Chemical Composition and Biological Activity of Five Essential Oils from the Ecuadorian Amazon Rain Forest

The chemical composition and biological activity of essential oils isolated from the leaves of Siparuna aspera, Siparuna macrotepala, Piper leticianum, Piper augustum and the rhizome of Hedychium coronarium were evaluated. These species are used medicinally in different ways by the Amazonian communities that live near the Kutukú mountain range. Chemical studies revealed that the main components for the two Siparuna species were germacrene D, bicyclogermacrene, α-pinene, δ-cadinene, δ-elemene, α-copaene and β-caryophyllene; for the two Piper species β-caryophyllene, germacrene D, α-(E,E)-farnesene, β-elemene, bicyclogermacrene, δ-cadinene and for H. coronarium 1,8-cineole, β-pinene, α-pinene and α-terpineol. The antioxidant activity of all essential oils was evaluated by 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), photochemiluminescence (PCL) quantitative assays, and DPPH and ABTS bioautographic profiles, with different results for each of them. Antimicrobial activity studies were carried out on three yeasts, six Gram positive and four Gram negative bacteria, by means of the disc diffusion method. The essential oil of H. coronarium showed the most relevant results on L. grayi, K. oxytoca and S. mutans, P. augustum and P. leticianum on S. mutans. An antibacterial bioautographic test for H. coronarium was also carried out and highlighted the potential activity of terpinen-4-ol and 1,8-cineole.


Introduction
According to the Monitoring Center for the Conservation of the Environment, Ecuador, with just 0.19% of the surface of the Earth, is one of 17 mega-diverse countries, home to 10% of all plant species in the world [1].Additionally, in Ecuador, diverse ancestral peoples are possessors of millenary knowledge about the use and management of these resources.The Shuar, with some 110,000 people, Molecules 2019, 24, 1637 2 of 12 are one of these populations, whose members reside mainly in the provinces of Morona Santiago, Pastaza and Zamora Chinchipe [2].All these arguments make it necessary to corroborate and to valorize the uses of medicinal plants within the Shuars' region.For the present investigation, five species, used as medicines by the Shuar indigenous people living near the Kutukú mountain range, in the Morona Santiago province, were selected.
Siparuna aspera (Ruiz & Pav.) A. DC., is a plant native to Ecuador, which can also be found in Bolivia, Colombia, Peru and Venezuela [3].It is commonly known as "limoncillo" and among the Shuar it is called "mejentsuna".The infusion of its leaves is used for lowering fevers.Siparuna macrotepala Perkins, is a plant native to Ecuador that is also distributed in Colombia and Peru [3], whose common name is "limoncillo", known among the Shuar as "tTsuna"-.The infusion of the leaves is used to fight malaria and influenza.Piper leticianum C. DC., a plant native to Ecuador, also found in Colombia and Peru [4], is known as "untuntuntup" among the Shuar, that use the leaves to fight tooth decay.Piper augustum Rudge, a plant native to Ecuador, is found throughout tropical America [5]; the Shuar ethnic group calls it "untuntup" and it is used to fight tooth decay.Hedychium coronarium J. Koenig, a plant native to tropical Asia, is an introduced species in Ecuador with the common name of "lirio de muerto" and known among the Shuar as "ajejà".It is used for its analgesic, antiseptic and digestive properties.
The scientific literature reports few chemical and biological studies carried out on these native species.In the case of S. aspera, there is a work that evaluates the leishmanicidal properties of the plant extracts [6].For S. macrotepala a chemical study denotes the presence of cadinane-sesquiterpenes [7].Regarding P. augustum, an investigation of the chemical composition of the essential oil, isolated from its leaves, reports α-phellandrene (14.7%), β-caryophyllene (13.5%), limonene (13.0%), α-pinene (10.5%) and linalool (10.3%) as main components [8].A second study assessed its anti-leishmanial activity [9].For P. leticianum, no investigations have been found.
Of the five species studied, H. coronarium is the only species about which the scientific literature presents more information, highlighting its essential oil isolated from various parts of the world such as China [10], in the Himalayas [11], Brazil [12] and India [13].Comparing the chemical studies, it is possible to appreciate a diversity in its components depending on the origin of the species.From a pharmacological point of view, there are studies that confirm its analgesic [14], antibacterial [11,13,15], anti-inflammatory [16], anthelmintic [17], antioxidant [18,19], cytotoxic [20] and hepatoprotective [21] activity.
One of the objectives of the present investigation is to reach a chemical characterization of the essential oils of the five Amazonian species; especially for S. aspera and P. leticianum, whose chemical composition was never previously described.A second objective is related to the evaluation of in vitro biological activity, performing antimicrobial and antioxidant activity studies.The research described in this manuscript ultimately is driven by the need to valorize the biodiversity and the knowledge of the native peoples of Ecuador, for their own benefits based on sustainable exploitation and in general for the advantage of the Ecuadorian population.Some of these medicinal plants could be used as an alternative health products to synthetic medicines, whose economic benefits generally fall to transnational pharmaceutical corporations.

Essential Oils Yield and Density
The essential oils yield (%w/w) and density were as follows: S. aspera, a yield of 0.15% and a density of 0.929 g /mL; S. macrotepala, a yield of 0.15% and a density of 0.930 g/mL; P. augustum a yield of 0.02% and a density of 0.908 g /mL; P. leticianum a yield of 0.02% and a density of 0.905 g/mL; H. coronarium a yield of 0.04% and a density of 0.895 g/mL.

Chemical Composition
The detailed chemical compositions of each essential oil, determined above 90%, can be seen in Table 1.S2) [23].All %area had a standard deviation < 5.0%.

DPPH and ABTS Assays
The IC 50 values are expressed in mg/mL and represent the concentration capable of inhibiting 50% of the oxidation of DPPH and ABTS.The Thymus vulgaris essential oil was used as a positive control, the activity of some pure compounds was also evaluated.The IC 50 of germacrene D, separated by silica gel column, was performed: the results are shown in Table 2. Due to the lipophilic nature of the essential oils the method used is the ACL, in which the activity is expressed as µmol of Trolox/mL (Table 3), and the positive control is T. vulgaris essential oil.The results revealed a high antioxidant activity of the Siparuna and Piper species, corresponding to the fraction with Rf = 0.8 where we found germacrene D and β-caryophyllene, for H. coronarium the activity was observed in the band Rf = 0 corresponding to 1,8-cineole (Figure 1).Due to the lipophilic nature of the essential oils the method used is the ACL, in which the activity is expressed as μmol of Trolox/mL (Table 3), and the positive control is T. vulgaris essential oil.The results revealed a high antioxidant activity of the Siparuna and Piper species, corresponding to the fraction with Rf = 0.8 where we found germacrene D and β-caryophyllene, for H. coronarium the activity was observed in the band Rf = 0 corresponding to 1,8-cineole (Figure 1).

Evaluation of the Minimum Inhibitory Concentration (MIC)
The results of the minimum inhibitory concentration are expressed in mg/mL and shown in Table 4.

Bioautographic Antibacterial Activity of the Essential Oil of H. coronarium
The interesting activity of the essential oil on several bacteria made it necessary to find the components responsible for this effect.In Figure 2 it is showed that 1,8 cineole, terpinen-4-ol explain the activity on the Gram positive bacteria.Another unidentified minor compound seems to contribute to the antibacterial effect.
The results of the minimum inhibitory concentration are expressed in mg/mL and shown in Table 4.

Discussion
The chemical composition of S. aspera and P. leticianum essential oils was studied for the first time in this research.The main molecules in S. aspera essential oil were germacrene D (23.2%), bicyclogermacrene (7.8%) and α-pinene (7.0%).In a previously study we found germacrene D and bicyclogermacrene as major compounds in Siparuna schimpffi spice [24] and α-pinene as a minor component.For S. macrotepala, the presence of cadinane compounds in interesting amounts was evidenced [7], not revealed in our essential oil.P. leticianum essential oil showed β-caryophyllene (21.8%) and germacrene D (9.0%) as main compounds, and P. augustum essential oil had a similar composition.Studies of other Piperaceae family species, like P. nigrum [25], P. marginatum [26] and P. cernuum [27], highlighted a high β-caryophyllene content.Research on P. augustum essential oil confirmed β-caryophyllene as the main molecule [8,28].Numerous studies in the essential oil from H. coronarium rhizomes reported very similar chemical compositions, with 1,8-cineole and β-pinene as main components [12,13], with exception of the data reported by Prakash et al.where linalool and limonene were the principal molecules [11].The antioxidant activities of the essential oils were not comparable with the positive control, Thymus vulgaris essential oil.However, it is important to note the interesting radical scavenging effect of germacrene D, isolated from S. macrotepala essential oil, with a DPPH IC 50 of 2.1 mg/mL and ABTS IC 50 of 1.1 mg/mL, also shown through the HPTLC bioautographic test.Photochemiluminescence assays confirmed the low antioxidant activity of the essential oils compared to the positive control.Finally, we studied the antimicrobial activity against a wide spectrum of bacteria and yeasts.The essential oil of H. coronarium showed an interesting antimicrobial effect vs. L. grayi, K. oxytoca and S. mutans and the literature has documented good results for an essential oil with similar composition against Trichoderma sp. and Candida albicans [13].Other paper studied the antimicrobial activity, but the chemical composition was different from our essential oil [11] or the chemical characterization was not investigated [15].P. augustum and P. leticianum highlighted interesting results against S. mutans.The antimicrobial bioautographic assay of H. coronarium essential oil on S. aureus, chosen as model for this experimental approach, showed that 1,8-cineole and terpinen-4-ol were the molecules responsible for the activity.Some studies have highlighted the appreciable antimicrobial capacity of these molecules [29,30].

Plant Material
Plants were collected in different sites in the province of Morona Santiago, and the coordinates and sectors are listed in Table 5.For the isolation of essential oils, the method known as hydrodistillation [31], was utilized using 250 L equipment (The Essential Oil Company, Portland, OR, USA) belonging to the Chankuap Resources for the Future Foundation.

GC-MS and GC-FID Analyses
The essential oil composition was determined by gas-chromatography coupled to mass-spectrometry, and the quantification of individual components was performed by GC-FID, calculating the relative peak average area of three separated injections.A Varian 3800 gas chromatograph (Varian, Palo Alto, CA, USA) was used, equipped with a Factor four VF-5ms column (poly-5% phenyl-95% dimethylsiloxane) of 30 m length, with an internal diameter of 0.25 mm and a film of 0.25 µm, directly coupled to a Varian 4000 mass spectrometer.The carrier gas was helium with a flow of 1 mL/min and a split ratio of 1:50.The analysis starts at 45 • C and reaches 100 • C at a rate of 1 • C per minute, then rises to a temperature of 250 • C at a speed of 5 • C, staying at that temperature for 15 min: the total analysis time was 90 min.The conditions of the mass spectrometer were: ionization energy: 70 eV; emission current: 10 µAmp, scan rate: 1 scan/s, mass range: 35-400 Da, trap temperature: 220 • C, transfer line temperature: 260 • C. The identification of compounds were performed by comparing their arithmetic indices (AI) and the MS fragmentation pattern with those of other known essential oils, with pure compounds and by matching the MS fragmentations patterns and arithmetic indices with mass spectra libraries and with those in the literature [22,32].The experimental arithmetic index of each component was determined adding a C 8 -C 32 n-alkanes mixture (Sigma-Aldrich Italy, Milano, Italy) to the essential oil before injection in the GC-MS equipment and analyzing it under the same conditions reported above [22].For the quantitative analysis a ThermoQuest GC-Trace gas-chromatograph (ThermoQuest Italia, Rodano, Italy) equipped with a FID detector and the same column above described were used.The operating conditions for gas chromatograph were reported above.FID temperature was 250 • C. The oil percentage composition was performed by the normalization method from the GC peak areas, without using correction factors [32] and was the average of three injections.

Quantitative Free Radical Scavenging Activity: DPPH and ABTS Assays
For the DPPH test, the essential oils and some of their constituents, germacrene D (isolated from S. macrotepala, through silica gel column chromatography using n-hexane as mobile phase), β-pinene, 1,8-cineole, E-β-caryophyllene were diluted 2, 5, 10, 50, 100, 200-fold in dimethylsulfoxide (DMSO) and an aliquot of 100 µL of each solution (or DMSO, for the blank) was added to 2.9 mL of DPPH (1 × 10 −4 in ethanol).All solutions were stirred vigorously for 30 min in the dark at room temperature.The absorbances were measured at 517 nm in a Helios spectrophotometer, (Thermo Spectronic, Cambridge, UK).ABTS radical was prepared mixing 10 mL of 2 mM ABTS aqueous solution with 100 µL of 70 mM K 2 S 2 O 8 aqueous solution: the reaction is complete after 12-16 h, in the dark and at room temperature.1 mL of the last solution was diluted with ethanol since to achieve an absorbance of 0.70 ± 0.02 at 734 nm.Similarly to DPPH test, we proceeded mixing 10 µL of each diluted essential oils (or DMSO for the blank) with 0.990 mL of ABTS solution.Absorbances were measured at 734 nm.The antiradical activity for each mixture was calculated according to the following formula: where Ab and Aa are the absorbances of the blank and the samples respectively after 30 min for DPPH and 1-min for ABTS assay.The antiradical activity of the essential oil is evaluated by calculation of the IC 50 value, which is equivalent to the concentration providing 50% of the DPPH or ABTS inhibition, calculating from curves obtained plotting inhibition percentage against essential oil concentration [35].

Photochemiluminscence Assay
Photochemiluminescence (PCL) measures the antioxidant capacity of either lipophilic (ACL) or hydrophilic (ACW) pure compounds or complex mixtures.To measure the antioxidant activity of the essences, the (ACL) methodology was used as it was the most advisable to work with essential oils [35].The PCL bioactivity of essential oil samples was compared to that of T. vulgaris essential oil, taken as positive control, and expressed as µmol of Trolox/mL [37].

Qualitative Radical Scavenging Activity: HPTLC Bioautographic Assay
Bioautographic high performance thin layer chromatography (HPTLC) is an assay of antiradical activity that uses the DPPH and ABTS radicals to reveal the activity of the separate compounds or fractions in a complex mixture [34].For the test, 30 µL of each essential oil was dissolved in 1 mL of methanol.15 µL of these solutions were then applied directly to a Merck 60 HPTLC silica gel plate (Darmstadt, Germany), with F 254 fluorescence indicator, with a Camag LinomatV instrument (Muttenz, Switzerland).The mobile phase was n-hexane.In the developed plate, methanolic solutions of DPPH and ABTS were nebulized to determine the active fractions and to analyze their chemical composition with a subsequent analysis in GC-MS.

Antimicrobial Activity: Evaluation of the Minimum Inhibitory Concentration
The methodology known as disk diffusion was used, which is described in a number of investigations for essential oils [38][39][40] Mother cultures of each bacteria were set up 24 h before the assays in order to reach the stationary phase of growth.The tests were assessed by inoculating from the mother cultures Petri disks with proper sterile media with the aim of obtaining the microorganisms concentration 10 6 CFU/mL.For bacteria, aliquots of dimethylsulfoxide (DMSO) were added to the essential oils in order to obtain a 0.05-500.0mg/mL concentration range and then deposited on sterile paper disk (6 mm diameter, Becton Dickinson Italia S.p.A., Milan, Italy).
Bioactivity against the yeasts was also processed.Mother cultures were set up inoculating 100 mL Yeast Extract and Potato Dextrose (YEPD) liquid medium in 250 sterile flasks and for each mother culture at the stationary phase of growth, broth dilutions were made to obtain a strain concentration of 10 5 CFU/mL to inoculate Petri dishes with agarized YEPD for bioassays.Then, 10 µL of DMSO-essential oil sample solutions were prepared in order to have an assay range 0.55-500 mg/mL, and then deposited on sterile paper disk (6 mm diameter, Difco).The Petri dishes were successively incubated at 30 • C in the dark and checked for evaluating the growth inhibition after 48 h, both for bacteria and yeasts streams: the lowest concentration of each essential oil showing a clear zone of inhibition was taken as the Minimum Inhibitory Concentration (MIC).Negative controls were set up with 10 µL of DMSO in the test solution, while positive ones were assessed with T. vulgaris essential oil [41].Data reported for each assay are the average of three independent experiments.

Table 1 .
Chemical composition of essential oils.

Table 2 .
Free radical scavenging activity of the essential oils evaluated by DPPH and ABTS spectrophotometric methods.

Table 3 .
Results of the antioxidant activity of essential oils by the ACL methodology.

Table 2 .
Free radical scavenging activity of the essential oils evaluated by DPPH and ABTS spectrophotometric methods.

Table 3 .
Results of the antioxidant activity of essential oils by the ACL methodology.

Table 4 .
Antimicrobial activity expressed with minimum inhibitory concentration (MIC mg/mL).

Table 4 .
Antimicrobial activity expressed with minimum inhibitory concentration (MIC mg/mL).

Table 5 .
Collection sites for plant species.