1. Introduction
Lavender is one of the most famous among the medicinal and aromatic plants [
1]. It belongs to the
Lamiaceae family; the most well-known species are
Lavandula angustifolia,
Lavandula latifolia,
Lavandula intermedia,
Lavandula dentata, and
Lavandula stoechas, but only the first three of them are commonly used in distillation for essential oil production. The most valuable essential oil comes from
L. angustifolia (LA) Miller, which is also known as true lavender or English lavender. The name “lavender” comes from the Latin word “lavare”, meaning “to wash”, since in ancient Arabia, Greece, and Rome, it was mainly used in washing [
2,
3].
Lavender
Lavandula angustifolia Miller (
L. angustifolia) is indigenous to the Mediterranean area and has been cultivated for thousands of years in Greece, Bulgaria, and France, with the latter two countries being the biggest European lavender cultivators [
4,
5]. The cultivation of lavender and the extraction of its essential oil is a growing enterprise in Mediterranean countries [
2]. The Mediterranean area offers a suitable phytosociological environment for lavender to grow and obtain its characteristics and increased concentration of secondary metabolites, due to which, the medicinal properties and the multiple benefits of lavender to human health have been recognized even from the ancient times [
6]. It is regarded that the medicinal attributes of lavender and its products to human health originated from its physicochemical composition, particularly from the large amount of volatile aromatic compounds and non-volatile phenolic compounds [
4]. Lavender oil can be used topically or orally, or it can be inhaled to cure or mitigate edema or pain caused by a variety of medical conditions because of its apparent disinfecting, carminative, cicatrizing, calming, and sedative effects [
3]. In addition, lavender also contains high quantities of phenolic acids and flavonoids, which are known for their anti-inflammatory, antiproliferative, and antimicrobial properties [
7,
8], as well as their sedative and anxiolytic activities known to treat stress and depression [
9]. Nowadays, lavender oil is often used by different industries in scenting cosmetic products, in perfume production, and in food flavoring [
10].
Several studies have also reported on the effects of lavender oil as a means to mitigate oxidative stress in humans. Free radicals that are considered to be the main responsible oxidative stress factors in humans can be combated by various antioxidants [
11]. Practically, the role of antioxidants is the capacity to prevent or delay cellular damage caused by the effect of free radicals [
12]. They can act either by interfering with the oxidative process by reacting themselves with free radicals, or by acting as oxygen scavengers [
13].
Indeed, the strong free radical scavenging ability of lavender oil was previously reported by Bouyahya et al. [
14], while other studies have reported on its antioxidant properties, as lavender oil showed protective properties against mutagen-induced DNA damage by increasing the levels of enzymatic and non-enzymatic antioxidants in the human hepatoma cell line HepG2 in vitro and in rat hepatocytes ex vivo [
9]. Moreover, certain compounds, such as linalool, linalyl acetate, eucalyptol, and camphor, all found in lavender essential oil, are reported to show anticancer and anti-mutagenic properties [
15], through bacterial reverse mutation assay [
16], or via cytotoxic actions [
10,
17,
18].
Two
Oreganum vulgare subspecies are especially valued from an economic viewpoint,
Origanum vulgare L. subsp.
vulgare and
Origanum vulgare ssp.
hirtum. The first one (common oregano) occurs in the Northern and Central Europe area, while the second one (
Origanum vulgare ssp.
hirtum), native to Greece, is known as Greek oregano worldwide, and is especially important due to the presence of pure carvacrol (up to 80% of the essential oil is carvacrol) [
19]. Oregano may adapt and develop in various soils and climates, in rich and poor soils, from coastal to mountainous areas, from islands to mainland Greece. Oregano can be grown in arid areas and withstand drought. However, in prolonged drought, especially during spring, it should be watered once or twice in order to enhance its efficiency along with its quality. The dry form of oregano (leaves, flowers) is mainly used in cooking, and in small quantities in the production of essential oil and water. Moreover the essential oil is used as a natural antibiotic in feed for pigs, poultry, and lamb. Furthermore, it possesses strong antioxidant, antibacterial, and antiseptic properties but also diuretic, expectorant, simulative, carminative, antispasmodic, and anticancer activities [
20]. The antioxidant and antimicrobial activity of oregano essential oil is known to be related to the high quantities of carvacrol and/or thymol, followed by rosmarinic acid and its derivatives within the non-volatile fraction [
21,
22]. The chemical composition of the genus
Origanum (Lamiaceae) is dominated by phenolic compounds in both the volatile and non-volatile fractions [
23].
The chemical compositions of oregano essential oils may vary among several populations [
24,
25] and may be affected by various factors, such as the geographical environment and harvest period, thus affecting their antibacterial properties [
26,
27]. In the meantime, it has been proposed that the medicinal properties and the quality of lavender oil vary among the different species and areas of cultivation and are likely to depend on their chemical compositions [
28]. Τhe prefecture of Western Macedonia is one of the main areas for lavender and oregano cultivation in Greece, but there are no studies available reporting on the quality characteristics of their essential oils in Greece.
Thus, in this research, we provide for the first time the characteristics and the chemical composition of the lavender
L. angustifolia and the oregano
Origanum vulgare ssp.
hirtum, which are widely cultivated in the prefecture of Western Macedonia in Greece. A progression of information is introduced, including the specific kinds of development, the decision for developing boundaries (for example, a relative land examination of the area proposed for the specific harvest), as well as the refining system of lavender/oregano oil and lavender/oregano water. Regarding the essential oils, an examination of their synthetic structure and aromatic substances is introduced, while for the lavender and oregano water, an investigation of the normal compounds and microbial attributes is performed. Moreover, considering that a key mechanism through which antioxidants neutralize radicals is hydrogen atom transfer (HAT), where a proton (H
+) and an electron (e
−) are simultaneously transferred as a pair (H
+/e
−), herein, we apply the DPPH method, which is reliable in both natural antioxidant and hybrid antioxidant materials [
29], to assess the HAT antioxidant activity of the lavender and oregano extractants in oil and water. In addition, to explore the applicability and potential commercial use of lavender and/or oregano oil and water, we evaluate and present, for the first time in the literature to the best of our best knowledge, the effectiveness both of lavender oil- and oregano oil-based antiseptics against common bacteria that can present illnesses to humans. The resistance of bacteria against antiseptics has been observed by the scientific community in human health facilities, in animal production facilities and in food production plants. In accordance with the increased resistance to antibiotics, the resistance to antiseptics is recognized as a severe threat to public health and to food production [
30]. Therefore, there is constant demand for the sustainable production of substances that could be used as antiseptics, and oregano and lavender distillation bioextractants could be useful from that perspective, for ensuring public health. Since the literature is scarce with references to lavender oil and oregano oil in hand sanitizer applications, the present study aims to investigate the potential of the particular lavender and oregano bioextractants in hand sanitizers to address their resistance to bacteria and potential as alternatives to commonly used alcohol-based hand sanitizers.
4. Discussion
The results of the present work on lavender oil composition are in agreement with previous studies. Recently, Pokajewicz et al. [
43] analyzed the Ukrainian
L. angustifolia, and reported linalool and linalool acetate as the main components (ranging from 26.14 to 57.07% and from 9.08 to 24.45% respectively), followed by terpinen-4-ol (2.16–22.44%) and lavandulyl acetate (2.12–10.23%). However, Tarakemeh et al. [
44] identified lower levels of linalool (6.8–19.2%) in Iranian
L. angustifolia and reported 1,8-cineole as the major compound (29.0–38.0%) of the essential oil. In terms of linalool concentrations, similar results to our study have been obtained for another lavender species, i.e.,
L. officinalis, with linalool as the main component in Egyptian [
15], Tunisian [
45], Algerian [
46], and Jordanian [
47] essential lavender oil. Moreover, in Tunisian essential oil obtained from
L. latifolia species, the linalool concentration was found to be 32.3% [
48], while in Moroccan essential oil obtained from
L. dentate species, linalool was detected in 45.06% [
49].
According to Héral et al. [
4], the previously mentioned volatile components that were isolated from plants during the distillation process in order to obtain the essential oils, are regarded as the main source of the pleasant aroma of lavender plants. The results of the present study are in compliance with previous studies on lavender essential oils, supporting the findings that show they contain mainly oxygenated monoterpenes, such as linalyl acetate and linalool, which constitute 4–57% and 1–54% of true lavender oil, respectively [
50].
Indeed, our results show that linalyl acetate was determined at levels as high as (26.98 and 33.61%), followed by linalool (21.73 and 26.57%). According to Duskova et al. [
51], the floral aromatic and pharmaceutical quality of the oils is mainly attributed to the high concentration of the oxygenated monoterpenes, and it is common that the concentration of these compounds does not fall below 20% of the total substances in the lavender essential oils. More oxygenated monoterpenes are usually detected, such as terpineols, including terpinen-4-ol (mainly in
L. angustifolia) and
α-terpineol, with contents of 2–14% and 2–9%, respectively, and borneol. Eucalyptol (1,8-cineole) and camphor were also identified in the essential lavender oil in a study (0.97–2.61% and 0.53–0.73%), with the usual contents of 0.1–44% and traces of about 28%, respectively [
51]. These high values of eucalyptol and camphor are usually found in essential oils from lavender leaves and stems or flowers from some unique special chemotypes [
52], increasing antimicrobial action, while deteriorating the oil quality in the perfumery industry [
53,
54]. Moreover, unique irregular oxygenated monoterpenes, such as lavandulyl acetate, provide a characteristic herbal rosy scent [
36,
51], a compound that was also found in the lavender oil in this study by GS-MS analysis. The other terpene groups found in our study, such as monoterpene hydrocarbons (
β-ocimene) and sesquiterpene hydrocarbons (
β-farnesene and caryophyllene), usually constitute a lesser fraction of lavender oils [
55].
In accordance with our results on oregano oil, a previous study by Azizi et al. [
56] showed that the predominant components of the essential oil from 42 oregano accessions were carvacrol (up to 66%), thymol (up to 66%), γ-terpinene (up to 11%), and p-cymene (up to 5.7%). D’Antuono et al. [
57] analyzed native populations of
Origanum vulgare L. from the Liguria and Emilia regions of northern Italy for their essential oil contents and composition, where they found sixty-four compounds. According to the essential oil composition, the samples were divided into three groups, where the first one had high contents of carvacrol and thymol, the second one had different sesquiterpenes and linalool, and the third one had abundant sesquiterpenes. Our results are in compliance with the first group, which included the seven Ligurian accessions from Finale, Savona, Recco, Sestri, Levanto, Monterosso, and Cerri, where these two monoterpene phenols, their main precursors g-terpinene and p-cymene, and other related compounds represent the bulk of the essential oil, which has a low content of many of the sesquiterpenes [
56]. An older report by Kokkini et al. [
58] found thymol to be the main component in oils of
O. vulgare ssp. hirtum plants from the Northern part of Greece, whereas carvacrol prevailed in oils from the Southern part of the country. Samples rich in carvacrol were also found in Bulgaria, with a maximum carvacrol content of 73.4% [
59]. Kosakowska et al. [
60] analyzed
Origanum vulgare ssp.
hirtum and found 22 compounds, including γ-terpinene (17.31%, p-cymene (11.13%), thymol (0.58%), and phenol monoterpenes (39.79%) with a clear domination of carvacrol (37.21%). Shafiee-Hajiabad et al. [
61] analyzed Greek oregano oil and found that carvacrol had the highest content among all components, while Baranauskiene et al. [
62] analyzed Lithuanian
Origanum vulgare ssp.
hirtum and found carvacrol as the dominant component (72–88%).
The chemical composition of the Greek oregano essential oil from Western Macedonia analyzed in the present investigation allowed us to classify the oil as a mixed carvacrol/p-cymene/thymol/γ-terpinene chemotype. Regarding industrial applications, essential oils with up to 80% of carvacrol are considered the most valuable due to the proven biological activity of this phenolic monoterpene [
63]. In addition, according to European Pharmacopeia recommendations, the sum of thymol and carvacrol in Greek oregano essential oil should not be lower than 60% [
60,
64].
The results of the microbial content analysis suggest that the probability of growth of microbiological charge does not exist even during the storage of lavender/oregano oil in a special plastic small bottle of 100 mL.
The data shown in
Figure 5 demonstrate the far superior antioxidant activity of oregano oil, 1 mL of which is able to consume 45 μmoles of DPPH radicals. In terms of activity, lavender oil follows, with 1 mL consuming 0.28 μmoles of DPPH radicals. Finally, 1 mL of oregano water and 1 mL of lavender water neutralize 0.067 and 0.022 μmoles DPPH, respectively. Overall, the oregano and lavender oils presented much better antioxidant effects compared to the oregano and lavender water. Between lavender and oregano oil, the best antioxidant activity by far is that of oregano oil, with the others in the following order: antioxidant activity of oregano oil >>> lavender oil >> oregano water > lavender water. Moreover, all the studied distillates showed antioxidant activity, which is mass-dependent, against the DPPH radical through the HAT mechanism, where one H
+ and one e
− are simultaneously transferred as {H
+/e
−} from the OH group of the antioxidant to the DPPH radical, resulting in its inactivation.
Nowadays, there is an increased usage of antiseptics by consumers, which drives the industry towards the increased production of such products, but on the other hand, there are concerns about the deleterious effects of disinfectant and sanitizer use on humans, animals, and the environment [
65]. The resistance to disinfectants leads to an increase in the bacterial load and can undermine food safety in food production plants or biosecurity status in medical facilities. Bacteria can combat chemical stress either by intrinsic mechanisms or, usually, by the transfer of mobile genetic elements [
66,
67].
Thus, there is a need to fulfill consumers’ needs but also to control the side effects of disinfectant use. Essential oil-based sanitizers for common everyday use could be an alternative, environmental, and human friendly approach in an attempt to mitigate the adverse effects that chemical-based disinfectants may cause.
Our results show that all the disinfectants tested possess excellent bactericidal activity under the conditions of the evaluation (EU protocol EN 1040), irrespective of the amount of ethanol used for the disinfectant preparation (i.e., 70%
v/
v, 75%
v/
v, and 80%
v/
v) and of the origin of the essential oil (lavender or oregano). It should be noted that it was beyond the scope of the current study to carry out sophisticated experimentation in order to further evaluate to which extent the antibacterial properties of these disinfectants are attributed to the inclusion of the essential oils. It has been shown earlier that ethanol, as a chemical substance, is capable of inactivating
Staphylococcus aureus and
Pseudomonas aeruginosa when used as such or as a substance in alcohol-based hand sanitizers [
68,
69].
Although the literature is scarce with references to lavender oil and oregano oil, some recent studies have demonstrated that alcohol-free hand sanitizers prepared either with 1.25% (
v/
v) clove oil [
70] or 10% tea tree oil [
71] are effective for hand disinfection and could serve as a potential alternative to commonly used alcohol-based hand sanitizers. In addition, the antimicrobial properties of essential oils also are known for their antioxidant attributes and have been extensively used for skincare formulations [
72]. Nevertheless, the antibacterial and antioxidant dynamics of lavender oil and oregano oil as substances in hand sanitizers remain to be evaluated.