Mellissa officinalis L. popularly known as lemon balm, sweet balm or common balm, belongs to the Laminaceae family (Awad et al., 2009). This plant is of Asian and European origin; it is cultivated in Brazil for more than a century; a perennial and can vary from 20 to  80  cm  and 30-100 cm in height, with its membranous leaves dark green in the upper and light green. On the underside, it has a large size, petiolate, opposite, lanceolate, oval, hairy and well protruding (Couto, 2006). Authors such as Osbaldeston (2000) point out that M. officinalis  was used for medicinal purposes more than 2000 years ago. It is known in traditional European medicine aslemonbalm. Saad and Said (2011) point out that lemon balm was used in the Middle Ages to stop bleeding, treat toothache, earache, bent neck and baldness.

M. officinalis L. is a plant used as sedative, and tonic properties are attributed to the nervous system (Aghilikhorasani and Makhzan, 2008) as well as being implicated in relaxation processes and anti-anxiety, insomnia, anti-diarrheal, anti-ulcer properties (Lin et al., 2012; Shakeri et al., 2016; Ghsemi-dehkordiet al., 2002); it presents other functions such as improving benign palpitation and sexual dysfunction (Alijaniha et al., 2015).

In the food industry, according to Bisset and Wichtl (2001), it is a plant used to give fragrance to different foods and beverages; it is also used in the pharmaceutical industry. The essential oil is obtained from flowers with a light yellow color and citric odor, especially the presence of citral, geranial, neral and citronel acetate in their chemical composition (Dawson et al., 1988). Essential oil is responsible for the antibacterial and antifungal properties of the plant (Mimica-dukic et al., 2004). Essential oil of M. officinalis has antioxidant activity, mainly attributed to phenolic acids such as hydrocinamic acid and rosmarinic acid (Caniova and Brandsteterova, 2001). The objective of this work is to study the chemical composition of the essential oil of M. officinalis in the Roraima region (Brazil) in the northern Amazon as well as its antioxidant activity and total phenolic compounds

Preparation of samples

Samples were collected in the Boa Vista-Roraima city (Brazil) and taken to the Laboratory of Environmental Chemistry of the Nucleus of Research and Postgraduate Studies in Technology. The essential oil is separated from the hydrolate and assembled in the amber and refrigerated bottle; it is made in different analyses where a part of the essential oil is sent to the Department of Chemistry of the Federal University of Minas Gerais (UFMG). It is carried out with chromatography analyses. Another part of the oil and hydrolatewere used to carry out the antioxidant activity and total phenolic compoundswere analyzed.

GC-FID analysis

The essential oil was analyzed on a HP 7820A Gas Chromatograph (GC) equipped with a flame ionization detector (FID) using a capillary column (HP5 30 m × 0.32 mm × 0.25 microns, Agilent): Column temperature: 50°C (0 min) at 3°C min-1 up to 230°C. Gun: 250°C Split (1:30). FID Detector: 250°C. Carrier gas: hydrogen at 3 mL min^-1. Vol injection: 1 μL. Essential oil was diluted at 1% in chloroform. Data acquisition software used was Compact EZChrom Elite (Agilent). The quantitative analysis was accomplished using Standard  areas   from   the  chromatograms  obtained  by  GC-FID.

GM-MS analysis

A GCMS-QP2010 ULTRA (Shimadzu) was used. Column: Rxi-1MS dos Santos et al. (2014) 923 30 m × 0.25 mm × 0.25 microns (Restek). Column Temp: 50°C (3 min), 3°C min^-1 to 250°C. Injector: 250°C Split (1:10), GC-MS interface at 250°C. MS detector (electron impact at 70 eV) temperature was 250°C. Carrier gas: helium at 1.5 mL min^-1. Vol injection: 1 μL. Essential oil was diluted at 0.1% in chloroform. Data acquisition software used was GC-MS Solution (Shimadzu) together with NIST11 library. Identification of peaks was made by comparison of the mass spectra obtained by GC-MS spectra with the NIST11 library and also by comparing the Kovatsíndices calculated by GC-FID and literature data.

Total phenolic compounds

The determination of total phenolic compounds was performed by the FolinCiocateau method, where a stock solution of 250 g mL^-1 of essential oil in methanol was initially prepared. Subsequently, 0.1 mL of this solution was transferred to a test tube and 0.1 mL of methanol was added. Then 2.5 mL FolinCiocateau and 2.0 mL 7.5% sodium carbonate were added to the test tube.The formed solution was taken to a 50°C water bath for 5 min and read on a 760 nm spectrophotometer. The calibration curve was made with a gallic acid standard at concentrations of 5, 10, 20, 40 and 80 g mL^-1 of each of the standard solutions was removed and placed in a test tube to which 2.5 mL of FolinCiocateau reagent and 1.5 mL of sodium carbonate solution were added and the absorbance readings at 760 nm (Nakashima, 1993).

Antioxidant activity

For the determination of antioxidant activity, the 2,2-diphenyl-2-picrylhydrazine (DPPH) reduction method was used, according to the methodology proposed by Kondo (2002), where primarily the crude samples of essential oil were solubilized in ethanol at concentrations of8, 20, 40 and 80 g mL^-1 and subsequently a 60uM DPPH ethanol solution was prepared. Samples were prepared by mixing 50 L of DPPH solution and a control solution, where the sample volume was replaced with 50 uL of ethanol, and absorbance readings at 517 nm were taken. 30 min.

The determination of total phenolic compounds was performed by the FolinCiocateau method, where a Stock solution of 250 g mL^-1 of essential oil in methanol was initially prepared. Subsequently, 0.1 mL of this solution was transferred to a test tube and 0.1 mL of methanol was added. Then 2.5 mL Folin Ciocateau and 2.0 mL 7.5% sodium carbonate were added to the test tube. The formed solution was taken to a 50 C water bath for 5 minutes and read on a 760 nm spectrophotometer. The calibration curve was made with a gallic acid standard At concentration of 5, 10, 20, 40 and 80 g mL^-1 of each of the standard solutions was removed and placed in a test tube to which 2.5 mL of FolinCiocateau reagent and 1.5 mL of sodium carbonate solution were added and the absorbance readings at 760 nm (Nakashima, 1993).

The present work provides information on the chemical profile of 22 constituents of the M. officinalis L. essential oil by the hydro distillation method. It is a simple, fast and free of any residual solvent, being a method used to quantitatively determine constituents, volatile foods and medicine.

The authors have not declared any conflict of interests.