Influence of drying on the chemical composition and bioactivity of Piper aduncum (Piperaceae) essential oil against Aedes aegypti (Diptera: Culicidae)

Piper species are producers of essential oils with high yield and promising chemical composition for both perfumery and the pharmaceutical industry. They present bioactivity against pathogens and against insect pests, whether agricultural or medical, such as Aedes aegypti, for example, a vector of arboviruses with a high incidence in tropical and subtropical regions. In this study, an investigation was carried out to elucidate the chemical composition of essential oils from the leaves and inflorescences of Piper aduncum collected in the state of Goiás, Brazil. Evaluating the interference of the drying process on yield, chemical composition and larvicide potential against Ae. aegypti. Leaves and inflorescences of P. aduncum were collected in the rural area of the municipality of Iporá-GO. Fresh and dried samples were processed separately and subjected to hydrodistillation for two hours. The oil obtained was qualitatively evaluated by gas-coupled chromatography and mass spectrometry. Greater yield was observed in samples submitted to the drying process. Oils obtained from fresh samples had a higher percentage of monoterpene hydrocarbons. Variation was observed between the major components of samples of fresh leaves and inflorescences, with eupatoriochrome being the major component in dried samples. Larvicidal activity against Ae. aegypti was considered promising (LC50<100μg/mL) in all samples. The results obtained showed a chemical composition different from that generally presented by P. aduncum. This reinforces the idea of intraspecific variability of essential oils and the need for chemical evaluation between samples even if they belong to the same species.


Introduction
The family Piperaceae is represented by plants of herbaceous, shrub sizes or small trees (Gogosz et al., 2012), with specimens distributed in tropical and subtropical regions of the planet (Judd et al., 2009). They are part of the group of angiosperms, which generally present in their phytochemical composition alkaloids, cardiac glycosides, coumarins, flavonoids, saponins, and triterpenes associated with different biological and pharmacological activities (Albuquerque et al., 2020). The genus Piper is considered the largest genus of the family, encompassing more than 700 described species, of which approximately 170 are native to Brazilian biomes (Sousa et al, 2008). Distinct species of Piper are used for medicinal purposes as anti-inflammatory, anxiolytic, anticonvulsant, sedative, antidiarrheal, and in urinary disorders (Oliveira et al., 2012).
Piperaceans are also essential oils producers. Some constituents common to essential oils of Piper are: safrole, predominant in the species Piper hispidinervum; ɣ-Terpinene and ρ-Cymene in Piper marginatum; safrole and dillapiole in Piper aduncum (Pereira Filho et al., 2021;Dos-Santos et al., 2018;Star et al., 2006). These constituents are known to be bioactive against bacteria, fungi, protozoa, and insects (Carballo-Arce et al., 2019). Dillapiole for example showed insecticidal potential against agricultural pests such as Sitophilus zeamais (Coleoptera: Curculionidae), Spodoptera frugiperda, and Helicoverpa armigera (Lepidoptera: Noctuidae), and urban pests such as Aedes aegypti (Diptera: Culicidae) (Durofil et al., Research, Society andDevelopment, v. 10, n. 8, e46810817397, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i8.17397 3 2021; Morais et al., 2007;Estrela et al., 2006). This constituent is a potent inhibitor of cytochrome activity (P450 and CYP34A), acting synergistically with pyrethroids and causing insect mortality including strains resistant to current insecticides (Carballo-Arce et al., 2019). Inhibition of these cytochromes in the insect reduces the ability to excrete xenobiotics present in food, where the death of the insect occurs through the accumulation of toxic substances located in the digestive tract (Li et al., 2007). Essential oils are produced by aromatic plants for the purpose of protecting the species against various environmental parameters. The use of the term "essential" for volatile oils occurs because they have odorous components in their composition (Simões, 2017). In general, volatile oils have very unstable characteristics, especially in the presence of light, air, heat, moisture, and metals (Simões, 2010). According to the material acquisition condition, qualitative and quantitative variation is a parameter to be analyzed. In addition to genetic, phenological, edaphic, and climatic factors (Gobbo-Neto & Lopes, 2007; Morais, 2009), the chemical composition of essential oils can be variable depending on the extraction technique and factors such as the time and weather condition at the moment of collection, as well as the processing conditions of the plant material before extraction. These factors can modify the chemical profile of the oil obtained, modify the biosynthetic pathway of the plant, stimulating or inhibiting the production of compounds, as well as interfering with the yield of the process .
P. aduncum has the essential oil with the highest percentage of dillapiole and, therefore, is a promising species for the research and development of bioinseticides (Gainza et al., 2016). It is popularly known as monkey-pepper, long pepper, false jaborandi. It is distributed throughout Latin America, from sea level to high altitudes (Fazolin et al., 2006). Medicinal use of the plant is reported in popular preparations as a digestive stimulant, sedative, diuretic, antidiarrheal, antimalarial agent, and even as an insect repellent (Pohlit et al 2006). There are many studies involving the biopotential of P. aduncum in different Brazilian biomes and in other countries of the American continent.
This research aimed to evaluate the chemical composition of essential oil of leaves and inflorescences of P. aduncum from Cerrado of Goiás (Goiás savanna), comparing samples that went through the drying process with fresh samples and the bioactivity of these oils against larvae of Ae. aegypti to investigate possible variations in both chemical composition and insecticide potential, depending on the variables observed in the acquisition process.

Botanical material harvesting and obtaining the essential oil
Samples of P. aduncum were obtained in the rural area of the municipality of Iporá-GO (6°29'45.96"S and 51°10'46.87"O -828 m) in the morning period in the first half of March 2021, end of the wet season. The region is climatically classified as humid subtropical (Alves & Biudes, 2008). Leaves and inflorescences of various shrubs of the same locality were collected. Botanical material was identified by the biologist Camila Aline Romano, MSc. In the laboratory, the samples were sanitized and screened. Part of the material was dehydrated in a forced air convection oven at 37°C for 24 hours. Another part was immediately undergone to the extraction process.
To obtain the essential oil, fresh and dehydrated leaves and inflorescences were crushed in a conventional blender and subjected to hydrodistillation in a Clevenger apparatus for two hours (Farmacopeia Brasileira, 2019). The essential oil obtained was desiccated with sodium sulfate anhydrous and stored in amber vials under refrigeration at -22°C for further chemical evaluation and bioassays.

Gas chromatography-mass spectrometry (GC-MS)
Essential oil of P. aduncum was subjected to gas chromatography-mass spectrometry (GC-MS) in a Shimadzu GC-MS QP2010A chromatograph equipped with a DB-5 fused-silica capillary column (30 m × 0.25 mm ID × 0.25 µm and 5%-Phenyl-Methylpolysiloxane) and ramp programmed as follows: 60-240°C at 3°C/min, then at 280°C at 10°C/min, ending with 10min at 280°C. Helium was used as a carrier with a flow of 1mL/min and the injection port at 225°C. Operating conditions of the mass spectrometer were: interface temperature 240°C; electron ionization at 70 eV with scanning mass range of 40-350 m/z and sampling of 1 scan/s. Constituents were identified by comparing their retention indices (Dool;Krstz, 1963) to nalkanes C9-C26 and mass spectra with data from the literature (ADAMS 2007) and digital library (NIST, 1998).

Larvicidal activity against Aedes aegypti
The essential oils of fresh leaves, dehydrated leaves, fresh inflorescences, and dehydrated inflorescences were tested against third instar larvae of Ae. aegypti. Bioassays were performed in a heated chamber with temperature of 28°C±1°C, relative humidity of 85%±5% and photoperiod of approximately 12 hours. An aliquot of essential oils was solubilized with surfactant polysorbate 80 (v/v) and distilled water to produce a solution at a concentration of 100 µg/mL, with which test solutions were prepared in serial dilutions of 100 to 10 µg/mL. A total of 20 larvae were exposed to the test solutions. A solution of water and surfactant was used as negative control, temephos solution (Abate ® -Basf Chemical Company) at 0,012 µg/mL was used as a positive control. For each bioassay, three replicates were performed at various times (WHO, 2005).
Mortality events were verified after 24 hours of exposure. The larvae that did not respond to the mechanical stimulation and that presented blackening of the body and the cephalic capsule were considered dead. The data obtained in the larvicide assays were submitted to the nonlinear regression method of Probit to determine the LC of 50 and 90% mortality.
Analyses were performed with the software Statistica Version 12.0 (StatSoft 2013).

Results and Discussion
The extractive process resulted in essential oils of yellowish color, and gently sweetish odor. The yield of the extractive process varied between 0.219% for fresh samples and 0.886% for dehydrated samples. Chromatographic analysis revealed 50 substances, presented in Table 1. There was variability in the composition of essential oils that went through the drying process. Samples of fresh hydrodistillated leaves and inflorescences showed a higher percentage of monoterpene hydrocarbons. On the other hand, dehydrated leaves and inflorescences presented a higher percentage of sesquiterpene hydrocarbons ( Figure 1).
The extractive process showed higher yield in dehydrated samples. However, in general, the samples had lower yield than that observed in the literature. The samples of this study were collected during rainy periods. Souza et al. (2018) found lower yield values in the extractive process of essential oil of Spiranthera odoratissima obtained in Cerrado of Goiás (Goiás savanna). Lemos et al. (2012) observed the variation in the composition of essential oil of Melaleuca alternifolia subjected to different drying temperatures, suggesting that the increase in temperature favors the oxidation of monoterpenes such as α-Pinene, as well as the volatilization of these compounds.
aduncum collected in different locations in the Amazon region of Brazil, they showed that the oil has a high yield (2.5 to 3.5%) and presence of the phenylpropanoid dillapiole as the majority component, presenting a variation between 30-97% among the samples evaluated. The present study showed a different chemical composition, to those already present in the literature.
Eupatoriochromene, a chromene highly found in P. aduncum (Taher et al, 2020) was detected in all samples, being the majority in dehydrated samples of leaves and inflorescences. This compound is bioactive against microorganisms and insects (Taher et al, 2020;Torres et al, 2017). Studies carried out a few decades ago already showed the larvicidal potential of eupatoriochromene on culicides, especially linked to the ability of interfering in the hormonal regulation of immatures and in the process of ecdysis (Klocke et al, 1985;Proksch & Rodrígues, 1983).  Research, Society andDevelopment, v. 10, n. 8, e46810817397, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i8.17397 In the bioassays for investigation of larvicidal activity all samples showed promising larvicidal activity (LC50<100 µg/mL) ( Table 2). Although fresh leaf essential oil had a lethal effect in lower concentrations, there was no significant difference between the lethal concentrations obtained through the bioassay. Thus, it can be proposed that the oils from dehydrated leaves are more promising because they present bioactivity like the other samples tested, however present higher yield.  Oliveira et al. (2012) also investigated the larvicidal activity of essential oil of P. aduncum. The authors found values of LC 50=289.9 µg / mL, concentration higher than that considered promising and when evaluated 1,8-Cineole, they did not observe a lethal effect. Studies with the essential oil of fruits of P. aduncum presented LC50= 30.29 µg/mL, where the composition revealed β-Pinene and limonene as majority compounds (Costa et al., 2010). In the present study, the essential oil of the inflorescences of P. aduncum presented limonene in its composition. All investigated oils presented as majority compounds with larvicidal activity investigated and proven in previous studies, such as germacrene D (Lima et al., 2019) and the eupatoriochromene (Torres et al., 2017). Thus, although dillapiole is not present in abundant content in some samples, bioactivity remained promising, due to the action of other substances with equal potential, or the synergism and enhancement that the composition can promote.

Conclusion
The present study investigated the effect of drying on the chemical composition of essential oil of leaves and inflorescences of P. aduncum obtained in the Midwest of Goiás, in addition to its bioactivity against larvae of Ae. aegypti. The drying process proved to be efficient to increase the yield of the extractive process in relation to the fresh one. It was also possible to observe that the amount of monoterpenes in the dehydrated samples was lower, due to their volatilization. The chemical composition of essential oils was relatively different from most studies with P. aduncum where dillapiole and safrole are majority constituents. Despite the differences in the composition of the oils, the larvicidal bioactivity remained in promising concentrations, mainly because in all samples there is a predominance of substances with already known insecticidal potential, such as eupatoriochromene and germacrene D. These results reinforce the need to evaluate the chemical constitution of essential oils whenever the conditions of collection, processing and extraction vary.