Análise sazonal e atividade antibacteriana dos óleos essenciais das folhas de Croton adamantinus MÜLL. ARG. e Croton urticifolius LAM. (EUPHORBIACEAE)

Abstract

The essential oils of species from the Croton genus are rich in monoterpenes, sesquiterpenes, and phenylpropanoids and are known for their biological activities, such as anti-inflammatory, antioxidant, antimicrobial, cytotoxic, among others. The production of bioactive compounds can vary due to different seasons in response to environmental changes. Croton adamantinus is popularly known as "velame" or "purple marmeleiro," while Croton urticifolius is known as "white marmeleiro" or "velame." The aim of this study was to investigate the seasonal variation of the chemical constituents of the essential oils from the leaves of Croton adamantinus (OCA) and Croton urticifolius (OCU). The material was collected every month from June 2022 to May 2023 in the municipality of Areia-PB. The essential oils from the fresh leaves of both Croton adamantinus and Croton urticifolius species were extracted using the Clevenger-type hydrodistillation technique and analyzed by gas chromatography-mass spectrometry (GC/MS) to identify the chemical constituents. The antibacterial activity of the oils was tested against Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 25922) strains using the broth microdilution method to determine the Minimum Inhibitory Concentration (MIC) in 96-well plates. GC/MS analysis identified 20 compounds (87.0%) for each species, with the majority being sesquiterpenoids. The main compounds in all C. adamantinus oil samples were bicyclogermacrene (average 28.34%), D-germacrene (average 13.94%), and (E)-caryophyllene (average 12.36%). For C. urticifolius, the main compounds were α-pinene (average 38.50%), followed by bicyclogermacrene (average 16.96%), and (E)-caryophyllene (average 14.76%). In the seasonal analysis, the yields of C. adamantinus oils ranged from 0.05% to 0.08%, with the highest yield obtained in spring (0.08%). For C. urticifolius, the yields ranged from 0.08% to 0.26%, with the highest yield also obtained in spring (0.26%). OCA showed moderate activity against Staphylococcus aureus strains, with MIC of 128 μg/mL in April and May 2023, while OCU did not show activity against any tested strain. This study demonstrated that the harvesting period influences the percentage of chemical constituents in the oils of the studied species, and the best period for extraction is spring. It is important to note that this is the first study involving the seasonality of essential oils from the leaves of C. adamantinus and C. urticifolius from the Paraíba swamp region.