inFluence oF DrYing Air temperAture on the chemicAl composition oF the essentiAl oil oF melAleucA

This study was done to evaluate the influence of drying air temperature on the chemical composition of the essential oil of Melaleuca alternifólia Cheel. Three samples were taken at random from each treatment which were analyzed still fresh, determining the moisture content and chemical composition of the essential oil.The plants were chopped and placed in a fixed-bed dryer and dried with air temperature of 40, 50, 60, 70 and 80 °C. The identification of compounds was done using gas chromatography coupled to mass spectrometry. The major components of essential oil of melaleuca subjected to drying air temperatures of 40, 50, 60, 70 and 80 ° C were within the ISO Standard 4730, which classifies plant as medicinal or not.There was an increase in the levels of terpinen-4-ol and α-terpineol and decrease of α-pinene compared to the control.


introDuction
Melaleuca alternifolia Cheel, known as "tea tree", belong to the family Myrtaceae, is a small tree, up to 7 m height.It has a thin skin and leaves tapered, approximately 2 cm long.The leaves are small, sessile, alternate and are arranged spirally around the rachis and blooms in summer.It is native from the southeastern coast of Australia, New South Wales region, and grows in swampy areas or near rivers (VIEIRA, 2002).The essential oil of tea tree presents a complex mixture of 97 compounds and the main constituents are tepinen-4-ol, 1,8-cineol, α-terpinene, γ-terpinene, α-pinene, β-pinene, α-terpineol and p-cymene, representing approximately 90% of the essential oil (BROPHY et al., 1989).
The agronomic practices related to aromatic plant species are often managed in order to propitiate the abundant and homogenous vegetative material of the best final quality.The growing demand for medicinal species indicates the emergence of a market with high potential for consumption, requiring a consistent and readily available supply of high quality raw material.The post-harvesting process of medicinal plants has great importance in the production chain, because of its direct influence on the quality and quantity of the active principles in the product sold (SILVA & CASALI, 2000).
The yield and chemical composition of essential oils that originated from aromatic plants are related to a variety of internal and external factors, e.g., the drying process (RADÜNZ et al., 2002;BRAGA et al., 2005;BORSATO et al., 2009;SZUMNY et al., 2010).
According to Lorenzi and Matos (2002), drying of medicinal species is a preparation process, carried out to meet the needs of the pharmaceutical industry.For this reason, adequate dryers are needed, using temperature, velocity and humidity values for drying air that provides a rapid reduction in the moisture content without affecting the quality of the active principles of medicinal plants (CALIXTO, 2000).The essential oils are the most sensitive constituents in the drying process of medicinal species.The limits of drying air temperature are determined according to the sensitivity of these chemicals substances and from their storage structures, because the product temperature is increased during the drying process (MARTINS, 2000;VENSKUTONIS, 1997).
This study aimed to evaluate the influence of the drying air temperature on the chemical composition of Melaleuca alternifólia essential oil.

mAteriAl AnD methoDs
Fresh tea tree plants (M.alternifolia Cheel) were grown in São Miguel do Anta, Minas Gerais, Brazil.The plants were harvested at 9:00 am, because at this time there is the highest concentration of active principles (SILVA, 2001).After harvest the tea tree samples were transported to Agricultural Engineering Department at the Federal University of Viçosa for drying.
Three samples of 0.20 kg were taken randomly from each treatment which was analyzed fresh, evaluating the moisture content and the essential oil chemical composition.The moisture content of the samples was determined using the gravimetric method recommended by ASAE Standards (2000) for forage and similar plants.This was done by placing 25 g of the product in an oven with forced air circulation at 103 ± 2 °C for 24 h, each done in triplicate.
The drying treatments were arranged in randomized blocks with three repetitions.Five drying temperatures were evaluated: air heated at 40, 50, 60, 70 and 80 °C.For each temperature, 500 g from chopped plants (leaves and stems) were used, making a layer of 5 cm thick in the drying chamber.A fixed-bed dryer was used with upward air flow, equipped with a liquefied petroleum gas burner, used to heat the drying air (Figures 1 and 2), as described by Radünz (2004).The samples were drying until reached moisture content of 0.11 d.b.
The control of drying air temperature was performed with an automatic controller, with a variation of ± 2 °C, as described by Jesuz et al. (2001).Values of temperature and relative humidity of drying air was taken with thermocouples, previously calibrated and placed in pre-set points of the dryer and coupled to an automatic data acquisition system (ADAS) that registered their values in a microcomputer.The drying air velocity was tracked by an anemometer.Hydrodistillation with clevenger apparatus was used for the extraction of the volatile compounds of tea tree (fresh and dried).A suspension of 50 g of tea tree leaves was placed in a 2000 mL round flask together with 1000 mL of ultrapure distilled water.Sample flask was heated for 3 h, after the boiling point was reached (SILVA et al., 2002).After 3 h of extraction samples (mixture of water and oil) were collected.The oil was separated with pentane (3x30 mL) in a 500 mL separation funnel.The organic fraction (pentane and essential oil) obtained was transferred to a 125 mL Erlenmeyer flask and treated anhydrous magnesium sulfate (5 g).The mixture was filtered directly to a flask of 125 mL, concentrated in a rotary evaporator at 38 °C and the oil obtained was transferred into a 5 mL vial and kept at 4 o C until GC-FID analyses were performed.Analyses were run in triplicate.

REVENG
The isolation, identification, and quantification of the volatile compounds were performed on a gas chromatograph associated to flames ionization detection (GC-FID).The equipment model used was the gas chromatographer Shimadzu GC-17A coupled to the flames ionization detector, using a Supelco ® brand column SPB-5, with 30 m in length, internal diameter of 0.25 mm, film intern of 0.25 μm thickness, and nitrogen as the carrier gas.The equipment operation conditions were: column internal pressure of 100 kPa, split ratio of 1:10, gas flow in the column of 1.74 mL min -1 , gas linear velocity of 37.72 cm s -1 and temperatures in the injector and detector of 220 °C to 240 °C, respectively.The column temperature was programmed to begin at 45 °C for 2 minutes and then increase 3 °C per minute until 240 °C was reached, giving a total operation time of 87 minutes.The sample volume injected was 1 μL at a 10.000 ppm concentration and using hexane as a solvent.
Most of the compounds were identified by using three different analytical methods: (1) Kovats indices (KI), (2) GC-MS retention indices (authentic chemicals), and (3) mass spectra (authentic chemicals and spectral library collection).
Results were analyzed using the SAEG, version 9.1 (SAEG, 2007).A completely randomized block design was used, with three replications of treatments, applying the simple regressions on a significance level of P<0.05, relating drying temperature with essential oil composition.The averages of essential oil composition, obtained from the dried and fresh leaves (control) of chopped tea tree were compared with test Dunnett, 5% probability.

5-11 p. results AnD Discussion
Table 1 shows the average values of moisture content of fresh plant and dried samples.Also reported in the table are the average of relative humidity (ambient and plenum) and total drying time for the drying tests of 40, 50, 60, 70 and 80°C.
The main essential oil components found after being submitted to drying air temperatures and compared with the ISO 4730 standard as described in Table 2.
Table 2 shows that the main essential oil components of tea tree submitted to drying air temperatures of 40, 50, 60, 70 and 80 °C were within the ISO 4730 Standard, in other words, the drying process did not affect the samples medical characteristics studied, keeping the essential oil quality compared to the fresh plant.The chemical composition of the tea tree essential oil containing high levels of terpinon-4-ol was also observed in others studies (HAUSEN et al., 1999;KIM et al., 2004;SILVA, 2007).
Table 3 shows the percentage of main chemical constituents of essential oil extracted from chopped leaves of tea tree, submitted to drying at 40, 50, 60, 70 and 80 °C.
Fresh plant (control) of tea tree presents α-pinene level on average 20% higher than the dried plant at temperatures of 40, 50, 70 and 80 °C (P <0.05) (Table 3).However there was no significant difference between the fresh and dried plant at 60 °C.This decrease can be attributed to the oxidation of α-pinene during the drying process, converting it into p-cymene, which may also explain the increased of p-cymene level although no significant differences between the drying treatments when they were compared to fresh plant.The oxidation of terpenes (α-pinene, α-terpinene, γ -terpinene, terpinolene) to p-cymene was also observed by Hausen (1999) andShabir, (2005).No significant difference (P> 0.05) between fresh and dried plant at different temperatures for the constituents α-terpinene, p-cymene, 1.8-cineole, γ -terpinene and terpinolene, was observed.Fresh plant showed decrease of constituents terpinen-4ol (7.87%) and α-terpineol (9,57%) compared to the dried plant at different temperatures (P <0.05).The increase of the constituents terpinen-4-ol and α-terpineol may be related to volatilization in higher quantities of the others constituents present in the plant.In drying studies of several medicinal species, carried out by other authors, were also observed changes in the essential oil composition (RADÜNZ et al. 2002;BLANK et al., 2005, SOARES et al., 2007, BORSATO et al., 2009;SZUMNY et al., 2010).

conclusions
• It could be concluded that the major essential oil components of Melaleuca alternifólia were within ISO 4730 quality standards and that drying can be recommended with air heated up to 80 o C; and • The drying process caused a significant increase in the content of terpinen-4-ol and α-terpineol and significant decrease in α-pinene level compared to the fresh plant.

AcKnoWleDgments
The authors express their thanks to FAPEMIG, CNPq and CAPES for the financing support essential to conduct the project.

table 1 .
Parameters evaluated during the drying process of tea tree

table 2 .
Main components of the essential oil found after being submitted to drying air temperatures and compared with the ISO 4730 standard INFLUENCE OF DRYING AIR TEMPERATURE UPON THE CHEMICAL COMPOSITION OF...