 200 and 800 g/mol and its availability and reasonable price [93]. Although β-CD can be used with many guests, its solubility in water is low (1.8 g in 100 mL water at 25°C). In some cases, there is a need to enhance water solubility of β-CD by adding the hydroxyl-alkyl groups on the β-CD surface. A hydroxyl-alkylated or hydroxypropyl-β-CD derivative (HPβCD) is relatively high aqueous solubility (above 60 g in 100 mL water at 25°C) with low toxicity and satisfactory inclusion ability [94].

On the other hand, encapsulation of essential oils or their chemical components with CDs or CD derivatives for improvement of biological properties have been observed [5, 95–98] or their antimicrobial activity [99].

Indeed, a large amount of contributions about technologic applications of CD-inclusion complex of essential oils and their main components has been published in the last 10 years, some of them are included in **Table 1**.

Yarrow (*Achillea millefolium* L. s. l.) has a broad spectrum of pharmacological activities. It is widely used in folk medicine [80]. In Europe, it has been used as a remedy to treat digestive problems, diabetes, hepatic-biliary diseases, amenorrhea, and consumed for its antitumor and anti-inflammatory properties [81–83]. In addition, antimicrobial and antioxidant properties of yarrow have also been reported [84–86]. Chemical components of yarrow essential oil have been found to be carvacrol, linalool, 1,8-cineole, camphor and thymol was mostly found as a major component (**Figure 5**) [87]. However, some active chemical components of yarrow oil (such as carvacrol and thymol) are sensitive to environmental factors such as, light, oxygen and temperature. Encapsulation of yarrow essential oil could offer possible solutions for the

The use of CDs for the essential oils encapsulation can protect the active compounds of essential oils from environmental conditions [13, 14] and improve the aqueous solubility of essential oils for increasing their capacity to functionalize the products in which it is used as additive [88]. As quote above, CDs are cyclic oligosaccharides consisting of glucopyranosyl units linked by α-(1,4) bonds [89]. The widely used natural CDs are α-, β- and γ-CD consisting of 6, 7 and 8 glucopyranose units, respectively [90, 91]. These molecules have a unique structure with a hydrophobic cavity and a hydrophilic surface, which can form inclusion complex with a wide variety of guests. They can be used to enhance the solubility of insoluble compounds,

limitation.

**3. CDs and essential oils**

**Figure 5.** Main components of yarrow [87].

268 Cyclodextrin - A Versatile Ingredient


**Table 1.** Contributions abut host-guest complex formation between CDs and CDs derivatives and essential oils.
