**3.3. Evaluation of antioxidant activity of host-guest complex**

Antioxidant activity was evaluated in terms of DPPH scavenging capacity (%) of free and encapsulated guava leaf oil compared to a synthetic chemical antioxidant (BHT) at concentrations ranged from 5 to 50 μg/mL.

scavenging capacity decreased around 42–48%, while the decreasing of 30–39% was found at higher concentration range (30–50 μg/mL). The stability of encapsulated black pepper oil was improved from the free black pepper oil by 18–24%. This effect is lower that observed for

Encapsulation of Essential Oils by Cyclodextrins: Characterization and Evaluation

http://dx.doi.org/10.5772/intechopen.73589

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**Table 4** shows minimum inhibitory concentration (MIC) and minimum bactericidal concen-

Guava leaf oil displayed antibacterial activity against both bacteria with MIC value of 500 μg/ mL, that could be attributed to guava leaf oil monoterpenes (such as limonene) which have been found to play efficient role in antimicrobial activity via membrane structures increasing membrane fluidity and permeability [150]. Pure limonene was reported to give antimicrobial activity against *S. aureus* and *E. coli* with MIC values of 8.0 and 10.0 μg/mL, respectively [151]. The antibacterial activity of guava leaf oil was improved after encapsulation in HPβCD by 4 and 2 times against *S. aureus* and *E. coli*, respectively. It has been reported that inclusion complexes with HPβCD could increase aqueous solubility of the encapsulated guests, thus improving the antimicrobial efficiency of essential oils at lower concentrations [99] due to a

Yarrow oil exhibited antibacterial activity against *S. aureus* and *E. coli* with the MIC values of 250 μg/mL and 500 μg/mL, respectively. The antimicrobial activity of yarrow essential oil might be because its oxygenated phenolic compounds, such as carvacrol and thymol, have been reported to give strong antimicrobial activity. These compounds were found to increase membrane permeability and membrane disruption of microbial cells (*Pseudomonas aeruginosa* and *S. aureus*) [152]. Antimicrobial potential of oxygenated phenolic compounds, were also reported in the literature [153–157]. In addition, *S. aureus*, a representative for Gram-positive bacteria, was more sensitive to tested samples than *E. coli*. This was because the external surface of outer membrane of *E. coli* that composes of lipopolysaccharides and proteins is more

**MIC (μg/mL) MBC (μg/mL) MIC (μg/mL) MBC (μg/mL)**

tration (MBC) values of essential oil for *Staphylococcus aureus* and *Escherichia coli*.

guava and yarrow essential oils (26–38 and 27–30%, respectively).

**3.4. Evaluation of antibacterial activity of host-guest complex**

better accessibility of the active compounds to cells [111].

**Antimicrobial compound** *S. aureus E. coli*

\*

encapsulation efficiency).

*coli* for both free and encapsulated essential oil.

Free guava leaf oil 500 1000 500 1000 Encapsulated guava leaf oil\* 125 250 250 500 Yarrow oil 250 500 500 1000 Encapsulated yarrow oil\* 62.5 125 62.5 125 Black pepper oil 1000 2000 2000 >2000 Black pepper oil-HPβCD complex\* 250 500 500 1000

Values were based on the actual concentrations of essential oil encapsulated in the HPβCD (calculated from

**Table 4.** Minimum inhibitory and bactericidal concentration (MIC, MBC) against *Staphylococcus aureus* and *Escherichia* 

It was established that the components responsible for the antioxidant activity of guava leaf oil are limonene, α-pinene and β-caryophyllene [146]. While limonene has a moderate antioxidant activity [147], β-caryophyllene and α-pinene show weak and moderate DPPH scavenging activity, respectively [146, 147]. Unfortunately, the encapsulated guava leaf oil gave slightly lower DPPH scavenging activity than that of the free guava leaf oil. This could be because HPβCD blocks the functional groups of the active compounds that react with DPPH radicals [110].

In the case of yarrow oil carvacrol as a major component shows strong antioxidant activity (72% DPPH scavenging at 50 μg/mL). The most effective antioxidants usually contain aromatic or phenolic rings, which interrupt the free radical chain reaction by donating H• to the free radicals [148]. The encapsulated yarrow oil gave slightly lower antioxidant activity than the activity of the free yarrow oil. It was a result of the HPβCD was blocking the functional groups of active compounds during reacting with DPPH radicals [110]. However, the encapsulation has been reported to increase the stability of the essential oils [13, 14].

Black pepper oil shows antioxidant activity with 54% DPPH scavenging (50 μg/mL black pepper oil) (**Figure 5**). It was established that the components responsible for the antioxidant activity are β-caryophyllene, limonene and α-pinene [146]. β-caryophyllene, a major component of black pepper oil, was found to give a weak DPPH scavenging activity [146]. Limonene, a minor composition, has been reported to give a moderate antioxidant activity and another component, α-pinene, also possesses a moderate antioxidant property [147]. It should be noted that free HPβCD did not show antioxidant activity.

However, the inclusion complexes have been reported to increase the stability of the essential oils [13, 14]. After exposure to sunlight, the DPPH scavenging of free guava leaf oil drastically decreased around 43–54% at all tested concentrations (5–50 μg/mL), which was likely due to limonene and pinene sensitive to sunlight [149]. Then, the inclusion complexation of guava leaf oil with HPβCD could protect the active components against the effect of light. In effect, after sunlight exposure, the DPPH radical scavenging capacity of the encapsulated guava leaf oil was more stable than the free guava leaf oil by 26–38%.

Similar results were found for yarrow essential oil, where DPPH radical scavenging (with concentration range from 5 to 35 μg/mL of essential oil) decreased around 41–51% after exposure to sunlight for 12 h. The yarrow oil with higher concentration range (40–50 μg/mL) exhibited lower loss of DPPH radical scavenging (36–37%). Obviously, as in the previous case, the encapsulation of yarrow oil in HPβCD could protect the active components against the effect of sunlight. The complexation with HPβCD improved the stability of yarrow oil by 27–30% in a similar range that guava leaf oil (26–38% -*vide supra*-).

The DPPH radical scavenging capacity of black pepper oil drastically decreased after 12 h exposure to sunlight (**Figure 4**). At the sample concentration range of 5–25 μg/mL, the DPPH scavenging capacity decreased around 42–48%, while the decreasing of 30–39% was found at higher concentration range (30–50 μg/mL). The stability of encapsulated black pepper oil was improved from the free black pepper oil by 18–24%. This effect is lower that observed for guava and yarrow essential oils (26–38 and 27–30%, respectively).
