**5. Bioactivity of** *T. hyemalis* **EO**

### **5.1 Antioxidant activity**

Several studies have shown the antioxidant activity of *T. hyemalis* EO. In this sense, Ocaña and Reglero [49] analyzed the antioxidant properties of the EO of *T. hyemalis*, *T. zygis*, and *Thymus vulgaris* L. on a cellular model of inflammation/ atherogenesis, in which human macrophages, derived from THP-1 cells, were used. These cells were incubated with EOs of the different Thymus species. The expression of inflammatory (TNF-α, IL-1B and IL-6) and anti-inflammatory (IL-10) mediators was determined. The results showed that the production of inflammatory mediators took place and the production of the anti-inflammatory mediator IL-10 increased in the presence of EOs of any of the three species of Thymus (being *T. hyemalis* the one that had less activity). This effect is due to the antioxidant capacity of these EOs, which in turn is responsible for the anti-inflammatory activity observed in this test.

On the other hand, Jennan et al. [50] compared the activity of the EO of *T. hyemalis* with that of the EO of *Thymus bleicherianus* Pomel, measuring its capacity to eliminate the free radical 1,1-diphenyl-2-picrilhydracil, observing a greater antioxidant activity in the EO of *T. bleicherianus*. The activity of EO of *T. hyemalis* was also compared with that of BHT, the synthetic compound being a more potent antioxidant. These results suggested that, although the *T. hyemalis* EO is a good antioxidant, it is not as good as the EO of other *Thymus* species.

#### **5.2 Antibacterial activity**

Rota et al. [32] conducted a study on the antimicrobial activity of EOs from several thyme species, specifically, *T. hyemalis*, *T. zygis*, and *T. vulgaris*. The EO activity was tested against the pathogenic microorganisms *E. coli*, *L. monocytogenes*, *S. typhimurium*, *Shigella flexneri*, *Shigella sonnei*, *Staphylococcus aureus*, *and Yersinia enterocolitica*. The results showed that the antimicrobial activity seemed to be related to the content of phenolic compounds, specifically thymol and carvacrol. EOs that showed the greatest antimicrobial effectiveness were *T. hyemalis* (thymol and carvacrol chemotypes, in this order), *T. zygis* (thymol), and *T. vulgaris* (thymol). These results coincided with those found by Jennan et al. [50] which suggested that *T. hyemalis* EO affected survival and inhibited the growth of bacteria Gram+ and Gram−.

Some microorganisms, such as *S. typhimurium*, *Y. enterocolitica*, *S. flexneri*, *L. monocytogenes*, and *S. aureus*, showed a high sensitivity to EOs from *T. hyemalis* (thymol and thymol/linalool chemotypes), so a high concentration of them to be effective was not necessary. In other cases, such as *E. coli*, the presence of a high concentration of carvacrol or thymol was essential to observe a potent antibacterial activity. In addition, it has been observed that the greater the richness and variety of minority components, the greater the effectiveness of EO against microorganisms [32].

Tepe et al. [51] also investigated the in vitro antimicrobial activity of *T. hyemalis* EO (carvacrol chemotype), which turned out to be a potent bactericide at low

**123**

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

**Microorganisms MIC Commercially available essential oil component**

*Staphylococcus aureus* 1.95 0.48 250.00 *Bacillus cereus* 0.97 0.24 250.00 *Enterobacter aerogenes* 0.97 1.95 250.00 *Escherichia coli* 1.95 0.48 250.00 *Klebsiella pneumoniae* 1.95 3.90 250.00 *Proteus mirabilis* 1.95 1.95 250.00 *Pseudomonas aeruginosa* 15.62 7.81 250.00 *Candida albicans* 0.97 0.24 15.62

**Thymol Carvacrol p-cymene**

concentrations (31.2 mg/mL) against *Bacillus cereus* and *Bacillus subtilis*. In addition, it also inhibited the growth of *Enterococcus faecalis* and *S. aureus*, although at higher concentrations (62.5 mg/mL). They also studied the antimicrobial activity of isolated carvacrol, which showed a potent activity against *B. cereus*, showing inhibition of bacterial growth with a MIC of 0.24 mg/mL. It also showed activity against

*Antibacterial and antifungal activity of the three major components found in* T. hyemalis *EO [51].*

This activity of carvacrol was compared with the antibacterial activity of thymol, the second most important component of *T. hyemalis* EO (carvacrol chemotype). The results obtained suggested that thymol was a good bactericide, but not as much as carvacrol. However, when the isolated precursor of carvacrol (p-cymene) was used, no antimicrobial activity was observed. Also, neither the *T. hyemalis* EO nor the isolated carvacrol was effective against *Klebsiella pneumoniae*, *Pseudomonas* 

Tepe et al. [51] demonstrated the antifungal activity of *T. hyemalis* EO against *C. albicans*, which inhibited its growth at a MIC of 62.50 mg/mL. This activity was also measured using carvacrol, thymol, and p-cymene, major components of *T. hyemalis* EO. Carvacrol inhibited the growth of the fungus at a MIC of 0.24 mg/ mL, while p-cymene needed high concentrations to begin to inhibit fungal growth. Thymol was also a good antifungal against *C. albicans*, although not as good as

In general, all the data together show that *T. capitata* and *T. hyemalis* are two important sources of EOs, which have different types of bioactivity, being of great interest for human health as well as for food and cosmetics, due to their antifungal,

According to the literature reviewed, the biological activity found in the EOs is clearly related to the chemical composition of them. As regards the *T. capitata* EO, there are some controversies about its homogeneity. Several studies confirm the existence of a single chemotype in this species, determined by its major component, carvacrol [9, 23–28]. However, other studies support the existence of three

*E. coli*, although at higher concentrations (**Table 1**).

*aeruginosa*, *Pseudomonas fluorescens*, *and L. monocytogenes*.

carvacrol, since the MIC turned out to be 0.97 mg/mL.

antibacterial, and antioxidant properties.

**5.3 Antifungal activity**

**Table 1.**

**6. Discussion**

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


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

**Table 1.**

*Thymus*

**5. Bioactivity of** *T. hyemalis* **EO**

**5.1 Antioxidant activity**

observed in this test.

**5.2 Antibacterial activity**

Gram+ and Gram−.

microorganisms [32].

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.

Several studies have shown the antioxidant activity of *T. hyemalis* EO. In this sense, Ocaña and Reglero [49] analyzed the antioxidant properties of the EO of *T. hyemalis*, *T. zygis*, and *Thymus vulgaris* L. on a cellular model of inflammation/ atherogenesis, in which human macrophages, derived from THP-1 cells, were used. These cells were incubated with EOs of the different Thymus species. The expression of inflammatory (TNF-α, IL-1B and IL-6) and anti-inflammatory (IL-10) mediators was determined. The results showed that the production of inflammatory mediators took place and the production of the anti-inflammatory mediator IL-10 increased in the presence of EOs of any of the three species of Thymus (being *T. hyemalis* the one that had less activity). This effect is due to the antioxidant capacity of these EOs, which in turn is responsible for the anti-inflammatory activity

On the other hand, Jennan et al. [50] compared the activity of the EO of *T. hyemalis* with that of the EO of *Thymus bleicherianus* Pomel, measuring its capacity to eliminate the free radical 1,1-diphenyl-2-picrilhydracil, observing a greater antioxidant activity in the EO of *T. bleicherianus*. The activity of EO of *T. hyemalis* was also compared with that of BHT, the synthetic compound being a more potent antioxidant. These results suggested that, although the *T. hyemalis* EO is a good

Rota et al. [32] conducted a study on the antimicrobial activity of EOs from several thyme species, specifically, *T. hyemalis*, *T. zygis*, and *T. vulgaris*. The EO activity was tested against the pathogenic microorganisms *E. coli*, *L. monocytogenes*, *S. typhimurium*, *Shigella flexneri*, *Shigella sonnei*, *Staphylococcus aureus*, *and Yersinia enterocolitica*. The results showed that the antimicrobial activity seemed to be related to the content of phenolic compounds, specifically thymol and carvacrol. EOs that showed the greatest antimicrobial effectiveness were *T. hyemalis* (thymol and carvacrol chemotypes, in this order), *T. zygis* (thymol), and *T. vulgaris* (thymol). These results coincided with those found by Jennan et al. [50] which suggested that *T. hyemalis* EO affected survival and inhibited the growth of bacteria

Some microorganisms, such as *S. typhimurium*, *Y. enterocolitica*, *S. flexneri*, *L. monocytogenes*, and *S. aureus*, showed a high sensitivity to EOs from *T. hyemalis* (thymol and thymol/linalool chemotypes), so a high concentration of them to be effective was not necessary. In other cases, such as *E. coli*, the presence of a high concentration of carvacrol or thymol was essential to observe a potent antibacterial activity. In addition, it has been observed that the greater the richness and variety of minority components, the greater the effectiveness of EO against

Tepe et al. [51] also investigated the in vitro antimicrobial activity of *T. hyemalis*

EO (carvacrol chemotype), which turned out to be a potent bactericide at low

antioxidant, it is not as good as the EO of other *Thymus* species.

**122**

*Antibacterial and antifungal activity of the three major components found in* T. hyemalis *EO [51].*

concentrations (31.2 mg/mL) against *Bacillus cereus* and *Bacillus subtilis*. In addition, it also inhibited the growth of *Enterococcus faecalis* and *S. aureus*, although at higher concentrations (62.5 mg/mL). They also studied the antimicrobial activity of isolated carvacrol, which showed a potent activity against *B. cereus*, showing inhibition of bacterial growth with a MIC of 0.24 mg/mL. It also showed activity against *E. coli*, although at higher concentrations (**Table 1**).

This activity of carvacrol was compared with the antibacterial activity of thymol, the second most important component of *T. hyemalis* EO (carvacrol chemotype). The results obtained suggested that thymol was a good bactericide, but not as much as carvacrol. However, when the isolated precursor of carvacrol (p-cymene) was used, no antimicrobial activity was observed. Also, neither the *T. hyemalis* EO nor the isolated carvacrol was effective against *Klebsiella pneumoniae*, *Pseudomonas aeruginosa*, *Pseudomonas fluorescens*, *and L. monocytogenes*.

#### **5.3 Antifungal activity**

Tepe et al. [51] demonstrated the antifungal activity of *T. hyemalis* EO against *C. albicans*, which inhibited its growth at a MIC of 62.50 mg/mL. This activity was also measured using carvacrol, thymol, and p-cymene, major components of *T. hyemalis* EO. Carvacrol inhibited the growth of the fungus at a MIC of 0.24 mg/ mL, while p-cymene needed high concentrations to begin to inhibit fungal growth. Thymol was also a good antifungal against *C. albicans*, although not as good as carvacrol, since the MIC turned out to be 0.97 mg/mL.

### **6. Discussion**

In general, all the data together show that *T. capitata* and *T. hyemalis* are two important sources of EOs, which have different types of bioactivity, being of great interest for human health as well as for food and cosmetics, due to their antifungal, antibacterial, and antioxidant properties.

According to the literature reviewed, the biological activity found in the EOs is clearly related to the chemical composition of them. As regards the *T. capitata* EO, there are some controversies about its homogeneity. Several studies confirm the existence of a single chemotype in this species, determined by its major component, carvacrol [9, 23–28]. However, other studies support the existence of three

chemotypes: thymol, carvacrol, and thymol/carvacrol, resulting in a crossover from the previous two [10, 29]. Regarding *T. hyemalis*, there is no doubt about the heterogeneity of its EO, being the chemotypes: thymol, thymol/linalool, and carvacrol [32].

For both species (*T. capitata* and *T. hyemalis*), the reason for these differences in the chemical composition of their EOs extracted from different specimens could be due both to the genetic endowment of the plants and to the influence of climatic and edaphic conditions of their habitat. In fact, the influence of climate on the composition of EOs has also been described for other species within the genus Thymus, such as *T. zygis* and *T. piperella*. In general, carvacrol-rich chemotypes have been associated with arid climates and high areas. However, thymol-rich chemotypes have higher water requirements than the carvacrol chemotypes [11, 52].

Likewise, the moment in which the specimens are harvested influences the composition of EOs, since it varies throughout the life cycle of these plants, affecting their bioactivities. In fact, in *T. capitata*, the highest content of phenolic monoterpenes occurs during the flowering stage, exhibiting greater antioxidant activity at this time. This coincides with what has been demonstrated for other thyme species, such as *T. vulgaris* [53]. For this reason, it is recommended to collect them during this stage, achieving the highest qualities of this EO. Regarding *T. hyemalis*, there is controversy about the best time to harvest. Extensively works support that it is better to collect the specimens in winter, between the flowering stage and the beginning stage of fruit ripening. However, other authors propose that the best month to harvest is August, since, during this month, there is a high content of 1,8-cineol in the EO. These results point to the possible existence of a 1,8-cineol chemotype, but further studies would be necessary to confirm this hypothesis. If this compound is a major component in *T. hyemalis*, the exploitation of this chemotype at an industrial level could be interesting, since it has been shown that 1,8-cineol has anti-inflammatory and analgesic properties [54]. It has also been observed that it can act as a natural insecticide in certain plant species of the *Myrtaceae* family [55].

On the other hand, the results show that in the absence of environmental variations, the different chemotypes are genetically determined. This has been observed for the EO of other medicinal plants, such as *Lupinus argenteus* Pursh and *Piper methysticum* G. Forst, whose mutations in a few genes influence the biosynthetic pathways which promote the greater or lesser accumulation of one or another compound, giving rise to different chemotypes [56, 57].

Regarding the antioxidant activity, the results indicate that it depends on the concentration. The EO of *T. capitata* (carvacrol chemotype) is effective at high concentration to avoid lipid oxidation of egg yolk and sunflower oil and may be even more effective than BHA and BHT. However, this is only possible if *T. capitata* specimens have been harvested during the flowering stage [7, 9].

This is due, in large part, to the fact that the antioxidant activity of EO (as well as the rest of activities) does not depend only on the majority component but also depends on the synergistic or antagonistic interactions of the majority component with other minority components, which according to the phenological stage will be different [58]. However, in the literature reviewed, some authors indicate the absence of these interactions because isolated carvacrol has been shown to have activity on its own [27, 39]. However, the EO of *T. capitata* did not prove to be a good antioxidant for olive oil. This is the difference between sunflower oil and olive oil. This difference can be due to the different compositions of fatty acids in both oils, being the most effective in sunflower oil (rich in linoleic) than in olive (rich in oleic) [39].

On the other hand, both EOs extracted from *T. capitata* specimens and *T. hyemalis*, at low concentrations, have antioxidant activity, which gives them

**125**

affected.

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

anti-inflammatory properties, which could be used for the treatment of chronic inflammatory diseases. However, at high concentrations, EOs of these species show oxidant activity, which could be toxic to the cells and so inhibit their proliferation. This effect of EOs on cell proliferation is of great interest since they could be used as

Regarding their antibacterial activity, EOs have shown a potent bactericidal effect against a large number of Gram+ and Gram- species. In this sense, EO of *T. capitata* could be used for the treatment of bacterial vaginosis together with chitosan in hydrogel; this could be a good alternative to treatment with antibiotics, which usually provoke resistance. In addition, it has been observed that EOs are well

Likewise, both EOs from *T. capitata* and *T. hyemalis* (all the chemotypes, although the most effective is the thymol chemotype) are useful against *L. monocytogenes*, so they could be used in the food industry to avoid contamination due to

In relation to the antifungal activity, it has been demonstrated for the EO of *T. capitata* (carvacrol chemotype) against *Candida* spp., *Aspergillus* spp., and some species of dermatophytes (*Trichophyton rubrum*, *T. mentagrophytes*, *Microsporum canis*, and *M. gypseum*). This EO has also shown activity against the intestinal parasite *Giardia* spp. This fact suggests that it could be used for the treatment of

In addition, the *T. hyemalis* EO (carvacrol chemotype) and carvacrol by itself also showed effectiveness against *C. albicans*. However, it has not been demonstrated for its precursor, p-cymene. Although the antimicrobial activity depends on the presence of carvacrol, it is believed that p-cymene acts synergistically with

Currently, the trade and use of thyme EOs is more focused on species such as *T. vulgaris*. This species has been widely used in aromatherapy and natural medicine for some years, as a hot poultice that relieves the pain of cystitis and renal colic, due to its analgesic properties, and in the form of vapors and inhalations for asthma and colds, among other conditions of the respiratory system. It is also used as a natural disinfectant, due to its antiseptic power. Its antimicrobial, antioxidant, and anticancer properties have been widely studied. However, the information reviewed here indicates that these two species, *T. capitata* and *T. hyemalis*, could be a very important source of economic resources, due to their properties, since they can be exploited by the pharmaceutical, food, livestock, and agricultural industries, its conservation being fundamental in the ecosystems where they are found.

Finally, in relation to the mechanism of action by which EOs have their different effects, it is not clear. It is known that all the activities mentioned are dependent on the concentration at which they are used. As we have seen throughout this work, the results vary depending on the dose of EO used. With regard to the antifungal and antibacterial activity, the EO acts by affecting the membrane permeability of the pathogen. At high concentrations, the EO denatures the proteins, whereas if the concentration is low, the enzymatic activity related to the production of energy is

It has also been observed that, in the case of *Sclerotium cepivorum* Berk, in the presence of monoterpenes, its lipid composition is modified, the cell membrane is altered, and lipid peroxidation is increased, so that these compounds are toxic for the cells. Therefore, these EOs, rich in monoterpenes, could be used to treat crops affected by diseases caused by fungi, such as white rot, which would be a great economic benefit, since it would avoid large agricultural losses. However, it would be necessary to carry out further studies on the mechanism of action of the compounds present in the EOs, specifically the content of monoterpenes in both

carvacrol, helping to destabilize the membrane of these microorganisms.

tolerated by the beneficial flora, since it is not damaged [43, 44].

giardiasis together with other compounds such as chitosan.

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

potent anticancer agents [49].

this bacterium [15].

anti-inflammatory properties, which could be used for the treatment of chronic inflammatory diseases. However, at high concentrations, EOs of these species show oxidant activity, which could be toxic to the cells and so inhibit their proliferation. This effect of EOs on cell proliferation is of great interest since they could be used as potent anticancer agents [49].

Regarding their antibacterial activity, EOs have shown a potent bactericidal effect against a large number of Gram+ and Gram- species. In this sense, EO of *T. capitata* could be used for the treatment of bacterial vaginosis together with chitosan in hydrogel; this could be a good alternative to treatment with antibiotics, which usually provoke resistance. In addition, it has been observed that EOs are well tolerated by the beneficial flora, since it is not damaged [43, 44].

Likewise, both EOs from *T. capitata* and *T. hyemalis* (all the chemotypes, although the most effective is the thymol chemotype) are useful against *L. monocytogenes*, so they could be used in the food industry to avoid contamination due to this bacterium [15].

In relation to the antifungal activity, it has been demonstrated for the EO of *T. capitata* (carvacrol chemotype) against *Candida* spp., *Aspergillus* spp., and some species of dermatophytes (*Trichophyton rubrum*, *T. mentagrophytes*, *Microsporum canis*, and *M. gypseum*). This EO has also shown activity against the intestinal parasite *Giardia* spp. This fact suggests that it could be used for the treatment of giardiasis together with other compounds such as chitosan.

In addition, the *T. hyemalis* EO (carvacrol chemotype) and carvacrol by itself also showed effectiveness against *C. albicans*. However, it has not been demonstrated for its precursor, p-cymene. Although the antimicrobial activity depends on the presence of carvacrol, it is believed that p-cymene acts synergistically with carvacrol, helping to destabilize the membrane of these microorganisms.

Currently, the trade and use of thyme EOs is more focused on species such as *T. vulgaris*. This species has been widely used in aromatherapy and natural medicine for some years, as a hot poultice that relieves the pain of cystitis and renal colic, due to its analgesic properties, and in the form of vapors and inhalations for asthma and colds, among other conditions of the respiratory system. It is also used as a natural disinfectant, due to its antiseptic power. Its antimicrobial, antioxidant, and anticancer properties have been widely studied. However, the information reviewed here indicates that these two species, *T. capitata* and *T. hyemalis*, could be a very important source of economic resources, due to their properties, since they can be exploited by the pharmaceutical, food, livestock, and agricultural industries, its conservation being fundamental in the ecosystems where they are found.

Finally, in relation to the mechanism of action by which EOs have their different effects, it is not clear. It is known that all the activities mentioned are dependent on the concentration at which they are used. As we have seen throughout this work, the results vary depending on the dose of EO used. With regard to the antifungal and antibacterial activity, the EO acts by affecting the membrane permeability of the pathogen. At high concentrations, the EO denatures the proteins, whereas if the concentration is low, the enzymatic activity related to the production of energy is affected.

It has also been observed that, in the case of *Sclerotium cepivorum* Berk, in the presence of monoterpenes, its lipid composition is modified, the cell membrane is altered, and lipid peroxidation is increased, so that these compounds are toxic for the cells. Therefore, these EOs, rich in monoterpenes, could be used to treat crops affected by diseases caused by fungi, such as white rot, which would be a great economic benefit, since it would avoid large agricultural losses. However, it would be necessary to carry out further studies on the mechanism of action of the compounds present in the EOs, specifically the content of monoterpenes in both

*Thymus*

carvacrol [32].

chemotypes: thymol, carvacrol, and thymol/carvacrol, resulting in a crossover from the previous two [10, 29]. Regarding *T. hyemalis*, there is no doubt about the heterogeneity of its EO, being the chemotypes: thymol, thymol/linalool, and

have higher water requirements than the carvacrol chemotypes [11, 52].

compound, giving rise to different chemotypes [56, 57].

specimens have been harvested during the flowering stage [7, 9].

Likewise, the moment in which the specimens are harvested influences the composition of EOs, since it varies throughout the life cycle of these plants, affecting their bioactivities. In fact, in *T. capitata*, the highest content of phenolic monoterpenes occurs during the flowering stage, exhibiting greater antioxidant activity at this time. This coincides with what has been demonstrated for other thyme species, such as *T. vulgaris* [53]. For this reason, it is recommended to collect them during this stage, achieving the highest qualities of this EO. Regarding *T. hyemalis*, there is controversy about the best time to harvest. Extensively works support that it is better to collect the specimens in winter, between the flowering stage and the beginning stage of fruit ripening. However, other authors propose that the best month to harvest is August, since, during this month, there is a high content of 1,8-cineol in the EO. These results point to the possible existence of a 1,8-cineol chemotype, but further studies would be necessary to confirm this hypothesis. If this compound is a major component in *T. hyemalis*, the exploitation of this chemotype at an industrial level could be interesting, since it has been shown that 1,8-cineol has anti-inflammatory and analgesic properties [54]. It has also been observed that it can act as a natural insecticide in certain plant species of the *Myrtaceae* family [55]. On the other hand, the results show that in the absence of environmental variations, the different chemotypes are genetically determined. This has been observed for the EO of other medicinal plants, such as *Lupinus argenteus* Pursh and *Piper methysticum* G. Forst, whose mutations in a few genes influence the biosynthetic pathways which promote the greater or lesser accumulation of one or another

Regarding the antioxidant activity, the results indicate that it depends on the concentration. The EO of *T. capitata* (carvacrol chemotype) is effective at high concentration to avoid lipid oxidation of egg yolk and sunflower oil and may be even more effective than BHA and BHT. However, this is only possible if *T. capitata*

This is due, in large part, to the fact that the antioxidant activity of EO (as well as the rest of activities) does not depend only on the majority component but also depends on the synergistic or antagonistic interactions of the majority component with other minority components, which according to the phenological stage will be different [58]. However, in the literature reviewed, some authors indicate the absence of these interactions because isolated carvacrol has been shown to have activity on its own [27, 39]. However, the EO of *T. capitata* did not prove to be a good antioxidant for olive oil. This is the difference between sunflower oil and olive oil. This difference can be due to the different compositions of fatty acids in both oils, being the most effective in sunflower oil (rich in linoleic) than in olive

On the other hand, both EOs extracted from *T. capitata* specimens and *T. hyemalis*, at low concentrations, have antioxidant activity, which gives them

For both species (*T. capitata* and *T. hyemalis*), the reason for these differences in the chemical composition of their EOs extracted from different specimens could be due both to the genetic endowment of the plants and to the influence of climatic and edaphic conditions of their habitat. In fact, the influence of climate on the composition of EOs has also been described for other species within the genus Thymus, such as *T. zygis* and *T. piperella*. In general, carvacrol-rich chemotypes have been associated with arid climates and high areas. However, thymol-rich chemotypes

**124**

(rich in oleic) [39].

*T. capitata* and *T. hyemalis*. In addition, most of the studies reviewed were carried out in in vitro experiments, so to ensure the potential of these EOs, it would be necessary to study their properties in vivo.
