**3. Bioactive compounds of** *T. hyemalis* **EO**

In a study conducted by [32], it was observed that *T. hyemalis* EO had a high heterogeneity, there being three different chemotypes: thymol, thymol/linalool, and carvacrol. The main components for the thymol chemotype were thymol (43%) followed by p-cymene (16%) and γ-terpinene (8.4%). For the thymol/linalool chemotype, the major compounds were linalool (16.6%), thymol (16%), γ-terpinene (9.8%), 1–8-cineol (5.4%), borneol (4.7%), and verbenone (4.8%). Finally, the carvacrol chemotype was characterized by a majority composition of carvacrol (40.1%), *p*-cymene (19.8%), borneol (5.0%), and thymol (2.9%).

The variability in the chemical composition of *T. hyemalis* EO may be related to seasonal variations [33, 34] as well as to the edapho-climatic factors [35].

One of the studies that supports the previous statement were carried out by Jordán et al. [36], where it was observed that, in the case of thymol chemotype, the

**119**

*Essential Oils of* Thymbra capitata *and* Thymus hyemalis *and Their Uses Based on Their…*

synthesis of this major compound occurred during the flowering/fruit ripening stage. The precursors of thymol, γ-terpinene, and *p*-cymene (**Figure 1**) were at their maximum concentration during the flowering stage. Therefore, between the stage of flowering and that of the beginning of fruit maturation, the composition of the EO of *T. hyemalis* reached its highest quality. This phenological stage coincides with winter, being recommendable to harvest the specimens in this season of the year. However, according to this study, it is also possible to obtain a high thymol content in the *T. hyemalis* EO during the spring season, but to achieve this, it is necessary to increase the irrigation, a condition that is not always achieved in arid and semiarid regions. In contrast to these results, Cabo et al. [33] proposed that August was the best time to harvest because the *T. hyemalis* EO contained a high concentration of 1,8-cineol in specimens collected during different phases of the vegetative cycle of *T. hyemalis*. These results seem to indicate the existence of a 1,8-cineol chemotype,

Finally, similar to the results of *T. capitata,* it should be noted that although the phenolic compounds, thymol and carvacrol, are mainly responsible for the bioactivity of the EO, the existence of synergistic or antagonistic effects between these phenolic components and other minor compounds (alcohols, other terpenoids, ketones, etc.) of *T. hyemalis* EO has been observed, which are essential for the qual-

It has been observed that the EO of *T. capitata* shows a potent antioxidant activity due to its high content of phenols (thymol or carvacrol) [37]. This statement is supported by Aazza et al. [38], when compared with the antioxidant activity of several thyme species. The results showed a higher antioxidant activity in EO rich in phenolic monoterpenes, like those of *Thymus caespititius* Brot. and *T. capitata*. This antioxidant capacity has been widely researched in order to prevent lipid oxidation during the storage of vegetable oils for culinary use, such as olive or sunflower. Likewise, Miguel et al. [26] showed that *T. capitata* EO, rich in carvacrol, avoided the lipid oxidation of sunflower oil and even turned out to be a more potent antioxidant than butylated hydroxytoluene (BHT), a synthetic antioxidant commonly used in the food industry. In addition, it has been seen that by isolating the carvacrol from the EO, this one by itself showed an antioxidant activity like EO, indicating an absence of synergistic or antagonistic effects due to the interaction between the different components of the EO. However, when the antioxidant activity of the EO of *T. capitata* was tested on the lipid oxidation of olive oil, it was observed that the EO was less potent than BHT [27, 39]. This low antioxidant capacity is also evident in the studies conducted by Saavedra et al. [40], in which it was observed that *T. capitata* EO did not help to avoid the oxidation of olive oil during storage and even increased the peroxidation levels, which indicated a greater

Another study conducted by Miguel et al. [9] on the lipid oxidation of peanut and sunflower oils showed a low antioxidant activity of *T. capitata* EO compared to two synthetic antioxidants, hydroxybutylanisole (BHA) and BHT, as well as a low effectiveness in elimination of free radicals compared to BHT, which contradicts the previous results found in sunflower oil. In addition, when comparing the EO of *T. capitata* with those of other species of the family Lamiaceae (*T. mastichina* and *T. camphoratus*), rich in *p*-cymene-2,3-diol, it was observed that the EO of *T. capitata*,

*DOI: http://dx.doi.org/10.5772/intechopen.89309*

with a very low concentration of thymol and carvacrol.

ity of this EO [32].

**4. Bioactivity of** *T. capitata* **EO**

**4.1 Antioxidant activity**

number of oxidation products.

*Essential Oils of* Thymbra capitata *and* Thymus hyemalis *and Their Uses Based on Their… DOI: http://dx.doi.org/10.5772/intechopen.89309*

synthesis of this major compound occurred during the flowering/fruit ripening stage. The precursors of thymol, γ-terpinene, and *p*-cymene (**Figure 1**) were at their maximum concentration during the flowering stage. Therefore, between the stage of flowering and that of the beginning of fruit maturation, the composition of the EO of *T. hyemalis* reached its highest quality. This phenological stage coincides with winter, being recommendable to harvest the specimens in this season of the year. However, according to this study, it is also possible to obtain a high thymol content in the *T. hyemalis* EO during the spring season, but to achieve this, it is necessary to increase the irrigation, a condition that is not always achieved in arid and semiarid regions. In contrast to these results, Cabo et al. [33] proposed that August was the best time to harvest because the *T. hyemalis* EO contained a high concentration of 1,8-cineol in specimens collected during different phases of the vegetative cycle of *T. hyemalis*. These results seem to indicate the existence of a 1,8-cineol chemotype, with a very low concentration of thymol and carvacrol.

Finally, similar to the results of *T. capitata,* it should be noted that although the phenolic compounds, thymol and carvacrol, are mainly responsible for the bioactivity of the EO, the existence of synergistic or antagonistic effects between these phenolic components and other minor compounds (alcohols, other terpenoids, ketones, etc.) of *T. hyemalis* EO has been observed, which are essential for the quality of this EO [32].

### **4. Bioactivity of** *T. capitata* **EO**

#### **4.1 Antioxidant activity**

*Thymus*

of three different chemotypes for *T. capitata*. In this sense, Miceli et al. [29] found 75 components and the majority being carvacrol and thymol, which, in all cases, constituted more than 50% of the composition of EO, followed by γ-terpinene, borneol, and *p*-cymene, when the chemical composition of the EO of *T. capitata* specimens were analyzed in flowering stage. The analysis of the compounds found in this EO revealed that there was a direct correlation between myrcene, α-terpinene, and γ-terpinene, whose concentrations decreased as the thymol concentration increased. An inverse relationship between linalool and myrcene was also observed. Thus, the analysis of the compounds presents in the EO of the specimens studied revealed that there were three distinct chemotypes: thymol, carvacrol, and thymol/ carvacrol, the most common being those of chemotype thymol. For the first two chemotypes, a negative correlation was observed between thymol and carvacrol, so when one of the components was majority, the other was at low concentration. The thymol /carvacrol chemotype resulted from the crossing between the specimens with the two previous chemotypes. In short, independently of the chemotype, it was observed that the content of monoterpenes reached 78% of the total of com-

In this sense, the experiments carried out by [10] confirmed the existence of these three chemotypes, which supports the hypothesis that *T. capitata* has a high polymorphism in the EO composition. To carry out these experiments, specimens grown in areas at different temperatures and degrees of humidity were used. As a result of this experiment, it was observed that those of carvacrol chemotype only appeared under conditions of high temperatures and low humidity. On the other hand, an experiment was carried out in which nine specimens were used, collected from three different areas, to later be cultivated under the same controlled climatic conditions. The results showed that the specimens maintained the chemotype that they originally presented, which is determined genetically, and did not change in the absence of climatic variations. These data suggest that the chemical composition of the EO is determined by the genetic endowment of the specimen and the different chemotypes are distributed according to the environmental conditions of the

Finally, in relation to other components found in smaller proportion (such as geraniol, camphor, or β-caryophyllene, among others), there is a high variability between populations and even within the same population [24, 31]. This variability can influence the bioactivity of *T. capitata* EO, which does not only depend on the majority component but also depends on the synergistic and antagonistic interactions that occur among all the phenolic and non-phenolic components [9, 25–27].

In a study conducted by [32], it was observed that *T. hyemalis* EO had a high heterogeneity, there being three different chemotypes: thymol, thymol/linalool, and carvacrol. The main components for the thymol chemotype were thymol (43%) followed by p-cymene (16%) and γ-terpinene (8.4%). For the thymol/linalool chemotype, the major compounds were linalool (16.6%), thymol (16%), γ-terpinene (9.8%), 1–8-cineol (5.4%), borneol (4.7%), and verbenone (4.8%). Finally, the carvacrol chemotype was characterized by a majority composition of carvacrol

The variability in the chemical composition of *T. hyemalis* EO may be related to

One of the studies that supports the previous statement were carried out by Jordán et al. [36], where it was observed that, in the case of thymol chemotype, the

(40.1%), *p*-cymene (19.8%), borneol (5.0%), and thymol (2.9%).

seasonal variations [33, 34] as well as to the edapho-climatic factors [35].

pounds present in the EO of *T. capitata* [29].

area in which they are cultivated [30].

**3. Bioactive compounds of** *T. hyemalis* **EO**

**118**

It has been observed that the EO of *T. capitata* shows a potent antioxidant activity due to its high content of phenols (thymol or carvacrol) [37]. This statement is supported by Aazza et al. [38], when compared with the antioxidant activity of several thyme species. The results showed a higher antioxidant activity in EO rich in phenolic monoterpenes, like those of *Thymus caespititius* Brot. and *T. capitata*.

This antioxidant capacity has been widely researched in order to prevent lipid oxidation during the storage of vegetable oils for culinary use, such as olive or sunflower. Likewise, Miguel et al. [26] showed that *T. capitata* EO, rich in carvacrol, avoided the lipid oxidation of sunflower oil and even turned out to be a more potent antioxidant than butylated hydroxytoluene (BHT), a synthetic antioxidant commonly used in the food industry. In addition, it has been seen that by isolating the carvacrol from the EO, this one by itself showed an antioxidant activity like EO, indicating an absence of synergistic or antagonistic effects due to the interaction between the different components of the EO. However, when the antioxidant activity of the EO of *T. capitata* was tested on the lipid oxidation of olive oil, it was observed that the EO was less potent than BHT [27, 39]. This low antioxidant capacity is also evident in the studies conducted by Saavedra et al. [40], in which it was observed that *T. capitata* EO did not help to avoid the oxidation of olive oil during storage and even increased the peroxidation levels, which indicated a greater number of oxidation products.

Another study conducted by Miguel et al. [9] on the lipid oxidation of peanut and sunflower oils showed a low antioxidant activity of *T. capitata* EO compared to two synthetic antioxidants, hydroxybutylanisole (BHA) and BHT, as well as a low effectiveness in elimination of free radicals compared to BHT, which contradicts the previous results found in sunflower oil. In addition, when comparing the EO of *T. capitata* with those of other species of the family Lamiaceae (*T. mastichina* and *T. camphoratus*), rich in *p*-cymene-2,3-diol, it was observed that the EO of *T. capitata*, rich in carvacrol, had a lower antioxidant activity than those of these two species. These results could be due to the differences found at the time of harvest, since, in this study, the *T. capitata* specimens were collected in the vegetative phase, while in the studies that demonstrated an important antioxidant activity for the EO of *T. capitata*, the specimens were collected during the flowering phase.

On the other hand, Galego et al. [41] carried out a study on the antioxidant capacity of EOs extracted from *T. capitata*, *Origanum vulgare* L., *T. mastichina*, and *Calamintha baetica* Boiss & Reut. For this, the antioxidant activity was determined using modified thiobarbituric acid (TBARS), which consists of the formation of a pink pigment produced by the reaction of thiobarbituric acid with malondialdehyde, a product of lipid peroxidation. Their results indicated that *T. capitata* and *O. vulgare* had the highest antioxidant activity, like BHT and BHA, but although they were effective in eliminating free radicals, at low concentrations, they did not become as effective as BHT and BHA.

In addition, it was observed that the antioxidant capacity of the EO of *T. capitata* was higher than that of the EO of *T. mastichina* and *C. baetica*, since the composition of the EO of these species was lower in phenolic compounds than the EO of *T. capitata*.

Faleiro et al. [15] also used the TBARS method to observe the effectiveness of the EO of *T. capitata* against the lipid oxidation of the egg yolk. Their results showed that, at high concentrations, EO could be as effective as synthetic antioxidants, BHA and BHT.

It should be noted that the antioxidant activity of *T. capitata* EO has not only been investigated in the food industry. In this sense, Hortigón-Vinagre et al. [42] studied the ability of this EO to prevent the cell death of cardiomyocytes in neonatal rats treated with 4-hydroxy-2-nonenal, a compound that induces lipid peroxidation in these cells. The results showed that at low concentrations (less than 40 ppm), the EO of *T. capitata* prevented the loss of membrane potential of the mitochondria and decreased the levels of reactive oxygen species (ROS), preventing the death of cardiomyocytes. However, concentrations higher than the mentioned one caused cell death, since they were toxic for the cells. In addition, this toxicity can be used as antiproliferative activity in in vitro experiments, since the EO extracted from fruits of *T. capitata* inhibited the growth of cells isolated from cervical cancer (HeLa). Likewise, the EO extracted from flowers and fruits of this species inhibited the growth of histiocytosis cells (U937) [30] and tumor cells responsible for acute monocytic leukemia (THP-1) [37].

#### **4.2 Antibacterial activity**

The antibacterial activity of the EO of *T. capitata* as well as its main component, carvacrol, was demonstrated against *Gardnerella vaginalis* by Machado et al. [43, 44]. The EO of *T. capitata* showed a potent activity against *G. vaginalis*, which was evidenced by the low minimum inhibitory concentration (MIC) (0.16 μL/mL) and the minimum lethal concentration (MLC) (0.16–0.31 μL/mL).

This antibacterial activity of *T. capitata* EO has also been observed against *Listeria monocytogenes*, the bacteria responsible for listeriosis, in a study conducted by Faleiro et al. [15].

In addition, Delgado-Adámez et al. [30] showed that the EO extracted from both flowers and fruits of *T. capitata* had a high efficacy against *Listeria innocua* (Gram+), at concentrations higher than 0.01% (v/v), and *Escherichia coli* (Gram−), at concentrations above 0.1% (v/v). Also, Karampoula et al. [45] showed the antibacterial effectiveness of the EO of *T. capitata* in hydrosol (a complex mixture of 24 components, which came from hydrodistillation of the plant, where the

**121**

complexity of this oil.

**4.4 Antiparasitic activity**

*Essential Oils of* Thymbra capitata *and* Thymus hyemalis *and Their Uses Based on Their…*

major compound was carvacrol). This antibacterial activity was studied against planktonic cells and biofilms of *Salmonella typhimurium*. The biofilms formed by the bacteria showed a slightly higher resistance to the planktonic cells, but in general, hydrosol was effective as antibacterial agent. In fact, when comparing this hydrosol with benzalkonium chloride, a commonly used synthetic antibacterial, it was observed that the hydrosol from *T. capitata* EO was much more effective as bactericide, since in order for benzalkonium chloride to show the same results as the hydrosol on planktonic cells and biofilms of *S. typhimurium*, a 200 times higher

According to Salgueiro et al. [46], the EO of 22 specimens of *T. capitata* carvacrol chemotype (60–66%), with high percentages of p-cymene (6–7.5%) and γ-terpinene (8.2–9.5%), was effective as a natural antifungal agent against *Candida* spp., *Aspergillus* spp., and some species of dermatophytes (*Trichophyton rubrum*, *T. mentagrophytes*, *Microsporum canis*, and *M. gypseum*), and its effect was mainly due to the generation of lesions on the membrane surface of the microorganism. These results agree with Palmeira-de-Oliveira et al. [47, 48], whose studies demonstrated that the EO of *T. capitata*, rich in carvacrol (75%), showed a great antifungal potential on biomass of *Candida* spp. and on preformed biofilms, since, at concentrations close to MIC (0.32 μL/mL), it caused the inhibition of its metabolism by up to 50%. In the case of biofilms, when the concentration of the EO doubled the MIC, a decrease of 80% of its metabolism was observed. Antifungal activity of the EO of *T. capitata* was also compared with the classic antifungal agents amphotericin B and

fluconazole, proving to be even more effective in some of the fungi studied.

interaction of this formula with the cell wall of *Candida* spp. [46].

Likewise, it has been observed that carvacrol or *p*-cymene isolated from the EO of *T. capitata* by themselves showed antifungal capacity. Therefore, this EO, or its isolated components, could be used for the treatment of mucocutaneous candidiasis and dermatophytosis. In this sense, the EO of *T. capitata* could be used alone or together with other antifungal components used so far [46, 47], as in the case of the association of the EO of *T capitata* with chitosan or chitosan in hydrogel, whose antifungal activity has been demonstrated in in vitro studies. The mechanism of action of this hydrogel has been studied by confocal microscopy, observing the

On the other hand, Russo et al. [23] observed that the EO of *T. capitata* carvacrol chemotype had an antifungal effect at a concentration of 250 ppm against *Sclerotium cepivorum*, a fungus responsible for white rot in garlic, onion, and leek crops. These authors suggested that the EO of *T. capitata* could be used as a natural antifungal, for its plant origin, not being harmful to the environment. In addition, it would be difficult to develop resistance in the fungus, due to the high chemical

Machado et al. [22] analyzed the antiparasitic activity of EOs rich in phenolic compounds of the species *T. capitata*, *O. virens* (Hoffmanns & Link), *T. zygis* subsp. *Sylvestris* (Hoffmanns & Link) Cout., and *Lippia graveolens* Kunth against *Giardia* spp. All EOs, including that of *T. capitata*, decreasing the viability of the parasite; altering its morphology, membrane permeability, and internal organization; and inhibiting its growth, as well as its adhesion capacity, which is essential for the parasite, to be able to bind to the intestine and not be eliminated by peristalsis. EOs blocked this adhesion from the first hours of exposure, not being more than 10% of

*DOI: http://dx.doi.org/10.5772/intechopen.89309*

concentration was needed.

**4.3 Antifungal activity**

*Essential Oils of* Thymbra capitata *and* Thymus hyemalis *and Their Uses Based on Their… DOI: http://dx.doi.org/10.5772/intechopen.89309*

major compound was carvacrol). This antibacterial activity was studied against planktonic cells and biofilms of *Salmonella typhimurium*. The biofilms formed by the bacteria showed a slightly higher resistance to the planktonic cells, but in general, hydrosol was effective as antibacterial agent. In fact, when comparing this hydrosol with benzalkonium chloride, a commonly used synthetic antibacterial, it was observed that the hydrosol from *T. capitata* EO was much more effective as bactericide, since in order for benzalkonium chloride to show the same results as the hydrosol on planktonic cells and biofilms of *S. typhimurium*, a 200 times higher concentration was needed.

#### **4.3 Antifungal activity**

*Thymus*

*T. capitata*.

BHA and BHT.

rich in carvacrol, had a lower antioxidant activity than those of these two species. These results could be due to the differences found at the time of harvest, since, in this study, the *T. capitata* specimens were collected in the vegetative phase, while in the studies that demonstrated an important antioxidant activity for the EO of

On the other hand, Galego et al. [41] carried out a study on the antioxidant capacity of EOs extracted from *T. capitata*, *Origanum vulgare* L., *T. mastichina*, and *Calamintha baetica* Boiss & Reut. For this, the antioxidant activity was determined using modified thiobarbituric acid (TBARS), which consists of the formation of a pink pigment produced by the reaction of thiobarbituric acid with malondialdehyde, a product of lipid peroxidation. Their results indicated that *T. capitata* and *O. vulgare* had the highest antioxidant activity, like BHT and BHA, but although they were effective in eliminating free radicals, at low concentrations, they did not

In addition, it was observed that the antioxidant capacity of the EO of *T. capitata* was higher than that of the EO of *T. mastichina* and *C. baetica*, since the composition of the EO of these species was lower in phenolic compounds than the EO of

Faleiro et al. [15] also used the TBARS method to observe the effectiveness of the EO of *T. capitata* against the lipid oxidation of the egg yolk. Their results showed that, at high concentrations, EO could be as effective as synthetic antioxidants,

It should be noted that the antioxidant activity of *T. capitata* EO has not only been investigated in the food industry. In this sense, Hortigón-Vinagre et al. [42] studied the ability of this EO to prevent the cell death of cardiomyocytes in neonatal rats treated with 4-hydroxy-2-nonenal, a compound that induces lipid peroxidation in these cells. The results showed that at low concentrations (less than 40 ppm), the EO of *T. capitata* prevented the loss of membrane potential of the mitochondria and decreased the levels of reactive oxygen species (ROS), preventing the death of cardiomyocytes. However, concentrations higher than the mentioned one caused cell death, since they were toxic for the cells. In addition, this toxicity can be used as antiproliferative activity in in vitro experiments, since the EO extracted from fruits of *T. capitata* inhibited the growth of cells isolated from cervical cancer (HeLa). Likewise, the EO extracted from flowers and fruits of this species inhibited the growth of histiocytosis cells (U937) [30] and tumor cells responsible for acute

The antibacterial activity of the EO of *T. capitata* as well as its main component, carvacrol, was demonstrated against *Gardnerella vaginalis* by Machado et al. [43, 44]. The EO of *T. capitata* showed a potent activity against *G. vaginalis*, which was evidenced by the low minimum inhibitory concentration (MIC) (0.16 μL/mL) and

This antibacterial activity of *T. capitata* EO has also been observed against *Listeria monocytogenes*, the bacteria responsible for listeriosis, in a study conducted

In addition, Delgado-Adámez et al. [30] showed that the EO extracted from both flowers and fruits of *T. capitata* had a high efficacy against *Listeria innocua* (Gram+), at concentrations higher than 0.01% (v/v), and *Escherichia coli* (Gram−), at concentrations above 0.1% (v/v). Also, Karampoula et al. [45] showed the antibacterial effectiveness of the EO of *T. capitata* in hydrosol (a complex mixture of 24 components, which came from hydrodistillation of the plant, where the

the minimum lethal concentration (MLC) (0.16–0.31 μL/mL).

*T. capitata*, the specimens were collected during the flowering phase.

become as effective as BHT and BHA.

monocytic leukemia (THP-1) [37].

**4.2 Antibacterial activity**

by Faleiro et al. [15].

**120**

According to Salgueiro et al. [46], the EO of 22 specimens of *T. capitata* carvacrol chemotype (60–66%), with high percentages of p-cymene (6–7.5%) and γ-terpinene (8.2–9.5%), was effective as a natural antifungal agent against *Candida* spp., *Aspergillus* spp., and some species of dermatophytes (*Trichophyton rubrum*, *T. mentagrophytes*, *Microsporum canis*, and *M. gypseum*), and its effect was mainly due to the generation of lesions on the membrane surface of the microorganism.

These results agree with Palmeira-de-Oliveira et al. [47, 48], whose studies demonstrated that the EO of *T. capitata*, rich in carvacrol (75%), showed a great antifungal potential on biomass of *Candida* spp. and on preformed biofilms, since, at concentrations close to MIC (0.32 μL/mL), it caused the inhibition of its metabolism by up to 50%.

In the case of biofilms, when the concentration of the EO doubled the MIC, a decrease of 80% of its metabolism was observed. Antifungal activity of the EO of *T. capitata* was also compared with the classic antifungal agents amphotericin B and fluconazole, proving to be even more effective in some of the fungi studied.

Likewise, it has been observed that carvacrol or *p*-cymene isolated from the EO of *T. capitata* by themselves showed antifungal capacity. Therefore, this EO, or its isolated components, could be used for the treatment of mucocutaneous candidiasis and dermatophytosis. In this sense, the EO of *T. capitata* could be used alone or together with other antifungal components used so far [46, 47], as in the case of the association of the EO of *T capitata* with chitosan or chitosan in hydrogel, whose antifungal activity has been demonstrated in in vitro studies. The mechanism of action of this hydrogel has been studied by confocal microscopy, observing the interaction of this formula with the cell wall of *Candida* spp. [46].

On the other hand, Russo et al. [23] observed that the EO of *T. capitata* carvacrol chemotype had an antifungal effect at a concentration of 250 ppm against *Sclerotium cepivorum*, a fungus responsible for white rot in garlic, onion, and leek crops. These authors suggested that the EO of *T. capitata* could be used as a natural antifungal, for its plant origin, not being harmful to the environment. In addition, it would be difficult to develop resistance in the fungus, due to the high chemical complexity of this oil.

#### **4.4 Antiparasitic activity**

Machado et al. [22] analyzed the antiparasitic activity of EOs rich in phenolic compounds of the species *T. capitata*, *O. virens* (Hoffmanns & Link), *T. zygis* subsp. *Sylvestris* (Hoffmanns & Link) Cout., and *Lippia graveolens* Kunth against *Giardia* spp. All EOs, including that of *T. capitata*, decreasing the viability of the parasite; altering its morphology, membrane permeability, and internal organization; and inhibiting its growth, as well as its adhesion capacity, which is essential for the parasite, to be able to bind to the intestine and not be eliminated by peristalsis. EOs blocked this adhesion from the first hours of exposure, not being more than 10% of cells able to adhere after 7 hours of treatment. In addition, by affecting membrane permeability, they caused swelling in the cells and alterations in the cytoplasm, which ultimately leads to cell death. Therefore, these EOs could be used as an alternative treatment for giardiasis, since they are not toxic to mammalian cells.
